There is about 1000cm� of dilute hydrochloric acid in your stomach

It is there to help you digest the food you eat so it can be made into simpler substances and then used by your body.

Too much acid in the stomach causes indigestion, and since dilute hydrochloric acid is about pH1.0, a very, very strong acid, so you can imagine the pain in your stomach when it is in excess. Taking ant-acid tablets cures indigestion. The substances are weak alkalis and neutralise excess acidity.

In the following piece of coursework I will find out and explain how and why these tablets work, and which are the best to use.


Neutralisation is when an acid and an alkali react to cancel each other out forming a salt and water.

An acid is an aqueous solution containing water molecules. The acidity comes from H+ molecules (hydrogen ions) in the solution, which are released when the acid is broken down.

An alkali is an aqueous solution. The alkalinity comes from OH- molecules (hydroxide ions) in the mixture.

During neutralisation the following reaction takes place…-

Acid + Alkali –> Water + Salt

H+ + OH- –> H2O + ‘salt’


I predict that the tablet with the highest pH would be the most effective because the higher the pH of the tablet, the more alkali substances in the tablet, and the least amount needed to neutralise the acid, the more effective it would be to neutralise the excess acid in your stomach.

The tablets available to me were…-


Rennie Rap-eze

Boots Double Action

Rennie Peppermint Flavour

Boots Fruit Flavour

To work out the pH of each tablet I completed the following preliminary experiment…-

Preliminary Work

Fair Test

Use the same size and shape beaker.

Use both indicators to make sure the colour of the tablet does not affect the results.

Repeat the whole process at least 2 more times then take an average to get a precise and reliable result.

If you a completely wrong result



Pestle and Mortar

Distilled Water

Precise Measuring Device

Measuring Cylinder

Glass Rod


Universal Indicator Paper

Universal Indicator Solution

Precise pH Scale



1. Choose one brand of tablet then grind the tablet using the pestle and mortar.

2. Weigh out one gram of the ground tablet.

3. Measure out 20cm� of distilled water using the measuring cylinder.

4. Pour the water into the beaker then add the gram of tablet.

5. Mix the two together until the tablet is fully dissolved.

6. Dip one end of the universal indicator paper into the solution then match up the colour of the paper with the colour on the pH scale.

7. Add 4-5 drops of universal indicator solution to the solution then again match up the colour of the indicator with the colour on the pH scale.

8. Repeat stages 1-7 two more times recording each result separately, and then take an average pH number.

9. Repeat all these steps with the other brands of tablets.



So in conclusion to this, I believe that the most effective ant-acid tablet would be the Rennie Peppermint Flavour with a pH 10.

Fair Test / Variables

Repeat the experiment more than once to get a precise and reliable result.

If a result is out of place or seems wrong repeat that result.

Make sure the conical flask is the same size at all times.

Don’t change the temperature of it if possible.

Always wash and dry the apparatus between use and before each different experiment.

Use the apparatus carefully and safely – don’t mess around with it.

Don’t balance the apparatus on anything or keep it too close to the edge of the bench.

Wear safety goggles at all times to protect your eyes.

Work on a heatproof mat to protect the bench from the acid.

If you get acid on your hands or body wash the area with soap and water straight away.

Don’t eat any of the tablets – they may be indigestion tablets but you could be allergic and remember you are in a lab and any chemicals could get on them.

The variables of this experiment are the amount of acid and the amount of tablet.

The acid amount will remain the same throughout the experiment to ensure a fair test.

The amount of tablet used will change.


Pestle and Mortar

Measuring Cylinder

Hydrochloric Acid

Universal Indicator Solution

Precise Weighing Device

Weighing Boat

Glass Rod


Conical Flask

Distilled Water

Variety of Ant-acid Tablets


I chose to do this method because it works the same way as an ant-acid tablet does in your stomach and also it was quite easy to carry out and produced good reliable results when I tested it out.

However, during the preliminary work I found that some tablets could not be dissolved in acid but all of them could be dissolved in water very easily. Therefore in the method it states that you can add water to the tablet to help it dissolve. This was the only problem with our method, however the added water does affect the results. This is because although it helps the tablet dissolve, it also affects the concentration of the acid and tablet.

1. Take one brand or type of tablet and grind it up using a pestle and mortar.

2. Weigh the weighing boat using the precise measuring device. Record the result.

3. Pour the ground tablet into the weighing boat and put it on the precise measuring device. Record the result and take away the weight of the weighing boat from it. This is the amount of tablet there is to use.

4. Using the measuring cylinder weigh up 20cm� of hydrochloric acid and pour it into the conical flask.

5. Add a few drops of universal indicator solution.

6. Slowly add the tablet, but by bit, to the acid constantly swirling.

7. If the tablet doesn’t seem to be dissolving use the glass rod to mix it. However, if you don’t want your results to be dead on accurate you can use a small amount of distilled water.

8. When the universal indicator turns green the solution is neutral.

9. Weigh the remaining tablet. Then subtract the weight of the weighing boat from it. This is the final weight of the tablet. Then take away the final weight of the tablet from the starting weight of the tablet. This is how much tablet you have used.

10. Repeat stages 1-9 two more times recording all results, and then take an average. Then repeat the whole experiment again with the other tablets.

11. The one that takes the least tablet to neutralise the acid is the most effective.


Suggested Results Table and Graph



Result 1 Mass (g)

Result 2 Mass (g)

Result 3 Mass (g)

Average Result Mass (g)


Rennie Rap-eze

Boots Double Action

Rennie Peppermint Flavour

Boots Fruit Flavour



GCSE Science Textbook

Encarta CD-ROM Encyclopaedia

Dorling Kindersley Children’s Encyclopaedia

Anita Eivazmohammadi Chemistry Coursework Dr. Lear – 09-05-02