## Search found 59 matches

Sat Jan 16, 2021 2:00 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Question #4
Replies: 6
Views: 47

### Re: Sapling Question #4

Because only the initial pressure for PCl5 is given, it is assumed that the reactants do not yet have an initial pressure, meaning the reaction has to go in the reverse direction. Because it is going in the reverse, PCl5 will decrease in pressure because it is being converted into PCl3 and Cl2, whic...
Sat Jan 16, 2021 1:43 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH of Weak Acids
Replies: 11
Views: 55

### pH of Weak Acids

From what I know to be true, the lower the pH the stronger the acid, and the closer the pH of an acid is to about seven, the weaker it is. However, after doing the sapling homework, acids that are classified as weak (#1 weak monoprotic acid and #3 lactic acid as examples) once solved, have extremely...
Sat Jan 16, 2021 1:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Strong Base Dissociation Example
Replies: 1
Views: 12

### Re: Strong Base Dissociation Example

In Dr. Lavelle's first lecture on acid and base equilibria, he gave us a worked example: what are the molarities of H30+ and OH- 0.0030 M Ba(OH)2, where Ba(OH)2 <-> Ba+ + 2OH-? He then went on to state that because the base is a strong base, it completely dissociates in water. That much I understoo...
Sat Jan 16, 2021 1:22 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: What is autoprotolysis? lavelle's lecture 1/15 [ENDORSED]
Replies: 7
Views: 50

### Re: What is autoprotolysis? lavelle's lecture 1/15[ENDORSED]

Adding onto what has been said above, autoprotolysis is an automatic process and occurs in molecules that are amphiprotic. Dr. Lavelle actually first mentions this in Monday's lecture, 1/11.
Sat Jan 16, 2021 1:16 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Classifying Salts
Replies: 2
Views: 16

### Re: Classifying Salts

A salt will be basic if it contains the conjugate base of a weak acid A salt will be acidic if it contains the conjugate acid of a weak base. To add onto this, a salt will be neutral when it contains the cation of a strong base, and an anion of a strong acid. For example, KCl is a neutral acid beca...
Thu Jan 07, 2021 6:43 pm
Forum: Ideal Gases
Topic: Reaction Quotient(Q) vs. Equilibrium Constant(K)
Replies: 9
Views: 63

### Re: Reaction Quotient(Q) vs. Equilibrium Constant(K)

The reaction quotient is used to calculate the ratio of products to reactants at any point during its reaction, and its most important purpose is how it compares to K, the fixed ratio of products and reactants at equilibrium. If Q = K, then the reaction is at equilibrium, however if it does not equa...
Thu Jan 07, 2021 6:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 11
Views: 65

### Re: ICE tables

I is the initial concentration, C, is the change, and E is the equilibrium concentration. For example, in A -> B + C, with initial concentration of A being 0.25M and C at equilibrium being 0.15 A B C I 0.25 0 0 C -x +x +x E 0.25-x x x Then you know x = 0.15 and can use it to find K. Just to add ont...
Thu Jan 07, 2021 6:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 11
Views: 65

### Re: ICE tables

To answer the first part of your question, we would use them if we're given the initial concentrations and the Kc/p of a reaction, and we are asked to find the the concentrations at equilibrium.
Thu Jan 07, 2021 6:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs. Q
Replies: 53
Views: 159

### Re: K vs. Q

Yup! They are both calculated the same way, and Q is used as a way to compare the state of the system and whether what direction the reaction is going relative to the value of K.
Thu Jan 07, 2021 6:12 pm
Forum: Ideal Gases
Topic: K and PV=nRT
Replies: 9
Views: 66

### Re: K and PV=nRT

Partial pressures are mainly used when the products and reactants are both gases. Therefore, if a problem gives you their concentrations, you would use PV=nRT, and manipulate the equation to give you P=(n/V)RT, where n/V is equal to the concentration. After calculating their pressures, you would the...
Thu Dec 10, 2020 2:45 pm
Forum: Amphoteric Compounds
Topic: Amphoteric: acid and/or base
Replies: 4
Views: 47

### Re: Amphoteric: acid and/or base

H2PO4- is also another great example of an amphoteric molecule.
For a molecule to be amphoteric, it has to be able to donate an H+ ion (a Brønsted-Lowry acid), and it needs to be able to accept an H+(a Brønsted-Lowry base), so it must also carry a negative charge.
Thu Dec 10, 2020 2:40 pm
Forum: Conjugate Acids & Bases
Topic: Can strong acids become conjugate bases?
Replies: 3
Views: 52

### Re: Can strong acids become conjugate bases?

Yes, however the strength of the conjugate base will be very weak.
The formula for this will be
HA + H20 -> conjugate base + H3O+
Thu Dec 10, 2020 2:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Textbook 2E #25
Replies: 3
Views: 33

### Re: Textbook 2E #25

SF4 has a total of 34 valence electrons to share, seven electrons per fluorine and six electrons per sulfur. Added together, this creates a total of 34 electrons, and after drawing the lewis structures and placing the needed electrons around the fluorines, you are left with a single lone pair that h...
Thu Dec 10, 2020 2:30 pm
Forum: Hybridization
Topic: Determining Hybridization
Replies: 4
Views: 47

### Re: Determining Hybridization

In addition to what has been mentioned above, lone pairs that take part in resonance structures are not included in the electron densities that make up an atom's hybridization, because they are delocalized electrons.
Wed Dec 09, 2020 10:00 pm
Forum: General Science Questions
Topic: Textbook Questions on the Final
Replies: 11
Views: 99

### Textbook Questions on the Final

In Dr. Lavelle's Final announcement, he states, "Final covers all material (approximately weighted to the amount of time covered in the syllabus). Quantum was the biggest section. Questions will come from the textbook homework listed in the syllabus." Does this mean that all of the questio...
Fri Dec 04, 2020 9:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.13 Part D, Determining the bond angle of N2O
Replies: 5
Views: 46

### Re: 2E.13 Part D, Determining the bond angle of N2O

chinmayeec 3L wrote:I'm not sure if your answer key is different, but 180 degrees is correct and that's what the answer key says.

I copied this from the answer key: (d) The structure of N2O is linear with a bond angle of 180 degrees. AX2

Hope that helps!

Huh my answer key must be different, thank you so much!
Fri Dec 04, 2020 9:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E.13 Part D, Determining the bond angle of N2O
Replies: 5
Views: 46

### 2E.13 Part D, Determining the bond angle of N2O

My lewis structure for N2O is O as the central atom, and is double bonded to N on the left and right, with two lone pairs on each nitrogen. Therefore the shape is linear, but I am confused on the bond angle. Because it's linear, I assumed the bond angle would be 180 degrees, but upon checking the an...
Wed Dec 02, 2020 2:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Week 9 Q2
Replies: 5
Views: 56

### Re: Sapling Week 9 Q2

Ag can take on the oxidation states of +1, +2. & +3 because it is a transition metal. Therefore to determines its oxidation state within this question lies on the overall charge of the molecule, which is -1. Cl has an oxidation state of -1, and because there are two Cl, it contributes to a total...
Wed Dec 02, 2020 2:40 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Numbers in Molecules
Replies: 3
Views: 32

### Re: Coordination Numbers in Molecules

The coordination number of five is only applicable to Fe. CO would not have coordination numbers because it is not the central atom, but they do play a role in determine the coordination number for Fe since they are the surrounding atoms of Fe.
Wed Dec 02, 2020 2:23 pm
Forum: Bronsted Acids & Bases
Topic: Acidic and Basic Substance
Replies: 1
Views: 19

### Re: Acidic and Basic Substance

Water is amphoteric! Water can take on the form H3O+ or OH- depending on the other molecule it is reacting with in an aqueous environment.
Water acts as a base with reacting with an acid.
HCl + H20 -> H30+ + Cl-
And acts as an acid when reacting with a base
H2O +NH−2 -> OH− +NH3
Wed Dec 02, 2020 2:17 pm
Forum: Ionic & Covalent Bonds
Topic: lone pairs -polar molecule
Replies: 10
Views: 92

### Re: lone pairs -polar molecule

In some molecules, the presence of a lone pair causes the molecule to lose its symmetry, therefore its dipoles would not cancel out causing it to be a polar molecule. But as many have mentioned, lone pairs are not determinedly a factor of polar molecules. It is best to look at how the lone pairs are...
Wed Dec 02, 2020 2:12 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge and Ions
Replies: 7
Views: 81

### Re: Formal Charge and Ions

Yes, in addition, to having the lowest formal charges, negative formal charges must also be on the most electronegative atom within the compound.
Wed Dec 02, 2020 2:05 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Strength of Acids
Replies: 8
Views: 67

### Re: Strength of Acids

Yes! Because Br is larger, it has a weaker bond to H, allowing it to dissociate more easily and completely, as all strong acids are assumed to completely dissociate within a solution.
Wed Nov 25, 2020 2:41 am
Forum: Bond Lengths & Energies
Topic: electron repulsion
Replies: 15
Views: 130

### Re: electron repulsion

Yes! Lone pairs repulsion is the most has the greatest repulsion strength. However there is still repulsion among long bonding pairs, and bonding-bonding pairs, with their strength decreasing in that order.
Wed Nov 25, 2020 2:35 am
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 4
Views: 45

### Re: Resonance Structures

The resonance structures that will contribute the most are the ones with the smallest magnitudes of charges, with the negative charge being on the most electronegative atom. This makes the most stable resonance structure.
Wed Nov 25, 2020 2:30 am
Forum: Formal Charge and Oxidation Numbers
Topic: Charge of a Molecule / Distribution of Charge
Replies: 5
Views: 66

### Re: Charge of a Molecule / Distribution of Charge

Finding the overall charge of the molecule can be found through adding all of the formal charges of the atoms within the molecule.
Wed Nov 25, 2020 2:25 am
Forum: Lewis Structures
Topic: NO2 Polarity
Replies: 6
Views: 54

### Re: NO2 Polarity

It's polarity is due to the difference in electronegativites between nitrogen and oxygen, but also because its molecular shape. Due to a lone pair on Nitrogen, the central atom, it causes the shape to be trigonal planar, therefore the dipole moments between nitrogen and oxygen do not cancel out, cau...
Wed Nov 25, 2020 2:14 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Reason why lone pairs decrease bond angle
Replies: 7
Views: 45

### Re: Reason why lone pairs decrease bond angle

Lone pairs have a greater repulsion in comparison to boned pairs. These lone pairs therefore force the bonded pairs close to one another, as the lone pairs take up a greater space due to the repulsion.
Sun Nov 22, 2020 5:13 pm
Forum: Lewis Acids & Bases
Topic: Explanation of Lewis acids & Bases
Replies: 7
Views: 65

### Re: Explanation of Lewis acids & Bases

Lewis acids are electron acceptors and lewis bases are electron donators. Because F- has a negative charge, it can donate an electron to the neutral atom BF3. Additionally, BF3 is electron deficient, giving it another reason why it can accept electrons, further making it a lewis acid.
Sun Nov 22, 2020 4:55 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Plausible Formal Charges
Replies: 6
Views: 28

### Re: Plausible Formal Charges

In addition, if a charge of zero is not possible, then a stable resonance structure would also have the smallest magnitude of charges, specifically, the smallest negative charge would be on the most electronegative atom.
Sun Nov 22, 2020 4:48 pm
Forum: Electronegativity
Replies: 8
Views: 42

### Re: Electronegativity versus atomic radius

Electronegativity decreases as atomic radius increases because the distance between the nuclei and the valence electrons increases, so the atoms ability attract electrons decreases.
Sun Nov 22, 2020 4:00 pm
Forum: Dipole Moments
Topic: Finding Dipole Moments in Multi-Element Molecules
Replies: 2
Views: 48

### Re: Finding Dipole Moments in Multi-Element Molecules

Another way to determine whether multi-element molecules have dipole moments or not is by drawing out the dipoles between the elements of the molecule, specifically between atoms that are bonded with other atoms. Atoms within the molecule that do not have dipole moments that cancel out are an overal...
Sun Nov 22, 2020 3:51 pm
Forum: Bond Lengths & Energies
Topic: Electron Relationship in Bonding
Replies: 6
Views: 84

### Re: Electron Relationship in Bonding

The more bonds there are, the less lone pairs the atoms will have (i.e. two atoms joined with a triple bond have less lone pairs than two atoms joined in a single bond because more electrons are involved in the bond). Thus, molecules with single bonds have more free electrons, which repel each othe...
Sat Nov 14, 2020 8:07 pm
Forum: Bond Lengths & Energies
Topic: boiling point and IMS
Replies: 5
Views: 35

### Re: boiling point and IMS

Because molecules prefer to be in a lowest state of energy, an input of energy is required to break bonds as it makes them unstable and undesirable for the molecules to be bonded. This needed increase in energy relates to a higher boiling point, which will provide said energy.
Sat Nov 14, 2020 7:58 pm
Forum: Electronegativity
Topic: Sapling #14
Replies: 10
Views: 73

### Re: Sapling #14

Hydrogen bonding occurs with molecules of O, F, & N. This is due to their electronegativities which will cause a partial negative charge that will allow hydrogen bonding to occur with a partial positive charge from the H in the water molecule. Molecule C is the only one that represents the corre...
Sat Nov 14, 2020 7:51 pm
Forum: Formal Charge and Oxidation Numbers
Topic: formal charge and stability
Replies: 8
Views: 55

### Re: formal charge and stability

This is a good question. I know it's best to get formal charges of 0 to make it most stable. But how do we know when to stop manipulating the Lewis Structure? How do we know when we are close enough to the most stable form? We know we're close to the most stable form when the most electronegative i...
Sat Nov 14, 2020 7:46 pm
Forum: Ionic & Covalent Bonds
Topic: Sapling #13
Replies: 8
Views: 36

### Re: Sapling #13

For an hydrogen bond to form, a hydrogen atom has to be bonded to a strongly electronegative atom of one molecule, and another strongly electronegative atom of another molecule. N-H bonds are polar, as nitrogen is an electronegative atom. So the H in that bond is slightly positive and will create a ...
Sat Nov 14, 2020 7:36 pm
Forum: Lewis Structures
Topic: Recognizing lowest formal charge
Replies: 11
Views: 50

### Re: Recognizing lowest formal charge

To draw a Lewis strucutre with the lowest formal charge, the first step is have the central atom be the one with the lowest ionization energy, then when calculating the formal charges, the negative charges should be on the most electronegative atoms. It should also have the fewest and smallest magni...
Sun Nov 08, 2020 8:59 pm
Forum: Properties of Light
Topic: Is c always the speed of light?
Replies: 88
Views: 457

### Re: Is c always the speed of light?

Yes, and it will always be the product of the wavelength and frequency.
Sun Nov 08, 2020 8:52 pm
Forum: Ionic & Covalent Bonds
Topic: Electronegativity
Replies: 16
Views: 90

### Re: Electronegativity

It's the most electronegative because of its orbital 2P which optimally would contain six electrons. Because Fluorine only has five, it's attraction is due to being so close to its most stable configuration, making it the most electronegative.
Sun Nov 08, 2020 6:14 pm
Forum: Electronegativity
Topic: Noble Gases
Replies: 40
Views: 1723

### Re: Noble Gases

Catherine Bubser 2C wrote:If asked to compare an element that is in the group to the left of the noble gas, would that element have a higher electronegativity then?

in comparison to noble gases I believe the answer would be yes since those elements do not have a full octet like the noble gases do.
Sun Nov 08, 2020 6:11 pm
Forum: Bond Lengths & Energies
Topic: ionization energy
Replies: 6
Views: 75

### Re: ionization energy

Because Oxygen has a lower ionization energy where it requires less energy to be removed an electron than nitrogen and fluroine to add onto why it requires less energy, oxygen has a lower amount of protons in comparison to nitrogen and fluorine, therefore oxygen has a larger radius in comparison as...
Sun Nov 08, 2020 6:05 pm
Forum: Bond Lengths & Energies
Topic: Hydrogen Bonding
Replies: 13
Views: 329

### Re: Hydrogen Bonding

Hydrogen bonding occurs when an H atom is bonded to a more electronegative atom, N, O, or F. The higher electronegativity of these atoms pulls on Hydrogen's only electron closer to themselves. This causes the more electronegative atoms to have a partial negative charge and the hydrogen atoms to have...
Sun Nov 01, 2020 7:19 pm
Forum: Empirical & Molecular Formulas
Topic: Empirical formula question
Replies: 7
Views: 46

### Re: Empirical formula question

Empirical numbers have to contain whole numbers since you can't have a fraction of an atom. Therefore, if you get nonwhole numbers in your conversation to the empirical formula, multiple the ratios by whole numbers until your product is close to the nearest whole number!
Sun Nov 01, 2020 7:10 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 2
Views: 28

### Re: Electron Affinity

Energy is released when an electron is added to an atom and is absorbed when an atom releases an electron. Atoms want to be their most stable, accounting for why there are anions and cations. When electrons are added, the atom is stabilized, hence the release of energy, and releasing an electron req...
Sun Nov 01, 2020 7:04 pm
Forum: Trends in The Periodic Table
Replies: 14
Views: 68

In order of smallest to largest ionic radius, it goes cation, normal, and anion.
Sun Nov 01, 2020 7:00 pm
Forum: DeBroglie Equation
Topic: Sapling HW #17
Replies: 6
Views: 47

### Re: Sapling HW #17

Hey guys, thank you for these tips but I am still really stuck on this question. I did: (6.26x10^-34) / (6.31 x 10^23) (442.4) to find the wavelength. My units gave me my answer in m like the question asks for, but I still keep getting it wrong. I'm not sure what else to do... Because plank's const...
Sun Nov 01, 2020 6:44 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Sapling #24
Replies: 16
Views: 72

### Re: Sapling #24

Wait so the wave needs to be able to connect to itself at the end? Do you want identical starts/finishes basically? I'm still a bit confused. Not exactly identical starts and finishes. For a wave to be compatible, and for how the images are displayed for this question, the waves have to go through ...
Mon Oct 26, 2020 5:54 pm
Forum: DeBroglie Equation
Topic: Ch.1 #41 [ENDORSED]
Replies: 7
Views: 885

### Re: Ch.1 #41[ENDORSED]

The answer to this solution actually requires three sigfigs, signified by the dot at the end of 100. pm. Therefore the answer is 3960 m/s
Sun Oct 25, 2020 12:27 pm
Forum: Photoelectric Effect
Topic: Intensity vs. Frequency
Replies: 22
Views: 140

### Re: Intensity vs. Frequency

Emilie_Paltrinieri_1K wrote:So what was the new equation that they found after doing the experiment of the photoelectric effect?

They found that the energy of a photon is proportional to planks constant and frequency
Ephoton=(h)(v)
Sun Oct 25, 2020 12:21 pm
Forum: Properties of Light
Topic: Sapling Homework Question 7
Replies: 5
Views: 86

### Re: Sapling Homework Question 7

How many photons with a wavelength of 793 nm are needed to melt 445 g of ice? The enthalpy of fusion of water can be found in this table. What formulas are needed to solve this and why? Im stuck. Thanks The energy of a photon can be found by using the equation (h)(c)/lambda, and this equation is th...
Sun Oct 25, 2020 12:06 pm
Forum: DeBroglie Equation
Topic: question 9 sapling
Replies: 4
Views: 77

### Re: question 9 sapling

Hi! So I'm pretty sure I have the same problem as you for #9 (metal objects inside a microwave oven). This is how I approached the problem. We're looking for wavelength without frequency, so I rearranged these two equations: c=λv and v=E/h. First, I rearranged the first equation to be in terms of f...
Sun Oct 25, 2020 11:59 am
Forum: Photoelectric Effect
Topic: unit conversion hw Q 1.3
Replies: 7
Views: 231

### Re: unit conversion hw Q 1.3

You always want to covert any units into the SI base units before beginning the problem. The only time you'd convert SI units into different units is if the problems asks for it in your final answer!
Sun Oct 25, 2020 11:44 am
Forum: DeBroglie Equation
Topic: Sapling Question #10
Replies: 8
Views: 108

### Re: Sapling Question #10

Everyone in this thread is mentioning Avogadro's number, but as I look through my notes, I can't seem to find anything about it. Does anyone know which lecture talked about this? It most likely is from one of the first lectures we had on fundamentals, but the textbook explains Avogadro's number on ...
Sun Oct 11, 2020 7:33 pm
Forum: Limiting Reactant Calculations
Topic: Help finding limiting reactant
Replies: 4
Views: 59

### Re: Help finding limiting reactant

Wait so we have to solve for the product of each reactant in order to determine which one is the limiting reactant? Is there not a shorter way? No not really. The limiting reactant determines how much product can be made, therefore one has to convert the moles of reactant to the moles of product to...
Sun Oct 11, 2020 7:27 pm
Forum: Balancing Chemical Reactions
Topic: States of Matter in Chemical Equations
Replies: 13
Views: 88

### Re: States of Matter in Chemical Equations

While it may be difficult to know which states all of the compounds may exist in, there are diatomic elements that would be best to know. These diatomic elements are O2, F2, I2, H2, N2, and Cl2 which cannot exist as a singular atom, and are therefore a compound of two of itself that must also exist ...
Sat Oct 10, 2020 8:48 pm
Forum: Limiting Reactant Calculations
Topic: How do we find the amount of oxygen in combustion?
Replies: 10
Views: 525

### Re: How do we find the amount of oxygen in combustion?

Question: In a combustion reaction, how do we find the amount of oxygen? In every combustion reaction, O2 is a necessary reactant, and CO2 is an absolute product. Therefore, the first steps in solving the amount of oxygen in a reaction is to ensure the reagent and product are present, and then bala...
Sat Oct 10, 2020 8:40 pm
Forum: Limiting Reactant Calculations
Topic: Double Check my Understanding
Replies: 10
Views: 138

### Re: Double Check my Understanding

Hi, so just to double check my understanding, when calculating molar mass of compounds, we ignore the coefficient in front of the compound (ie. if there is a two, we don't multiply molar mass by two) because the coefficient simply represents the molar ratio of reactants/products, at least when we a...
Sat Oct 10, 2020 8:21 pm
Forum: SI Units, Unit Conversions
Topic: Rounding
Replies: 20
Views: 160

### Re: Rounding

Some elements of the periodic table have 4 sig figs as their molar mass and others have far more. When calculating the molar mass of a compound, how many sig figs should there be or number be rounded to? For molar masses, typically the most sig figs that should be accounted for in the compound is f...