The objective is to determine the percentage of calcium carbonate (CaCO3) in toothpaste by performing back titration and demonstrating quantitative transfer of solids and liquids. Firstly pipette 10.0ml of 0.1600M of HCl into a conical flask, using analytical balance measure 0.1-0.2g of toothpaste, and mix it with the HCl with 10.0ml of deionised to wash it down. Next, insert a funnel and heat the flask over a hot plate until the reaction is completed, allow it to cool to room temperature before adding 1 to 2 drops of methyl orange indicator and back titrate excess HCL with 0.0800M NaOH. Repeat experiment 2 times. Back titration results indicate at 16.1ml solution is red, at 16.15 ml its red-orange, at 16.20ml its orange, at 16.25ml its orange yellow and at 16.30ml its yellow. At 16.20ml, the indicator is orange indicating the point of neutralisation. The findings show the amount of CaCO3 present in the toothpaste sample is 21.5%, which is between 18%-22% in the acceptable range, therefore, the experiment is a success.

Using back titration to determine calcium carbonate (CaCO3) content. The substance being analysed in this case is CaCO3 which is insoluble and does not dissolve in water. Therefore, using titration would not yield a result. Hence it is preferable to add more acid (or base) to dissolve it first then back titrate the unreacted acid (or base) with a base (or acid).
Toothpaste contains about 18%-22% of calcium carbonate, humectant systems, fluoride, flavouring and detergents. Calcium carbonate is a white powder with low solubility in water, decompose to produce carbon dioxide when heated and liberates carbon dioxide as a by-product. It is used as a material for construction as an ingredient in cement. Medicinal purposes like manufacturing antacids, calcium supplements and manufacture of paper, plastics and paints, etc. (ByJu, 2018)

Sodium Hydroxide is a white solid, popularly known as a caustic soda. It is soluble in polar solvents but insoluble in non-polar solvents. Used to manufacture paper, soaps and detergents. It is also used for degreasing metals and remove sulphurous impurities from crude oil via caustic washing. (ByJu, 2018)

Hydrochloric acid is a strong monoprotic acid it is colourless and has a sour with a pungent odour. Industrial uses include manufacture of plastics, dyes and fertilizers, also in the textile and rubber industries, cleaning products and gelatine. (Softschool, 2018)

Methyl orange is used as an indicator for titration changing colour at the pH3.4-4.1of an acid, as the solution becomes less acidic it changes from to red to orange and to yellow, and vice versa for a solution becoming more acidic.

The rationale of conducting the experiment is to determine the concentration of calcium carbonate (CaCO3) in toothpaste. As CaCO3 acts as an abrasive, too little of it reduces the effect of cleaning the teeth and removing plaque. While too much of it is not good as well, because it can harm the teeth sensitivity by weakening enamel, discolouration and cause teeth to become sensitive. Therefore, conducting the experiment to determine acceptable amount is more effective.