Aim

To study the properties of acids (dilute HCl) by their reaction with
i) Litmus solution (Blue/Red)
ii) Zinc metal
iii) Solid Sodium Cabonate

Materials Required

• Test tubes
• Test tube stand
• Delivery tube with cork
• Litmus solutions (blue and red)
• Zinc metal (granulated)
• Solid sodium carbonate
• Sodium hydroxide solution
• Distilled water
• Lime water

Principle

An acid can be tested as follows:

• It turns blue litmus red.
• Most of the dilute acids liberate hydrogen gas with active metals like zinc.
  Zn + 2HCl → ZnCl₂ + H₂
• With carbonates, dilute acids gives carbon dioxide. For example, dill. HCL gives CO₂ with sodium cabonate, Na₂CO₃.
  Na₂CO₃ + 2HCL → NaCl + H₂O + CO₂

Procedure

• Take nearly 5 ml of the given acid in a test tube. Dilute it with nearly 10 mL of distilled water.
  In two test tube take nearly 1 mL each of red and blue litmus solution. To each of the test tube add 2-3 drops of the diluted acid. Note the colour of the two solutions.
• Take a small piece of granulated Zinc in a test tube. Add to it nearly 2mL of diluted acid. If there is no reaction, wait for 5 minutes or till a vigorous reactions starts. Fit a cork with a delivery tube in the mouth of the test tube in the month of the test tube and perform the following experiments.
  (i) Note the colour of the gas evolved.
  (ii) To note the odour of the gas evolved, fan the gas gently towards your nose.
  (iii) Ignite the gas coming out of delivery tube. Note the colour of the flame produced.
• Take a pinch of the solid sodium carbonate in a clean and dry test tube. Add to it 1-2 mL of dilute acid. A vigorous reaction starts. Note the colour of the gas evolved. Pass the gas through freshly prepared lime water and observe the changes produced.
  To note the odour of the gas evolved, fan the gas gently towards your nose.

Observations

S. No.	Experiment	Observation
1.	(a) Colour developed with blue litmus solution. (b) Colour developed with red litmus solution.	No change in colour. Blue.
2.	Treat some granulated zinc with dil. NaOH solution in a test tube fitted with a cork and delivery tube.	A colourless, odourless gas is evolved. The gas burns with a blue flame.
3.	Add a pinch of sold sodium carbonate to the NaOH solution.	Neither any gas is evolved nor any precipitate is formed.

Inference :- Dilute acid turns blue litmus red, liberates hydrogen with active metals like Zinc and gives CO₂ with solid sodium carbonate.

Precautions

• Wash and clean the test tubes before starting the experiment.
• Ignite the hydrogen evolved carefully. Hydrogen forms an explosive mixture with oxygen. Therefore, use a test tube with a delivery tube to carry out this test.