Class 10 Science Chapter 2 MCQ

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.

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

When equal volumes of hydrochloric acid (strong acid) and sodium hydroxide (strong base) solution of same concentration are mixed, the result is salt and water. This is a neutralisation reaction. You can easily understand by this equation: HCl + NaOH → NaCl + H2O

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

Firstly, Bleaching powder (CaOCl2) is used bleach clothes and removes colour from clothes. It decomposes on reaction with water and releases chlorine which acts as oxidising, bleaching and disinfecting agent. Baking soda is a natural antacid. It is used to relieve acidity in stomach and heart burn. Washing soda is used in the preparation of glass, soap and paper industries. Sodium chloride is used to produce H2 and Cl2 gases. And lastly, Aqueous sodium chloride on electrolysis yields hydrogen and chlorine.

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.

Citric acid is not a mineral acid. It is an organic acid or edible acid that is derived from organic compounds. Note: Mineral acids or inorganic acids are generally prepared from inorganic compounds such as minerals present in the earth’s crust. For examples, HCl (hydrochloride acid), H2SO4 (sulphuric acid) and HNO3 (nitric acid) are mineral acids. These acids dissolve in water to produce H+ ions.

All the options are characteristics of acids except one. They feel soapy. Hence, your answer will be option [B].

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 juice is acidic in nature. It has high amount of citric acid present in it.

When a small amount of acid such as hydrochloric acid is added to water, individual ions of the acid are dissociated. This process is known as “Ionization”. So hydrochloric acid separates into positively charged hydrogen ions and negatively charged chlorine ions. Mixing of an acid with water is also called dilution. Addition water results in the decrease in the concentration of ions, (H3O+) per unit volume.

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.

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.

Baking powder is a mixture of baking soda NaHCO3 (sodium hydrogen carbonate) and a mild edible acid such as tartaric acid. When baking powder is mixed with water, sodium hydrogen carbonate reacts with tartaric acid and accepts hydrogen ions from it. This process releases carbon dioxide gas which is trapped in the dough when baking powder is used to make bread and cake.

When carbon dioxide gas is passed through lime water, the lime water turns milky due to the formation of a white precipitate of calcium carbonate: You can easily understand by this equation: Ca(OH)2 (aq) + CO2 (g) → CaCO3 (s) + H2O (l) Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water

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).

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.

Firstly, we have to understand that a strong base cannot be used to neutralise the acid as it can corrode the skin. Wash the hand immediately with plenty of water as it helps to wash away most of the acid. Thereafter apply a paste of baking soda (NaHCO3) to neutralise the little acid if any, left over the hand. Baking soda has weak basic properties that is used to neutralise the acid.

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.

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.

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.

Baking soda does not contain water of crystallization. The chemical formula of baking soda is NaHCO3. Its formula does not show any association with water molecules. Other three contain water of crystallization blue vitriol (CuSO4.5H2O), washing soda (Na2CO3.10H2O) and gypsum (CaSO4.2H2O).

Calcium chloride is a good dehydrating agent. It absorbs moisture or water content from the gas making it dry. Calcium chloride is widely used in many industries due to its ability to absorb water.