Search found 101 matches

by Catie Donohue 2K
Mon Mar 08, 2021 1:14 am
Forum: Balancing Redox Reactions
Topic: Balancing Redox in Acidic/Basic Conditions
Replies: 5
Views: 11

Re: Balancing Redox in Acidic/Basic Conditions

I believe that the amount of hydronium and hydroxide ions, just like water, will be in excess in an aqueous solution. Therefore, you can add as many of those ions or molecules as you need to make a balanced chemical reaction - they will never be limited in the reaction itself and therefore can be ad...
by Catie Donohue 2K
Mon Mar 08, 2021 1:06 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: experiment graph
Replies: 2
Views: 21

Re: experiment graph

I agree! To add on, you can verify that the reaction is first order by graphing the natural log of the concentration of your reactant against time, which should produce a linear graph. The slope would then be -k.
by Catie Donohue 2K
Mon Mar 08, 2021 1:03 am
Forum: Balancing Redox Reactions
Topic: Exercise 6K Question 3
Replies: 2
Views: 14

Re: Exercise 6K Question 3

For part C, you're right in saying that you don't need to add h2o for the half reaction. Unless there is already an oxygen in the equation that you need to balance on the other side, you can't add additional elements (the oxygen in this case) that aren't already present in the equation because that ...
by Catie Donohue 2K
Mon Mar 08, 2021 12:56 am
Forum: General Science Questions
Topic: Pre-Law/Pre-Med Students
Replies: 8
Views: 54

Re: Pre-Law/Pre-Med Students

I'm leaning towards pre-law and I am a neuroscience major. I would say that if you think medical school is something you might want to do in the future, then it would probably be best to take the required classes anyways. I'm not 100% sure about what I want yet, so I am taking the pre-med classes a...
by Catie Donohue 2K
Mon Mar 08, 2021 12:51 am
Forum: Balancing Redox Reactions
Topic: Studying for finals?
Replies: 8
Views: 15

Re: Studying for finals?

I agree with everything that's been said! Going to UA review sessions is really helpful as well as reviewing textbook problems.
by Catie Donohue 2K
Sun Feb 28, 2021 1:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Sapling Week 7/8 #15
Replies: 3
Views: 22

Re: Sapling Week 7/8 #15

Hi! For this question I used the equation E=Enot-(RT/nF)*ln(Q), where Enot would be calculated by using the standard reduction potentials found in the table (flip the sign for equation that corresponds to the oxidation value and add the two values together). T would be 298K, n is the number of elect...
by Catie Donohue 2K
Sun Feb 28, 2021 1:12 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: E° vs. E and G° vs. G
Replies: 25
Views: 62

Re: E° vs. E and G° vs. G

I'm seeing both 273.15 K and 298 K on this thread for standard temperature. I thought that it was 298 K (25 degrees celsius), but could someone please clarify which one it is?
by Catie Donohue 2K
Sun Feb 28, 2021 1:09 pm
Forum: Balancing Redox Reactions
Topic: Sapling Week 7/8 #18
Replies: 3
Views: 19

Re: Sapling Week 7/8 #18

Hi! I got the same answer as Emma except I used the half reactions, since the Fe is oxidized to Fe(+3) and the oxygen is reduced from an oxidation number of 0 in the reactant oxygen molecule to -2 in the product (water molecule). Then, I balanced both half reactions by adding water molecules, hydrog...
by Catie Donohue 2K
Sun Feb 28, 2021 2:11 am
Forum: Balancing Redox Reactions
Topic: Understanding Oxidation Agents
Replies: 13
Views: 31

Re: Understanding Oxidation Agents

To add on to the other responses, we can either calculate the E(reduction) of the reaction using the equations in the equations sheet, or it's directly given to us. We don't need to use 14A material for this, and a higher E(reduction) means it is a stronger oxidizing agent. So, to order oxidizing ag...
by Catie Donohue 2K
Sun Feb 28, 2021 2:00 am
Forum: Balancing Redox Reactions
Topic: Adding H20 and OH-/H+
Replies: 3
Views: 34

Re: Adding H20 and OH-/H+

Some important things to remember are that you balance non oxygen/hydrogen atoms first. Then, you use H2O to balance oxygen, followed by your ions (either H+ or OH-). If the solution is acidic, use H+. If the solution is basic, use OH-. After adding electrons, the charges and number of each type of ...
by Catie Donohue 2K
Sun Feb 21, 2021 4:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Difference between salt bridge and porous disc?
Replies: 3
Views: 25

Difference between salt bridge and porous disc?

Hi! I understand that the purpose of a salt bridge and porous disc is to neutralize the solutions so that the reaction keeps occurring, but is there an instance where using a salt bridge would be better than using a disc (or vice versa)? Would this change how we calculate the standard cell potential...
by Catie Donohue 2K
Sun Feb 21, 2021 4:18 pm
Forum: Balancing Redox Reactions
Topic: Cathode v Anode
Replies: 8
Views: 26

Re: Cathode v Anode

Hi! From what I understood in lecture, the anode will always be used in the oxidation solution and the cathode will always be used in the reduction solution. I'm a little bit confused on the charges of the anode and the cathode, so if anyone could clear up when the anode is negative and when the ano...
by Catie Donohue 2K
Sun Feb 21, 2021 4:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy related to Enthalpy
Replies: 12
Views: 44

Re: Entropy related to Enthalpy

To add on, the temperature will only need to be factored in to determine spontaneity when ∆S and ∆H are the same sign (one is negative and the other is positive). Using the equation, when ∆S and ∆H are both negative, the reaction will be spontaneous only at a lower threshold temperature. When ∆H and...
by Catie Donohue 2K
Sun Feb 21, 2021 4:06 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Q and K
Replies: 38
Views: 94

Re: Q and K

Hi! When Q is equal to K, the reaction is at equilibrium and the reaction is not "moving" in either direction. When Q>K, there are more products than what is needed at equilibrium, so the reaction will move in the reverse direction (towards the reactants to make more reactants) to make up ...
by Catie Donohue 2K
Wed Feb 17, 2021 11:39 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Textbook Problem 4.15
Replies: 5
Views: 44

Re: Textbook Problem 4.15

Ohh, got it thank you :)
by Catie Donohue 2K
Tue Feb 16, 2021 7:28 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Textbook Problem 4.15
Replies: 5
Views: 44

Re: Textbook Problem 4.15

Hi! The solutions manual for this problem says that we calculate enthalpy of the reaction using "tabulated enthalpies of formation," so I tried to look at Appendix 2A to find them but most of the values weren't there. Is there another table we should be using? Thanks!
by Catie Donohue 2K
Sun Feb 14, 2021 6:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law of Thermo Question
Replies: 6
Views: 50

Re: First Law of Thermo Question

To add on, I think that that since the equation is U=q+w, this has to be applicable to open systems since work (w) can only be done by changing the volume of a system, and you can't change the volume of a closed system.
by Catie Donohue 2K
Sun Feb 14, 2021 6:08 pm
Forum: Calculating Work of Expansion
Topic: Work Done on System?
Replies: 12
Views: 47

Re: Work Done on System?

I believe that whenever the system is expanding, the system is doing work and therefore work is negative here.
by Catie Donohue 2K
Sun Feb 14, 2021 6:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Bomb Calorimeter
Replies: 12
Views: 35

Re: Bomb Calorimeter

I'm pretty sure that a bomb calorimeter is a closed system, since the change in internal energy is simply the q value (which means that heat has to be transferred). Even though no work can be done (since it is a fixed volume), heat can still be exchanged in a bomb calorimeter.
by Catie Donohue 2K
Sun Feb 14, 2021 5:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Sign of G,H,S
Replies: 4
Views: 26

Re: Sign of G,H,S

How do you find change in Gibbs energy using change in enthalpy and change in entropy? You would use the equation: delta G=deltaH - T*deltaS , where deltaG= change in Gibbs free energy, deltaH=change in enthalpy, deltaS=change in entropy, and T=temperature ( so I'm pretty sure you also need to know...
by Catie Donohue 2K
Sun Feb 14, 2021 5:55 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Work on a system
Replies: 27
Views: 84

Re: Work on a system

So, just to clarify - if you were given an equation and asked whether work was being done by the system, you would know that it was if there were more moles of reactant than moles of product (and vice versa if work was being done for the system)?
by Catie Donohue 2K
Sun Feb 07, 2021 3:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Sapling Week 5 Number 18
Replies: 5
Views: 55

Re: Sapling Week 5 Number 18

After finding q, how do we find ∆u? I know we use the equation ∆u= q+w but I'm not sure how to find work done with the variables given? For this part, you would have to manipulate your PV=nRT equation to find the change in volume, which you can then substitute into your w=-PdeltaV equation. Then, j...
by Catie Donohue 2K
Sun Feb 07, 2021 3:17 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Using R in thermodynamic equations
Replies: 24
Views: 88

Re: Using R in thermodynamic equations

When performing calculations for thermodynamics, when do you use R = 8.314 J·K-1·mol-1 vs R= 8.206 x 10-2 L·atm·K-1·mol-1. I'm a little confused on which types of equations I should use the different Rs in, Thanks! Hi! For these constants you will have to pay attention to the units you have from th...
by Catie Donohue 2K
Sun Feb 07, 2021 3:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Sapling week 3/4 Question 5
Replies: 9
Views: 30

Re: Sapling week 3/4 Question 5

Hi! My numbers were a little bit different than yours for this Sapling question, but one mistake that I kept making was that I didn't convert my MCl3 from aqueous to solid. So, just make sure to add the negative value of deltaH for equation #4 at the end when calculating the final enthalpy of your r...
by Catie Donohue 2K
Sun Feb 07, 2021 2:53 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Sapling Week 5 Number 18
Replies: 5
Views: 55

Re: Sapling Week 5 Number 18

Hi! Since you have to find the amount of heat q in the first part of the question, look at the equation q=n*C*deltaT. You do not know your C value yet, but you know the temperature change (13.7) and the moles of the sample (0.981). Using the information they give you, calculate C using C=7R/2 - subs...
by Catie Donohue 2K
Sun Feb 07, 2021 2:40 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: deltaU=nCvdeltaT
Replies: 9
Views: 25

Re: deltaU=nCvdeltaT

Mahnoor_Wani_1I wrote:does that mean at constant volume there is no work done on the system? So the U must equal to heat

Yes! Since the equation for work is w=-PdeltaV, the work would be zero for this system because the volume is not changing.
by Catie Donohue 2K
Sun Feb 07, 2021 2:36 pm
Forum: Administrative Questions and Class Announcements
Topic: tips if you're struggling!
Replies: 77
Views: 422

Re: tips if you're struggling!

Yes, thank you! I definitely realized how important it was to do the textbook problems after last quarter. For people who go to the UA sessions, about how many do you go to? Do you think that they're better to attend in the week leading up to a test or is it worth it to attend them more consistently...
by Catie Donohue 2K
Sun Jan 31, 2021 9:35 pm
Forum: Student Social/Study Group
Topic: Work Life Balance
Replies: 44
Views: 175

Re: Work Life Balance

Hi! I can definitely relate- I feel like it's easy to feel overwhelmed especially when all our classes are over zoom and we're doing work online for majority of the day. I really like what Connie said about purposefully sectioning off times where you aren't focused on school, because setting time li...
by Catie Donohue 2K
Sun Jan 31, 2021 9:18 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp & Cv
Replies: 7
Views: 60

Re: Cp & Cv

You're right that volume and pressure are related! If you think about when we were talking about in earlier classes, decreasing the volume actually increases the pressure of a gas, so there is an inverse relationship between the two (as one goes up, the other goes down). Therefore, Cp and Cv won't a...
by Catie Donohue 2K
Sun Jan 31, 2021 9:04 pm
Forum: Calculating Work of Expansion
Topic: Energy and the System/Surroundings
Replies: 8
Views: 35

Re: Energy and the System/Surroundings

Yes, energy lost from the system would be equal to the energy gained by the surroundings. Professor Lavelle essentially said that the "system" is defined by us and the "surroundings" are everything else. I believe that this also means that the energy lost to the environment may b...
by Catie Donohue 2K
Sun Jan 31, 2021 2:02 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Exothermic vs Extothermic
Replies: 13
Views: 45

Re: Exothermic vs Extothermic

I was confused on this at first too, because I thought that the thermometer was directly measuring the temperature difference of the system. However, the temperature change detected is actually from the surroundings, which means that the system had to give off energy in order for the surroundings to...
by Catie Donohue 2K
Sun Jan 31, 2021 1:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Factors that affect the equilibrium constant
Replies: 31
Views: 88

Re: Factors that affect the equilibrium constant

To add on to the other responses, the value of Q can be different from K immediately following a change in reactant or product concentration, but Q will quickly change back to that constant K value because of Le Chatelier's Principle (since equations need to remain balanced). When Q<K, there are too...
by Catie Donohue 2K
Sat Jan 23, 2021 10:18 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Convert K to Kc
Replies: 2
Views: 11

Re: Convert K to Kc

I just read that too, and I'm pretty sure that K can be used as a universal Kc or Kp (concentration or pressure) depending on the context of the problem. I'm not sure why they only used K in the first example, but it should be the same calculation regardless.
by Catie Donohue 2K
Sat Jan 23, 2021 10:12 pm
Forum: Administrative Questions and Class Announcements
Topic: Material Accessible during Exams
Replies: 6
Views: 35

Re: Material Accessible during Exams

I'm assuming that anything not given on the equation sheet will be provided on the test if we need it!
by Catie Donohue 2K
Sat Jan 23, 2021 10:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Polyprotic acids and bases
Replies: 2
Views: 25

Re: Polyprotic acids and bases

To find the pH value of a polyprotic acid (once the reactant has been fully deprotonated), you need to set up multiple dissociation reaction equations. The first ka will be larger, because it's easier for an acid to ionize in the first reaction to produce H+. In following reactions, the ka value wil...
by Catie Donohue 2K
Sat Jan 23, 2021 9:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exothermic and Endothermic Reactions
Replies: 9
Views: 36

Re: Exothermic and Endothermic Reactions

So just to clarify what's already been said, catalysts control the speed of endothermic and exothermic reactions, but do not affect the change in enthalpy of the reaction?
by Catie Donohue 2K
Sat Jan 23, 2021 9:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Do concentrations change at equilibrium?
Replies: 9
Views: 39

Re: Do concentrations change at equilibrium?

Adding on to the other responses, the only way that the K value will change (and thus the concentrations of products and reactants) would be if there was a change in temperature.
by Catie Donohue 2K
Sun Jan 17, 2021 11:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Box Units
Replies: 6
Views: 45

Re: ICE Box Units

I don't think it's possible to create it without using the molarity of the solutions, since we rely on the K value (which uses the equilibrium concentrations in mol/L) to figure out what x is and therefore what the equilibrium concentrations are for a certain initial concentration of reactant or pr...
by Catie Donohue 2K
Sun Jan 17, 2021 11:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: quadratic formula values
Replies: 13
Views: 79

Re: quadratic formula values

I believe Dr Lavelle said that you take that value that is smaller than the initial concentrations of reactants, because it wouldn't make sense for a product to increase by that higher X amount when there aren't enough reactants available to complete that reaction.
by Catie Donohue 2K
Sun Jan 17, 2021 11:14 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Ka vs. Kb
Replies: 30
Views: 132

Re: Ka vs. Kb

You'll use Ka when dealing with acids, and the larger the Ka value the stronger the acid will be (in the same way, the larger the Kb value the stronger the base will be if you're dealing with bases). You can also find the other value when you're given just one (kw=ka*kb).
by Catie Donohue 2K
Sun Jan 17, 2021 11:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Simplifying Quadratic Equations
Replies: 5
Views: 20

Re: Simplifying Quadratic Equations

I agree that 10^-4 is a safer cutoff. I also remember Lavelle talking about using 10^-3 at one point in lecture (this may have been before he said that 10^-4 was better to use). Can someone confirm if there is ever a case where we can use 10^-3?
by Catie Donohue 2K
Sun Jan 17, 2021 11:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Box Units
Replies: 6
Views: 45

Re: ICE Box Units

I don't think it's possible to create it without using the molarity of the solutions, since we rely on the K value (which uses the equilibrium concentrations in mol/L) to figure out what x is and therefore what the equilibrium concentrations are for a certain initial concentration of reactant or pro...
by Catie Donohue 2K
Sun Jan 17, 2021 11:03 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Conjugate acid/base
Replies: 3
Views: 27

Re: Conjugate acid/base

This is caused by a stronger acid or base (respectively) being disassociated, and the stronger the acid/base the weaker its conjugate base/acid will be. I think this just means that the solution is very acidic if there is a weak conjugate base and vice versa.
by Catie Donohue 2K
Sun Jan 10, 2021 2:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When to use ice table
Replies: 4
Views: 31

Re: When to use ice table

If you are given any initial concentrations (either implicitly or explicitly) in the equation along with the value for K (which can be given directly or calculated if you're given equilibrium concentrations), it seems like you use the ICE Box method for this class.
by Catie Donohue 2K
Sun Jan 10, 2021 1:58 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Adding more of only one reactant
Replies: 4
Views: 60

Re: Adding more of only one reactant

I was also confused on this at first! I think it also has to do with the fact that when there is more of even one reactant (A), that reactant is therefore more likely to collide and react with other reactants to produce products. In other words, the likelihood that an A reactant will react with a B ...
by Catie Donohue 2K
Sun Jan 10, 2021 1:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Example from lecture
Replies: 3
Views: 39

Re: Example from lecture

I agree with the first response! And for solving equilibrium concentrations using the ICE Box method (equilibrium table) he showed, you'll need to manipulate the expressions so that everything is on one side and equal to zero to get a quadratic equation, solve for x, and plug that x value into the c...
by Catie Donohue 2K
Sun Jan 10, 2021 1:48 pm
Forum: Student Social/Study Group
Topic: Advice for someone who didn't take 14A with professor Lavelle
Replies: 61
Views: 350

Re: Advice for someone who didn't take 14A with professor Lavelle

I'd recommend doing textbook problems and going to UA sessions. Staying on top of Chemistry Community and Sapling to get all of those points was also a significant grade boost for me last quarter. Personally, the Sapling questions were not as helpful as the textbook problems. It can be tempting to s...
by Catie Donohue 2K
Sun Jan 10, 2021 1:44 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 7
Views: 57

Re: Le Chatelier's Principle

Yes, when decreasing volume the reaction will still shift left or right to minimize the effect of the change and maintain the equilibrium constant. I'm also not sure specifically on why Le Chatelier's Principle is applied when changing the temperature, but it could be because in order to "minim...
by Catie Donohue 2K
Sat Dec 12, 2020 4:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw vs. trigonal pyramidal
Replies: 22
Views: 162

Re: Seesaw vs. trigonal pyramidal

Brandon Pham 1K wrote:What Ashley said was correct, and:
-See-saw has bond angles of <90 and <120
-Trigonal pyramidal has bond angles of <107.5

Hi! Could you tell me how you figured out how bond angles were 107.5 - I thought it would be < 109.5 since there's a tetrahedral electron arrangement.
by Catie Donohue 2K
Sat Dec 12, 2020 3:58 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Textbook Problem 6C.17
Replies: 2
Views: 13

Re: Textbook Problem 6C.17

I approached this problem by seeing how the negative charge to the hypobromite ion makes it likely to attract a proton (and a strong base), and that the other molecule had N which is often indicative of a weaker base. However, I'm not sure how you would use pka to approach this problem.
by Catie Donohue 2K
Sat Dec 12, 2020 3:55 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Textbook 6b1
Replies: 4
Views: 62

Re: Textbook 6b1

I couldn't find the solution for this in the textbook - would the correct answer be ~0.921?
by Catie Donohue 2K
Sat Dec 12, 2020 3:50 pm
Forum: Conjugate Acids & Bases
Topic: H-bonding Sites for DNA Base Pairs
Replies: 1
Views: 37

Re: H-bonding Sites for DNA Base Pairs

Each N atom has a lone pair, which can act as a site for hydrogen bonding if another H attaches there. Additionally, each H can attach to a nitrogen, oxygen, or fluorine on another compound to form an H bond. This is what I understood from it - feel free to correct me or add anything. Hope it helps!
by Catie Donohue 2K
Sat Dec 12, 2020 3:47 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Why isn't HF a strong acid?
Replies: 23
Views: 150

Re: Why isn't HF a strong acid?

I agree with the previous response - because the bond between H and F is so strong due to their electronegativity difference, the molecule will not be inclined to lose the H atom (the easier an acid gives off H, the stronger it is).
by Catie Donohue 2K
Sat Dec 12, 2020 3:30 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Oxoacids
Replies: 3
Views: 47

Re: Oxoacids

When determining the strength of acids, size is correlated with electronegativity in a group since a bigger atom is more likely to give up its outer electrons - therefore I believe both oxoacids and regular acids are reliant on electronegativity. My guess is the trends in oxoacid strength are due to...
by Catie Donohue 2K
Sun Dec 06, 2020 9:53 pm
Forum: Naming
Topic: Prefixes
Replies: 5
Views: 45

Re: Prefixes

I believe the greek prefixes are the most important one to know when naming a ligand: 1: Mono (but we don't really use this since it's like using 1x in math) 2 : di 3 : tri 4: tetra 5: penta 6: hexa Also, if the ligand already has a Greek prefix in the name (ex: ethyleneDIamine) then we would use 2...
by Catie Donohue 2K
Sun Dec 06, 2020 9:49 pm
Forum: Naming
Topic: Sapling 1
Replies: 34
Views: 184

Re: Sapling 1

Hi! Just to clarify, do we never use a Greek prefix for the anion at the end? The solution said that as long as the Roman numeral (III) was included after cobalt the anion would just be called chloride instead of trichloride.
by Catie Donohue 2K
Sun Dec 06, 2020 9:45 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angle
Replies: 4
Views: 51

Re: Bond angle

That oxygen has two lone electron pairs (in order to complete its octet and have a formal charge of 6). So, there are overall 4 regions of electron density which causes the bond angles to take on a tetrahedral arrangement. Even though there are not 4 atoms bonded, the electrons act in a similar way ...
by Catie Donohue 2K
Sun Dec 06, 2020 9:40 pm
Forum: Lewis Acids & Bases
Topic: Strong Acids and Strong Bases
Replies: 6
Views: 56

Re: Strong Acids and Strong Bases

I believe Professor Lavelle also mentioned that acids with longer bonds (basically acids involving an atom with a larger atomic radius) will be more likely to break and will therefore be stronger acids, so I assume as you go down a period the acids will get stronger.
by Catie Donohue 2K
Sun Dec 06, 2020 9:37 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number
Replies: 13
Views: 125

Re: Coordination Number

Coordination number is essentially the number of bonding sites that a TM will form with ligands. It's important to know the denticity of the ligands since they will affect the coordination number. For example, a bidentate ligand counts as 2 bonds, a tridentate ligand forms 3, and so on. I'm not com...
by Catie Donohue 2K
Sun Nov 29, 2020 7:06 pm
Forum: Electronegativity
Topic: Sapling Week 8 Polarity
Replies: 5
Views: 66

Re: Sapling Week 8 Polarity

I think that the explanation is saying that, since the shape of the molecule does not "cancel out" the polar character of the bonds (since oxygen is only on one side and there are lone pairs with an uneven distribution of hydrogen atoms), the molecule itself is polar. Even if it didn't spe...
by Catie Donohue 2K
Sun Nov 29, 2020 6:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Linear Shape and Lone Pairs
Replies: 8
Views: 99

Re: Linear Shape and Lone Pairs

Brandon Pham 1K wrote:Linear geometry (correct me if I'm wrong) can only occur in 2 specific circumstances:
- 2 electron groups + 0 lone pairs
- 5 electron groups + 3 lone pairs


Would these three lone pairs lie on the equitorial plane?
by Catie Donohue 2K
Sun Nov 29, 2020 6:10 pm
Forum: Hybridization
Topic: Hybridization
Replies: 2
Views: 17

Re: Hybridization

From what I understand, hybridization is determined based on the number of regions of electron density there are (considering both lone pair and bonded electrons). I don't remember using formal charge to play a role in at least determining how many hybrid orbitals there need to be, but it can be use...
by Catie Donohue 2K
Sun Nov 29, 2020 6:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: molecule shape polarity
Replies: 5
Views: 56

Re: molecule shape polarity

To synthesize what has already been said, a molecule's shape has to be taken into consideration when determining polarity, as polar bonds do not always mean that the molecule as a whole will be polar. I had a follow up question about shape, though, because I believe we learned that a molecule with n...
by Catie Donohue 2K
Sun Nov 29, 2020 5:59 pm
Forum: Student Social/Study Group
Topic: How have your study habits changed?
Replies: 45
Views: 353

Re: How have your study habits changed?

For this class in particular, I've payed a lot more attention to the textbook problems and explanations because they help go into more depth what is covered in the lectures. I think something that I'm going to work on for the final is making my notes more organized, such as having headers for differ...
by Catie Donohue 2K
Sun Nov 22, 2020 7:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sapling HW #3
Replies: 3
Views: 48

Re: Sapling HW #3

I agree with the previous responses: the bond angles along the equitorial axis will be 90 degrees in a square pyramidal shape (and I believe 180 degrees along the axial plane). Since a lone pair is present, the actual angles will be slightly smaller. I was also wondering if, since there are 6 region...
by Catie Donohue 2K
Sun Nov 22, 2020 7:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: BOND ANGLES FOR CERTAIN MOLECULAR SHAPES
Replies: 4
Views: 38

Re: BOND ANGLES FOR CERTAIN MOLECULAR SHAPES

Dr Lavelle mentioned that we only use the VSEPR model to provide qualitative predictions, but can't rely on them to find exact quantitative bond angles unless all bonded atoms are the same (for example, CH4). We can use these known bond angles to predict how they will change when atoms are replaced ...
by Catie Donohue 2K
Sun Nov 22, 2020 7:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape of XeF2
Replies: 2
Views: 22

Re: Shape of XeF2

There are 5 total regions of electron density, which means that it has a trigonal bipyramidal shape. Since there are three lone pairs, these are all placed along the equitorial positions and the two remaining bonds would therefore be placed in the axial positions, meaning that their bond angles woul...
by Catie Donohue 2K
Sun Nov 22, 2020 7:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question About Seesaw Molecular Geometry
Replies: 3
Views: 26

Re: Question About Seesaw Molecular Geometry

Hi! From what I understand, placing the lone pair in the equitorial plane as a lone pair allows for the regions of electron density to be as spaced out as possible. If one of the axial regions had a lone pair, it would mean that the rest of the bonded atoms are not as spaced out as they could be sin...
by Catie Donohue 2K
Sun Nov 22, 2020 7:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: CH3F Molecular Shape
Replies: 7
Views: 77

Re: CH3F Molecular Shape

Hi! I agree, the molecule would still have a tetrahedral shape. Since the bonded atoms are not all the same (and their electronegativities are therefore not the same), the bond angles would be different than those in a CH4 molecule, for example.
by Catie Donohue 2K
Sun Nov 15, 2020 1:26 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Sapling Week 5/6 #9
Replies: 1
Views: 19

Re: Sapling Week 5/6 #9

We know that oxygen has an oxidation number of -2. Since the overall charge of the ion is -1, the sum of the oxidation numbers in the ion must equal the overall charge of the ion. We also know that the oxidation number of Cl is +7 based on the previous response, so the structure with the largest for...
by Catie Donohue 2K
Sun Nov 15, 2020 2:40 am
Forum: Student Social/Study Group
Topic: Test Anxiety
Replies: 62
Views: 358

Re: Test Anxiety

I agree that listening to music before a test helps me feel more confident and less anxious about it. One of my teachers also made us all stand up and do a power pose before our tests, which I know sounds so cheesy but it actually kind of helped me. I know that there is a lot of emphasis on getting ...
by Catie Donohue 2K
Sun Nov 15, 2020 2:30 am
Forum: Ionic & Covalent Bonds
Topic: Delta Negative and Positive
Replies: 3
Views: 21

Re: Delta Negative and Positive

I think that this has to do with the electronegativity of the atom, as electronegativity was described as the pulling power of the atom to attract electrons. If it has higher electronegativity, that atom will be more negative because it is pulling the electrons closer to it, while the other atom wil...
by Catie Donohue 2K
Sun Nov 15, 2020 2:24 am
Forum: Dipole Moments
Topic: Sapling number 17
Replies: 10
Views: 80

Re: Sapling number 17

Adding on to everything that's been said, it's helpful to look at the formal charge of each atom (and figure out the overall charge of the molecule) to determine if it is polar or non-polar. If either side has an additional charge and is no longer neutral overall, then it will be attracted to a mole...
by Catie Donohue 2K
Sun Nov 15, 2020 2:19 am
Forum: Dipole Moments
Topic: Rod-shaped molecules
Replies: 6
Views: 53

Re: Rod-shaped molecules

In spherical molecules, the electrons and the molecules themselves take up more space and occupy a bigger volume than in the rod-shaped molecules. This limits how close the two molecules can be, because they cannot align side by side like the rod-shaped molecules due to their shape (they can only &q...
by Catie Donohue 2K
Sun Nov 08, 2020 6:51 pm
Forum: Ionic & Covalent Bonds
Topic: Identifying Ionic and Covalent Bonds
Replies: 10
Views: 39

Re: Identifying Ionic and Covalent Bonds

In Prof Lavelle's lecture, I think he mentioned that you can use electronegativity to figure out if the molecule exhibits more covalent or ionic character. If the difference is greater than 2, the bond is ionic, and if it's less than 1.5, it's covalent.
by Catie Donohue 2K
Sun Nov 08, 2020 6:47 pm
Forum: Electronegativity
Topic: Electron Affinity vs. Electronegativity vs. Ionization Energy
Replies: 4
Views: 19

Re: Electron Affinity vs. Electronegativity vs. Ionization Energy

Hi! From what I've understood, electron affinity measures how likely an atom is to receive an electron, while ionization energy is how much energy it would take for that atom to release an electron. I'm a little more confused on electronegativity, but Prof Lavelle said that it was the "pulling ...
by Catie Donohue 2K
Sun Nov 08, 2020 6:38 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Energy Levels in electron configurations
Replies: 5
Views: 32

Re: Energy Levels in electron configurations

So basically the 4s subshell gets filled first before 3d. This is because, at the time where there are no electrons in the 3d subshell, the 4s subshell is lower in energy. However, once the 3d subshell starts getting filled, it has lower energy than the 4s subshell and therefore gets written before...
by Catie Donohue 2K
Sun Nov 08, 2020 6:33 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Energy Levels in electron configurations
Replies: 5
Views: 32

Re: Energy Levels in electron configurations

Hi! If you remember the diagrams we write to represent the electron shells for n, you can see that the lines for each n level become increasingly closer together. Since the variation becomes so small between levels as you increase n, the 4s orbital can actually be occupied before the 3d orbital. If ...
by Catie Donohue 2K
Sun Nov 08, 2020 6:22 pm
Forum: Lewis Structures
Topic: Lone Pairs Question
Replies: 22
Views: 126

Re: Lone Pairs Question

Lone pairs are useful when drawing diagrams of ions, as you want to make sure that you have the correct charge. By including all bonded and lone pair electrons in the diagram, you have a visual representation of the electrons that have been incorporated already, and can compare that to the total num...
by Catie Donohue 2K
Sun Nov 08, 2020 6:19 pm
Forum: Trends in The Periodic Table
Topic: memorizing trends
Replies: 14
Views: 59

Re: memorizing trends

For me, it helps to memorize how size changes, and from there how ionization energy and electron affinity change depending on the size. We know that size increases down a group because more shells are being added to the element (n is increasing). It decreases as you go along a period because more el...
by Catie Donohue 2K
Sun Nov 01, 2020 5:10 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration
Replies: 3
Views: 41

Re: Electron Configuration

I'm not sure if he's covered this yet because I didn't hear anything about it in the lectures, but to answer the Sapling homework I assumed that the excited state of an electron was one that did not follow the normal pattern of filling up the s, p, and d orbitals as you would typically expect. For e...
by Catie Donohue 2K
Sun Nov 01, 2020 4:54 pm
Forum: General Science Questions
Topic: Sapling Homework
Replies: 5
Views: 81

Re: Sapling Homework

Same here, if it logs me out I always have to go back through CCLE to access the problems again.
by Catie Donohue 2K
Sun Nov 01, 2020 3:57 pm
Forum: Lewis Structures
Topic: ionization energy
Replies: 3
Views: 60

Re: ionization energy

I believe Professor Lavelle stated in his lecture that ionization energy is correlated with element size, although there are some exceptions. A higher ionization energy means more energy is required to remove an electron, so ionization energy therefore increases across a period (as electrons are mor...
by Catie Donohue 2K
Sun Nov 01, 2020 3:47 pm
Forum: Trends in The Periodic Table
Topic: Sapling #30
Replies: 1
Views: 40

Re: Sapling #30

Since neon is a noble gas, it is already in its most stable state. Therefore, much more energy is required to move it from this state (aka gain an electron) since atoms naturally want to be in the lowest energy state possible. Cl is one electron away from being in its lowest energy state (and fillin...
by Catie Donohue 2K
Sun Nov 01, 2020 3:43 pm
Forum: Trends in The Periodic Table
Topic: ionic radius
Replies: 14
Views: 72

Re: ionic radius

I believe that cations have fewer electrons than their parent atom and are therefore smaller. Anions are negative and therefore have more electrons, so anions are larger than the original atom.
by Catie Donohue 2K
Sun Oct 25, 2020 1:22 pm
Forum: Properties of Electrons
Topic: Sapling Week 2,3,4 #12
Replies: 7
Views: 67

Re: Sapling Week 2,3,4 #12

Hi! Do you know when we should be using each equation as well as their different constant values to solve for the change in electron energy states? I've seen a lot of posts about it but I didn't see Professor Lavelle cover them in the lectures, so I was wondering if there were guidelines or recommen...
by Catie Donohue 2K
Sun Oct 25, 2020 1:10 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation and Negative Signs
Replies: 11
Views: 110

Re: Rydberg Equation and Negative Signs

Hi! I agree with all the other answers here - in general, there is never going to be a loss of energy in the system because it is conserved and just transformed into different types of energy or transmitted to another object. I would say only if the question has wording similar to "total change...
by Catie Donohue 2K
Sun Oct 25, 2020 1:04 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post Assessment
Replies: 3
Views: 32

Re: Atomic Spectra Post Assessment

Could someone please walk me through this problem using the deltaE = -hR/n^2-(-hR/n^2) method that he showed in the lecture? I've used the deltaE=hv equation to solve for the total change in energy, which I got to be 7.55*10^-20 J. I then substituted that into the equation with the necessary constan...
by Catie Donohue 2K
Sun Oct 25, 2020 12:50 pm
Forum: Photoelectric Effect
Topic: Mass of atoms
Replies: 18
Views: 105

Re: Mass of atoms

Hi! Adding on to the previous response, I would say that it's a good idea to use your SI units when you're unsure or when there are no units specified in the question (kg, m, s). If they use specific units in the question itself, I would change your units back to the same type the question uses unle...
by Catie Donohue 2K
Sun Oct 25, 2020 12:45 pm
Forum: Properties of Electrons
Topic: Lyman and Balmer series
Replies: 6
Views: 64

Re: Lyman and Balmer series

Hi! I would memorize that any light with a wavelength between 400 and 700 nm is in the visible region and would therefore be dealing with the Balmer series (with changes in electron energy states involving n=2). Any wavelength that is shorter than that (in the UV region) would be dealing with the Ly...
by Catie Donohue 2K
Fri Oct 16, 2020 11:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectroscopic Analysis
Replies: 4
Views: 45

Re: Spectroscopic Analysis

From my understanding so far, I think shorter wavelengths actually result in higher energy light. When we were working through the photoelectric effect module, it was said that the researchers had to change to shorter wavelength (UV) light in order for electrons to be ejected. Therefore, the photons...
by Catie Donohue 2K
Fri Oct 16, 2020 10:51 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Equation
Replies: 3
Views: 67

Re: Heisenberg Equation

-In the Heisenberg questions, after finding delta p from the equation, do u always have to plug it back into delta p=mV to find uncertainty in position? I might have misunderstood your question, but if velocity and mass are given to you, you can solve for delta p using delta p = mass * velocity. Thi...
by Catie Donohue 2K
Fri Oct 16, 2020 10:35 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation
Replies: 7
Views: 44

Re: Rydberg Equation

I'm a little bit confused on this, because in the lecture Professor Lavelle said it was more useful to us to understand the concepts if we used the Bohr frequency condition equation (freq = delta E / h) and Esubn = - hr/n^2 rather than the equation. However, I think I saw in the discussion section t...
by Catie Donohue 2K
Fri Oct 16, 2020 10:27 pm
Forum: Einstein Equation
Topic: Lecture Example 10/16/20
Replies: 4
Views: 47

Re: Lecture Example 10/16/20

Since the electron releases energy as it moves from a higher energy level to a lower energy level, the energy emitted (and thus the energy absorbed initially) has to be positive in order to excite the electron, and that same energy is re-emitted as the electron moves back down to the ground state. B...
by Catie Donohue 2K
Fri Oct 16, 2020 10:08 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Uncertainty Equation Post-Module Assessment #23
Replies: 4
Views: 51

Re: Heisenberg Uncertainty Equation Post-Module Assessment #23

I'm looking at my notes right now and I believe you would plug in delta x as 10 rather than 5. One of the examples he gave was "x = 20m +/- 1m, delta x = 2 m," so that's essentially the same thing here except instead of 2 it would be 10. Hope this helps!
by Catie Donohue 2K
Wed Oct 07, 2020 8:05 pm
Forum: Significant Figures
Topic: Clarification on Significant Figures
Replies: 9
Views: 69

Re: Clarification on Significant Figures

For me, it helps to think about converting the number to scientific notation, because then it's clearer which zeros should be counted. In your example 0.034, you would move the decimal to the right two places and the two leading zeros would disappear. It would be 3.4E^-2 and it's clearer to see that...
by Catie Donohue 2K
Wed Oct 07, 2020 7:57 pm
Forum: SI Units, Unit Conversions
Topic: SI Units
Replies: 13
Views: 128

Re: SI Units

I would say it's a good idea to copy whatever unit the question itself uses unless it explicitly says to change the units.
by Catie Donohue 2K
Wed Oct 07, 2020 7:55 pm
Forum: Molarity, Solutions, Dilutions
Topic: Audio Visual Modules
Replies: 4
Views: 67

Re: Audio Visual Modules

Professor Lavelle's email said that those modules would help with the material in Week 2, so I'd say it's a good idea (or before your next discussion section in case you have any questions about the material). There's also a Wave Properties of Elections module that I don't think he's mentioned on hi...
by Catie Donohue 2K
Wed Oct 07, 2020 7:43 pm
Forum: Limiting Reactant Calculations
Topic: Actual and Theoretical yields
Replies: 14
Views: 145

Re: Actual and Theoretical yields

I agree that it's not possible to get a theoretical yield that's the same as the actual yield. Professor Lavelle mentioned in the learning modules that there are side reactions, impurities, and some of the solution can get stuck to the side of the beaker (all of which will reduce the overall product).

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