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Acids, Bases and Salts

Reactions of Acids and Bases – I

You must have observed that in a laboratory, almost all acids are stored in a glass or plastic bottle. However, acids are never kept in metal containers. Do you know why?

This is because acids are corrosive in nature. They can react with metals and destroy them.

Do you know what happens when metals react with acids?

When an acid reacts with metals, salt and hydrogen gas are produced. Thus, metals react with acids and replace the available hydrogen(s) to form salt. This can be represented as follows:

For example, sulphuric acid (H2SO4) reacts with calcium (Ca) to produce hydrogen gas (H2). Calcium sulphate (metal salt) is also produced in the reaction. The chemical equation involved is as follows:

DO YOU KNOW?

When acid-containing food items such as pickles, curd, and citrus fruits are kept in metallic utensils, a reaction between the metal and the acid (present in the food item) takes place. Iron, aluminium, and copper are more prone to acid attack. Sometimes, these reactions result in the formation of toxic substances.

The following activity can be performed to confirm that hydrogen gas is produced when metals react with acids.

Now, let us see what happens when metals react with bases.

Metals react with bases and replace the available hydrogen(s) to form salt as follows:

For example, metal (Zn) displaces hydrogen from the base (NaOH) and produces hydrogen gas. The reaction between sodium hydroxide and zinc can be represented as:

However, it should be noted that not all metals react with bases.

The following activity can be performed to confirm that hydrogen gas is produced on reacting metals with bases.

Activity:

Place a few pieces of zinc granules in a test tube. Then, add 2 mL sodium hydroxide (NaOH) in it and heat the solution. A reaction between bases (such as NaOH) and metals (such as Zn) is initiated on heating.

Figure 2: Experiment showing the reaction of bases with metals

We will observe that bubbles are formed in the test tube as soon as dilute sodium hydroxide solution is added to the zinc granules. This proves that gas is evolved in the reaction. The gas evolved in the test tube is then passed to the soap solution through the delivery tube. Soap bubbles filled with hydrogen gas will be seen in the soap solution. The presence of hydrogen gas is confirmed by its burning with a ‘pop’ sound when a candle is brought near the bubbles.

Hence, hydrogen gas is formed and evolved in the reaction.

Now, let us study some other chemical properties of...

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