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S6 Chemistry Project

Topic 5: Does toothpaste protect Teeth?

� Member

- Hui Wing Sum (7)

- Lau Kin Lai (13)

- Lee Yee Lam (15)

- Yan Chi Hei (28)

� Introduction

Tooth enamel consists mostly of calcium hydroxyphosphate, Ca5(PO4)3OH, also

known as the mineral hydroxylapatite. Apatite is a hard, insoluble compound. Acid

(H+), produced especially after a high-sugar meal, attacks the apatite. The equation of

tooth decay as follow:

Ca5(PO4)3OH(s) + H+(aq) → Ca5(PO4)3

+(aq) + H2O(l)

The degradation of apatite by loss of OH-causes the enamel to dissolve. The process is

reversible as saliva supplies back OH- to reform apatite. If fluoride, F-, ions are

present in saliva, fluorapatite, Ca5(PO4)3F, also forms.

Ca5(PO4)3+(aq) + F-(aq) → Ca5(PO4)3F(s)

Fluoride salts are used to enhance the strength of teeth by the formation of fluorapatite.

� Objective

This experiment is going to simulate the tooth decay process by using chicken

eggshells to substitute for human teeth and investigate whether toothpaste can really

slow down the rate of reaction between teeth and acids.

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� Assumption

1. No gaseous loss when connecting to the pressure sensor.

2. All Ca5(PO4)3F (s) reacted.

3. No other substances of eggshells react with hydrochloride acid.

4. The distribution of CaCO3 in each eggshell is even.

5. The concentrations of hydroxide ions in each brand of toothpaste are the same so

that the initial concentrations of hydrochloride acid are the same / do not change

� Apparatus

Chicken Egg 4 brand of toothpaste

Oven (Oral B, Darlie, Lion, Colgate)

4M hydrochloride acid Measuring Cylinder

beaker Mortar and pestle

Pressure Sensor

Distilled water

Electronic balance

filter paper

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� Procedure

Aim (1): Prepare eggshells

1. Boil the eggs.

2. Removing the eggshells by a spatula (scrape away

any membrane that presents inside the eggshell).

3. Pestle the eggshells into powder.

4. Dry them in an oven overnight.

5. After one day, take it out and cool down to the

room temperature.

Aim (2): To simulate tooth brushing

6. Dissolve about 3g of toothpaste in 100cm3

distilled water by a beaker.

7. Put dried eggshell powders into the beaker, which

contains dissolved toothpaste, for several hours

(e.g. 3-4hrs) to form a Ca5 (PO4)3F layer.

8. Filtrate the mixture, wash the residue with

distilled water and dry them again in the oven and

label it.

9. Repeat steps 6-8, by dissolving the other 4 brand

of toothpastes.

10. On the other hand, put original dried eggshell

powders into a beaker which contains water, repeat steps 7-8, to be a control

experiment.

1 2 3 4 5

Oral B Colgate Darlie Lion Water

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Aim (3): To simulate the tooth decay process

11. After one day, take them out and cool down to the room temperature. Weigh 1g

eggshell powders of 5 samples respectively.

12. Put (1) eggshell powders into a conical flask of 50cm3 4M hydrochloride acid ,

which is connected to the pressure sensor.

13. When all of the Ca5(PO4)3F reacted, the acid

will start to react with the eggshell(CaCO3).

14. When CO2 (g) is formed, the pressure sensor

will start to measure the pressure of CO2 is

formed.

15. Repeat steps 12-14, by replace the other

sample of eggshell powders.

16. By comparing the graphical results from the

pressure sensor, the best brand of toothpaste

have the lowest initial rate (flattest slope) and

shows its ability of prevent teeth to react with

acid causing tooth decay.

� Result

1 2 3 4 5

Brand Oral B Colgate Darlie Lion Water

Slope 6.69 ± 0.29 7.18 ± 0.30 5.80 ± 0.31 4.97 ± 0.41 7.32 ± 1.4

According to the graphical results, Lion toothpaste has the lowest initial rate, and

hence its ability of prevent teeth to react with acid causing tooth decay which is the

best brand of toothpaste. In contrast, the control experiment (water) has the highest

initial rate because the teeth can react with acid more easily without any protection.

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� Error and improvement

1. The temperature is the same when conducting the experiment

� conduct it in a thermostat

2. Movement of the set-up may affect the actual rate of reaction

� minimize any move to the setup

3. There may be some gaseous loss in the system

� Covered it by plastic sheet well

� Limitation

1. The volume of the system is not the same when conducting each experiment.

2. The total surface area of eggshell is not the same.

3. We brush our teeth everyday; however the effect of brushing teeth cannot be

replaced by soaking the eggshell powders in the solution, which dissolved

toothpaste, for several hours.

� Questions and Answers

1. Why 4M hydrochloric acid is used?

Since the rate of reaction is too low by using other hydrochloric acid with lower

concentration.

2. Why eggshell in powder form is used instead of that of pieces?

Eggshell in powder form can increase the rate of reaction instead of pieces of

eggshells.

3. How to ensure that the set-up does not have gases loss?

First put some calcium into 4M hydrochloric acid contained by conical flask

which is connected to the pressure sensor to see if the pressure decreases after the

end of reaction.

4. Why original toothpaste is chosen instead of the whitening one/ other function?

To prevent toothpastes containing other substance that can react with hydrochloric

acid.

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� Conclusion

The most effective brand of toothpaste is Lion, while Darlie is less effective. Oral B is

less effective than Darlie. Colgate is the least effective toothpaste. All brand of

toothpaste do lower the rate of the reaction between hydrochloric acid and eggshell,

by comparing with that of water. As a result, Lion can help teeth form the thickest

layer of fluorapatite and protect the teeth well.