[IAmError]

I just finished up a 100 question review and these 7 questions I had no clue where to start. Any help would be greatly appreciated. Thanks!

A solution at 25°C contains an H+ ion concentration of 1 × 10-9 M. What is the OH- ion concentration of this solution at 25°C?
 1 × 10-1 M
 1 × 10-5 M
 1 × 10-9 M
 1 × 10-14 M

What is the pH of a solution that has an OH- ion concentration of 1× 10-5 mole per liter
 (Kw = 1 × 10-14)?
 1
 5
 7
 9

Given the reaction at equilibrium: NH4+ + OH- ↔ H2O + NH3
Which species is the Brönsted-Lowry acid in the forward reaction?
NH3
H2O
OH-
NH4+

The value of the ionization constant of water, Kw, will change when there is a change in
temperature
pressure
hydrogen ion concentration
hydroxide ion concentration

Which of the following aqueous solutions is the poorest conductor of electricity? [Refer to Reference Table Adv-8.]
 0.1 M H2S
 0.1 M HF
 0.1 M HNO2
 0.1 M HNO3

The diagram illustrates an apparatus used to test the conductivity of various solutions.



When the switch is closed, which of the following 1-molar solutions would cause the bulb to glow most brightly?
ammonia
acetic acid
carbonic acid
sulfuric acid

[Borek]

You have to show your attempts at solving the question to receive help. This is a forum policy.

http://www.chembuddy.com/?left=pH-calculation&right=water-ion-product

[IAmError]

1.) 1 × 10-9 M

I assume because [H+] = [-OH]

2.) 9

(1 x 10-14) / (1 x 10-5) = 10-9

log(10^9) = 9

3.) NH4+

I'm not quite sure how to solve this one but I would assume NH4+ is the one donating protons.

4.) Hydroxide ion concentration

I assume because kw = [OH-][H+]

5.) H2S

I assume because it's at the bottom of table adv-8

6.) Carbonic Acid? I really have no idea on this one.

Also I accidentally left out 7:



I assume 1 because reactants over products.

Thanks.

 

[IAmError]

Ok, I figured out the right answers to all of them except 4 and 5.

The value of the ionization constant of water, Kw, will change when there is a change in
temperature
pressure
hydrogen ion concentration
hydroxide ion concentration - Wrong

Which of the following aqueous solutions is the poorest conductor of electricity? [Refer to Reference Table Adv-8.]
 0.1 M H2S
 0.1 M HF
 0.1 M HNO2
 0.1 M HNO3

I've been chatting on skype with a couple friends on how to figure it out. We can't decide between temperature (since many problems include temperature) or hydrogen ion concentration (because of H+). For number 5, we really haven't a clue. At the moment we feel H2S wouldn't work but its an assumption without much backing.

[Sophia7X]

K constants never change if you alter concentration.
Kw = [OH-][H+]. If you change the H+ concentration (for example, if you increase it), the the OH- concentration will decrease to keep Kw the same value.
Temperature affects K.

The ionization of water is endothermic.
H2O   H⁺ + OH^-    ΔH>0
So if you increase the temperature, the forward reaction toward the H+ and OH- is favored and more H+ and OH- are produced so Kw increases as T increases.

The next problem tells you to "Refer to Reference Table Adv-8." because that may be a table of Ka values. The stronger the acid, the better the electrolyte because strong acids completely ionize. I think H2S is the weakest acid because HF, HNO2 are strong-ish acids and HNO3 is a strong acid. So H2S would be the worst conductor.

[confusedstud]

Hi, I'm also quite confused about 6) too. I'm thinking it should be H2SO4 because it is a strong acid so there is a lot more H+ ions and SO4 2- ions compared to the other acids given, so it is better able to conduct electricity than the others? But I'm not quite sure about this though.

[Jorriss]

The value of the ionization constant of water, Kw, will change when there is a change in
temperature
pressure
hydrogen ion concentration
hydroxide ion concentration - Wrong

This is why I highly dislike conceptual multiple choice questions.

Kw DOES have a pressure dependence as well as a temperature dependence but, as is the case in most solid and liquid equilibria, the pressure dependence is small in normal pressure ranges and is neglected.

4.) Hydroxide ion concentration

I assume because kw = [OH-][H+]

That equation has OH- and H+ on completely equal footing. Why would you say hydroxide ion and not hydrogen ion concentration?