Calcium Carbonate Back Titration

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This experiment is carried out to determine the percentage of calcium carbonate, CaCO3 in the toothpaste provided with the experimental technique known as back titration. A back titration is also known as indirect titration. A known mass of toothpaste is neutralised with a known concentration and volume of hydrochloric acid, HCl. The mixture is then further neutralised by a known concentration and volume of sodium hydroxide solution, NaOH to determine the number of mole of HCl that reacted with CaCO3 in the toothpaste. As the number of mole of CaCO3 is found through the mole ratio thus the mass of CaCO3 is known and the percentage of CaCO3 can be calculated. The percentage of CaCO3 from this experiment is about 20.14% which is close with the…show more content…
It accounts for about 20% to 30% of weight in the whole toothpaste.
In common cases, a titrant may be titrated directly with a analyte. However, calcium carbonate is an insoluble salt so it is unsuitable to be titrated directly with acid for the neutralisation process. Hence as to determine the percentage of calcium carbonate in the toothpaste, a back titration method is required as toothpaste which contains calcium carbonate are generally insoluble thus it is difficult to be titrated as the end point of the titration maybe hard to be observed.
Excess hydrochloric acid is added to the toothpaste to neutralise the calcium carbonate and the remaining unreacted hydrochloric acid is further titrated by sodium hydroxide solution to determine the volume of hydrochloric acid reacted with calcium carbonate in the
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This can also speed up the reaction between calcium carbonate and hydrochloric acid with a higher temperature as a higher temperature can let the particles to have a higher kinetic energy for more effective collisions to have a higher rate of reaction.
From the calculation, the percentage if calcium carbonate in the toothpaste is found to be at about 20.14% which has a small difference from the literature value of 20%. This maybe cause by the errors when carried out the experiment such as parallax errors. For example, the position of eye level when taking reading or measuring which are not perpendicular to the scale of the instrument will result in the inaccuracy of the data.
Next, the other error that might happen is the filter funnel is not inserted properly into the mouth of the conical flask causing some of the hydrochloric acid to be evaporated in the form of vapours. As some of the hydrochloric acid is evaporated, the concentration of the hydrochloric acid will be affected which will lead to the inaccuracy of the
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