CHEMICAL EQUATIONS ACTIVITY ANSWERS

Clean a magnesium ribbon about 3-4 cm long by rubbing it with sandpaper. Hold it with a pair of tongs. Burn it using a spirit lamp or burner and collect the ash so formed in a watch-glass as shown in Fig. 1.1. Burn the magnesium ribbon keeping it away as far as possible from your eyes. What do you observe

Burning of a magnesium ribbon in air and collection of magnesium oxide in a watch-glass

Take lead nitrate solution in a test tube. Add potassium iodide solution to this. What do you observe

Yellow precipitate of lead nitrate and potassium nitrate

Take a few zinc granules in a conical flask or a test tube. Add dilute hydrochloric acid or sulphuric acid to this (Fig. 1.2). CAUTION: Handle the acid with care. Do you observe anything happening around the zinc granules? Touch the conical flask or test tube. Is there any change in its temperature?

Formation of hydrogen gas by the action of dilute sulphuric acid on zinc

Take a small amount of calcium oxide or quick lime in a beaker. Slowly add water to this. Touch the beaker as shown in Fig. 1.3. Do you feel any change in temperature?

Formation of slaked lime by the reaction of calcium oxide with water. Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat

Take about 2 g ferrous sulphate crystals in a dry boiling tube. n Note the colour of the ferrous sulphate crystals. n Heat the boiling tube over the flame of a burner or spirit lamp as shown in Fig. 1.4. n Observe the colour of the crystals after heating

heating the boiling tube containing crystals of ferrous sulphate and of smelling the odour. Ferrous sulphate crystals (FeSO4 . 7H2 O) lose water when heated and the colour of the crystals changes. It then decomposes to ferric oxide (Fe2 O3 ), sulphur dioxide (SO2 ) and sulphur trioxide (SO3 ). Ferric oxide is a solid, while SO2 and SO3 are gases.

Take about 2 g lead nitrate powder in a boiling tube. n Hold the boiling tube with a pair of tongs and heat it over a flame, as shown in Fig. 1.5. n What do you observe? Note down the change, if any

Heating of lead nitrate and emission of nitrogen dioxide, emission of brown fumes. These fumes are of nitrogen dioxide (NO2 )

Take a plastic mug. Drill 2 holes at its base and fit rubber stoppers in these holes. Insert carbon electrodes in these rubber stoppers as shown in Connect these electrodes to a 6 volt battery. Fill the mug with water such that the electrodes are immersed. Add a few drops of dil.H2So4 to the water. Take2 test tubes filled with water and invert them over the 2 carbon electrodes. Switch on the current and leave the apparatus undisturbed for some time. observe the formation of bubbles at both the electrodes. These bubbles displace water in the test tubes. Is the volume of the gas collected the same in both the test tubes? n Once the test tubes are filled with the respective gases, remove them carefully. Test these gases one by one by bringing a burning candle close to the mouth of the test tubes.: This step must be performed carefully by the teacher. What happens in each case? Which gas is present in each test tube

Electrolysis of water

Take about 2 g silver chloride in a china dish. n What is its colour? n Place this china dish in sunlight for some time (Fig. 1.7). n Observe the colour of the silver chloride after some time.

Silver chloride turns grey in sunlight to form silver metal. Silver bromide also behaves in the same way.

Take three iron nails and clean them by rubbing with sand paper. n Take two test tubes marked as (A) and (B). In each test tube, take about 10 mL copper sulphate solution. n Tie two iron nails with a thread and immerse them carefully in the copper sulphate solution in test tube B for about 20 minutes [Fig. 1.8 (a)]. Keep one iron nail aside for comparison. n After 20 minutes, take out the iron nails from the copper sulphate solution. n Compare the intensity of the blue colour of copper sulphate solutions in test tubes (A) and (B) [Fig. 1.8 (b)]. n Also, compare the colour of the iron nails dipped in the copper sulphate solution with the one kept aside

the iron nail become brownish in colour and the blue colour of copper sulphate solution fades. iron has displaced or removed another element, copper, from copper sulphate solution. This reaction is known as displacement reaction.

Take about 3 mL of sodium sulphate solution in a test tube. In another test tube, take about 3 mL of barium chloride solution. Mix the two solutions (Fig. 1.9). What do you observe?

Formation of barium sulphate and sodium chloride. The white precipitate of BaSO4 is formed by the reaction of 2 4 and Ba2+. The other product formed is sodium chloride which remains in the solution. Such reactions in which there is an exchange of ions between the reactants are called double displacement reactions.

Heat a china dish containing about 1 g copper powder (Fig. 1.10). What do you observe?

The surface of copper powder becomes coated with black copper(II) oxide. Why has this black substance formed? This is because oxygen is added to copper and copper oxide is formed.