Download Acid-Base Equilibrium (10 questions)

King Saud University
Faculty of Science
Chemistry Department
101-Chem Final Exam
General Chemistry-I
Second Term 1432-33
Name: --------------------------------------------Student No. --------------------------------------
Mon. 14/7/1433
Time: 8:00-11:00
Signature: ----------------------------------------
Put your answers in the following boxes
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Total: _________
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NA = 6.02 x 1023 mol-1
R = 0.082 atm.L/mol.K = 8.314 J/mol.K
Atomic Weight: H:1, He:4, C:12, O:16, Na:23, Cl:35.5, K:39, Ca:40, Br:80,
Kr:83.8 amu.
1 atm = 760 mmHg = 101.325 kPa
1 Cal = 4.18 J
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Choose the correct answer:
1) A compound was analyzed and found to contain 75%w/w carbon and 25%w/w
hydrogen. What is the compounds empirical formula?
A) CH
B) CH2
C) CH3
D) CH4
--------------------------------------------------------------------------------------------------------------------2) Given the reaction:
N2(g) + 3 H2(g)
2 NH3(g)
What is the total number of moles of NH3(g) produced when 10.0 moles of H2(g) reacts
completely with N2(g)?
A) 6.7
B) 2.0
C) 3.0
D) 1.5
--------------------------------------------------------------------------------------------------------------------3) The molecular formula of a compound is represented by X3Y6. What is the empirical
formula of this compound?
A) X3Y
B) X2Y
C) XY2
D) XY3
--------------------------------------------------------------------------------------------------------------------4) What is the total number of moles of sulfur atoms in 1 mole of Fe2(SO4)3?
A) 1
B) 3
C) 17
A. D) 15
--------------------------------------------------------------------------------------------------------------------5) Which sample contains a total of 6.02 x 1023 atoms?
A) 23 g Na
B) 24 g Ca
C) 42 g Kr
D) 78 g K
------------------------------------------------------------------------------------------------------------------6) A mixture of CO2, O2, and He is held at constant temperature. Which molecule has the
highest average molecular speed?
A) CO2
B) O2
C) He
D) all are the same
--------------------------------------------------------------------------------------------------------------------7) Three 1.00 L flaskes at 25 ºC and 725 torr contain the gases CH4 (flask A), CO2 (flask B),
and C2H6 (flask C). In which flask is there 0.039 mole of gas?
A) flask A
B) flask B
C) flask C
D) all
------------------------------------------------------------------------------------------------------------------8) An ideal gas is contained in a volume V in L at temperature T in K. If the volume is
doubled at constant pressure, the temperature will be:
A)Unchanged B)halved C)doubled D)unable to be determined without more information
--------------------------------------------------------------------------------------------------------------------9) Consider three one-liter flasks at STP. Flask A contains NH3 gas, flask B contains NO2
gas and flask C contains N2 gas. Which contains the largest number of molecules?
A) flask A
B) flask B
C) flask C
D) all are the same
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10) What is the mass of 1 mole of a gas that has a density of 2.00 grams per liter at STP?
A) 11.2 g
B) 22.4 g
C) 33.6 g
D) 44.8 g
--------------------------------------------------------------------------------------------------------------------11) The value of ΔHfº for NaCl(s) is (- 410. kJ/mol.) How many kJ are liberated when 19.3 g
of NaCl(s) is produced?
B) 410 kJ
C) 1233 kJ
D) 7942 kJ
A) 135 kJ
------------------------------------------------------------------------------------------------------------------12) The standard enthalpy of reaction, Horxn, for following reaction;
NH3(g) + HCl(g)  NH4Cl(s)
Is (-175.9 kJ mol-1). Determine the value of Eorxn for this reaction.
A) -164.8 kJ mol-1
B) -170.9 kJ mol-1
C) -173.4 kJ mol-1
D) -180.9 kJ mol-1
-----------------------------------------------------------------------------------------------------------------13) How much energy is required to raise the temperature of 38.0 g of liquid
H2SO4 from 25ºC to 75ºC? [Specific heat, cS = 1.67 J/gºC]
A) 4.8 kJ
B) 1.6 kJ
C) 63 kJ
D) 3.2 kJ
14) Calculate the enthalpy of reaction for the formation of phosphoric acid from the
following unbalanced equation:
------ P4O10(s) + ---- H2O(l) → ------- H3PO4(aq)
Using the following enthalpies of formation:
ΔHof(P4O10(s)) = -2984 kJ/mol , ΔHof(H2O(l)) = -286 kJ/mol , ΔHof(H3PO4(aq)) = -1288 kJ/mol
A) - 452 kJ/mol
B) - 4520 kJ/mol
C) - 8283 kJ/mol
D) 8283 kJ/mol
--------------------------------------------------------------------------------------------------------------------15) When work is done by a system at constant temperature, which of the following is true?
A) q + W = 0
B) W is positive.
C) W is negative.
D) ∆E(surr) is negative.
--------------------------------------------------------------------------------------------------------------------16) The following data were measured for the reaction
BF3 (g) + NH3(g) → F3BNH3(g)
Exp. [BF3](M) [NH3](M) Rate(M/s)
1
0.250
0.250
0.2130
2
0.250
0.125
0.1065
3
0.200
0.100
0.0682
4
0.350
0.100
0.1193
The rate law is; rate = ____________.
A) k [BF3]2[NH3]3
B) k [BF3][NH3]
C) 3 k [BF3]2[NH3]
D) k [BF3][NH3]2
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17) Which energy difference in figure below corresponds to the activation energy for the
forward reaction?
A) x
B) y
C) x+y
D) x-y
---------------------------------------------------------------------------------------------------18) The reaction A → B is first order in [A]. Consider the following data. The rate constant
k, for this reaction is __________s-1.
A) 0.013
B) 0.030
C) 0.14
D) 3.0
--------------------------------------------------------------------------------------------------19) If the rate law for the reaction
2A + 3B → product
Is first order in A and second order in B, then the rate law is; rate = ____________.
A) k[A][B]
B) k[A]2[B]3
C) k[A][B]2
D) k[A]2[B]
-----------------------------------------------------------------------------------------------------------------20) The initial concentration of reactant in a first-order reaction is 0.27 M. The rate
constant for the reaction is 0.75 s-1. What is the concentration of reactant after 1.5 s?
B) 1.7 M
C) 8.8 x 10-2 M
D) 2.0 x 10-2 M
A) 3.8 M
-----------------------------------------------------------------------------------------------------------------21) The osmotic pressure of (C12H22O11) solution is 37 torr at 20 °C. What is the molarity of
sucrose?
A) 0.02 x 10-1 M
B) 0.025 x 10-2 M
C) 0.025 x 102 M
D) 0.03 M
--------------------------------------------------------------------------------------------------25) Calculate the vapor pressure of water above a solution prepared by adding 22.5 g of
lactose (C12H22O11) to 200.0 g of water at 338K. (Vapor pressure of water is 187.5 torr).
A) 186.4 torr
B) 189 torr
C) 187.5 torr
D) 0.247 atm
--------------------------------------------------------------------------------------------------23) The solubility of oxygen gas in water at 25 °C and 1.0 atm pressure of oxygen are
0.041 g/L. The solubility of oxygen in water at 3.0 atm and 25 °C is __________ g/L.
A) 0.041
B) 0.014
C) 0.31
D) 0.12
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24) The concentration of KBr in a solution prepared by dissolving 2.21 g of KBr in 897 g of
water is __________ molal.
A) 2.46
B) 0.0167
C) 0.0207
D) 2.07 x 10-5
---------------------------------------------------------------------------------------------------25) What is the freezing point (°C) of a solution prepared by dissolving 11.3 g of nonelectrolyte, non-volatile solute (formula weight = 164 g/mol) in 115 g of water? The molal
freezing point depression constant for water is 1.86 °C/m.
A) - 3.34
B) - 1.11
C) 3.34
D) 1.11
---------------------------------------------------------------------------------------------------26) The equilibrium constants for the following gas-phase reactions at 200oC.
N2(g) + O2(g)  2 NO(g)
Kc= 2.3 x 10-19
2 NO(g) + O2(g)  2 NO2(g) Kc = 3 x 106
What is Kc for reaction below?
N2(g) + 2 O2(g)
A) 7.7 x 10-26

2 NO2(g)
B) 7 x 10-25
C) 7 x 10-13
D) 1.3 x 1025
---------------------------------------------------------------------------------------------------27)
CO2 + H2  CO + H2O
If all species are gases and H2O is added, the amount of CO2 present at equilibrium will;
A) Increase.
B) Decrease.
C) Remain unchanged.
D) Disappear.
---------------------------------------------------------------------------------------------------28) Given the following reaction at equilibrium, if Kp =1.05 at 250.0 °C, Calculate KC?
PCl5(g)  PCl3(g) + Cl2(g)
A) 3.90 x 10-6
B) 2.45 x 10-2
C) 1.05
D) 42.9
-------------------------------------------------------------------------------------------------------------------29) Given the following reaction at equilibrium at 300.0 K:
NH4HS(s)  NH3(g) + H2S(g)
If pNH3 = pH2S = 0.111 atm, Kp= ___________.
A) 1.23 x 10-2
B) 4.99 x 10-4
C) 1.11 x 10-1
D) 8.12 x 10-2
---------------------------------------------------------------------------------------------------30) Given the following reaction at equilibrium at 450.0 °C:
CaCO3(s)  CaO(s) + CO2(g)
If pCO2 =0.0160 atm, KC= __________.
A) 0.0160
B) 0.0821
C) 7.23
D) 2.70 x 10-4
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31) At 0 oC, the Kw for water is 1.2 x 10-15. The pH of pure water at this temperature is:
A) 7.00
B) 6.88
C) 7.54
D) 7.46
--------------------------------------------------------------------------------------------------------------------32) The pOH of a solution is 9.60 Calculate [H3O+] in this solution.
A) 2.5 × 10–10 M
B) 6.0 × 10–9 M
C) 4.0 × 10–5 M
D) 2.4 × 10–4 M
---------------------------------------------------------------------------------------------------33) An acid with Ka = 1.23 x 10-4. Calculate the value of pKb for its conjugate base.
A) 3.91
B) 8.23
C) 9.00
D) 10.09
---------------------------------------------------------------------------------------------------34) A 0.100 M solution of an acid has a pH = 2.00. What is the value of Ka for this acid?
A) 1.1 x 10-2
B) 1.0 x 10-3
C) 1.1 x 10-4
D) 1.0 x 10-5
---------------------------------------------------------------------------------------------------35) Which is the most acidic?
A) 0.5 M H2S
B) 0.5 x 10-4 M HCl
(Ka = 1.00 x 10-7)
C) 0.15 M HCN
(Ka = 4.0 x 10-10)
D) 0.136 M NH3
(Kb = 1.8 x 10-5)
---------------------------------------------------------------------------------------------------36) All of the following species can act as Bronsted-Lowry acid in solution EXCEPT:
A) NH3
B) S2-
C) NH4+
D) HCO3-
---------------------------------------------------------------------------------------------------37) According to the Arrhenius definition, a base is:
A) A substance that increases the hydroxide ion concentration of a solution.
B) A substance that can accept a proton from an acid.
C) A substance that increases the hydronium ion concentration of a solution.
D) A substance that donates a proton.
--------------------------------------------------------------------------------------------------38) Calculate the H3O+ ion concentration in lemon juice having a pH of 2.4?
A) 4.0 × 10–2 M
B) 250 M
C) 0.38 M
D) 4.0 × 10–3 M
---------------------------------------------------------------------------------------------------39) Calculate the H+ ion concentration in a 8.8 × 10–4 M Ca(OH)2 solution.
A) 8.8 × 10-4 M
B) 1.8 × 10–3 M
C) 2.2 × 10–11 M
D) 5.7 × 10–12 M
---------------------------------------------------------------------------------------------------40) The following acids are listed in order of decreasing acid strength in water.
HI > HNO2 > CH3COOH > HClO > HCN
According to Bronsted-Lowry theory, which of the following ions is the weakest base?
A) I-
B) NO2-
C) CN-
D) ClO-
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