Dispersed phase

Dispersion medium

Type of colloid

Example

Solid

Liquid

Sol

Paints, cell fluids

Liquid

Liquid

Emulsion

Milk, hair cream

Gas

Liquid

Foam

Froth, soap lather

 OR

(i) The colloidal particles are charged and carry either a positive or a negative charge. The dispersion medium carries an equal and opposite charge. This makes the entire system neutral. Under the influence of an electric current, the colloidal particles move towards the oppositely charged electrode. When they come in contact with the electrode, they lose their charge and coagulate.

(ii) When a beam of light is passed through a colloidal solution, a scattering of light is observed. This is known as Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.

(iii) When NaCl is added to hydrated ferric hydroxide sol, it dissociates to give Na+ and Cl- ions. Particles of ferric hydroxide sol are positively charged. This neutralises the colloidal particles which then unite to form bigger particles that are consequently precipitated. Thus, they get coagulated in the presence of negatively charged Cl- ions.

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Dispersed phase

Dispersion medium

Type of colloid

Example

Solid

Liquid

Sol

Paints, cell fluids

Liquid

Liquid

Emulsion

Milk, hair cream

Gas

Liquid

Foam

Froth, soap lather

 OR

(i) The colloidal particles are charged and carry either a positive or a negative charge. The dispersion medium carries an equal and opposite charge. This makes the entire system neutral. Under the influence of an electric current, the colloidal particles move towards the oppositely charged electrode. When they come in contact with the electrode, they lose their charge and coagulate.

(ii) When a beam of light is passed through a colloidal solution, a scattering of light is observed. This is known as Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.

(iii) When NaCl is added to hydrated ferric hydroxide sol, it dissociates to give Na+ and Cl- ions. Particles of ferric hydroxide sol are positively charged. This neutralises the colloidal particles which then unite to form bigger particles that are consequently precipitated. Thus, they get coagulated in the presence of negatively charged Cl- ions.

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Dispersed phase

Dispersion medium

Type of colloid

Example

Solid

Liquid

Sol

Paints, cell fluids

Liquid

Liquid

Emulsion

Milk, hair cream

Gas

Liquid

Foam

Froth, soap lather

 OR

(i) The colloidal particles are charged and carry either a positive or a negative charge. The dispersion medium carries an equal and opposite charge. This makes the entire system neutral. Under the influence of an electric current, the colloidal particles move towards the oppositely charged electrode. When they come in contact with the electrode, they lose their charge and coagulate.

(ii) When a beam of light is passed through a colloidal solution, a scattering of light is observed. This is known as Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.

(iii) When NaCl is added to hydrated ferric hydroxide sol, it dissociates to give Na+ and Cl- ions. Particles of ferric hydroxide sol are positively charged. This neutralises the colloidal particles which then unite to form bigger particles that are consequently precipitated. Thus, they get coagulated in the presence of negatively charged Cl- ions.

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Surface Chemistry

Surface Chemistry

Question

Classify colloids where the dispersion medium is water. State their characteristics and write an example of each of these classes.

OR

Explain what is observed when

(i) An electric current is passed through a sol

(ii) A beam of light is passed through a sol

(iii) An electrolyte (say NaCl) is added to ferric hydroxide sol

Answer

Colloids containing dispersion medium as water can be classified as follows:

Dispersed phase

Dispersion medium

Type of colloid

Example

Solid

Liquid

Sol

Paints, cell fluids

Liquid

Liquid

Emulsion

Milk, hair cream

Gas

Liquid

Foam

Froth, soap lather

 OR

(i) The colloidal particles are charged and carry either a positive or a negative charge. The dispersion medium carries an equal and opposite charge. This makes the entire system neutral. Under the influence of an electric current, the colloidal particles move towards the oppositely charged electrode. When they come in contact with the electrode, they lose their charge and coagulate.

(ii) When a beam of light is passed through a colloidal solution, a scattering of light is observed. This is known as Tyndall effect. This scattering of light illuminates the path of the beam in the colloidal solution.

(iii) When NaCl is added to hydrated ferric hydroxide sol, it dissociates to give Na+ and Cl- ions. Particles of ferric hydroxide sol are positively charged. This neutralises the colloidal particles which then unite to form bigger particles that are consequently precipitated. Thus, they get coagulated in the presence of negatively charged Cl- ions.

More Chapters from Surface Chemistry