Surface Chemistry

JEE Chemistry · 85 questions · Page 9 of 9 · Click an option or "Show Solution" to reveal answer

Q81

TLC analysis of a mixture having 3 components (A, B, C) using silica gel as the stationary phase gave following Rf values; for A = 0.72, B = 0.48, C = 0.20. Regarding the above observations, which one of the following statements is not correct for column chromatography of the mixture?

A A is the most non-polar component

B C is the most soluble component in mobile phase

C A will be eluted first

D C is the most strongly absorbed component

Correct Answer

Option B

Solution

The $\mathrm{R}_{f}$ (retardation factor) value is the ratio of the Solute's distance travelled to the Solvent's distance travelled.

Polar molecules will attract more toward adsorbent and cover smaller distance from the baseline.

A has maximum $\mathrm{R}_{f}$ so it will less adsorbed on the adsorbent surface and travel faster and will be eluded first. $\mathrm{C}$ has minimum $\mathrm{R}_{f}$ value.

So it is more strongly adsobred and less soluble in mobile phase.

Q82

Peptization is a :

A process of converting soluble particles to form colloidal solution

B process of converting precipitate into colloidal solution

C process of bringing colloidal molecule into solution

D process of converting a colloidal solution into precipitate

Correct Answer

Option B

Solution

Peptisation is the process of converting a precipitate into a colloidal solution by shaking it with dispersion medium in the presence of small amount of electrolyte.

Q83

A sample of red ink (a colloidal suspension) is prepared by mixing eosin dye, egg white, HCHO and water. The component which ensures stability of the ink sample is :

A HCHO

B Water

C Eosin dye

D Egg white

Correct Answer

Option D

Solution

Egg white is used to stabilise the prepared colloidal sol.of red ink.

Q84

Alum helps in purifying water by :

A forming Si complex with clay particles

B sulphate part which combines with the dirt and removes it

C coagulating the mud particles

D making mud water soluble

Correct Answer

Option C

Solution

Alum furnishes

A{l^{3 + }}

ions which bring about coagulation of negatively charged clay particles, bacteria etc.

Q85

Given below are two statements : Statement I : Emulsions of oil in water are unstable and sometimes they separate into two layers on standing. Statement II : For stabilisation of an emulsion, excess of electrolyte is added. In the light of the above statements, choose the most appropriate answer from the options given below :

A Both Statement I and Statement II are correct.

B Both Statement I and Statement II are incorrect.

C Statement I is correct but Statement II is incorrect.

D Statement I is incorrect but Statement II is correct.

Correct Answer

Option C

Solution

Oil in water emulsions can sometimes separate into two layers on standing.

The most relevant example for the above case is milk, which can separate into two layers on standing for a longer time.

Therefore, statement (I) is correct.

On adding excess of electrolyte, coagulation occurs and emulsion is further destabilised.

Therefore, statement (II) is incorrect.

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