calculating percentage of caco3 in a limestone sample (help)

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username4221054
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Here is the question:

"Limestone is an ore of calcium that contains a high proportion of calcium carbonate (CaCO3).

Calcium carbonate reacts with hydrochloric acid (HCl) according to the equation:

CaCO3 + 2HCl -> CaCl2 + CO2 +H2O

A 1.75g sample of limestone is added to a solution of excess hydrochloric acid at a pressure of 101 kPa. 280cm3 of carbon dioxide gas (CO2) is formed at a temperature of 22.0 degrees C. It was assumed that all of the CO2 gas produced was formed during the reaction between CaCO3 and HCl.

Calculate the percentage of CaCO3 in the limestone sample. (The gas constant, R = 8.31 J K^-1 mol^-1)"

Very wordy question, idk where to begin. I think by calculating the number of moles in the CO2 gas? What would I do next?
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maths_student6
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(Original post by earthworm206)
Here is the question:

"Limestone is an ore of calcium that contains a high proportion of calcium carbonate (CaCO3).

Calcium carbonate reacts with hydrochloric acid (HCl) according to the equation:

CaCO3 + 2HCl -> CaCl2 + CO2 +H2O

A 1.75g sample of limestone is added to a solution of excess hydrochloric acid at a pressure of 101 kPa. 280cm3 of carbon dioxide gas (CO2) is formed at a temperature of 22.0 degrees C. It was assumed that all of the CO2 gas produced was formed during the reaction between CaCO3 and HCl.

Calculate the percentage of CaCO3 in the limestone sample. (The gas constant, R = 8.31 J K^-1 mol^-1)"

Very wordy question, idk where to begin. I think by calculating the number of moles in the CO2 gas? What would I do next?
1. Calculate moles of CO2 like you said (using pV=nRT)

2. Use the balanced equation to work out the ratio of CaCO3: CO2 and therefore the number of moles of CaCO3 used

3. Calculate the mass of CaCO3 used (by doing moles x molecular mass found from periodic table)

4. Calculate the percentage of CaCO3 by doing (mass of CaCO3 from step 3)/(mass of limestone sample) x 100%

Hope that helps! Don't panic about long questions - you will get used to how to approach them with practice. As a general rule, work from the end of the question backwards.
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charco
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(Original post by earthworm206)
Here is the question:

"Limestone is an ore of calcium that contains a high proportion of calcium carbonate (CaCO3).

Calcium carbonate reacts with hydrochloric acid (HCl) according to the equation:

CaCO3 + 2HCl -> CaCl2 + CO2 +H2O

A 1.75g sample of limestone is added to a solution of excess hydrochloric acid at a pressure of 101 kPa. 280cm3 of carbon dioxide gas (CO2) is formed at a temperature of 22.0 degrees C. It was assumed that all of the CO2 gas produced was formed during the reaction between CaCO3 and HCl.

Calculate the percentage of CaCO3 in the limestone sample. (The gas constant, R = 8.31 J K^-1 mol^-1)"

Very wordy question, idk where to begin. I think by calculating the number of moles in the CO2 gas? What would I do next?
moles CO2 ==> mol calcium carbonate ==> mass calcium carbonate ==> percentage purity
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ChemistryWebsite
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Good start!

When you have the moles of CO2 you can relate that to the number of moles of CaCO3 from the equation ratio.

WHen you have the number of moles of CaCO3, calculate the mass of that number of moles.
Calculate the % of the original mass that was due to the CaCO3 mass you have worked out above.

(Original post by earthworm206)
Here is the question:

"Limestone is an ore of calcium that contains a high proportion of calcium carbonate (CaCO3).

Calcium carbonate reacts with hydrochloric acid (HCl) according to the equation:

CaCO3 + 2HCl -> CaCl2 + CO2 +H2O

A 1.75g sample of limestone is added to a solution of excess hydrochloric acid at a pressure of 101 kPa. 280cm3 of carbon dioxide gas (CO2) is formed at a temperature of 22.0 degrees C. It was assumed that all of the CO2 gas produced was formed during the reaction between CaCO3 and HCl.

Calculate the percentage of CaCO3 in the limestone sample. (The gas constant, R = 8.31 J K^-1 mol^-1)"

Very wordy question, idk where to begin. I think by calculating the number of moles in the CO2 gas? What would I do next?
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username4221054
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(Original post by maths_student6)
1. Calculate moles of CO2 like you said (using pV=nRT)

2. Use the balanced equation to work out the ratio of CaCO3: CO2 and therefore the number of moles of CaCO3 used

3. Calculate the mass of CaCO3 used (by doing moles x molecular mass found from periodic table)

4. Calculate the percentage of CaCO3 by doing (mass of CaCO3 from step 3)/(mass of limestone sample) x 100%

Hope that helps! Don't panic about long questions - you will get used to how to approach them with practice. As a general rule, work from the end of the question backwards.
(Original post by charco)
moles CO2 ==> mol calcium carbonate ==> mass calcium carbonate ==> percentage purity
(Original post by TutorsChemistry)
Good start!

When you have the moles of CO2 you can relate that to the number of moles of CaCO3 from the equation ratio.

WHen you have the number of moles of CaCO3, calculate the mass of that number of moles.
Calculate the % of the original mass that was due to the CaCO3 mass you have worked out above.
Thank you everyone. I got 64.8% as my answer. Could someone check if this is correct? (I don't have a mark scheme and my teacher doesnt check homework)
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charco
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(Original post by earthworm206)
Thank you everyone. I got 64.8% as my answer. Could someone check if this is correct? (I don't have a mark scheme and my teacher doesnt check homework)
65.9%
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