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Practice each question, then open the answer or worked solution.
What happens when the electric field is applied to a colloidal solution?
When an electric field is applied to a colloidal solution, colloidal particles move towards different electrode depending on their respective charge.
What causes Brownian motion in colloidal dispersion?
Brownian motion is due to the collision between the colloidal particles and with the dispersion medium. The movement results in the stabilisation of the colloidal solution.
A colloid is formed by adding FeCl3 in excess of hot water. What will happen if excess sodium chloride is added to this colloid?
FeCl3 when added into hot water, it forms hydrated ferric oxide, which is a positively charged sol due to absorption of Fe3+ ions. On adding NaCl the negatively charged chloride ions neutralize the positive charge of the solution and coagulation of the sol takes place.
How do emulsifying agents stabilise the emulsion?
Emulsifying agents stabilize the emulsion by forming an interfacial film between suspended particle and dispersion medium. For example, agar is an emulsifying agent used in food.
Why are some medicines more effective in the colloidal form?
The colloidal solution has a larger surface area than a true solution. The surface area is directly proportional to the rate of assimilation in our body. So most of the medicines act more effective in colloidal form.
Why does leather get hardened after tanning?
When leather is soaked in tannin, coagulation takes place due to the interaction of positively charged animal skin and negatively charged tannin. Thus leather gets hardened.
How does the precipitation of colloidal smoke take place in Cottrell precipitator?
Cottrell precipitator is a filtration device that removes the fine particles like dust and smoke from a flowing gas. It neutralizes the charge on carbon particles.
How will you distinguish between the dispersed phase and dispersion medium in an emulsion?
An emulsion is a dispersion of one liquid in another immiscible liquid. The dispersed phase is always present in fewer amounts than the dispersion medium.
Based on Hardy-Schulze rule explain why the coagulating power of phosphate is higher than chloride.
According to Hardy-Schulze rule, the coagulation property of an electrolyte depends upon the valency of the coagulation ion. Higher the charge on flocculating ion smaller is the amount of electrolyte required for precipitation. Phosphate ion has -3 charge while chloride ion carries only -1 charge. So coagulating power of phosphate is higher than chloride.
Why does the bleeding stop by rubbing moist alum?
Moist alum has highly charged Al3+ and SO42- ions which neutralize the charged protein molecules present in the blood. This results in the coagulation of blood proteins and stops bleeding.