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Limestone (CaCO3) contributes to the hardness of water by releasing Ca^2+ ions in water - HSC - SSCE Chemistry - Question 27 - 2060 - Paper 1
Question 27
Limestone (CaCO3) contributes to the hardness of water by releasing Ca^2+ ions in water. The chemical equation for this exothermic reaction is shown. CaCO3(s) + H2O... show full transcript
Worked Solution & Example Answer:Limestone (CaCO3) contributes to the hardness of water by releasing Ca^2+ ions in water - HSC - SSCE Chemistry - Question 27 - 2060 - Paper 1
Step 1
Explain why increasing the temperature of hard water would reduce its hardness.
Answer
According to Le Chatelier's Principle, an increase in temperature will favour the endothermic direction of the reaction, which is to the left. This shift will partially counteract the increase in temperature, leading to a decrease in the calcium ion concentration in the water. As a result, this will reduce the hardness of the water, as hardness is primarily due to the presence of calcium ions.
Step 2
Describe how atomic absorption spectroscopy (AAS) could be used to measure the effectiveness of heating water to reduce its hardness.
Answer
Atomic absorption spectroscopy (AAS) can be utilized to measure the concentration of Ca^{2+} ions in water. To assess the effectiveness of heating water in reducing hardness, the following steps can be taken:
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Preparation of Samples: Two water samples are taken—one before heating and one after.
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Calibration Curve: A calibration curve is established using standard solutions of Ca^{2+}. This involves measuring known concentrations of Ca^{2+} and plotting absorbance against concentration.
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Measurement of Samples: The absorbance of the two water samples is measured using AAS.
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Analysis of Results: Compare the absorbance readings to the calibration curve to determine the concentration of Ca^{2+} in each sample. If the heated sample shows a significantly lower concentration of Ca^{2+}, it indicates that heating was effective in reducing the hardness of the water.