O Lvl Chem: Nov 2003/Paper 3/ Section A/ Q7
Some properties of four solid, I, J, K, L, are given in Fig. 7.1. Use this information to complete the last column of the table.
| solid | percentage composition by mass | solid conducts electricity | strong heat in air | element or mixture or compound |
| I | constant | no | decomposes | |
| J | varies | no | burns | |
| K | varies | yes | melts | |
| L | constant | yes | oxidises to one substance |
Answer:
| solid | percentage composition by mass | solid conducts electricity | strong heat in air | element or mixture or compound |
| I | constant | no | decomposes | COMPOUND |
| J | varies | no | burns | ELEMENT |
| K | varies | yes | melts | MIXTURE |
| L | constant | yes | oxidises to one substance | COMPOUND |
I is a compound. Firstly, its percentage composition by mass is constant. Hence it is not a mixture. Secondly, it does not conducts electricity in the solid state. This information does not tell us anything. However, we know that it decomposes in strong heat in air. Element do not decomposes in strong heat. Hence I is a compound. Examples includes sugar.
J is an element. Firstly, its percentage composition by mass varies. This tell us that it is not a compound. For compound, the percentage composition by mass is fixed. Hence it can be an element(with isotopes) or it can be a mixture. It does not conduct electricity when in the solid state. This tell us that it is not a metal. Next, it burns when heated strongly in air. This two of information give us the information that it is an element. Burning is a phenomenon of oxidation. This means that a new substance (compound) is being form. Elements cannot be broken down into two or more simpler substances by ordinary chemical methods. Examples includes Arsenic, Bromine and so forth.
K is a mixture. Firstly, it percentage composition by mass varies. This means that it is not a compound. It conduct electricity in the solid state. This means that it might be a metal(conduct electricity) or a mixture. However, it melts when heat strongly in air. A mixture melts over a range of temperature. Metals do not melts when burn in air. Instead it is oxidised. Melting means that it is a mixture, since it cannot be an element (metal)
L is a compound. Firstly, its percentage by composition is constant. Hence, it is not a mixture. The next piece of information is that it oxidised to one substance when heated strongly in air. Mixture will not be oxidised to a single substance but several substance. Hence it is a compound.
