Students, I want to help you learning back the concepts that you have learnt during this semester. Please test yourself by using the following item tests. These are about colligative properties, balancing redox reaction and electrochemical cells.
1. A solution is prepared from 50.0 g of solid sucrose, C12H22O11 in 250 g of water at 25.0oC. The vapor pressure of pure water is 23.8 torr at 25oC. What is the vapor pressure of the solution? (Ar C = 12, H = 1, O = 16).
a. 22.8
b. 23.0
c. 23.3
d. 23.6
e. 23.8
2. A solution consists of 5,85 grams of table salt, NaCl (Mr = 58,5) in 800 g of water. This solution boils at the same temperature with a solution which contains of 3 g X (a non electrolyte substance) in 200 g of water. Mr of X is ….
a. 40
b. 50
c. 60
d. 80
e. 120
3. A solution prepared by dissolving x 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. The mass of nicotine is …. (Mr nicotine = 160; R = 0,082 L atm/K mol)
a. 0,20
b. 0,60
c. 0,80
d. 1,40
e. 2,80
4. Which of the following solutes will produce the highest solution boiling point when dissolved in water?
a. 1,5 moles of MgCl2
b. 2 moles of methanol
c. 3 moles of NaCl
d. 4,5 moles of urea
e. 5 moles of ethanol
5. After balancing the redox reactions below, the value of a, b, c, d, and e in order are ….
aK2C2O4 + bK2Cr2O7 + cH2SO4 à dCO2 + Cr2(SO4)3 + K2SO4 + eH2O
a. 3, 1, 7, 3, 7
b. 3, 1, 7, 6, 7
c. 3, 2, 7, 3, 7
d. 6, 2, 7, 6, 7
e. 6, 1, 7, 3, 7
6. In an electrochemical cell of Zn – Cu, what occurs when the circuit is closed?
a. Zn(s) --> Zn2+(aq) + 2e
b. Cu(s) --> Cu2+(aq) + 2e
c. 2H2O(l) --> 2H2(g) + O2(g)
d. Electrons flow from Cu to Zn.
e. Electric current flows from Zn to Cu
7. 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
a. Sn(s)+Hg2+(aq) --> Sn2+(aq)+Hg(s)
b. Sn(s)+Cu2+(aq) --> Sn2+(aq)+Cu(s)
c. Hg(s)+Cu2+(aq) --> Hg2+(aq)+Cu(s)
d. Mg(s)+Cu2+(aq) --> Mg2+(aq)+Cu(s)
e. Mg(s)+Hg2+(aq) --> Mg2+(aq)+Hg(s)
8. Na2SO4(aq) is electrolysed by using graphyte as electrodes. The reaction that is occured at the positive electrode is ....
a. Na(s) --> Na+(aq) + e
b. Na+(aq) + e --> Na(s)
c. 2H+(aq) + 2e --> H2(g)
d. 2H2O(l) + 2e --> H2 + 2OH-(g)
e. 2H2O(l) --> 4H+(aq) +O2(g) +4e
9. How many hours will it take to plate out 4,85 g of Cr from a Cr2(SO4)3 solution using a current of 1.50 A? (Ar Cr = 52)
a. 5
b. 4,8
c. 3
d. 2,4
e. 1,2
10. Draw the Zn - Cu cell and electrolysis cell, then explain the comparison of these two electrochemical cells.
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