Please show all work!!!! Thanks! 1. Consider the rxn A---P 2nd order in A with K
ID: 784480 • Letter: P
Question
Please show all work!!!! Thanks!
1. Consider the rxn A---P 2nd order in A with K=.20min^-1
Starting with conc A=10.0 M what is the conc. after 120.0s
a. 9.6 M b. 2.0 M c. 6.7M d. .04M
2. Fe2S3(s) has S=2.1x10^-18M. What is its S in pure water?
a. 4.5x10^-6 b. 2.1x10^-3 c. 2.9x10^-4 d. 1.1x10^-4
3. Addition of H (increasing acidity) will increase S (entropy) for each
of the following except
a. Ca(OH)2 b. BaF2 c. AgCl d. PbS
4. Which of the following does not have higher exp. S (entropy) than calculated S
in pure H20
a. CaCO3 b. AgCl c. PbSo4 d. MgF2
5. Consider the reaction:
NH3(aq) + H20(l)---- NH4(aq) = OH(aq)
a. the NH3 is acting as an Arrhenius base and a B.L. acid
b. the H20(l) is acting as both a B.L. acid and B.L. base
c. The NH3 is acting as an Arrhenius base and a B.L. base
d. The NH3 is acting as a B.L. base and its conj. acid is OH
6. Consider a solution .10M NaA, the sodium salt of HA with
Ka= 1.0x10^-5 Calculate the pH of this solution in pure H20
a. 9.00 b. 5.00 c. 7.00 d. 8.00
Explanation / Answer
1) t = (1/k) (1/a-x -1/a) , t = 120sec = 120/60 = 2 min ,
2 =(1/0.2)(1/a-x -1/10)
a-x = 2 hence answer is B
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2)Fe2S3(s) == 2Fe+3 + 3s-2
=(2s)^2(3s)^3
=108 s^5 =2.1x10^-18M
So S = 1.1x10^-4 hence answer = D
------------------------
3) answer is A
a. Ca(OH)2 because H20 will be formed
--------------------
4)d. MgF2
in water MGF2------------------->Mg +2F-
--------------------------
5) Answer iS D
Lowry base is defined as anything that accepts H1+ ions
-------------------------
6) A-(from NA) + H2O <---> OH- + HA ,
hence Kb for reaction Kw/Ka(HA) = 10^-14/10^-5 = 10^-9
Kb = 10^-9 = [OH-][HA]/[A-] = x^2/(0.1-x)
x = 10^-5 =[OH-] , pOH = 5, pH = 14-5 = 9
hence ansewer is A
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