Virtual Experiments - Acids, Bases and Salts - Class 10 PDF Download

• The pH value is greater than 7 at 25°C

• Take a small amount of finely chopped onions along with some strips of clean cloth in a plastic bag.
• Tie up the bag tightly and leave it as such in a refrigerator for a night. In the morning, take two of these strips and check their odour.
• Now put a few drops of dilute HCl solution on one strip and a few drops of dilute NaOH solution on the other.
• Rinse both the cloth strips with water and again check their odour and note down in your notebook.
• You will see that onion will give different odour in HCl and NaOH.
• You can repeat the activity by taking dilute vanilla essence. Smell dilute vanilla essence.
• Now take some dilute HCl solution in one test tube and dilute NaOH solution in another test tube add a few drops of dilute vanilla essence to both the test tubes and shake well.
• Check the odour once again.
• You will feel different smells in both the test tubes.
• Lastly, you can repeat the activity by taking clove oil in place of vanilla essence.
• From this activity, we conclude that vanilla, onion or clove oil can also be used as olfactory indicators since these change their odour.
  
  

Activity

Procedure

• Take about 5 ml of dilute sulphuric acid in a boiling tube.
• Add a few pieces of zinc metal into it and place an inverted boiling tube over its mouth.
• You can see the bubbles of hydrogen gas coming out of the mixture in the lower tube.
• After a few minutes, remove the upper boiling tube (Keeping its mouth downwards) near to its mouth. What do you see?
• The gas in the upper boiling tube burns with a blue flame producing the popping sound.
• Repeat a similar experiment with different acids and a few other metals. Write down your observations.

The reaction of Acids with Metals

Observation: Colourless, odourless gas is evolved. It burns explosively with a 'pop' sound.
Zn(s) + H₂SO₄ (dil) → ZnSO₄ (aq) + H₂(g)

Conclusion: Reactive metals react with dilute acid to liberate hydrogen gas. Metals which can displace hydrogen from dilute acid are known as active metals.
Example: Na, K, Zn, Fe, Ca, Mg etc.

Activity

Aim: To study the reaction of sodium carbonate and sodium hydrogen carbonate with dilute acids.

Materials required: Sodium carbonate (Na₂CO₃), Sodium hydrogen carbonate, Hydrochloric acid (dil.), Limewater, Boiling tubes, Delivery tube.
Procedure

• Take about 0.5g of sodium carbonate in a boiling tube and 2-3 mL of freshly prepared limewater in another test tube.
• Set a delivery tube, as shown in fig. given alongside. Add about 2mL of dilute hydrochloric acid into the boiling tube containing sodium carbonate.
• A brisk effervescence is seen in the reaction mixture. Pass the gas evolved through limewater with the help of a delivery tube.
• What do you observe? The limewater turns milky.
• When an excess of carbon dioxide is passed, the milkiness disappears. Repeat the similar experiment with sodium hydrogen carbonate (NaHCO₃), and if desired with other acids also.

The reaction of Acids with Sodium Carbonate and Sodium Hydrogen Carbonate

Conclusion: All acids decompose carbonates and hydrogen carbonates with the liberation of carbon dioxide gas.

Activity

Aim: To study the reaction of dilute acid with metal oxides (or basic oxides).

Materials required: Copper (II) oxide, Dilute hydrochloric acid, Test tube.

Procedure

• Take about 0.5g of copper (II) oxide (black in colour) in a test tube.
• Add dilute hydrochloric acid dropwise with occasional shaking till copper (II)  oxide dissolve.
• Note the colour of the solution. I not it bluish-green? It is the solution of copper (II) chloride.
  

Conclusion: Acids react with metal oxides to give the corresponding salt & water.

Activity

Aim: To study a reaction of an acid, say hydrochloric acid with an alkali or base.

Materials required: The hydrochloric acid solution, sodium hydroxide solution, phenolphthalein indicator, Boiling tube, dropper, trough.

Procedure

• Take about 5 mL of a dilute solution of sodium hydroxide (NaOH) in a test tube. Add 2 drops of phenolphthalein indicator in it.
• The solution in the test tube turns pink.
• Now, add a dilute solution of hydrochloric acid (HCl) when the pink colour of the solution just disappears.
• Now, add a drop of sodium hydroxide solution and shake the test tube to mix the solution. What do you see? The solution turns pink.
• Add a drop of HCl solution to the solution in the test tube. The pink colour disappears.
• Keep repeating the addition of sodium hydroxide and hydrochloric acid solution one after the other and watch the appearance and disappearance of pink colour.
  

Conclusion

• This experiment shows that the addition of the HCl solution destroys the alkaline nature of NaOH.
• On the other hand, the addition of the NaOH solution destroys the acidic nature of HCl.
• That is, both NaOH and HCl appear to cancel the effect of each other.
• Such a reaction between an acid and alkali is called neutralisation.
  

Activity

Aim: To find the characteristics common between acids and bases.

Materials required: Dilute hydrochloric acid, Dilute sulphuric acid, Dilute solution of sodium hydroxide, Ethanol, Glucose solution & Beaker, Carbon electrodes, Dry cells, bulb 1.5 V, Key.

Procedure

• Take a beaker and place two carbon electrodes into it.
• Connect the electrodes to a battery bulb through a key and a dry cell. Pour dilute hydrochloric acid into the beaker and press the key. 
• Did the bulb glow? Perform a similar experiment with all the given solutions, and record your observations.

Acid Solution in Water Conducts Electricity 

Observation

Conclusion: The solutions of acids and bases are good conductors of electricity. The solution of glucose and ethanol are nonconductors of electricity.

Activity

Aim: To show that acids furnish H⁺(aq) ions only in the presence of water.

Materials required: Common salt, Conc. sulphuric acid, anhydrous calcium chloride, blue litmus paper, boiling tube, delivery tube packed with anhydrous calcium chloride.

Procedure

• Take 0.5g of dry common salt in a dry boiling tube. 
• Add a few drops of concentrated sulphuric acid over common salt in the boiling tube. What do you see? 
• A colourless, irritating gas is evolved. 
• Fit a cork carrying a calcium chloride packed delivery tube into the mouth of the boiling tube.
• Bring a dry blue litmus paper near the opening of the calcium chloride tube. Observe, if there is any change in colour. Colour of the litmus paper remains unchanged. 
• Now, bring a moistened blue litmus paper near the mouth of the calcium chloride tube. 
• Do you observe any change in the colour of litmus paper? Yes, blue litmus has changed to red.

Conclusion

• Dry HCl gas on coming in contact with dry blue litmus paper does not produce H⁺ ions, and hence the colour of the litmus paper does not change. So, we can say that separation of H⁺ ions from acid takes place only in the presence of water.

Activity

Aim: To show that water of crystallisation can be removed by heating.
Materials required: CuSO₄.5H₂O (Blue vitriol), boiling tube, burner, cork, delivery tube, test tube, clamp stand.

Procedure

• Take 2 g of CuSO₄.5H₂O in a boiling tube fitted in a clamp stand. 

Removing Water of Crystallisation

• Observe its colour. Fit it with cork, and delivery tube bent at two right angles which dip into a test tube.
• Heat crystals in a boiling tube. Observe vapours being condensed in the test tube.
• Cool the crystals and add few drops of water into it 

Observation

• Water vapours get condensed in a test tube, and the colour of blue crystals changes into white.
• On adding water to anhydrous copper sulphate, it changes into blue again.

Conclusion: Crystalline substances have water of crystallization which is lost on heating.