Search found 19507 matches

by Chem_Mod
Sun Feb 28, 2021 10:36 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Textbook Question 6.53 Part b) [ENDORSED]
Replies: 1
Views: 17

Re: Textbook Question 6.53 Part b) [ENDORSED]

The anode side is the product side (reaction starts with lower concentration product), 0.0010 M CrCl 3 (aq). Diluting [P] therefore makes Q << 1, which makes ln Q even more negative, and therefore E more positive. Work through the concentration cell example I did in class. Lower concentration produc...
by Chem_Mod
Sat Feb 27, 2021 3:32 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Potential Difference
Replies: 1
Views: 18

Re: Potential Difference

As I said in class the more positive potential (cathode) pulls the negatively charged electrons towards it.

The cathode has a compound that 'wants' electrons, meaning more stable gaining electrons.
by Chem_Mod
Fri Feb 26, 2021 7:26 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: sapling 6.57
Replies: 1
Views: 12

Re: sapling 6.57

For 6.57 from the hw problems why do we square root the value K? I just want to confirm if my thought is correct that we have to square root K because it is K a *K b and the question is just asking for K a since I got rusty on acids/bases When you balanced the two half reactions, your overall react...
by Chem_Mod
Fri Feb 26, 2021 7:23 pm
Forum: Balancing Redox Reactions
Topic: OH- cancels out in basic solution- Sapling week 7/8 #5
Replies: 3
Views: 44

Re: OH- cancels out in basic solution- Sapling week 7/8 #5

In the Sapling week 7/8 #5, part b, this equation is given to be balanced. N2H4(g)+ClO−3(aq)⟶NO(g)+Cl−(aq). It says it takes place in an aqueous solution, but no matter how many times I rebalance it, my OH- keep canceling each other out when I put the half-reactions together. Anyone else have this ...
by Chem_Mod
Fri Feb 26, 2021 7:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Sapling HW Week 7/8 #17
Replies: 1
Views: 28

Re: Sapling HW Week 7/8 #17

I am not sure how to start this problem as I can't identify which equation I would have to use. Question: What would the potential of a standard hydrogen electrode (S.H.E.) be under the given conditions? [H+]=0.23 M PH2=2.1 atm T=298 K If your cell is at non-standard conditions (ie. concentrations ...
by Chem_Mod
Fri Feb 26, 2021 2:03 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Sapling Week 7/8 #5 glitch [ENDORSED]
Replies: 3
Views: 233

Re: Sapling Week 7/8 #5 glitch [ENDORSED]

I asked Sapling and they responded: Typically this error will come up when a student copies and pastes an answer into the textbox. I would first suggest the student tries to enter the answer manually. If they are having trouble removing the error message, I would suggest, they select the Try Again b...
by Chem_Mod
Fri Feb 26, 2021 11:04 am
Forum: Balancing Redox Reactions
Topic: Balancing Under Basic Conditions [ENDORSED]
Replies: 2
Views: 12

Re: Balancing Under Basic Conditions [ENDORSED]

These should help: Balancing Redox Reactions: Acidic Conditions https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Balancing_Redox_Reactions_Acidic_Conditions.pdf Balancing Redox Reactions: Basic Conditions https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Balancing_Re...
by Chem_Mod
Fri Feb 26, 2021 11:00 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook 6M.1 error [ENDORSED]
Replies: 2
Views: 28

Re: Textbook 6M.1 error [ENDORSED]

I will remove this question as it is too confusing with the negative voltage.
by Chem_Mod
Fri Feb 26, 2021 10:52 am
Forum: Balancing Redox Reactions
Topic: Textbook 6K.1 [ENDORSED]
Replies: 2
Views: 15

Re: Textbook 6K.1 [ENDORSED]

Good answer. C 2 H 5 OH Make all the H 1+ and the O 2-. 6 x H = 6+ O = 2- This gives 4+. Since molecule is neutral each C is 2-. C 2 H 4 O Make all the H 1+ and the O 2-. 4 x H = 4+ O = 2- This gives 2+. Since molecule is neutral each C is 1-. I should do an example like this in class. But then some...
by Chem_Mod
Fri Feb 26, 2021 9:45 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electrolyte question [ENDORSED]
Replies: 2
Views: 113

Re: electrolyte question [ENDORSED]

This question was copied from:
https://www.researchgate.net/post/is_th ... t_reacting

"Is there any electrolyte or ionic liquid that dissolves metal oxides at room temperature without reacting?"
by Chem_Mod
Fri Feb 26, 2021 9:41 am
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Corrosion Prevention
Replies: 2
Views: 6

Re: Corrosion Prevention

Corrosion is the reaction of the surface layer of a metal with oxygen or water in the air to create an oxide or hydroxide layer on top of the metal. Over time, this layer can grow larger until it oxidizes the entire piece of metal. By coating a metal with a different material such as paint, or with ...
by Chem_Mod
Fri Feb 26, 2021 9:23 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: textbook problem 6L.9 [ENDORSED]
Replies: 1
Views: 17

Re: textbook problem 6L.9 [ENDORSED]

Since K + (aq) is not part of the redox reaction, don't need to include it. If you do include it shows on the left and right side of the chemical equation and cancels out as it is the same species at the same concentration on both sides of the chemical equation. We saw this in class when calculating...
by Chem_Mod
Fri Feb 26, 2021 9:15 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Equilibrium Cell Potential [ENDORSED]
Replies: 1
Views: 26

Re: Equilibrium Cell Potential [ENDORSED]

One can measure E o when solutions are 1M, pressure 1atm/1bar, 25 o C. Or One can measure the concentrations of reactant and product at equilibrium and use them to calculate (infer) E o . K and E o are related. The reason a redox reaction has a large K is because the E o is a high positive value. At...
by Chem_Mod
Fri Feb 26, 2021 9:04 am
Forum: Balancing Redox Reactions
Topic: textbook 6L.7 a [ENDORSED]
Replies: 1
Views: 26

Re: textbook 6L.7 a [ENDORSED]

This is a harder one to figure out with the information given. If one was given the cell diagram then straight forward. Ag(s) is the same electrode for anode and cathode. What makes the two half-reactions different are the solutions (electrolytes) the electrodes are in. Ag(s) anode is in contact wit...
by Chem_Mod
Fri Feb 26, 2021 8:44 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Textbook 6L.5d [ENDORSED]
Replies: 1
Views: 30

Re: Textbook 6L.5d [ENDORSED]

The anode and cathode are both Au(s). What makes the oxidation and reduction half reactions different are the solutions (electrolytes) at each electrode. The anode, Au(s), is in contact with Au 3+ (aq). The cathode, Au(s), is in contact with Au + (aq). Since Au + (aq) going to Au 3+ (aq) is favorabl...
by Chem_Mod
Thu Feb 25, 2021 9:07 pm
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 5
Views: 22

Re: Oxidation Numbers

You do not have to memorize all of them, but there are some you should be familiar with. For example, Oxygen is usually -2, Cl is usually -1, H is usually +1. There are exceptions to these rules, which you can find here: http://ocw.umb.edu/chemistry/chem-116-chemical-principles-ii/Handouts%20PDF/oxn...
by Chem_Mod
Thu Feb 25, 2021 8:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Electromotive Force
Replies: 1
Views: 15

Re: Standard Electromotive Force

The cell potentials are measured with reference to the standard hydrogen electrode. If electrons flow to the electrode of interest, then it has a positive standard reduction potential. If electrons flow to the hydrogen electrode instead, the electrode of interest has a negative standard reduction po...
by Chem_Mod
Thu Feb 25, 2021 8:40 pm
Forum: Balancing Redox Reactions
Topic: Textbook Problem 6K.3 part d [ENDORSED]
Replies: 1
Views: 38

Re: Textbook Problem 6K.3 part d [ENDORSED]

Yes you are correct. I'll update the file on my class website. Equation in question should be: Cl 2 (g) ---> ClOH(aq) + Cl - (aq) [Hypochlorous acid (ClOH) is a weak acid that forms when chlorine dissolves in water, and itself partially dissociates, forming hypochlorite, ClO - . HClO and ClO - are o...
by Chem_Mod
Thu Feb 25, 2021 8:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Kate's Week 8 Workshop Winter 2021
Replies: 0
Views: 28

Kate's Week 8 Workshop Winter 2021

Hello everyone,

I attached my Week 8 Worksheet and answer key below. Happy studying :-)

Best,
Kate
by Chem_Mod
Thu Feb 25, 2021 8:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electrolyte question [ENDORSED]
Replies: 2
Views: 113

Re: electrolyte question [ENDORSED]

The metal oxides vary in their chemistry. Depends on what metal oxide. Dissolving a metal oxide like CaO and MgO in regular water is reactive as you are breaking the metal oxygen bonds and making something else with the reactive O. There are some ionic liquid formulations that can dissolve silver ox...
by Chem_Mod
Thu Feb 25, 2021 8:12 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Sapling 7/8 #15
Replies: 7
Views: 51

Re: Sapling 7/8 #15

Try using the Nernst equation to find E given E naught and the concentrations of the reactants (which you can use to find Q)
by Chem_Mod
Thu Feb 25, 2021 8:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell [ENDORSED]
Replies: 6
Views: 30

Re: Concentration Cell [ENDORSED]

The lower concentration is on the product because if you are oxidizing a metal into aqueous cations, it would occur on the side with the lower concentration of cations. Which textbook problem are you referencing? For question 6N.3 (b), the equilibrium quotient of the equation has the larger concent...
by Chem_Mod
Thu Feb 25, 2021 6:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electromotive Force
Replies: 2
Views: 23

Re: Electromotive Force

Dylan_K_3B wrote:An electromotive force is any force/work done that is being driven by a difference in potential that results in an electric current.


Good answer.
by Chem_Mod
Thu Feb 25, 2021 6:14 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell [ENDORSED]
Replies: 6
Views: 30

Re: Concentration Cell [ENDORSED]

The lower concentration is on the product because if you are oxidizing a metal into aqueous cations, it would occur on the side with the lower concentration of cations. Which textbook problem are you referencing?
by Chem_Mod
Thu Feb 25, 2021 6:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cathode vs. Anode
Replies: 8
Views: 45

Re: Cathode vs. Anode

Do you mean if a diagram were drawn? Or are you referring to the cell diagram notations involving | and , ? If the former, it doesn't matter on which side the cathode is drawn. If the latter, the anode will always be on the left side. Also, note that electrons go from anode to cathode, not ions
by Chem_Mod
Thu Feb 25, 2021 6:09 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Sapling 6N.3 part d
Replies: 1
Views: 8

Re: Sapling 6N.3 part d

products/reactants does not mean anode/cathode. Combine the half reactions to get the overall reaction, which will tell you what the products and reactants are
by Chem_Mod
Thu Feb 25, 2021 4:03 pm
Forum: Administrative Questions and Class Announcements
Topic: Thursday Drop in
Replies: 1
Views: 24

Re: Thursday Drop in

It wasn't canceled but by my zoom is acting weird. If you still need help send me an email and we can set up another time that works with your schedule :)

-Mel
by Chem_Mod
Thu Feb 25, 2021 3:48 pm
Forum: Balancing Redox Reactions
Topic: sapling q.3
Replies: 2
Views: 13

Re: sapling q.3

Please see this document on the class website: https://lavelle.chem.ucla.edu/wp-conten ... itions.pdf
You can also balance as in acidic conditions, then neutralize all the H+ by adding the same amount of OH- to each side of the reaction
by Chem_Mod
Thu Feb 25, 2021 3:47 pm
Forum: Balancing Redox Reactions
Topic: Sapling Question 3
Replies: 4
Views: 17

Re: Sapling Question 3

Please include the entire question, especially because the Sapling problems tend to be different for each student. My guess is you had to multiply by 4 to balance the number of electrons in the two half reactions to be the same. This problem also references a basic solution, so you can balance as fo...
by Chem_Mod
Thu Feb 25, 2021 3:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Sapling Weeks 7/8 #13
Replies: 2
Views: 8

Re: Sapling Weeks 7/8 #13

Find the standard reduction potentials and look for one that is more positive than that of Cr3+ -> Cr but less positive than that of Pb2+ -> Pb. This means it would be reduced, thereby oxidizing Cr, but would not oxidize Pb
by Chem_Mod
Thu Feb 25, 2021 2:02 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Sapling Question 17
Replies: 1
Views: 29

Re: Sapling Question 17

See this previous post: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=140&t=5159&p=12748&hilit=use+a+mixed+equilibrium+expression%2C+containing+both+concentrations+pressures&sid=9147d6ac6f16ea9bdc08d91e453db005#p12748 Bars and atmospheres are both OK to use since they are appro...
by Chem_Mod
Thu Feb 25, 2021 1:49 pm
Forum: Balancing Redox Reactions
Topic: Balancing OH- and H2O
Replies: 4
Views: 21

Re: Balancing OH- and H2O

The second method is to balance as if in acidic solution, then at the end, add equal amounts of OH- on each side of the reaction to neutralize all the H+ into H2O. This will leave you with H2O and OH-
by Chem_Mod
Thu Feb 25, 2021 1:37 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Sapling Q15 week 7/8
Replies: 2
Views: 42

Re: Sapling Q15 week 7/8

Your values seem correct but when I plugged them into the equation I got a different cell potential from what you have inputted. Perhaps you made a calculation mistake or are maybe using log instead of ln?
by Chem_Mod
Thu Feb 25, 2021 1:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Sapling Week 7/8 #10
Replies: 4
Views: 23

Re: Sapling Week 7/8 #10

Using the standard reduction potentials is a good idea :)
by Chem_Mod
Thu Feb 25, 2021 1:26 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Ion Selective Electrodes
Replies: 1
Views: 22

Re: Ion Selective Electrodes

It is because for these ion selective electrodes, you would use an electrode containing the same ion as whatever solution whose ion concentration you are trying to measure. For instance, in the pH electrode, this electrode contains H+ ions and would be used to measure [H+] of different solutions
by Chem_Mod
Thu Feb 25, 2021 11:53 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to use a comma or | in cell diagrams?
Replies: 2
Views: 22

Re: When to use a comma or | in cell diagrams?

Yes, you are correct. Include Pt(s) when it is needed as an inert electrode
by Chem_Mod
Thu Feb 25, 2021 11:48 am
Forum: Balancing Redox Reactions
Topic: Week 7 and 8 Sapling 5
Replies: 2
Views: 41

Re: Week 7 and 8 Sapling 5

Balance the Cl by adding stoichiometric coefficeint of 2. Then add H2O to balance oxygen. Finally add H+ then electrons.
For the other half-reaction, balance H by adding H+, then balance electrons
by Chem_Mod
Thu Feb 25, 2021 10:51 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell (from lecture 20 on Wednesday)
Replies: 1
Views: 15

Re: Concentration Cell (from lecture 20 on Wednesday)

n is the number of moles of electrons that are transferred per reaction. Ag --> Ag+ involves the transfer of 1 mole of electron. Zn--> Zn2+ involves the transfer of 2 moles of electrons. You can see by the change in charge of the substances that are involved. E naught is 0V because it is the cell po...
by Chem_Mod
Thu Feb 25, 2021 10:47 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: hydrogen and electrolysers
Replies: 1
Views: 18

Re: hydrogen and electrolysers

Is there a specific homework or textbook problem that corresponds to this question? If so, please indicate which one it is
by Chem_Mod
Thu Feb 25, 2021 9:41 am
Forum: Balancing Redox Reactions
Topic: 6K.1 Textbook
Replies: 1
Views: 6

Re: 6K.1 Textbook

First, add up the total charges on each side of the equation. Without the e-, you have -2+14=+12 on the left and 2(+3)=+6 on the right. You will then add 6e- to create a charge of +6 on the left so that the charges are the same on both sides.
by Chem_Mod
Thu Feb 25, 2021 9:26 am
Forum: Balancing Redox Reactions
Topic: Textbook 6L.3 (d) [ENDORSED]
Replies: 2
Views: 139

Re: Textbook 6L.3 (d) [ENDORSED]

Great answer above. As there are many questions on 6L.3 I'll add additional comments to assist everyone with similar and related questions. In cell diagrams the left side represents the anode (oxidation half-reaction) and the right side the cathode (reduction half-reaction). The conducting electrode...
by Chem_Mod
Thu Feb 25, 2021 8:03 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolysis and electrolytes
Replies: 1
Views: 15

Re: Electrolysis and electrolytes

Changing the concentration of the electrolyte alters the resistance. Lower concentration correlates with higher resistance. Higher resistance means a lower current flow, for a given applied voltage. So lowering the concentration will lower the current flow.
by Chem_Mod
Thu Feb 25, 2021 8:00 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: water electrolysis
Replies: 1
Views: 25

Re: water electrolysis

2H2O + 2e- = > H2 + 2OH- cathode
H2O => 1/2 O2 + 2H+ + 2e- anode
by Chem_Mod
Thu Feb 25, 2021 7:58 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst equations
Replies: 1
Views: 20

Re: Nernst equations

E = Eo- 0.05916 V/n(log Q) or E = Eo- RT/nF(ln Q ) are the two versions that can be used interchangeably when calculating for a reaction not at equilibrium based on the Q value.
by Chem_Mod
Wed Feb 24, 2021 5:09 pm
Forum: Administrative Questions and Class Announcements
Topic: Matthew's Workshop - Week 8
Replies: 0
Views: 149

Matthew's Workshop - Week 8

Hi everyone!

Happy Week 8 :)

Here's the worksheet for tonight's session. See ya'll at 6!

*TYPO: The first reaction given in 3b should have 2H2O.

*Answers are posted!

-Matt
by Chem_Mod
Wed Feb 24, 2021 2:40 pm
Forum: Balancing Redox Reactions
Topic: remembering oxidation vs reduction
Replies: 9
Views: 34

Re: remembering oxidation vs reduction

Another way of thinking about it is looking at the oxidation number: if it goes down, it is reduction. For example, from 6+ -> 3+, the number is going down, so the number is reducing. Similarly, if you are going form 1- -> 3-, the number is reducing.
by Chem_Mod
Wed Feb 24, 2021 2:27 pm
Forum: Balancing Redox Reactions
Topic: Acidic or Basic
Replies: 3
Views: 25

Re: Acidic or Basic

The redox reactions will be done in basic or acidic conditions, and the question should specify this in some way. Sometimes it will tell you directly that it is in acidic conditions, or sometimes it will have an acid in the equation. In each case, you can use the H + ions to balance. Similarly for b...
by Chem_Mod
Wed Feb 24, 2021 2:25 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Chromium Plating
Replies: 2
Views: 17

Re: Chromium Plating

The general idea of electroplating is just that you are using the base metal (in the example, Fe) as a passive electrode to donate electrons to reduce the plating metal cations (in the example, Cr) to metal. For example, if using trivalent chromium, Cr^{3+}(aq) +3e^{-}\rightarrow Cr(s...
by Chem_Mod
Wed Feb 24, 2021 2:24 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Sapling 7/8 Question 17 [ENDORSED]
Replies: 3
Views: 111

Re: Sapling 7/8 Question 17 [ENDORSED]

Since both pressure (1 atm approximately equal to 1 bar) and concentration are referenced (standard reduction potentials) with respect to standard conditions (gases 1 bar, solutions 1M), one can use (bar or atm) and molarity in the Nernst equation.
by Chem_Mod
Wed Feb 24, 2021 1:50 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: lecture 20 [ENDORSED]
Replies: 2
Views: 60

Re: lecture 20 [ENDORSED]

The [H 3 O] + concentration difference in the electrode and in the solution generate a voltage difference which is measured, and using the Nernst equation the concentration of [H 3 O] + is calculated. More specifically the pH (log [H 3 O + ]) is calculated. Re-watch my lecture discussing the applica...
by Chem_Mod
Wed Feb 24, 2021 12:45 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ion-selective electrode
Replies: 4
Views: 29

Re: Ion-selective electrode

These ion-selective electrodes measure the concentration of the product or the reactant. For example, the pH meter (glass electrode) measures the H+ concentration, where all variables of the Nernst equation are known except for the concentration of the product or reactant.
by Chem_Mod
Wed Feb 24, 2021 10:27 am
Forum: Administrative Questions and Class Announcements
Topic: Internet Restrictions
Replies: 4
Views: 61

Re: Internet Restrictions

Bethany Yang 2E wrote:Oh man, sorry to hear about the internet. If you are in the chem groupme, there is a drive with the UA worksheets that people post in! I find it helpful when I can't make it to a session to do it after on my own. People often post the answers too so it helps!


Great. Thank you. This also helps.
by Chem_Mod
Wed Feb 24, 2021 9:28 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm 2 score release
Replies: 13
Views: 145

Re: Midterm 2 score release

Most likely tomorrow, Thursday. CCLE does not allow bonus points. It forces all calculations out of total points (84). For example CCLE calculates 80/84 as 95%. I am implementing a work around so that everything is calculated out of 80 points. I will explain in class email Thursday. CCLE will show t...
by Chem_Mod
Wed Feb 24, 2021 6:55 am
Forum: Administrative Questions and Class Announcements
Topic: Internet Restrictions
Replies: 4
Views: 61

Re: Internet Restrictions

Fortunately I organized over 60 hours a week of zoom sessions. Attend UA and TA hours that are available when your internet is on. Also many post their worksheets, etc., on Chemistry Community which is available 24/7. My lectures and Sapling Learning are also available 24/7. Hope this helps and thin...
by Chem_Mod
Tue Feb 23, 2021 2:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When to put Pt(s) in a cell [ENDORSED]
Replies: 4
Views: 56

Re: When to put Pt(s) in a cell [ENDORSED]

Charlotte Adams 1A wrote:
Arya Adibi 1K wrote:As stated by Chem_Mod, Whenever a conducting electrode is needed, use Pt.

You would need a conducting electrode whenever either the reactants or products are aqueous and don't have a solid conductor.

Just to clarify, can a conducting electrode be an anode or a cathode?


Yes
by Chem_Mod
Tue Feb 23, 2021 2:42 pm
Forum: Calculating Work of Expansion
Topic: Reversible pathways [ENDORSED]
Replies: 2
Views: 37

Re: Reversible pathways [ENDORSED]

Anyone working on this. :-)
by Chem_Mod
Tue Feb 23, 2021 2:38 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Water Entropy [ENDORSED]
Replies: 5
Views: 32

Re: Water Entropy [ENDORSED]

Correct.

To determine a favorable process need:

Total entropy > 0
or
Gibbs free energy system < 0
by Chem_Mod
Tue Feb 23, 2021 12:34 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 220
Views: 15955

Re: Advice from a Medical Student - Part II [ENDORSED]

Thank you so much for the part 2! Reading this is really inspiring and motivating, especially right now during week 8. Wishing you the best of luck!! Thank you so much! Once I graduate in April, I'm hoping to have a bit of time where I can do a part 3 and detail the process of residency application...
by Chem_Mod
Tue Feb 23, 2021 12:31 am
Forum: Administrative Questions and Class Announcements
Topic: Advice from a Medical Student - Part II [ENDORSED]
Replies: 220
Views: 15955

Re: Advice from a Medical Student - Part II [ENDORSED]

I was wondering what particular classes made you interested in medicine/ particular clubs? As an MCDB major, I really enjoyed many of the upper division courses. My favorite was a stem cell bio course. To me it's just fascinating to study the pluripotency of various cells. I think going into colleg...
by Chem_Mod
Mon Feb 22, 2021 11:20 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Max potential Difference [ENDORSED]
Replies: 1
Views: 33

Re: Max potential Difference [ENDORSED]

I'll use the example I gave in class.

You have two beakers. One with 1L water. The other empty.
When does the maximum difference in water volume occur?

Ans. When no water is flowing.
by Chem_Mod
Mon Feb 22, 2021 8:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: table for potential difference [ENDORSED]
Replies: 1
Views: 28

Re: table for potential difference [ENDORSED]

The Appendix in the textbook list the standard reduction values and half-reactions.
by Chem_Mod
Mon Feb 22, 2021 4:22 pm
Forum: Balancing Redox Reactions
Topic: Sapling Week 7/8 #3
Replies: 2
Views: 28

Re: Sapling Week 7/8 #3

For a particular redox reaction, BrO− is oxidized to BrO 3 - and Ag+ is reduced to Ag . Complete and balance the equation for this reaction in basic solution. Can someone explain how to balance the half reaction BrO- --> BrO 3 - for this problem? Balancing the half reaction with Ag was similar to t...
by Chem_Mod
Mon Feb 22, 2021 4:06 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity [ENDORSED]
Replies: 1
Views: 20

Re: Molecularity [ENDORSED]

We are covering electrochemistry this week.

Next week I will discuss 1st order, 2nd order, and zero order reactions.
When I cover reaction mechanisms it will be clear why we focus on these three in general chemistry.
Hint, they are the most common.
by Chem_Mod
Mon Feb 22, 2021 4:01 pm
Forum: Second Order Reactions
Topic: 2nd order Half Life [ENDORSED]
Replies: 1
Views: 34

Re: 2nd order Half Life [ENDORSED]

For a second-order reaction, the half-life is inversely related to the initial concentration of the reactant (A). t 1/2 = 1/k[A] o As the reactant concentration decreases the half-life is longer (slower reaction as there are fewer bimolecular collisions due to lower reactant concentration). Converse...
by Chem_Mod
Mon Feb 22, 2021 3:07 pm
Forum: Balancing Redox Reactions
Topic: Balancing Resources
Replies: 2
Views: 9

Re: Balancing Resources

Hi Marlene, Not a resource, but I can try to explain the thought process I use. I'll go through one of the book self-tests to help illustrate this. "Copper reacts with dilute nitric acid to form copper(II) nitrate and the gas nitric oxide, NO. Write the balanced net ionic equation for the react...
by Chem_Mod
Mon Feb 22, 2021 2:37 pm
Forum: Balancing Redox Reactions
Topic: salt bridge?
Replies: 8
Views: 23

Re: salt bridge?

Most of these replies are correct. The salt bridge shuffles ions between the two sides to balance out the charge of the ions being generated/reacted away on either side of the cell. For example, at the anode during the discharge of a battery, positive ions are being created through oxidation of the ...
by Chem_Mod
Mon Feb 22, 2021 2:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: mols in calculating gibbs free energy
Replies: 5
Views: 26

Re: mols in calculating gibbs free energy

Correct, the moles used in the Nernst equation are the moles of electrons being transferred from the oxidized species to the reduced species. When forming a balanced redox equation, you are looking to balance the number of electrons so an equal number are donated by the species being oxidized and ac...
by Chem_Mod
Mon Feb 22, 2021 2:14 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Giibbs Free Energy and Equilibrium
Replies: 3
Views: 15

Re: Giibbs Free Energy and Equilibrium

Yes, whenever Q<K the reaction will be spontaneous. We can show this by relating standard Gibbs free energy to the equilibrium constant K, \Delta G ^\circ = -RTlnK and the equation for the nonstandard Gibbs free energy \Delta G = \Delta G^\circ +RTlnQ you get the equation \Delta G = RTln(\frac{Q...
by Chem_Mod
Sun Feb 21, 2021 7:59 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Charging a cell [ENDORSED]
Replies: 1
Views: 37

Re: Charging a cell [ENDORSED]

It is experimental observation. A battery can do work (chemical energy in a redox reaction converted to electrical energy): delta G is negative for the redox reaction. When a battery is recharged the reverse redox reaction occurs: delta G is positive. Here electrical energy is converted to chemical ...
by Chem_Mod
Sun Feb 21, 2021 7:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Hydrogen Electrode [ENDORSED]
Replies: 2
Views: 35

Re: Standard Hydrogen Electrode [ENDORSED]

To measure a voltage difference one needs two electrodes. Cannot measure a voltage difference with one electrode. Correct, I give all the standard reduction half reactions and their E o (standard voltage) values that were measured under standard conditions while connected to the standard hydrogen el...
by Chem_Mod
Sun Feb 21, 2021 7:44 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: electrodes [ENDORSED]
Replies: 1
Views: 68

Re: electrodes [ENDORSED]

The most common reference electrode is the standard hydrogen electrode (SHE). This is the reference electrode I discuss in class. There are other reference electrodes: https://en.wikipedia.org/wiki/Reference_electrode The calomel electrode uses mercury, but given its toxicity and environmental impac...
by Chem_Mod
Sun Feb 21, 2021 7:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge [ENDORSED]
Replies: 2
Views: 38

Re: Salt Bridge [ENDORSED]

The Na+ and Cl- diffuse through the salt bridge.
The salt bridge is a high water content gel-like material that enables ion diffusions.

Good questions. In class I focus on the main concepts. I think I mentioned the salt bridge is gel-like.
by Chem_Mod
Sun Feb 21, 2021 6:57 pm
Forum: Balancing Redox Reactions
Topic: Electrolyte Used [ENDORSED]
Replies: 4
Views: 53

Re: Electrolyte Used [ENDORSED]

In a redox reaction, does the electrolyte used make a difference in the reaction? Or do electrolytes serve the same purpose and thus it is not important to know which electrolyte is used? Since electrolytes are not directly involved in the redox reaction (not oxidized or reduced) they are less impo...
by Chem_Mod
Sat Feb 20, 2021 6:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Textbook Problem 6L.1
Replies: 5
Views: 26

Re: Textbook Problem 6L.1

Think of "n" as the number of moles of electrons that would be transferred during this reaction. To do this, you can break down the reaction into two simple half reactions. In doing so, you will see that two moles of electrons are being used to reduce 2 Ce 4+ to 2 Ce 3 +. In general, it is...
by Chem_Mod
Sat Feb 20, 2021 3:43 pm
Forum: Balancing Redox Reactions
Topic: Chemical Reactions and Electrical Energy
Replies: 6
Views: 13

Re: Chemical Reactions and Electrical Energy

Chemical reactions produce electrical energy via reactions such as redox (reduction and oxidation) reactions. In these reactions, the species that is oxidized gives up electrons at the anode, where it is then transferred to the cathode where species gain electrons to be reduced. It is through the tr...
by Chem_Mod
Sat Feb 20, 2021 1:36 am
Forum: Student Social/Study Group
Topic: Post Midterm 2 De-stressing
Replies: 90
Views: 240

Re: Post Midterm 2 De-stressing

Audra Mcleod 3G wrote:I unfortunately still have a fair amount of work to do over the weekend for Chem 14BL, but right after the midterm I went out to eat with my family which really helped unwind and forget about chemistry!


But good food is good chemistry.
:-)
by Chem_Mod
Fri Feb 19, 2021 11:05 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework 3/4 #12
Replies: 2
Views: 29

Re: Homework 3/4 #12

May you give a little more information about the problem, so that the text does not need to be referenced please. Thanks :)
by Chem_Mod
Fri Feb 19, 2021 10:37 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Combustion and Spontaneity [ENDORSED]
Replies: 3
Views: 55

Re: Combustion and Spontaneity [ENDORSED]

Yes they are.

The ignition is to overcome the energy barrier (which is kinetics), it does not change the thermodynamics (favorable reaction).
by Chem_Mod
Fri Feb 19, 2021 10:32 am
Forum: Student Social/Study Group
Topic: New Joke Chain
Replies: 46
Views: 212

Re: New Joke Chain

Please post all jokes here: viewtopic.php?f=156&t=4291

Thank you
by Chem_Mod
Thu Feb 18, 2021 11:09 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry question outline 3
Replies: 2
Views: 8

Re: Calorimetry question outline 3

Exothermic reactions release heat. If the reaction is done in a calorimeter, the heat will be absorbed by the calorimeter, which will then increase in temperature. So if given the change in temperature of the calorimeter and its heat capacity, you should be able to find how much heat was released by...
by Chem_Mod
Thu Feb 18, 2021 11:07 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: delS at Equilibrium
Replies: 4
Views: 16

Re: delS at Equilibrium

If the substance is changing phase, it is not at equilibrium. It will be at equilibrium once the process is complete
by Chem_Mod
Thu Feb 18, 2021 10:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: textbook 4D.9
Replies: 1
Views: 6

Re: textbook 4D.9

Don’t get hung up on the negative sign; it’s the same as giving a positive answer when one is asked how much energy is released
by Chem_Mod
Thu Feb 18, 2021 10:54 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: delta U=nCvdeltaT
Replies: 4
Views: 28

Re: delta U=nCvdeltaT

At constant volume, dU=q and q=nCvdT
by Chem_Mod
Thu Feb 18, 2021 10:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5J.15
Replies: 3
Views: 17

Re: 5J.15

Check out the free energy of formation for each molecule. If formation is spontaneous than the reverse reaction of decomposition is not spontaneous, meaning the molecule is stable relative to its constitutive elements, which is what it would decompose into
by Chem_Mod
Thu Feb 18, 2021 10:45 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: calc entropy through direction/position [ENDORSED]
Replies: 3
Views: 26

Re: calc entropy through direction/position [ENDORSED]

(a) are all aligned in the same direction There is one unique structure: all 64 molecules are aligned in the same direction degeneracy, W = possible positions N = 1 64 (b) lie in any one of four orientations with the same energy each molecule can have one of four possible orientations degeneracy, W ...
by Chem_Mod
Thu Feb 18, 2021 10:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Problem 4C.3
Replies: 1
Views: 20

Re: Textbook Problem 4C.3

Enthalpy is q at constant pressure, so in b you can think of finding enthalpy as finding how much heat you would have had to add at constant pressure instead of constant volume to reach 373K. dU= q+w = dH-PdV at constant pressure dH= dU + PdV then using PV=nRT, dH= dU + nRdT At constant volume w=0, ...
by Chem_Mod
Thu Feb 18, 2021 9:46 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: adiabatic reactions
Replies: 2
Views: 18

Re: adiabatic reactions

Adiabatic means heat does not leave the system. If your reaction is occurring in an adiabatic calorimeter, the temperature of the calorimeter’s contents can still change, the heat will just not be lost to the surroundings
by Chem_Mod
Thu Feb 18, 2021 9:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Textbook 4I.9
Replies: 3
Views: 16

Re: Textbook 4I.9

Please include the whole problem in your post
by Chem_Mod
Thu Feb 18, 2021 9:30 pm
Forum: Calculating Work of Expansion
Topic: Work Formula
Replies: 15
Views: 46

Re: Work Formula

Just consider the moles of gas because you are using the ideal gas law, which is only for gases.
by Chem_Mod
Thu Feb 18, 2021 9:28 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Temperature and Volume
Replies: 1
Views: 16

Re: Temperature and Volume

Yeah you're on the right track. For this question you want to assume that these events occur independently and not at the same time. So you can use Cv when calculating the change in entropy for a temperature change because now you assume that the volume is constant.
by Chem_Mod
Thu Feb 18, 2021 9:27 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Using Cv vs Cp
Replies: 1
Views: 21

Re: Using Cv vs Cp

There is a temperature and a volume change, but for this question you want to assume that these events occur independently and not at the same time. So you can use Cv when calculating the change in entropy for a temperature change because now you assume that the volume is constant.
by Chem_Mod
Thu Feb 18, 2021 8:45 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Kate's Midterm Review
Replies: 0
Views: 95

Kate's Midterm Review

Hello everyone!

I attached my midterm review worksheet below and the answer key as well. I hope it is helpful and best of luck on your midterm tomorrow! You guys got this :)

Kate
by Chem_Mod
Thu Feb 18, 2021 8:43 pm
Forum: Administrative Questions and Class Announcements
Topic: Office Hours 2/19
Replies: 5
Views: 29

Re: Office Hours 2/19

TA office hours are as scheduled (unless there is overlap/delay with proctoring for that TA).

UA sessions are as scheduled and not impacted by proctoring.
by Chem_Mod
Thu Feb 18, 2021 7:41 pm
Forum: General Science Questions
Topic: Question Regarding Midterm 2 and outlines
Replies: 1
Views: 29

Re: Question Regarding Midterm 2 and outlines

These topics were covered in MT1 (and are not covered in MT2):

• Calculate an overall reaction enthalpy from the enthalpies of the reactions in a reaction sequence (Hess's law/approach).

• Use bond enthalpies to calculate an unknown reaction enthalpy.

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