Diploma in Applied Chemistry
AY 2018 / 2019
Determination of CaCO? in Toothpaste
A Formal Report
Tan Yee Shin 1836758
Date of submission: 06/06/2018
Lecturer-in-charge: Dr Ong Chin Choon
Table of Contents
TOC o “1-3” h z u Synopsis Page PAGEREF _Toc516002285 h 3
Introduction Page 3
Theory Page 4
Procedure Page 4
Results and Calculation Page 5
Discussion Page 6
Conclusion Page 6
References Page 7
SynopsisThe objective is to perform back titration to determine the percentage of CaCO? in toothpaste to demonstrate quantitative transfer of solids and liquids. A weighed amount of toothpaste is dissolved in HCl with known concentration and volume in a conical flask. A filter funnel is then placed above the conical flask and it is gently heated over a hot plate until reaction in complete. The solution is then titrated with NaOH of known concentration and a colour indicator methyl orange. The average percentage of CaCO? in the toothpaste sample is then calculated. Results of the experiment show that the volume of 0.0797M NaOH used to titrate the mixture of toothpaste and 0.1672M HCl is 12.10ml for the first attempt and 14.00ml for the second attempt. Hence, the average percentage of CaCO? in toothpaste is 21.3%. The experiment is successful as it shows a result that is between 18% – 22%, which is the acceptable percentage of CaCO? in toothpaste.
Acids (or bases) are usually titrated directly using a standard solution of a base (or acid). However, in some circumstances, where the analysed substance is volatile or does not dissolve in water, back titration is used. An acid (or base) is added to dissolve the substance first then back titrate the unreacted acid (or base) with a base (or acid). CITATION Wor l 1033 (World Heritage Encyclopedia, n.d.)Toothpaste is something that is used in our daily lives. It is an important tool for oral hygiene. It not only freshens breath, but also lessens tooth sensitivity, whitens teeth and reduces plaque build-up. CITATION Ame171 l 18441 (American Dental Association, 2017) Toothpaste is usually made out of fluorides, abrasives, flavours, humectants and detergents to achieve optimum oral hygiene. CITATION Amy18 l 18441 (Freeman, n.d.) Calcium carbonate is a common substance found in rocks, naturally in chalk, limestone and marble. It is a safe natural choice for mild abrasiveness in toothpastes. CITATION Tom18 l 18441 (Tom’s of Maine, n.d.)Sodium Hydroxide is a vital compound in our lives because it is very versatile. It is very commonly used in the chemical industry and also in our daily lives. One of the most recognized uses of Sodium Hydroxide is to unclog drains. CITATION Hal18 l 18441 (White, n.d.)Hydrochloric acid is an important and commonly used chemical. The most prevalent uses of hydrochloric acid is for steel pickling, food manufacturing, oil well acidising, producing calcium chloride and ore processing. CITATION Oxy13 l 18441 (OxyChem, 2013)Methyl orange is one of the indicators commonly used in titration. Methyl orange is a dye that shows a red colour in an acidic medium (pH ; 3.1) and a yellow colour in a basic medium (pH ; 4.4). It is also used in dyeing and printing of textiles. CITATION Che18 l 18441 (Chemical Book, n.d.)Calcium carbonate is an abrasive used in toothpastes, however if the percentage of calcium carbonate is too high, it can affect consumers’ teeth sensitivity by weakening enamel. CITATION Flo18 l 18441 (Stay, n.d.) Too less calcium carbonate in toothpastes however, can reduce the toothpaste’s effect of cleaning the teeth and removing plaque. Hence, it is essential that that the toothpaste does not exceed the recommended percentage of 18% – 22% of calcium carbonate.
NaOH + HCl ? NaCl + H2O
Toothpaste is insoluble hence; back titration is used instead of direct titration. The excess hydrochloric acid is back titrated with sodium hydroxide. The results of the back titration can be used to calculate the amount of analyte, calcium carbonate in this case.
CaCO3 + 2HCl ? CaCl2 + CO2 + H2O
The solution is heated to remove the carbon dioxide produced in the reaction above through evaporation and to speed up the reaction. Carbon dioxide is not desirable as it is an acidic oxide that can decrease the pH of the solution, affecting the results of the back titration. Hence, it is removed.
The mass of toothpaste used is recorded, then the volume of NaOH used to titrate the HCl. Using the mole ratio, the volume of HCl in excess can be calculated to find the volume of HCl reacted. Next, the number of moles of HCl that reacted can be calculated through the mole ratio. The equation CaCO3 + 2HCl ? CaCl2 + CO2 + H2O can be used to find the amount of CaCO3 in the toothpaste sample using the mole ratio. Lastly, the percentage of CaCO3 in toothpaste can be calculated from the mass.
10.00ml of 0.1672M standard HCl was pipetted into a clean conical flask. Approximately 0.1g – 0.2g of toothpaste was removed with a glass rod from a container and the weight was recorded. The glass rod with the weighed toothpaste was placed in the conical flask the toothpaste was dislodged completely from the glass rod. 10.00ml of deionized water was then added to wash down the acid from the glass rod. A funnel was inserted into the flask and the flask was then gently heated over a hot plate until the reaction is complete (indicated by the complete dissolution of the calcium carbonate), taking about 3 – 5 minutes. The funnel and the side wall of the flask was then rinsed with a small amount of deionized water and left to cool at room temperature. Next, 1 to 2 drops of methyl orange indicator were added and the excess HCl was back titrated with 0.0797M NaOH. The indicator changed colour from red (or pink) to orange and that indicated the end point. A yellow colour indicated over titration. The steps were repeated two times.
Results and Calculation
Results 1st 2nd
Mass of toothpaste (g) 0.1690 0.1281
Initial burette reading (mL), (a) 8.40 6.60
Final burette reading (mL), (b) 20.50 20.60
Volume of NaOH used (mL), (b) – (a): 12.10 14.00
2245995421640MHCl x VHcl excess 1
00MHCl x VHcl excess 1
Using the mole ratio:
MNaOH x VNaOH = 1
VHCl excess (mL) (0.0797M x 12.10mL) ÷ 0.1672M = 5.77 (3 s.f.) (0.0797M x 14.00mL) ÷ 0.1672M = 3.33 (3 s.f.)
264795120650= 10.00ml – VHCl excess
020000= 10.00ml – VHCl excess
VHCl reacted (mL)
Using the mole ratio:
2252345121920MHCl x VHCl reacted 1
020000MHCl x VHCl reacted 1
Moles of HClreacted = 1Moles of HClreacted, (mol) 0.1672M x (4.23 x 10?³)L = 7.07 x 10?? (3 s.f.) 0.1672M x (3.33 x 10?³)L = 5.57 x 10?? (3 s.f.)
From equation: 2HCl + CaCO3 ? CaCl2 + H2O + CO2
2265045118745Moles of CaCO3 1
4000020000Moles of CaCO3 1
Moles of HClreacted = 2Moles of CaCO3 (mol) (7.07 x 10??) ÷ 2 = 3.54 x 10?? (3 s.f.) (5.57 x 10??) ÷ 2 = 2.78 x 10?? (3 s.f.)
Mass of CaCO3 (g) (3.54 x 10??) x (40.1 + 12 + 16 x 3) = 0.0354 (3 s.f.) (2.84 x 10??) x (40.1 + 12 + 16 x 3) = 0.0278 (3 s.f.)
% CaCO3 in toothpaste (0.0354 ÷ 0.1690) x 100% = 20.9 (3 s.f.) (0.0278 ÷ 0.1281) x 100% = 21.7 (3 s.f.)
Average % of CaCO3 in toothpaste sample (20.9% + 21.7%) ÷ 2 = 21.3
From the results, the more toothpaste used (the more CaCO3 is present), lesser sodium hydroxide is required to neutralise the hydrochloric acid.
My results show that the amount of calcium carbonate in toothpaste is within the acceptable range of 18% to 22%. It is important that the percentage is in that range as calcium carbonate is used as a mild abrasive in toothpaste and a higher percentage of it in toothpaste can weaken enamel of consumers, whereas a lower percentage can reduce the effectiveness of the toothpaste in cleaning plaque from teeth.
There is a 0.8% difference in the percentage of calcium carbonate in between the first and second attempt which was probably due to some toothpaste still being stuck on the glass rod even after rinsing with deionised water.
I have found that there is an average of 21.3% of calcium carbonate in toothpaste. The experiment was a success as the percentage of calcium carbonate found is within the acceptable range of 18% to 22%.
BIBLIOGRAPHY American Dental Association, 2017. Toothpastes. Online Available at: https://www.ada.org/en/member-center/oral-health-topics/toothpastesAccessed 4 June 2018.
Chemical Book, n.d. Methyl Orange. Online Available at: https://www.chemicalbook.com/ChemicalProductProperty_EN_CB2264381.htmAccessed 4 June 2018.
Freeman, A., n.d. What Is in Toothpastes, Ingredients, What to Do. Online Available at: https://www.colgate.com/en-us/oral-health/basics/selecting-dental-products/what-is-in-toothpaste-five-ingredients-and-what-they-do-0814Accessed 4 June 2018.
OxyChem, 2013. Hydrochloric Acid Handbook. Wichita: s.n.
Stay, F., n.d. What is toothpaste MADE of?. Online Available at: https://totalhealthmagazine.com/Dental-Health/What-is-toothpaste-MADE-of.htmlAccessed 4 June 2018.
Tom’s of Maine, n.d. Calcium Carbonate. Online Available at: https://www.tomsofmaine.com/our-promise/ingredients/calcium-carbonateAccessed 4 June 2018.
White, H., n.d. Uses – Sodium Hydroxide. Online Available at: https://sodiumhydroxide.weebly.com/uses.htmlAccessed 4 June 2018.
World Heritage Encyclopedia, n.d. Titration. Titration.