Practice MCQ Questions and answers on Chemistry-GK

When you stir a spoonful of sugar into a glass of water, you are forming a solution. This type of liquid solution is composed of a solid solute, which is the sugar, and a liquid solvent, which is the water. As the sugar molecules spread evenly throughout the water, the sugar dissolves.

Hard water is water that has high mineral content. In domestic settings, hard water is often indicated by a lack of suds formation when soap is agitated in water. Wherever water hardness is a concern, water softening is commonly used to reduce hard water’s adverse effects. Water’s hardness is determined by the concentration of multivalent cations in the water. Multivalent cations are cations (positively charged metal complexes) with a charge greater than 1+. Usually, the cations have the charge of 2+. The metallic constituents of hard water are Calcium, magnesium and iron.

Potassium permanganate is a point-of-entry treatment method that oxidizes dissolved iron, manganese, and hydrogen sulfide into solid particles that are filtered out of the water. It can also be used to control iron bacteria growth in wells.

Lead in water can cause kidney damage.

Hardness of the water is commonly measured in terms of calcium carbonate equivalents.

The 1959 WHO International Standards for Drinking Water suggested that concentrations of copper greater than 1.5 mg/litre would markedly impair the potability of the water. However, in the first edition of the Guidelines for Drinking Water Quality, published in 1984, a guideline value of 1.0 mg/litre was established for copper, based on its laundry and other staining properties.

The word “residual” means “remainder” or “that which is left”, and as the name suggests the chlorine residual is measure of the amount of chlorine remaining in the water after disinfection. The chlorine residual is usually tested in finished water which is ready to be released into the distribution system, although operators must also ensure that there is adequate residual at the extreme ends of the distribution system. Tests for chlorine residual are probably the most frequently performed tests at water treatment plants. There are three types of chlorine residual which must be considered in water treatment. Free chlorine residual - residual consisting of dissolved chlorine gas, Hypochlorous acid, and hypochlorite ions, Combined chlorine residual - residual consisting of other forms of chlorine such as chloramines which are capable of killing bacteria and oxidizing organic matter, Total chlorine residual - the sum of the free chlorine residual and the combined chlorine residual.

Maximum permissible concentration of total hardness in drinking water is 200.

Bleaching powder is extensively used in sterilizing water. Calcium hypochlorite is a chemical compound with formula Ca(OCl)₂. It is widely used for water treatment and as a bleaching agent (bleaching powder). This chemical is considered to be relatively stable and has greater available chlorine than sodium hypochlorite (liquid bleach). Calcium hypochlorite is a yellow white solid which has a strong smell of chlorine. It is not highly soluble in water, and is more preferably used in soft to medium-hard water. It has two forms: a dry form and a hydrated form. The hydrated form is safer to handle.

Both A and R is true and R is the correct explanation of A.