THE ANSWER OF COLLIGATIVE, REDOX, AND ELECTROCHEMICAL CELL TEST

1. A solution of K2CrO4 is 10.0% by mass and the mass of solution is 194 grams. The mol fraction of solute is …. (Ar: K = 39, Cr = 52, O = 16, H = 1).
Answer (0,01)
2. The molality of a 4.6% by mass aqueous solution of ethanol (CH3CH2OH) is …. (Ar: C = 12, H = 1, O = 16).
Answer (1,05)
3. A solution is prepared from mixing 18 g of solid glucose, C6H12O6 in 200 g of water and 11,1 g of CaCl2 in 400 g of water at 25oC. The vapor pressure of pure water is 24 mmHg at 25oC. What is the vapor pressure of this solution? Ar C = 12; H = 1; O = 16; Ca = 40; Cl = 35,5.
Answer (15 mmHg)
4. Dissolving 1 mol of KCl in 1000 grams of H2O affects ….
Answer : both the boiling point and the freezing point of the H2O
5. A solution contains 10,6 g of M2X (Mr = 106) in 500 g of water. If the melting point of this solution – 0,10C and Kf = 1,860C/m , ionization degree, α of M2X is ….
Answer (0,8)
6. A solution consists of 3 grams of urea (Mr = 60) in 100 grams of water. This solution boils at the same temperature with a solution which contains of 18 g X (a non electrolyte substance) in 200 g of water. Mr of X is ….
Answer (180)
7. Refer to the phase diagram below:
Which point could represent a boiling point for the substance?
Answer (A)
8. A solution prepared by dissolving 0,60 grams of nicotine (a non electrolyte) in water to make a 12 mL of solution has an osmotic pressure of 7,55 atm at 250C. Mr of nicotine is …. (R = 0,082 L atm/K mol)
Answer (160)
9. Which of the following solutes will produce the highest solution boiling point when dissolved in water?
Answer : 2 moles of NaCl
10. Balance the following equation in alkaline solution and determine the coefficient of OH- and its location (right or left side) in the equation.
MnO4- + Ni --> Ni(OH)2 + MnO2
Answer : 2, right
11. How many electrons are transferred in the following reaction?
CH4(g) + 2O2(g) --> CO2(g) + 2H2O(l)
Answer (8)
12. Given the balanced reaction:
2Al(s)+6H+(aq) --> 2Al3+(aq) +3H2(aq)
What is the total number of moles of electrons gained by H+(aq) when 2 moles of Al(s) is completely reacted?
Answer (6)
13. After balancing the redox reactions below, the value of a, b, c, d, and e in order are ….
aNa2C2O4 + bK2Cr2O7 + cH2SO4 --> dCO2 + Cr2(SO4)3 + K2SO4 + Na2SO4 + eH2O
Answer (3, 1, 7, 6, 7)
14. The diagram below represents an electrochemical cell of Zn – Cu.
What occurs when the switch is closed?
Answer : Electrons flow from Zn to Cu.
15. In an electrochemical cell, what is the purpose of the salt bridge?
Answer : It permits the migration of ions between the half-cells.
16. Based on the cell notation for a spontaneous reaction, at the anode ….
Zn(s)/ Zn2+(aq)// Fe3+(aq) /Fe2+ (C)
Answer : Zn becomes oxidized
17. From the following listed standard electrode potentials, the biggest Eo for the cell is ….
Mg2+(aq) + 2e ® Mg(s) Eo = --2,24 V
Sn2+(aq) + 2e ® Sn(s) Eo = --0,14 V
Hg2+(aq) + 2e ® Hg(s) Eo = +0,62 V
Cu2+(aq) + 2e ® Cu(s) Eo = +0,34 V
Answer : Mg(s)/Mg2+(aq)//Hg2+(aq)/Hg(s)
18. A metal, X can react with a solution of Y. Another metal, Z reacts with a solution of Y. However, Z cannot react with solution of X. The order of metal according to the decreasing reduction potentials is ….
Answer : Y – Z – X
19. From the listed standard electrode potentials, Eo for the cell is ….
(C) S2O32- /SO32- //O2/ OH- (C)
2 SO32-(aq) + 3 H2O(l) + 4 e- --> S2O32-+6OH- Eo = --0.580 V
O2(g) + 2 H2O(l) + 4 e- --> 4 OH-(aq) Eo = +0.401 V
Answer (+0.98)
20. Given the nickel-cadmium battery reaction:
2NiOOH+ Cd+ 2H2O --> 2 Ni(OH)2 + Cd(OH)2
What occurs during discharge in the nickel-cadmium battery?
Answer : Ni2+ is reduced to Ni3+.
21. CuSO4(aq) is electrolysed. Reaction which is occured at the positive electrode is ….
Answer : 2H2O(l) ® 4H+(aq) + 4e + O2(g)
22. Which metal is used as a coating on steel to limit corrosion?
Answer (Zn)
23. How many minutes will it take to plate out 5.00 g of Cr from a Cr2(SO4)3 solution using a current of 1.50 A? (Ar: Cr = 52)
Answer (309)
24. Sodium metal is produced commercially by the electrolysis of molten sodium chloride and chlorine is produced as a by product. How many liters of chlorine at 10 atm and 20oC will be produced if a current of 1.00 x 103 A is passed through NaCl (l) for 8.0 hours? (Ar: Cl = 35.5)
Answer (3.6 x 102)
25. The same electric current is flowed through CuCl2 (aq) and CrCl3 (aq) (Cu = 63,5 ; Cr = 52). If 0,635 grams of Cu is precipitated, the mass of Cr(s) is ….
Answer (0,35 grams)