Surface Chemistry Test

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Surface Chemistry Test - 10

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following statements is wrong?

A
Elastic gels undergo imbibitions.

B
Dilution test may be applied to distinguish between water in oil and oil in water type of emulsions.

C
Higher the gold number, greater the protective power of the lyophilic colloid.

D
Chemisorption increases with temperature to a maximum and then falls off.

Solution

Gold number is the minimum amount of lyophilic colloid required for protection. So, lower the gold number, greater is the protective power.
Question 2
1 / -0

Which of the following reactions yields a colloidal substance?

A
Na⁺ + OH^- → NaOH

B
2HNO₃ + 3H₂S → 3S + 4H₂O + 2NO

C
2K + 2H₂O → 2KOH + H₂

D
MgCO₃→ MgO + CO₂

Solution

This is the method of preparation of sulphur sol.
Question 3
1 / -0

In the table, 1 litre each of the two solutions X and Y is given and to coagulate each one of them, the numbers of millimoles of NaCl and MgCl₂ are also shown.

In litre → X Y

NaCI (mmol) 51 46

MgCI₂(mmol) 71 23

From the options, choose the value which is not reasonable for the amount of other salt required to cause precipitation.

A
X will be precipitated by 25 mmol of Na₂SO₄.

B
Y will be precipitated by 60 mmol of MgSO₄.

C
X will be precipitated by 90 mmol of AlCl₃.

D
Y will be precipitated by 20 mmol of AlCl₃.

Solution

X is a negative solution and the data shows that it can be precipitated with 51 mmol of Na⁺ in 1 L and will not be precipitated when the concentration is 50 mmol per litre.
Question 4
1 / -0

On the addition of 10 ml of 10% NaCl solution to 10 ml of gold sol in presence of 0.07 g of dextrin, the coagulation is just prevented. The gold number of dextrin is

A
5

B
6

C
7

D
8

Solution

On addition of 1 ml of 10% NaCl to 10 ml of gold sol in presence of 0.07/10 = 0.007 g, i.e. 7 mg of dextrin, the coagulation is just prevented. So, the gold number of dextrin is 7.
Question 5
1 / -0

Choose the incorrect statement about emulsion.

A
The size of the colloidal particles in an emulsion when compared with an ordinary sol is larger.

B
Emulsion can be stabilized by an emulsifier by decreasing the inter-facial tension between the dispersed phase and the dispersed medium.

C
Both dispersed phase and dispersed medium in emulsions are liquids

D
None of these

Solution

All the given statements about emulsion are correct.
Question 6
1 / -0

The method usually employed for the destruction of a colloidal solution is

A
addition of electrolytes

B
diffusion through animal membrane

C
condensation

D
dialysis

Solution

Lyophobic colloids are stabilized due to the charge acquired by the colloidal particles. The addition of an electrolyte neutralizes the charge on the dispersed phase and causes the particles to coagulate and hence destroys the colloid.
Question 7
1 / -0

Bredig's Arc Method involves dispersion as well as aggregation of Colloidal solutions. During their preparation, traces amount of caustic alkali is added for which of the following reasons?

A
To homogenize the solution

B
To act as an emulsifying agent

C
To act as a peptizing agent

D
To act as a coagulating agent

Solution

Caustic alkali stabilizes the sol by absorbing ion produced by the electrolyte.
Question 8
1 / -0

Which of the following will have the minimum flocculation value for the As₂S₃ sol?

A
CaCl₂

B
NaCl

C
Al₂(SO₄)₃

D
Na₂S

Solution

According to the Hardy Schulze law, the coagulation power of an electrolyte is inversely proportional to the valency of the active ion.
As₂S₃ is a negatively charged sol and therefore the active ion is the cation of the electrolyte.
Therefore, Al₂(SO₄)₃ has the maximum flocculation power and the minimum flocculation value.
Question 9
1 / -0

Bredig's arc method is a method for the preparation of colloidal solutions. This method is used for the preparation of the colloidal solution of which of the following metals?

A
Platinum

B
Nickel

C
Copper

D
Zinc

Solution

Bredig's arc method is used for the preparation of the colloidal solution, of metals such as gold, silver or platinum. This method consists of both dispersion and condensation techniques.

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In litre →	X	Y
NaCI (mmol)	51	46
MgCI₂(mmol)	71	23

Surface Chemistry Test - 10

Result

Surface Chemistry Test - 10

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Question 1

Elastic gels undergo imbibitions.

Dilution test may be applied to distinguish between water in oil and oil in water type of emulsions.

Higher the gold number, greater the protective power of the lyophilic colloid.

Chemisorption increases with temperature to a maximum and then falls off.

Solution

Question 2

Na+ + OH- → NaOH

2HNO3 + 3H2S → 3S + 4H2O + 2NO

2K + 2H2O → 2KOH + H2

MgCO3 → MgO + CO2

Solution

Question 3

X will be precipitated by 25 mmol of Na2SO4.

Y will be precipitated by 60 mmol of MgSO4.

X will be precipitated by 90 mmol of AlCl3.

Y will be precipitated by 20 mmol of AlCl3.

Solution

Question 4

5

6

7

8

Solution

Question 5

The size of the colloidal particles in an emulsion when compared with an ordinary sol is larger.

Emulsion can be stabilized by an emulsifier by decreasing the inter-facial tension between the dispersed phase and the dispersed medium.

Both dispersed phase and dispersed medium in emulsions are liquids

None of these

Solution

Question 6

addition of electrolytes

diffusion through animal membrane

condensation

dialysis

Solution

Question 7

To homogenize the solution

To act as an emulsifying agent

To act as a peptizing agent

To act as a coagulating agent

Solution

Question 8

CaCl2

NaCl

Al2(SO4)3

Na2S

Solution

Question 9

Platinum

Nickel

Copper

Zinc

Solution

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Na⁺ + OH^- → NaOH

2HNO₃ + 3H₂S → 3S + 4H₂O + 2NO

2K + 2H₂O → 2KOH + H₂

MgCO₃→ MgO + CO₂

X will be precipitated by 25 mmol of Na₂SO₄.

Y will be precipitated by 60 mmol of MgSO₄.

X will be precipitated by 90 mmol of AlCl₃.

Y will be precipitated by 20 mmol of AlCl₃.

CaCl₂

Al₂(SO₄)₃

Na₂S