does toothpaste protect teeth - 嶺南衡怡紀念中學 · tooth enamel consists mostly of calcium...
TRANSCRIPT
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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.