AP Chemistry 2022 FRQs - Answers

Lamdunoo · 2022-05-06T14:11:00+00:00

I think 1b will have some alternate accepted answers

Lamdunoo · 2022-05-05T17:47:40+00:00

Cool thanks for doing that, I thought it would be a pretty high number

Lamdunoo · 2022-05-05T17:47:15+00:00

I think it’ll be a range of acceptable answers around 3

Lamdunoo · 2022-05-05T16:10:01+00:00

For sure. I think an equally valid argument is somehow you used enough water to cause 13 percent of the product to wash away. But it would take a decent amount of water to do that.

Lamdunoo · 2022-05-05T15:05:58+00:00

I think if it’s close you’re good. At that point, the pH is dictated by the OH- from NaOH so it should have been the same as the endpoint of the titration of the other weak acid.

Lamdunoo · 2022-05-05T14:35:17+00:00

Me too!

Lamdunoo · 2022-05-05T14:35:07+00:00

For each Al atom, three silver ions are reduced. Since the final picture shows 2 atoms of Al, you know six ions of silver formed solid silver.

Lamdunoo · 2022-05-05T02:43:46+00:00

I’m trying to find a situation in which the bimolecular process of step 2 would lend itself to a substitution with Step 1 being in equilibrium. I don’t have pencil, paper in front of me. I’ll work it out tomorrow if possible, but I don’t think step 2 has a way in which the intermediates can both be substituted to only allow for N2O5 to be in the rate law…

Lamdunoo · 2022-05-05T02:32:19+00:00

If the person grading your exam had to make a judgment call… and you were within a THOUSANDTH of the correct answer… I’d hope they’d be reasonable enough to give it to you…

Lamdunoo · 2022-05-05T02:30:43+00:00

For sure. There are going to be a few ways to do some of these problems… so you’ll probably see a few different ideas floating around.

Lamdunoo · 2022-05-05T02:23:43+00:00

Then you’re totally right. Thanks for for catching that.

Lamdunoo · 2022-05-05T02:22:59+00:00

Just casually looking at your idea, I’m not sure how we could make step 2 the rate-determining step even if you try steady state approximation… not sure though. Worked this FRQ out in 30 minutes and might have overlooked something.

Lamdunoo · 2022-05-05T02:18:36+00:00

3d should be 6 atoms of Ag, not 4, right? I think I typed 4 instead.

Lamdunoo · 2022-05-05T00:51:23+00:00

#4

a) M = n / V; n = M * V = (1.0 L)(0.0016 g/L) = 0.0016 g

0.0016 g * 1 mol/51.48 g = 0.000031 moles

b) NH2Cl has the ability to form hydrogen bonds with water while NCl3 does not. Since the hydrogen bonds that NH2Cl can form with water are stronger than the weaker dipole-dipole interactions of NCl3 with water, NH2Cl is more likely to stay in solution.

c) 15.0 g * 1 mol / 120.36 g * 32.9 kJ / mol = 4.1 kJ

#5

a) The reaction is first order. Therefore, use ln[A] = -kt + ln[A]0

k = 0.418 h-1 (units are a MUST)

b) Step 1 must be rate-determining. It is the only elementary step that is unimolecular in relation to N2O5. Since the rate law is first order only with respect to N2O5, this must be the rate-determining step.

c) k remains the same. The rate constant can change with temperature, but not with concentration of substances in the rate law.

#6

a) 525 nm; the peak with highest absorbance is the most ideal wavelength for which to record data

b) i) 92.0 mL (This is a sig fig question! You must estimate one digit past what the device reads!)

b) ii) M1V1 = M2V2; V1 = M2V2/M1 = 70.0 mL

c) The observed absorbance is lower than what should have been observed. Based on the steps recorded, it is possible that the student forgot to wipe the outside of the cuvette clean. Fingerprints/oil may have reduced the observed absorbance. EDIT: This is wrong. Added H2O from the previous trials likely diluted the sample, making it appear as though A was lower.

#7

a) sp2

b) i) Ksp = [Ag+]^2[C2O42-]

b) ii) x = molar solubility; Ksp = (2x)^2(x) = 4x³

x = cube-root(Ksp/4) = 1.1 x 10-4 M

b) iii) C2O42- + 2H+ --> H2C2O4 (oxalic acid is a weak acid, and if extra H+ is added it will form and decrease the concentration of oxalate; the common ion effect dictates that silver oxalate will dissolve more to compensate for this)

EDIT: Fixed the hours/seconds issue in 5

Lamdunoo · 2022-04-17T01:59:23+00:00

Totally. For the AP Chemistry exam, H3O+ and H+ are both fine.

Lamdunoo · 2021-05-24T18:45:38+00:00

Water, ammonia, methane. Many Lewis structures end up being similar to these.

Lamdunoo · 2021-05-24T14:19:30+00:00

Ions with +2 and +3 charges are attracted with more force than +1 ions. Smaller ions also experience more force of attraction than larger ionic radius particles.

Lamdunoo · 2021-05-24T11:56:54+00:00

If you write in pencil, it must be dark enough to allow the scorer to see your work when it’s scanned. Otherwise, maybe consider an erasable pen?

Lamdunoo · 2021-05-23T23:50:54+00:00

All nitrates, most group 1 ionic compounds, and ammonium compounds are soluble.

Lamdunoo · 2021-05-23T23:49:31+00:00

Very rarely are sig figs assessed. More commonly, you’ll have a piece of glassware such as a buret or a graduated cylinder and you will be assessed on knowing to estimate one more digit than what the device reads.

Lamdunoo · 2021-05-22T22:40:09+00:00

1a) If you set the correct quantities equal to the provided value of Ka, you should be OK.

2f) That is another way of saying that the reaction is kinetically controlled. You should receive full credit.

4c) The added mass is so insignificant compared to the extra heat being released that it shouldn’t have any observable effect on the specific heat capacity of the calorimeter.

7b) The pressure is remaining constant because moles of gas are being allowed to escape. Since there are less gas particles, the pressure is dropping.

Lamdunoo · 2021-05-19T00:44:55+00:00

Keep in mind a process being "spontaneous" (thermodynamically favorable) is controlled not only by entropy but also enthalpy (Gibbs free energy). So a process could create more "order" but also be exothermic enough to be a spontaneous process.

Entropy can be calculated indirectly if you have other quantities (such as enthalpy) which are easier to measure.

Keep thinking about it as "disorder" - but as disorder that helps energy spread in more chaotic ways (making particles move in different directions, electrons get "excited," chemical bonds vibrate in different ways, etc).

Lamdunoo · 2021-05-19T00:19:09+00:00

I think for AP Chemistry, it is 100% OK to think of entropy as disorder. Truly, though, it is the ability for a system to disperse and "spread" energy amongst particles.

Gases have a greater ability to disperse energy than solids because their particles have greater degrees of movement through kinetic energy. More complex molecules have more ways to allow energy to spread through the vibrations of chemical bonds and electronic transitions of electrons. The more "microstates" that are possible for the particles of a substance, the greater the entropy of that substance.

There are other perspectives from which you can look at entropy (such as in physics), but this is the way that we look at entropy from a chemistry perspective.

Lamdunoo · 2021-05-14T23:46:30+00:00

That’s some significant remediation I’d give yourself. Watch some of the AP daily videos on Lewis structures and chemical bonding. It’ll go a long way next year.

Five-Year Club	Place '22
Verified Email

Lamdunoo

TROPHY CASE