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10ml of 0.1652 M of a standard HCl was pipetted into a clean conical flask. 0.1 to 0.2 grams of the toothpaste sample was weighed on a analytical balance by using a glass rod to remove the toothpaste from the container. The weighed toothpaste is then added into the same conical flask used earlier, using a glass rod. 10 ml of deionised water is used to wash down the acid on the glass rod. A funnel is then inserted in the flask before gently heating it over a hot plate for 3 to 5 minutes, till the reaction is completed. Rinse the funnel and the side of the conical flask with small amounts of deionised water. Allow the solution to cool till room temperature.
1 to 2 drops of methyl orange indicator is added into the conical flask, before it is being back titrated with 0.0792M of NaOH. When the indicator changes from pink to orange, the value of the amount of NaOH used was recorded. The experiment was then repeated again and the values were recorded. Calculations were done to determine the percentage of Calcium carbonate in the toothpaste sample by mass.

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