(b) When the fuel is burned, the student notices that a black solid forms on the bottom of the copper can. (i) Identify the black solid. (ii) Explain why the black solid forms. __

## Step 1<br />The black solid that forms on the bottom of the copper can when the fuel is burned is likely to be carbon. This is because when fuels are burned, they undergo a process called combustion. During combustion, the carbon in the fuel reacts with oxygen in the air to form carbon dioxide. However, if there is insufficient oxygen, the carbon does not fully react and instead forms a solid residue, which is carbon.<br /><br />## Step 2<br />The formation of the black solid, or carbon, is due to incomplete combustion. Incomplete combustion occurs when there is not enough oxygen available to fully react with the carbon in the fuel. This can happen if the fuel is burned in an enclosed space, such as a copper can, where the oxygen supply is limited.<br /><br />## Step 3<br />When there is insufficient oxygen, the carbon in the fuel does not fully react and instead forms a solid residue, which is carbon. This is why the black solid forms on the bottom of the copper can.