Science Lab Manual Experiment 3 Aim To perform and observe the following reactions and classify them into: (a) Combination reaction (b) Decomposition reaction (c) Displacement reaction (d) Double displacement reaction. 1. Action of water on quick lime. 2. Action of heat on ferrous sulphate crystals.3. Iron nails kept in copper sulphate solution. 4. Reaction between sodium sulphate and barium chloride solutions. Theory Action of water on quick time > Quick lime is calcium oxide (CaO). It combines with water to form calcium hydroxide [Ca(OH),] also called as slaked lime. CaO(s) + H,O(!) Ca(OH), (aq) + Heat Quick lime Water Slaked lime > Two substances are combining to form one product, hence it is a combination reaction. > Heat is released in the reaction, hence it is called as exothermic reaction. > Slaked lime solution turns red litmus blue, hence it is basic in nature. > The freshly prepared slaked lime is also called as lime water. > It turns milky when carbon dioxide gas is passed through it. Action of heat on ferrous sulphate crystals > Ferrous sulphate crystals are light green in colour. The colour is due to the water of crystallization. > On heating the crystals of ferrous sulphate, it undergoes following changes: 2FeSO. 7H 0(s)— Fe.O,(s)+ SO.(g)+ SO; (g)+14H.O Light prec (aon (cube > The colour changes to brown and gases are released due to the formation of new compounds. > Single compound decomposes to form three new compounds, hence it is called as decomposition reaction. > SO, and SO, gas turns moist blue litmus paper into red, hence it is acidic in nature. > SO, shows reducing property: It changes the orange colour of acidified potassium dichromate to green when SO, gas is allowed to pass through it. > Water of crystallisation is released by the crystals. > SO, gas has choking smell, do not inhale the gas, keep the mouth of the test tube away from your face. Iron nails kept in copper sulphate solution Fe(s )+ CuSO, (aq) —- FeSO. (aq)+ Cu(s) roe Copper spate (Grey (Blox) > Iron nails when kept in blue coloured solution of copper sulphate, shows following changes: (a) The blue colour solution changes slowly into light green colour. (b) Fe ions replace Cu ions and form iron sulphate in the solution, hence, this is called as displacement reaction. (c) Iron nail gets the deposit of reddish copper ions on it. (d) Fe atom forms Fe* ions by loss of electrons and undergoes oxidation and Cu ions gain electrons to become Cu atom and undergoes reduction.Reaction between sodium sulphate and barium chloride solutions Na,SO, (aq) + BaCl (aq) ——+ BaSO, (s) + 2NaC! (aq) Seis Sulphate arin Cherie ‘arian Sulphate Sodium Chloride (White ppt) » Sodium sulphate solution and barium chloride solution are colourless. > Mixing of both the solutions gives white colour precipitate due to the formation of barium sulphate > The exchange of ions takes place in the reaction and is called as double displacement reaction. > Barium sulphate is insoluble in water and hence it forms precipitate. Materials Required A beaker, four test tubes, test tube holder, tongs, test tube stand, a dropper, a piece of sand paper and bunsen burner. Chemicals required: A small piece of quick lime, ferrous sulphate crystals, Iron nails (clean and unrusted), copper sulphate solution,sodium sulphate solution, barium chloride solution and distilled water. |. | Combination Reaction: Take aclean | Reaction occurs with crackling beaker, add a small piece of lime in| sound and steamy vapours. are it, Add water drop by drop into the | released, The beaker becomes hot, beaker. | Equation: Ca0(s) + H,0(1) — Ca(OH), (aq) + Heat Decomposition Reaction: Take | The green crystals become reddish- a clean and dry test tube, add few | brown, tiny droplets of water are crystals of ferrous sulphate, Fix, setted near the neck of test tube and it on a test tube holder. Heat the | a colourless gas is evolved. test tube on bumer, keeping the | The acidified potassium dichromate mouth of test tube away from | changes its colour from orange to Tron sulphate green crystals decomposes due to heat. Water of enystallisation is collected in the test tube. Sulphur dioxide gas has choking smell. I changes potassium dichromate paper green. Its a your face. Waft the gas released | green when held in gas. decomposition reaction. to smell and test it with acidified potassium dichromate paper. Equation: 2FeSO,7H.O(s) = Fes0,(s) +80: (g) + $O,(g) +, 1MH.0 K, cx 0r(aq) + H,S0. (aq) + 380, (g) — Cr, 2) KS, (aq) +140 Displacement Reaction: Take a clean test tube, add 2-3 mL of, copper sulphate solution in it, Place clean iron nail in it, Keep it on the test tube stand and observe the changes for 30 minutes. Equation: CuSO, (aq) + Fe(s) — FeSO, (aq) +Cu(s) The blue colour copper sulphate slowly changes its colour. The iron nail gets the deposit of reddish copper ions. The blue colour of copper sulphate solution changes to green. en Iron metal is reactive than copper, displaces it to form iron sulphate solution, Its a displacement reaction ‘and red deposit of copper is formed ‘on the nail. Double Displacement Reaction: in a clean test tube, take sodium sulphate solution, to this add barium chloride solution. Shake the contents and observe. Equation: Na,SO,(aq)+ BaCl, (aq) Both sodium sulphate and barium chloride solutions are colourless, on mixing together a white precipitate is formed. ~ BaSO,(s) + 2NaCI(aq) The white insoluble precipitate of barium sulphate is formed. It isa double displacement reaction Precautions LE oo Re Do not touch quick lime with hands, use tongs. Mixing of quick lime and water releases large amount of heat, so add water drop by drop and use borosil beaker. For heating, use hard glass tubes. Never inhale any gas, just waft the gas. Do not touch any chemical with hands. Keep the mouth of the test tube away from your face while heating.