Table 1 shows readings from a pharmacy investigation of a calcium carbonate antacid powder. A technician placed 0.60 g of the powder into a flask containing...
Question 1 Report
Table 1 shows readings from a pharmacy investigation of a calcium carbonate antacid powder. A technician placed 0.60 g of the powder into a flask containing 40.0 cm3 of dilute hydrochloric acid. The flask was connected to a gas syringe. Carbon dioxide gas was collected while the reaction took place at 22 degrees C. The same mass of powder and the same acid solution were used for every repeat.
| Time / s | Volume of gas collected / cm3 |
|---|---|
| 0 | 0 |
| 15 | 18 |
| 30 | 27 |
| 45 | 31 |
| 60 | 32 |
(a) State the name of the gas collected in the syringe. [1]
(b) Complete the balanced chemical equation, including the formula of the salt.
CaCO3 + 2HCl → ______ + H2O + CO2 [2]
(c) Calculate the mean rate of gas production during the first 30 s. Give your answer in cm3/s. [2]
(d) Explain why the volume of gas changes very little between 45 s and 60 s. [2]
(e) Give two changes that would make this investigation more reliable. [2]
Answer Details
(a) The gas is carbon dioxide. [1]
(b) The salt is calcium chloride, \(\text{CaCl}_2\). The completed balanced equation is:
\[\text{CaCO}_3+2\text{HCl}\rightarrow\text{CaCl}_2+\text{H}_2\text{O}+\text{CO}_2\]
[2]
(c) In the first 30 s, 27 cm3 is collected:
\[\text{mean rate}=\frac{27\text{ cm}^3}{30\text{ s}}=\boxed{0.90\text{ cm}^3\text{ s}^{-1}}\] [2]
(d) By 45 s, one reactant, calcium carbonate or acid, has been used up. Therefore, little or no further carbon dioxide is made because the reaction has effectively finished. [2]
(e) Repeat the investigation and calculate a mean after excluding any anomalous result. More precise volume-measuring apparatus, and ensuring all powder is transferred into the flask, are also valid improvements. Any two. [2]
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