Table 1 shows results from an environmental laboratory. A technician decomposed different masses of sodium hydrogencarbonate in sealed tubes and measured th...
Question 1 Report
Table 1 shows results from an environmental laboratory. A technician decomposed different masses of sodium hydrogencarbonate in sealed tubes and measured the carbon dioxide collected. The reaction is 2NaHCO3 → Na2CO3 + CO2 + H2O. The water and gas were both retained in the apparatus when its final mass was recorded.
| Mass of sodium hydrogencarbonate heated / g | Mass of carbon dioxide / g | Final mass of sealed apparatus / g |
|---|---|---|
| 8.4 | 2.2 | 98.6 |
| 12.6 | 3.3 | 98.6 |
(a) Record the increase in carbon dioxide mass when the starting mass changes from 8.4 g to 12.6 g. [1]
(b) Use conservation of mass to calculate the combined mass of sodium carbonate and water made from 12.6 g of sodium hydrogencarbonate. [2]
(c) Give why both final masses in Table 1 are the same. [1]
(d) Draw a balanced symbol equation for the reaction. [2]
Answer Details
(a) The increase in carbon dioxide mass is:
\[3.3\text{ g}-2.2\text{ g}=1.1\text{ g}\]
1.1 g [1]
(b) The 12.6 g of sodium hydrogencarbonate forms carbon dioxide, sodium carbonate and water. By conservation of mass:
\[12.6\text{ g}-3.3\text{ g}=9.3\text{ g}\]
The combined mass of sodium carbonate and water is 9.3 g. [2]
(c) Both final masses are the same because each apparatus is sealed: no substance enters or leaves, so mass is conserved. [1]
(d) The balanced symbol equation is:
\[2\text{NaHCO}_3\rightarrow\text{Na}_2\text{CO}_3+\text{CO}_2+\text{H}_2\text{O}\]
There are equal numbers of Na, H, C and O atoms on both sides. [2]
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