Compounds Pg. 50, 51
Thursday, February 19, 2009
Pg. 50
1. Metals - Cadmium, Titanium, Plutonium
Non-metals - Xenon, Astatine, Bromine
Sand - Silicon, oxygen
Iron sulphide - Iron, sulphur
Water - Hydrogen, oxygen
Glucose - Hydrogen, oxygen, carbon
Carbon dioxide - carbon, oxygen
Sodium chloride - sodium, chlorine
2a) F. Compounds are made up of 2 or more elements chemically combined.
b) F. Compounds are made up of elements which have been chemically combined.
c) F. The constituent elements of a compound may be metals and / or non-metals (not either / or).
Pg. 51
1. Property 1 : The properties of a compound are different from the properties of its constituent elements. For example, at room temperature, mercuric oxide is a red solid while mercury is a silvery liquid metal and oxygen is a colourless gas.
Property 2 : The constituents of a compound can only be separated by chemical methods. Mercuric oxide is broken down into mercury and oxygen when it is heated.
2a) The formation of compounds usually involves an exchange of energy with the suroundings.
bi) 56 + 32 = 88g of iron sulphide.
264/88 = 3 times
mass of iron present in 264g of iron sulphide = 88 x 3 = 168g
mass of sulphur present in 264g of iron sulphide = 32 x 3 = 96g
ii) if 56g of iron is mixed with 50g of sulphur and heated, only 32g of sulphur will react.
(remember 56g iron : 32g of sulphur)
Sulphur : 50g - 32g (reacted) = 18g (left behind)
Mass of iron sulphide formed = 56g iron + 32g sulphur = 88g
