Science 5 Marks Questions

We will put a drop each of hydrochloric acid, sodium hydroxide, and sugar solution on the turmeric indicator. The liquid which changes the colour of turmeric indicator to red is basic in nature, that is, sodium hydroxide.

Now, we will put a drop of sodium hydroxide on a drop of each of the other two liquids separately. After that, we will put the drops of these mixtures on turmeric indicator. The drop which will change the colour of the turmeric indicator to red contains sugar solution. This is because the mixture of basic and neutral solutions is basic in nature. On the other hand, the drop which will not change the colour of turmeric indicator contains hydrochloric acid. This is because hydrochloric acid reacts with sodium hydroxide to form a neutral solution.

Since the drinks are edible, Dorji can take the decision by tasting the drinks. Acidic drinks will be sour to taste whereas basic drinks will be bitter to taste and neutral drinks will have no taste.

If Dorji has litmus indicator (solution or paper), then he can take its help. He should put one drop of each drink on blue litmus paper. If the colour of the litmus paper changes to red, then it is an acidic drink. Out of the remaining drinks, some are basic and some are neutral. Again, he should put one drop of the remaining drinks on red litmus paper. If the colour changes to blue, then it is basic and the others are neutral. In this way, he can serve all the three customers their respective drinks.

1. Nitric acid:

• It is used by goldsmiths for cleaning gold and silver ornaments.
• It is used to make fertilisers.

2. Hydrochloric acid:

• It is secreted in stomach for digestion.
• It is used to remove rust from iron before galvanising and painting.

3. Sulphuric acid:

• It is used in batteries of cars, buses and inverters.
• It is used for preparing alum.

• Acids are sour in taste.
• The chemical nature of such substances is acidic.
• Acid turns blue litmus red.
• It gives hydrogen ion when dissolves in water.
• Do not give any colour with phenolphthalein indicator.
• Do not absorb carbon dioxide gas.
• Acids do not react with ammonium salt.
• Acids are generally found in Vinegar, Curd, Spinach, lemons, Citrus fruits, Amla, Tamarind, grapes, unripe mangoes, Citrus fruits such as oranges, etc.

Universal indicator gives a range of colour that can be used to determine the level of acidity or basic of a solution, this level is called the pH value.

Turmeric is yellow in colour, when it is exposed to neutral (Sugar Solution) or acidic substances (Hydrochloric Acid) it will retain its yellow colouration. However, if turmeric is exposed to more alkaline substances (sodium hydroxide) it becomes a dark pink/ red. So first we detect sodium hydroxide a basic substance by a colour change from yellow to dark or red. Then will test for an acid or neutral substance with indication of no colour change. Now out of these two, we will mix one with already tested solution for basic substance sodium hydroxide with dark or red colour, if on mixing the colour reverses back to yellow, the liquid is an acid and the remaining third liquid is neutral.