Class 10 Science Chapter 2 MCQ

Most of the plants grow best when the pH of the soil is close to 7. If the soil is too acidic or too basic (too alkaline), the plants grow badly or do not grow at all. The soil may be acidic or basic naturally. The soil pH is also affected by the use of chemical fertilizers in the fields. The pH of acidic soil can reach as low as 4 and that of the basic soil can go up to 8.3. Chemicals can be added to soil to adjust its pH and make it suitable for growing plants.

Our stomach produces hydrochloric acid (of pH about 1.4). This dilute hydrochloric acid helps in digesting our food without harming the stomach. Sometimes, excess of acid is produced in the stomach due to various reasons. The excess acid in the stomach causes indigestion which produces pain and irritation.

HCl ionises completely in water to produce H+ and Cl– ions as it is a strong acid. This H+ ion combines with water molecules to produce hydronium ions. You can easily understand by this equation: HCL(aq) → H+ + Cl- OR H+ + H2O → H3O+ (Hydronium Ions)

Magnesium hydroxide is a weak base. Rest of all the statements are correct. Hence, your answer will be option [D].

The solutions having pH of 4, 5 and 6 are considered to be weak acid solutions.

C2H5OH is not a base. C2H5OH or ethyl alcohol has a functional OH– group. It cannot dissociate ions in a solution. Thus it cannot be a basic compound.

Aqua-regia is used for the dissolution of gold. It is a solution of concentrated HNO3 and concentrated HCl in the ratio of 1:3. Thus this solution is strongly acidic and is used to dissolve gold.

Lime (CaO) is the base that reacts with a dilute acid such as HCl to form a salt called “Calcium Chloride”. It is an exothermic reaction and releases water but no carbon dioxide. Mable or limestone (CaCO3) or baking soda (NaHCO3) react with HCl to release CO2.

Vanilla essence serves as an olfactory indicator. An olfactory indicator is a substance whose smell differs in when added to acids and bases respectively. Vanilla extract has a characteristic pleasant smell. If a basic solution like sodium hydroxide solution is added to vanilla extract, then we cannot detect the characteristic smell of vanilla extract. An acidic solution like hydrochloric acid, however, does not destroy the smell of vanilla extract. This can be used as a test for acids and bases.

The hydrogen containing compounds like glucose and alcohol do not produce hydrogen ions or some other ions in solution. So, due to the absence of ions, glucose solution and alcohol solution do not conduct electricity.

Generally, acids are stored in containers made of glass and ceramics because they are not attacked by acids. Acids are never stored in metal containers because they gradually corrode and eat up the metal container.

When the pH of an aqueous solution is higher, acidic properties are weak. Thus it is a base. When the pH an aqueous solution is lower, basic properties are weak. Thus it is an acid. Note: In 1909 Sorenson devised a scale (known as pH scale) on which the strength of acid solutions as well as basic solutions could be represented by making use of the hydrogen ion concentrations in them. A pH scale is used to measure the acidic and basic strength of an aqueous solution. This scale is marked from 0 to 14. A solution is neutral if its pH value is 7. An acidic solution has a pH less than 7. This means an acidic solution has more concentration of H+ ions. A basic solution has a pH more than 7. This means a basic solution has more concentration of OH– ions.

Here, all the statements are correct. Hence, your answer will be option [D].

Toothpastes we generally contain mild bases such as sodium fluoride or sodium bicarbonate in their composition. The base reacts with the acid formed during tooth decay and neutralises its bad effects thus, preventing tooth decay. Note: When we eat food containing sugar, then the bacteria present in our mouth break down the sugar to form acids (such as lactic acid). Thus, acid is formed in the mouth after a sugary food has been eaten. This acid lowers the pH in the mouth (making it acidic). Tooth decay starts when the pH of acid formed in the mouth falls below 5.5.

Here, all the statements are correct. Hence, your answer will be option [D].

Common salt (NaCl) is formed by reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH). It serves as an important raw material for the production of various chemical compounds such as caustic soda (sodium hydroxide), washing soda (sodium carbonate), baking soda (sodium bicarbonate) used in various industries. Chlorine gas obtained is used for making bleaching powder (calcium hypochlorite).

Water is added to concentrated acid to dilute it, then a large amount of heat is evolved at once. This heat changes some of the water to steam explosively which can splash the acid on our face or clothes and cause acid burns. Note: When a concentrated acid is added to water for preparing a dilute acid, then the heat is evolved gradually, and easily absorbed by the large amount of water

When sodium hydrogen carbonate is added to acetic acid, carbon dioxide (CO2) gas is evolved. Sodium hydrogen carbonate + Acetic acid → Sodium acetate + water + carbon dioxide You can easily understand by this equation: NaHCO3 + CH3COOH → CH3COONa + H2O + CO2

The acids prepared from the minerals of the earth are called mineral acids. Mineral acids are manmade acids. The three most common mineral acids are: Hydrochloric acid, Sulphuric acid and Nitric acid. Concentrated mineral acids are very dangerous. They can burn our hands and clothes. These acids should be handled with care.

The increasing order of acid strength is water < acetic acid < hydrochloride acid. Hydrochloride acid is a mineral acid and ionises completely in water. That’s why it is a strong acid. Acetic acid is an organic acid and ionises only partially in water. That’s why it is a weak acid. Water is almost neutral in nature. In pure water number of positive hydrogen ions is equal to the negative ions.

Here, all the statements are correct. Hence, your answer will be option [D].

The most common indicator used for testing acids and bases in the laboratory is litmus. Litmus can be used in the form of litmus solution or in the form of litmus paper. It is of two types blue litmus and red litmus.

Calcium phosphate Ca3(PO4)2 is basic salt, as it is formed by the combination of a weak acid (phosphoric acid) and slightly stronger base (calcium hydroxide). Bacteria feed on sugars commonly found in foods and produce acids in the mouth decreasing the pH level to 5.5 or lower. Thus, eroding the enamel that is basic in nature.

Sodium carbonate (Na2CO3) is the salt formed by the combination of a weak acid such as carbonic acid (H2CO3) and a strong base such as sodium hydroxide (NaOH). You can easily understand by this equation: 2NaOH + H2CO3 → Na2CO3 +2H2O Note: The salt formed by the combination of weak acid and a strong base is basic in nature. Basic salts have pH more than 7.

The aqueous solution is a base as it turns red litmus solution blue. An acidic solution such as hydrochloric acid (HCl) would reverse the change. In contrast, hydrochloric acid would turn blue litmus solution to red.