Pchem Formal Report

Topics: Sodium hydroxide, Calcium carbonate, Calcium hydroxide Pages: 4 (1267 words) Published: December 3, 2014
Synopsis:
The main aim of the experiment is to find out the amount of calcium carbonate in toothpaste through back titration since calcium carbonate does not dissolve in water. A roughly weighed amount of calcium carbonate is mixed with hydrochloric acid and then titrated against sodium hydroxide. When the indicator turns from pink to orange, the volume of sodium hydroxide used is taken down. After doing some calculations, the average percentage of calcium carbonate in toothpaste is 19.2%. This average percentage is relatively close to the expected percentage of 20% thus this experiment is a success. Generally after performing the experiment twice, the smaller the mass of toothpaste used, the more volume of sodium hydroxide is needed to neutralise the excess hydrochloric acid. Introduction:

Usually, the acid or (base) can be titrated straight against a primary standard base (acid). However, when the substance is volatile for example ammonia or is an insoluble salt for example calcium carbonate, back titration is used. Back titration is performed by reacting that insoluble or volatile substance of unknown concentration with excess acid or (base) of known concentration and then followed by a titration of the unreacted acid or (base) with a base or (acid). Toothpaste usually contains around 20% of calcium carbonate. Calcium carbonate acts an abrasive in toothpaste and helps to remove dental plague as well as food remains stuck in between the teeth. The rationale of conducting this experiment of finding out the amount of calcium carbonate in toothpaste is to make sure that the percentage of calcium carbonate is around 20%. If the percentage is more than 20%, the enamel protecting our teeth will wear off and become thinner resulting in decolouration and teeth sensitivity. Theory:

The experiment is performed using back titration as calcium carbonate is an insoluble salt and does not dissolves in water. To find out the percentage of calcium carbonate in toothpaste,...
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