Science [5 marks Questions]

1. Solution A turns universal indicator blue to purple so it is basic in nature and will turn litmus blue.
2. Solution B turns universal indicator orange to red so it is acidic in nature and will turn litmus red.
3. Milk of magnesia and sodium hydroxide solution are bases like solution A.
4. Lemon juice and hydrochloric acid are acids like solution B.
5. Neutralisation reaction.

1. Solution D, with a pH value of 11, is weakly alkaline.
2. Solution C, with a pH value of 7, is neutral.
3. Solution A, with a pH value of 1, is strongly acidic.A.
4. Solution E, with a pH value of 13, is strongly alkaline.
5. Solution B, with a pH value of 5, is weakly acidic.

1. Sodium hydroxide:

1. It is used for making soaps and detergents.
2. It is used in the manufacture of paper.

2. Chlorine:

1. It is used in the production of bleaching powder.
2. It is used in the production of hydrochloric acid.

3. Hydrogen:

1. It is used in the production of hydrochloric acid.
2. It is used in the hydrogenation of oils.

4. Hydrochloric acid:

1. It is used in medicines and cosmetics.
2. It is used in textile/ dyeing and tanning industries.

Activity: Take about 1g solid NaCl in a clean and dry test tube and add some concentrated sulphuric acid to it. Fit a rubber cork with a small delivery tube in the mouth of the test tube. Concentrated sulphuric acid reacts with sodium chloride to form hydrogen chloride gas. The hydrogen chloride gas starts coming out of the open end of the glass tube.

Now, hold a ‘dry’ blue litmus paper in HCl gas. There is no change in colour of the ‘dry’ blue litmus paper. This shows that HCl gas does not behave as an acid in the absence of water. However, when we hold a ‘moist’ blue litmus paper in HCl gas, we will see that the ‘moist’ blue litmus paper turns red. This indicates that HCl gas shows acidic behavior in the presence of water as hydrogen ions are formed. This proves that acids produce ions only in aqueous solutions or in presence of water.

Working: A soda-acid type fire extinguisher contains a solution of sodium hydrogencarbonate and sulphuric acid in separate containers in separate containers inside them. When the knob of the fire extinguisher is pressed, then sulphuric acid mixes with sodium hydrogencarbonate solution to produce carbon dioxide gas which forms a blanket around the burning substance and cuts off the supply of air to burning substance; this stops the process of burning and fire gets extinguished.

1. Universal indicator paper is used to measure the pH.
2. Lemon juice with pH = 2.5 is the most acidic.
3. Household ammonia with pH = 12 is the most alkaline.
4. Salt solution and sugar solution with pH = 7 are neutral.
5. Vinegar (acid) can be used to treat wasp stings since it injects an alkaline liquid into the skin.
6. Baking soda can be used to treat bee stings since it injects methanoic acid into the skin.

Activity.
Take solutions of glucose, alcohol, hydrochloric acid and sulphuric acid. Fix two nails on a cork, and place the cork in a 100 ml beaker. Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch. Now pour some dilute HCl in the beaker and switch on the current. The bulb starts glowing. This shows that HCl solution taken in the beaker conducts electricity. If we replace hydrochloric acid with sulphuric acid and perform the experiment, the bulb would glow again. This shows that an aqueous solution of an acid conducts electricity due to the presence of charged particles called ions in it.

Now, if we take glucose solution in the beaker and switch on the current, the bulb would not glow. If we repeat the experiment by taking alcohol solution in the beaker, the bulb would not glow again. This shows that due to the absence of ions, glucose and alcohol solutions do not conduct electricity. From this activity, we conclude that the hydrogen containing compounds such as glucose and alcohol are not categorised as acids because they do not dissociate (or ionise) in water to produce hydrogen ions [H(aq) ions].