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An investigation to compare the % by mass of calcium carbonate in a variety of common rocks.

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Introduction

An investigation to compare the ? by mass of calcium carbonate in a variety of common rocks. My aim is to accurately determine the ? by mass of calcium carbonate in 4 common rocks. To do this I will need to investigate the physical and chemical properties of suitable rocks and decide upon an appropriate practical procedure to achieve satisfactory results. I will also need to consider practicality, as resources are limited. All rocks are made of minerals and these minerals have certain predictable properties. Rocks can be dissolved, diluted, decimated, decomposed, etc. However I think the most appropriate process would either be a titration involving hydrochloric acid (CaCo3(s) + 2HCl(l) ? CaCl2(aq) + CO2(g) + H2O(l)) or a thermal decomposition (CaCo3(s) ?Heat? CaO(s) + CO2(g)). The titration would involve a reaction between the rock and hydrochloric acid, which will give off carbon dioxide, which would be measured and used to calculate the results. The thermal decomposition would 'break down' the calcium carbonate into Calcium oxide and carbon dioxide, either of which could be measured and used to calculate the mass required. ...read more.

Middle

Heat with a roaring blue flame, recording the weight every 5 minutes until there is no mass loss 5. Take the final weight from the initial weight to give the mass loss 6. Repeat as above for magnesium carbonate Results: CaCO3 (in g) MgCO3 (in g) 10 mins 10.921 13.186 15 mins 10.876 13.178 20 mins 10.806 13.172 25 mins 10.761 13.172 Crucible mass 8.183 12.765 Initial mass 11.184 13.769 Total mass loss 0.432 0.597 The calcium carbonate had not finished decomposing but it is clear to see that the magnesium had ceased to decompose after losing nearly 0.6g. This test re-enforces the evidence for a thermal decomposition being the best option as it clearly distinguishes between the two carbonates. So from this it can be acknowledged that magnesium carbonate will decompose before calcium carbonate. Test 2- this test will demonstrate how easily calcium carbonate will decompose compared to magnesium carbonate. 1. Weigh crucible 2. Add calcium carbonate and re-weigh 3. Heat over a gentle blue flame for 5 minutes 4. ...read more.

Conclusion

to give the mass loss of calcium carbonate 10. Using information from previously stated sources that for every CO2 molecule given off, there remains one molecule of CaO and for every mole of CO2 given off, there is one mole of CaCO3. 11. Subtract the mass of CaO remaining from the mass of the other remaining substances and add it to the mass of CO2 lost. This will give the mass of CaCO3 that was in the rock 12. Work out the percentage of CaCO3 that was originally in the rock Calculations: In order to demonstrate the scientific calculation, I will use some 'convenient' numbers. Example results: Total mass of sample = 50g Mass loss of CO2 = 5g (Number of moles = mass / mr) (Mass = number of moles x mr) Example calculation: Moles of CO2 = mass CO2 / mr CO2 = 5 / (12+(16x2)) = 0.113636 mol dm-3 Moles of CO2 = moles of CaCO3 Therefore moles CaCO3 = 0.113636 mol dm-3 Mass CaCO3 = moles CaCO3 x mr CaCO3 = 0.113636 x (40+12+(16x3)) = 11.3636g Therefore ? by mass of CaCO3 = (Mass CaCO3 / total mass of rock sample) x 100 = (11.3636/50) x 100 = 22. ...read more.

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