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Aim : To investigate the percentage of CaCO3 in a sample of marble

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Introduction

Chemistry Practical Write-up Aim : To investigate the percentage of CaCO3 in a sample of marble Materials used : * Beaker * Conical Flask * Measuring Cylinder of 15 cc * Burette * Indicator * Clamp Stand * Pipette * Beam Balance * HNO3 of 2M concentration * NaOH of 2M concentration Procedure : * Crush the sample of marble in to small pieces, and take 1 gram of it in a beaker * Add excess of acid into the beaker, allow to react completely * Pipette 25 cc of the mixture into the conical flask * Add 2 drops of indicator (phenolphthalein) ...read more.

Middle

In the process, shake the conical flask thoroughly * Calculate the amount of base reacted * Repeat the titration again to improve accuracy. Data Collection : Burette reading (NaOH) / cc HNO3 + marble used (cc) Initial Final Used 0 19 19 25 0 18.8 18.8 25 0 18.5 18.5 25 Mass of marble used = 3 grams Amount of acid used to dissolve the marble, 100 cc = 0.1 dm3 Volume of mixture taken = 0.025 dm3 Mean volume of NaOH used = 18.76 cm3 = 0.01876 dm3 CaCO3(s) ...read more.

Conclusion

0.02496 x 100 = 2.496 grams % of CaCO3 = 2.496/3 x 100% = 83.2 % Precautions taken : Make sure that the marble reacted completely with the acid, it may take quite a long time, but we are not allowed to proceed with the titration until the marble is completely reacted, because it will give us incorrect readings. Care should be taken when titrating the mixture of acid and marble with NaOH. Because color changes may occur more than once, so we need to be attentive in the process. ...read more.

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