Science Answer the questions.[Che-2M]

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,

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.

The acidic character of a substance is due to the presence of hydrogen ions [H⁺(aq) ions] in its aqueous solution. HCl, H₂SO₄ etc show acidic properties because they produce hydrogen ions when dissolved in water. The solution of compounds like alcohol and glucose do not show acidic character because they do not ionize in water to produce hydrogen ions or any other ions in solution.

CO₂ gas is liberated during the reaction. When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky. If excess of carbon dioxide gas is passed through the milky lime water, the solution becomes clear again. This confirms the presence of carbon dioxide gas.

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.

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.

Substance X, which gives sodium hydroxide, Cl₂ and H₂ upon electrolysis, is NaCl. The electrolysis of sodium chloride solution is called the chlor-alkali process because of the products formed, 'chlor' for chlorine and 'alkali' for sodium hydroxide (NaOH).

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.

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.

A strong acid is one that completely ionises in water to form a large amount of hydrogen ions whereas a weak acid only partially ionises in water and thus produces a small amount of hydrogen ions.
HCl, H SO, HNO are strong acids; CH COOH, H CO, H SO are weak acids.

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.

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.

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.

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.

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 a cold and concentrated solution of sodium chloride reacts with ammonia and carbon dioxide, sodium hydrogencarbonate and ammonium chloride are formed.
 NaCl + NH₃ + H₂O + CO₂ → NaHCO₃ + NH₄Cl

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.

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.

Organic acids are acids present in plant materials and animals. These are naturally occuring acids.
A mineral acid (or inorganic acid) is an acid derived from one or more minerals of the earth.

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.

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.

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

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 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.

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

Strong bases – Sodium hydroxide, NaOH, potassium hydroxide (KOH). Weak bases – Calcium hydroxide, Ca( OH₂ ), ammonium hydroxide, NH₄OH.

pH value will decrease when milk changes to curd. Curd contains lactic acid hence the pH decreases.