have ceased. l reaction equals that of the reverse. b) The rate of the f c) The
ID: 692179 • Letter: H
Question
have ceased. l reaction equals that of the reverse. b) The rate of the f c) The rate constant for the forward reaction equals that of the reverse. d) Both the rate of the forward reaction equals that of the reverse and the rate constant for the forward reaction equals that of the e) none of the above 37 What is the oxidation number of each sulfur atom in osmium (V) sulfate dihydrate? 38. A reaction with activation energy of 123 kJ/mol has a rate constant or0.200 s at 311 K. At what temperature will its rate constant be 39. The reduction half reaction occurring in the standard hydrogen electrode is double that at 311 K? a) Hdg. I atm) 2HTaq. IM) + 2e. c)02(g) 4H (aq) , 4e. 211,0(1) b) 211"(aq) +2011. Hyor) 40. The half-life for a certain first order reaction is 13 minutes. If the initial concentration of reactant is 0.085 M, how many minutes will it take for it to decrease to 0.055 M? 41. Ka for HF is 6.8 X 10+ What is the pH of a 0.35 M solution of HF? 42. Consider the titration of 25.0 ml. of 0.723 M HCIO, with 0.273 M KOH. Calculate the H,O' concentration before any KOH is added. 43. Calculate the concentration of hydronium ions in a solution with a pOH of 4.223. 44. In acidic solution MnO oxidizes HAsO, a weak acid, to HsAs0, a weak acid, and is reduced to Mn2 Write the balanced net ionie equation for this reaction. How many H' are there in the balanced equation? 45. Write the balanced formula unit cquation for the reaction of iron(ll) hydroxide with hydrochloric acid. What is the sum of the coefficients? (Do not forget coefficients of one.) 46. Which one of the following statements is true? CHN|12 + HsO ·-CHN11. +Explanation / Answer
Answered 4 questions:
36.
Answer is option (b)
The rate of forward reaction equals to rate of the reverse reaction (By definition).
37.
Osmium (V) sulfate dehydrate - Os2(SO4)5.2H2O
the dihydrate does not affect the oxidation number
O has always oxidation number = -2 ( except peroxides)
Os = +5
So,
2(+5) + 5 [x + 4(-2)] = 0
10 + 5 (x – 8) = 0
5 (x – 8) = - 10
x – 8 = - 2
x = - 2 + 8
x = +6
38.
Integrated Arrhenius equation is given by
ln(k2/k1) = (Ea/R) (1/T1 – 1/T2)
Here,
k1 = 0.200 s-1,
T1 = 311 K,
Ea = 123 kJ/mol = 123000 J/mol
k2 =2 x k1 = 2 x 0.200 s-1 = 0.400 s-1
T2 = ?
So,
ln(k2/k1) = (Ea/R) (1/T1 – 1/T2)
ln(0.400 s-1 / 0.200 s-1) = (123000 J mol-1 / 8.314 J K-1 mol-1) (1/311 K – 1/T2)
ln (2) = 14794 (1/311 – 1/T2)
0.693 = 14794 (1/311 – 1/T2)
(1/311 – 1/T2) = 0.693 /14794
(0.003215 – 1/T2) = 0.000047
1/T2 = 0.003215 – 0.0000468
1/T2 = 0.0031682
T2 = 1 / 0.0031682 = 316 K
So, the temperature is 316 K
41.
HF = H+ + F-
IC: 0.35 0 0
C: - x + x +x
EC: 0.35 – x x x
Ka = [H+] [F-] / [HF]
6.8 x 10-4 = (x) (x) / (0.35 – x)
6.8 x 10-4 = x2 / (0.35 – x)
x2 = 0.00068 (0.35 - x)
x2 = 0.000238 - 0.00068x
x2 + 0.00068x - 0.000238 = 0
Solving the quadratic equation, we get
x = 0.015 and x = -0.01577
Discarding the negative value of x, we have
x = 0.015
So, [H+] = x = 0.015
pH = - log [H+]
= - log (0.015)
= 1.82
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