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Describe experimental procedures to show the effect of heating substances.

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a)Substances that gain mass when heated.
Clean 25 cm of magnesium ribbon and cut into 1 cm pieces. Weigh a crucible plus lid, put the
pieces of magnesium ribbon in the crucible and weigh again. Put the crucible on a pipe clay
triangle supported on a tripod. Heat very gently then strongly. Hold the crucible lid in a pair
of tongs close to the crucible. The magnesium ribbon darkens just before it begins to melt.
At the first sign of burning, place the lid on the crucible and remove the Bunsen burner.
Every 4 seconds, raise the lid to allow more air to enter but do not allow any white
magnesium oxide smoke to escape. When the magnesium stops burning on raising the lid,
remove the lid. Heat the crucible again strongly but still hold the crucible lid in a pair of
tongs close to the crucible in case the magnesium starts to burn again. Leave the crucible to
cool. When cool, weigh the crucible plus lid plus contents. Calculate the increase in mass of
the magnesium.

(b) Substances that lose mass when heated
(i) Weigh a test-tube containing 1 cm potassium permanganate crystals and a 1 cm plug of
cotton wool at the mouth to prevent loss of any solid during heating. Heat the test-tube and
cotton wool and weigh it again. Note any change in the potassium permanganate crystals.
Note any loss in mass due to the loss of water of crystallization.
(ii) Weigh a test-tube containing 1 cm copper carbonate and a 1 cm plug of cotton wool at
the mouth to prevent loss of any solid during heating. Heat the test-tube and cotton wool
and weigh it again. Note any change in the copper carbonate. Note any loss in mass.

(c) Substances that neither gain nor lose mass when heated
Weigh a test-tube containing 1 cm dry zinc oxide and a 1 cm plug of cotton wool at the
mouth to prevent loss of any solid during heating. Heat the test-tube and cotton wool and
weigh it again. Note any change in the zinc oxide. Note any loss in mass.

(d) Effect of heat on copper sulphate crystals
Crush blue copper sulphate crystals and put them into a dry test-tube to a depth of 4 cm.
Heat the tube gently. Note whether vapour collects on the cooler parts, change of colour
from blue to white, and any liquid collecting in the receiving tube. Identity of the liquid by
measuring the boiling point. When all the copper sulphate crystals have changed to white
and the tube has cooled, hold the tube in your hand and pour the liquid back on to the white
crystals. Note whether the blue colour restored and if any heat is given back.
Blue copper sulphate crystals + heat -> white, anhydrous copper sulphate + water.
This is a reversible change.

sharon kalunda answered the question on April 12, 2019 at 07:19

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Describe experimental procedures to show the effect of heating substances.

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