[thebassoe]

Reviewing with a practice test and have no idea how some of these answers were derived. I'm using ICE tables/quadratic formulas etc. but I keep getting the wrong answers.

1. At a particular temperature, the H2O is initially 1.00M and the CO is initially 2.00M. What is the CO2 concentration when the reaction reaches equilibrium?
CO + H2O <---> H2 + CO2  Kc= 1.56  (all compounds are gas)

The supposed correct answer is 0.73 but I can't get to this conclusion.

2. At a particular temperature, the H2O concentration is initially .100M. What is the H2 Concentration when the reaction reaches equilibrium?
2H20 <---> 2H2 + O2  Kc= 7.3 x 10^-7   (all compounds are gas)

The supposed correct answer is 7.3 x 10^-14 and once again I can't get to that answer.

3. What is the pH of a 0.63 M solution of a weak base at 25C if the Kb= 9.5 x 10^-7?

The supposed correct answer is 10.89

-I've tried very hard on all three of these and think I know what I'm doing but come to different answers. Any help on any 1 or more of these problems would be greatly appreciated as my test is tomorrow morning and I'm stressing out pretty bad right now. Thank you.

-Shannon L.

[fledarmus]

What have you done so far?

[thebassoe]

What have you done so far?

For 1. I made an ice table from which I got 1.56= 2x/(2-x)(1-x). I factored and moved around until 1.56x^2 - 6.68x  + 3.12 = 0
Using the quadratic gave me I believe .53 rather than .73

For 2. I also made an ice table from which I got 7.3 x 10^-14 (from which I will just call Kc from now on) = (.5x^2)/(1-x). After moving things around I got .5x^2 + (Kc)(x) -Kc = 0
Using quadratic I don't remember my exact answer since I didn't write it down but it was wrong (or not what the paper says it should be).

For 3. I tried the ICE table set up like 1 and 2. I also tried taking Kw / Kb = Ka then using -log but that was wrong. I tried a whole mess of things with this one and am not very sure of the process for this one.

All help is greatly appreciated. Thank you.