chemistry : class12 Protective Power : Macromolecular colloids : Surface Chemistry MCQ Questions and Answers
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Protective Power
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MCQ Questions
1. The gold number of a protective colloid is defined as the minimum mass of that colloid required to prevent the coagulation of a standard gold sol when a specified amount of electrolyte is added. If colloid X has a gold number of 0.005 g and colloid Y has a gold number of 0.020 g, which conclusion is correct?
A.
Colloid X has four times the protective power of colloid Y
B.
Colloid Y has four times the protective power of colloid X
C.
Both colloids have equal protective power because their gold numbers are independent of mass
D.
The protective power cannot be compared without knowing the charge on the gold sol
Correct Answer:
Colloid X has four times the protective power of colloid Y
Explanation:
Protective power is inversely proportional to the gold number. Since 0.005 g is one-fourth of 0.020 g, colloid X has four times the protective power of colloid Y.
2. A standard gold sol requires 0.012 g of gelatin to remain uncoagulated under the gold-number test conditions. What is the gold number of gelatin in this experiment?
A.
0.0012 g
B.
0.012 g
C.
0.12 g
D.
12 g
Correct Answer:
0.012 g
Explanation:
The gold number is the minimum mass, in grams in this convention, of the protective colloid required to prevent coagulation of the standard gold sol. Therefore, the gold number is 0.012 g.
3. Two protective colloids P and Q are tested with identical standard gold sols. With 0.004 g of P, the gold sol remains red after electrolyte addition, whereas 0.004 g of Q permits a blue-violet colour change. Which statement is justified?
A.
P has a lower gold number than Q
B.
Q has a lower gold number than P
C.
P and Q have identical gold numbers because the same mass was used
D.
Q necessarily has a greater protective power because it changes the colour of the sol
Correct Answer:
P has a lower gold number than Q
Explanation:
P prevents coagulation at the tested mass, while Q does not. Hence the minimum required mass, and therefore the gold number, is lower for P. A lower gold number indicates greater protective power.
4. Which sequence correctly represents the protective power of the following colloids when their gold numbers are 0.003 g, 0.015 g, and 0.030 g, respectively?
A.
First colloid > second colloid > third colloid
B.
Third colloid > second colloid > first colloid
C.
Second colloid > first colloid > third colloid
D.
All three have equal protective power
Correct Answer:
First colloid > second colloid > third colloid
Explanation:
Protective power varies inversely with gold number. Thus, the colloid requiring 0.003 g has the greatest protective power, followed by those requiring 0.015 g and 0.030 g.
5. A protective colloid has a gold number of 8 mg. Under the same test conditions, which mass of this colloid represents the minimum amount required to protect the standard gold sol?
A.
0.008 g
B.
0.08 g
C.
8 g
D.
800 g
Correct Answer:
0.008 g
Explanation:
Since 1 mg equals 0.001 g, 8 mg equals 0.008 g. The gold number is the minimum mass required for protection under the specified standard conditions.
6. A gold sol is protected by a macromolecular colloid before sodium chloride is added. Which description best explains the protective action?
A.
The macromolecules form a stabilizing adsorbed layer around gold particles, reducing their coagulation tendency
B.
The macromolecules convert sodium chloride into an insoluble precipitate before it reaches the gold particles
C.
The macromolecules necessarily reverse the charge of every gold particle permanently
D.
The macromolecules increase the concentration of electrolyte needed by increasing the ionic strength of the sol
Correct Answer:
The macromolecules form a stabilizing adsorbed layer around gold particles, reducing their coagulation tendency
Explanation:
Protective macromolecules are adsorbed on the dispersed particles and form a protective layer. This layer hinders particle aggregation and allows the sol to resist electrolyte-induced coagulation.
7. Protective colloid A has a gold number of 2 mg, while protective colloid B has a gold number of 10 mg. If 10 mg of each is separately added to identical standard gold sols before the coagulation test, what is expected?
A.
Both sols are protected, but A provides protection with a larger safety margin
B.
Only B protects the sol because its larger gold number indicates stronger protection
C.
Only A protects the sol because any amount above its gold number causes coagulation
D.
Neither sol is protected because the masses exceed both gold numbers
Correct Answer:
Both sols are protected, but A provides protection with a larger safety margin
Explanation:
Each added mass is at least equal to the respective gold number, so both colloids can protect the gold sol under the test conditions. A has the lower gold number and therefore the greater protective power and larger excess over its minimum requirement.
8. A protective colloid prevents coagulation of a standard gold sol with 6 mg of colloid, but coagulation occurs with 5 mg. Which value is the best experimentally assigned gold number?
A.
5 mg
B.
6 mg
C.
11 mg
D.
30 mg
Correct Answer:
6 mg
Explanation:
The gold number is the minimum mass that successfully prevents coagulation. Since protection occurs at 6 mg but not at 5 mg, the experimentally assigned gold number is 6 mg.
9. If the gold number of protective colloid M is one-fifth that of protective colloid N, how are their protective powers related?
A.
M has five times the protective power of N
B.
N has five times the protective power of M
C.
M and N have the same protective power
D.
M has one twenty-fifth the protective power of N
Correct Answer:
M has five times the protective power of N
Explanation:
Protective power is inversely proportional to gold number. Therefore, a colloid whose gold number is one-fifth as large has five times the protective power.
10. In comparing protective colloids for the same gold sol and the same electrolyte challenge, which experimental condition is essential for a valid comparison of their gold numbers?
A.
The volume and concentration of the gold sol and the amount of added electrolyte must be kept constant
B.
The protective colloid with the larger molecular mass must always be used in the smaller amount
C.
The colour of the protective colloid solution must be identical for both colloids
D.
The electrolyte must be changed for each protective colloid to match its molecular mass
Correct Answer:
The volume and concentration of the gold sol and the amount of added electrolyte must be kept constant
Explanation:
Gold number is meaningful only under standardized test conditions. Keeping the gold sol and electrolyte conditions constant ensures that differences in the minimum protective mass reflect differences in protective power rather than changes in the coagulation challenge.
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