Question

Kb "weak base calculations"

1. The hydronium ion concentration of an aqueous solution of 0.538 M ammonia is

H3O+ _______ M

Kb WEAK BASE CALCULATIONS

2. The pOH of an aqueous solution of 0.408 M isoquinoline(a weak base with the formula C9H7N) is _______

* the formula for this is not -log[OH-]

Buffer:

3. A solution contains 0.460 M sodium cyanide and 0.314 M hydrocyanic acid.

The pH of this solution is _____.

4. 2NOBr <-----> 2NO + Br2

If 0.234 moles of NOBr, 0.336 moles of NO, and .350 moles of Br2 are at equilibrium in a 17.9 L container at 455 K, the value of the equilibrium constant, Kp, is ______.

5. A student ran the following the reaction in the laboratory at 584 K:

CO + Cl2 <-----> COCl2

When she introduced CO and Cl2 into a 1.00 L evacuated container, so that the initial partial pressure of CO was 2.78 atm and the initial partial pressure of Cl2 was 1.72 arm, she found that the equilibrium partial pressure of COCl2 was 1.38 atm.

Kp= ______

Answer 1

1) H2O + NH3 -----> NH4+ + OH-

------ 0.538M 0 0

------- 0.538-x x x

Kb ammonia 1.8x10^-5=[OH-][NH4+]/[OH-]= x²/0.538-x -------> x= 3.1x10^-3M

[H3O+][OH-]=1x10^-14

[H3O+]= 1x10^-14/3.1x10^-3= 3.23x10^-12M

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2) Kb isoquinoline= 2.5x10^-9

C9H7N + H2O -----> C9H7NH+ + OH-

0.408M ----- 0 0

0.408M -x x x

Kb= x²/0.408-x ----> x=3.19x10^-5M -----> pOH= -log 3.19x10^-5​= 4.5

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3) pH= pKa + log [A-][HA]= 9.21 + log 0.460/0.314= 9.37

A- is the conjugated base of the acid HA, in this case CN- is the conjugated base of the acid HCN

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4) Kc= [Br2][NO]²/[NOBr]² =(0.35mol/17.9L) x (0.336mol/17.9L)²/(0.234mol/17.9L)²= 0.0403

Kp= Kc(RT)^Dn

Dn= mol gas at product side - mol gas at the reagent side= 3-2 =1

Kp=0.0403 x 0.082L.atm/molK x 455K= 1.504

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5) CO + Cl2 <------> COCl2

2.78 1.72 0

2.78-x 1.72-x x

x=1.38 atm, because x is the pressure of COCl2 in equilibrium.

Kp= PCOCl2/PCOxPCl2= 1.38/(2.78-1.38)(1.72-1.38)= 2.899