Fig. 1 shows a school investigation into the thermal decomposition of calcium carbonate. A student heats powdered calcium carbonate in a hard-glass tube. Th...
Question 1 Report
Fig. 1 shows a school investigation into the thermal decomposition of calcium carbonate. A student heats powdered calcium carbonate in a hard-glass tube. The gas produced is bubbled into limewater. The calcium carbonate has a mass of 5.00 g. Ar values are Ca = 40, C = 12 and O = 16.
(a) Name the gas that makes the limewater cloudy. [2]
(b) Complete the word equation: calcium carbonate → calcium oxide + .... [2]
(c) Complete the balanced chemical equation, including state symbols: CaCO3(s) → CaO(...) + CO2(...). [3]
(d) Calculate the mass of carbon dioxide formed if the reaction is complete. [2]
(e) State the mass of calcium oxide remaining in the tube. [3]
Answer Details
(a) The gas is carbon dioxide. It is identified because it turns limewater milky or cloudy. [2]
(b) The missing product is carbon dioxide. [2]
(c) The balanced equation, including states, is:
\[\mathrm{CaCO_3(s)\rightarrow CaO(s)+CO_2(g)}\]
Heating causes thermal decomposition of calcium carbonate. [3]
(d)
\[M_r(\mathrm{CaCO_3})=40+12+(3\times16)=100\]
\[M_r(\mathrm{CO_2})=12+(2\times16)=44\]
\[5.00\times\frac{44}{100}=2.20\text{ g}\]
The mass of carbon dioxide is 2.20 g. [2]
(e) Mass is conserved. The original 5.00 g becomes calcium oxide plus carbon dioxide:
\[5.00-2.20=2.80\text{ g}\]
The mass of calcium oxide remaining is 2.80 g. [3]
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