Reactions of Acids

The reaction of acids with metals depends on factors such as the strength and concentration of the acid, the reactivity of the metal, and the temperature. Typically, dilute solutions of strong acids react easily with moderately reactive metals at normal temperature, producing a salt and hydrogen gas. This reaction shows the characteristic behaviour of acids when they interact with metals.

For example:

Cu(s) + 2HNO₃ (aq) →  Cu(NO₃)₂ (aq) + H₂ (g)

Reaction of Metals with Acids

1. Aim: To study the reaction of a metal (magnesium) with dilute hydrochloric acid and observe the release of hydrogen gas.

2. Requirements: magnesium ribbon (a few pieces), dilute hydrochloric acid (HCl), test tube, rubber stopper with a gas tube, and lighted candle.

3. Procedure

• Place a few pieces of magnesium ribbon in a clean test tube.
• Add dilute HCl to the test tube to cover the magnesium ribbon.
• Close the test tube with the rubber stopper fitted with a gas tube.
• Bring a lighted candle near the end of the gas tube. Observe the reaction inside the test tube and near the candle.

Reaction of a dilute solution of a strong acid with a metal

4. Observations: Bubbles of gas are seen forming in the test tube, indicating the release of hydrogen gas. When the gas comes into contact with the flame, it burns with a pop sound, confirming it is hydrogen.

5. Conclusion: Magnesium reacts with dilute hydrochloric acid to produce hydrogen gas and magnesium chloride. The reaction demonstrates the displacement of hydrogen from the acid by the metal. The general reaction is:

Metal + Dilute Acid → Salt + Hydrogen Gas

Example Reactions:

1. Mg(s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g) 
2. Zn(s) + H₂SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)

Reaction of Metal Oxides with Acids

1. Aim: To observe the reaction of a metal oxide (red oxide, Fe₂O₃) with a dilute acid (HCl) and identify the products formed.

2. Requirements: water, red oxide (Fe₂O₃), dilute hydrochloric acid (HCl), test tube, and dropper.

3. Procedure:

• Take some water in a test tube and add a small amount of red oxide (Fe₂O₃) to it.
• Shake the test tube and observe whether the red oxide dissolves in water.
• Add a small quantity of dilute HCl to the test tube and shake it again.
• Observe any changes in the appearance of the solution.

4. Observations: Red oxide does not dissolve in water, indicating its insolubility. On adding dilute HCl, the red oxide reacts, producing a yellowish solution, indicating the formation of a water-soluble salt (FeCl₃).

5. Conclusion: Metal oxides, such as red oxide (Fe₂O₃), are insoluble in water but react with dilute acids like HCl to produce a salt and water.

The reaction is represented as:

Fe₂O₃ (s) + 6HCl (aq) → 2FeCl₃ (aq) + 3H₂O (l)

Metal Oxide + Dilute Acid → Salt + Water

CaO (s) + 2 HCl (aq)  →  CaCl₂ (aq) + H₂O (l)

MgO (s) + 2 HCl (aq)  →  MgCl₂ (aq) + H₂O (l)

Reaction of Acids with Carbonates and Bicarbonates

1. Aim: To study the reaction of acids with carbonate and bicarbonate salts of metals and confirm the release of carbon dioxide gas.

2. Requirements: Baking soda (sodium bicarbonate, NaHCO₃), lemon juice, limewater (Ca(OH)₂ solution), test tubes, rubber cork with a bent tube, washing soda (sodium carbonate, Na₂CO₃), vinegar, dilute HCl, and dropper.

3. Procedure:

• Take some limewater in a test tube and keep it ready for observation.
• In another test tube, add a small amount of baking soda (NaHCO₃).
• Pour a few drops of lemon juice into the test tube containing baking soda. Immediately, fit the test tube with the rubber cork connected to the bent tube.
• Insert the other end of the bent tube into the limewater and observe.
• Repeat the experiment using washing soda (Na₂CO₃) and replace lemon juice with vinegar or dilute HCl. Record your observations in each case.

4. Observations: Effervescence is observed in the test tube containing baking soda or washing soda when acid is added, indicating the release of a gas. The limewater connected via the bent tube turns milky when exposed to the gas, confirming the presence of carbon dioxide.

5. Conclusion: The reaction between acids and carbonates/bicarbonates of metals produces carbon dioxide gas, which turns limewater milky. The reaction also produces salt and water.

This reaction can be represented by the following chemical equation:
Ca(OH)₂ (aq) + CO₂ (g) → CaCO₃ (s) + H₂O (l)

Carbonate Salt of Metal + Dilute Acid  →  Another salt of metal + Carbon Dioxide

CaCO₃ (s) + 2 HNO₃ (aq) → Ca(NO₃)₂ (aq) + CO₂ (g) + H₂O (l)

Bicarbonate salt of metal + dilute acid → Another salt of metal + carbon dioxide + water

KHCO₃ (s) + HNO₃ (aq) → KNO₃ (aq) + CO₂ (g) + H₂O (l)