Science [2 Mark Questions]

1. Wasp stings are alkaline in nature since they are treated using acids like vinegar.
2. Bee stings are acidic in nature since they are treated using bases like baking soda.

1. Milk is made slightly alkaline so that it may not become sour easily due to the formation of lactic acid in it.
2. The alkaline milk takes a longer time to set into curd because the lactic acid being formed has to first neutralise the alkali present in it.

Curd and other sour substances contains acids which can react with the metals of brass and copper vessels to form toxic (poisonous) metal compounds which can cause food poisoning and damage our health.

Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extracts are olfactory indicators. When a basic solution like sodium hydroxide solution is added to a cloth strip treated with onions (or onion extract), then the onion smell cannot be detected.

When an acid or base solution is added to the universal indicator, it produces a new colour which is used to find the pH value of the acid or the base solution by matching the colour with the colours on pH colour chart.

A salt is a compound formed from an acid by the replacement of the hydrogen in the acid by a metal.
Example: Sodium chloride – NaCl; It is obtained from hydrochloric acid and sodium metal. Ammonium chloride – NH Cl; It is obtained from ammonia and hydrochloric acid.

Baking powder is a mixture of baking soda and tartaric acid. When baking powder mixes with water, then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

Acidic solution will turn blue litmus red; This red litmus will turn blue in basic solution; Distilled water will have no effect on any type of litmus pape,

Our stomach produces hydrochloric acid. If there is excess of hydrochloric acid in the stomach, it causes indigestion which produces pain and irritation. Its effect can be cured by taking antacids.

1. It is used for disinfecting drinking water supply.
2. It is used in the manufacture of chloroform.

When baking powder mixes with water, then sodium hydrogencarbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

Substance X is tartaric acid. It can react with any sodium carbonate formed and neutralise it otherwise cakes and bread will taste bitter.

Universal indicator is a mixture of many different indicators which gives different colours at different pH values of the entire pH scale. It is used to obtain an idea of how acidic or basic a substance is.

Gypsum is calcium sulphate dihydrate, CaSO.2H O. When gypsum is heated to a temperature of 100?C, it loses 3/4th of its water of crystallisation and forms plaster of Paris.

1. Neither solution will turn blue litmus red. Solution P is sodium chloride, formed from a strong acid, hydrochloric acid (HCl), and a strong base, sodium hydroxide (NaOH). When sodium chloride is dissolved in water, it gets hydrolysed to give equal amounts of hydroxide and hydrogen ions, which makes its aqueous solution neutral. Therefore, the solution of sodium chloride will have no effect on red or blue litmus paper.
2. Sodium hydroxide solution (Q) will turn red litmus blue, because solution Q is basic.

Organic acids: Citric acid, lactic acid;
Mineral acids: Hydrochloric acid, sulphuric acid.

Tooth decay starts when the pH of the acid formed in the mouth falls below 5.5 because the acid becomes strong enough to attack the enamel of the teeth and corrode it.

Methanoic acid. The effect of methanoic acid can be neutralised by rubbing a mild base like baking soda solution on the stung area of the skin.

When Hydrochloric acid reacts with an active metal (like zinc), we observe that gas filled bubbles are formed on the surface of the metal. Pass the gas formed through soap solution. Then, bring a burning candle near the gas filled soap bubble. If the gas present in bubble burns with a ‘pop’ sound, then its hydrogen gas.

Baking powder; when baking powder mixes with water, then sodium hydrogen carbonate reacts with tartaric acid to evolve carbon dioxide gas which gets trapped in the wet dough and bubbles out slowly making the cake soft and spongy.

1. Potatoes grow better in acidic soil having pH = 5.5
2. Broccoli grows better in an alkaline soil since adding a lot of lime to acidic soil will make it basic in nature.

Uses of plaster of Paris:

1. It is used as a fire proofing material.
2. it is used in hospitals for setting fractured bones in the right position to ensure correct healing.

Substances having pH values above 7: Solution of washing soda and toothpaste; They will turn red litmus paper blue due to their basic nature.
Substances having pH values less than 7: Lemon juice, vinegar and stomach juices; They will turn blue litmus paper red due to their acidic nature.

a.	Copper sulphate crystals.	5
b.	Washing soda.	10
c.	Gypsum.	2

When a bee stings a person, it injects an acidic liquid into the skin which causes immense pain and irritation. Its remedy is to rub a mild base like baking soda solution on the stung are of the skin.

If the soil is too acidic, then it can be treated with materials like quicklime or slaked lime as these materials are bases and hence react with the excess acids present in the soil to reduce its acidity.

Acids are those chemical substances which have a sour taste.
Example: Acetic acid and citric acid.
Base is a chemical substance which has a bitter taste.
Example: Caustic soda and washing soda.

When a wasp stings, it injects an alkaline liquid into the skin. Rubbing a mild acid like vinegar on the stung area of the skin gives relief.

A person can prevent tooth decay by consuming less sweet foods, such as ice creams and chocolates. Tooth decay can also be prevented by brushing with toothpastes (which is basic) regularly and by cleaning the mouth carefully after meals.