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A piece of rock has a mass of 2.00 g - CIE - A-Level Chemistry - Question 17 - 2016 - Paper 1

Question 17

A piece of rock has a mass of 2.00 g. It contains calcium carbonate, but no other basic substances. It neutralises exactly 36.0 cm³ of 0.500 mol dm⁻³ hydrochloric ac... show full transcript

Worked Solution & Example Answer:A piece of rock has a mass of 2.00 g - CIE - A-Level Chemistry - Question 17 - 2016 - Paper 1

Step 1

Calculate the moles of hydrochloric acid neutralized

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Answer

First, we need to calculate the total moles of hydrochloric acid used in the reaction. The formula for moles is given by:

$moles = concentration \times volume$

Using the concentration of hydrochloric acid (0.500 mol dm⁻³) and the volume in dm³ (36.0 cm³ = 0.0360 dm³):

$moles_{HCl} = 0.500 \text{ mol dm}^{-3} \times 0.0360 \text{ dm}^3 = 0.0180 \text{ mol}$

Step 2

Determine the moles of calcium carbonate

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Answer

The neutralization reaction between calcium carbonate (CaCO₃) and hydrochloric acid (HCl) is:

$CaCO_3 + 2HCl \rightarrow CaCl_2 + H_2O + CO_2$

From the equation, it can be seen that 1 mole of calcium carbonate reacts with 2 moles of hydrochloric acid. Thus, the moles of calcium carbonate can be calculated as:

$moles_{CaCO_3} = \frac{moles_{HCl}}{2} = \frac{0.0180 \text{ mol}}{2} = 0.0090 \text{ mol}$

Step 3

Calculate the mass of calcium carbonate

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Answer

Now that we have the moles of calcium carbonate, we can calculate its mass using the molar mass of CaCO₃, which is approximately 100.09 g/mol:

$mass_{CaCO_3} = moles_{CaCO_3} \times molar \ mass_{CaCO_3} = 0.0090 \text{ mol} \times 100.09 \text{ g/mol} \approx 0.9009 \text{ g}$

Step 4

Calculate the percentage of calcium carbonate in the rock

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Answer

Finally, we can find the percentage of calcium carbonate in the rock piece using the formula:

$percentage = \left( \frac{mass_{CaCO_3}}{mass_{rock}} \right) \times 100 = \left( \frac{0.9009 \text{ g}}{2.00 \text{ g}} \right) \times 100 \approx 45.0\%$

A piece of rock has a mass of 2.00 g - CIE - A-Level Chemistry - Question 17 - 2016 - Paper 1

Worked Solution & Example Answer:A piece of rock has a mass of 2.00 g - CIE - A-Level Chemistry - Question 17 - 2016 - Paper 1

Calculate the moles of hydrochloric acid neutralized

Determine the moles of calcium carbonate

Calculate the mass of calcium carbonate

Calculate the percentage of calcium carbonate in the rock

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