Lab Report
Purpose
To measure the effects of surface area on the reaction rate between a tums tablet
and hydrochloric acid
Background Information
When a chemical reaction occurs the chemical bonds between the reactants change
and products are formed. The reaction between the tums tablet and the
hydrochloric acid is as follows:
Calcium carbonate + hydrochloric acid  Calcium chloride + water + carbon dioxide
The rate of this reaction depends on how quickly the products are produced. For a
reaction to occur two things have to be true: the activation energy must be achieved
and then if this is the case, then a reaction will occur if a collision occurs between
the reactants (calcium carbonate and hydrochloric acid).
The investigation we did looked at the relationship between surface area and rate of
reaction.
Hypothesis
The greater the surface area of the tums (independent variable) will mean there is a
shorter time for the phenol red turns yellow (dependent). This is because when the
tums tablet is crushed ie. Large surface area, there are more sides for the
hydrochloric acid atoms to collide with the tums and therefore react and produce
carbon dioxide. This carbon dioxide that is quickly produced is what turns the
phenol red to yellow quickly.
Materials
- 30 ml Hydrochloric acid
- 2 tums tablets
- 20 drops of phenol red
- Stopwatch
- Mortar and pestle
- 2 beakers
Variables
Independent – the surface area of the tums
Dependent – the time it takes for the phenol red to turn yellow
Controls – amount of hydrochloric acid, amount of phenol red, temperature, amount
of tums
Procedure
1.
2.
3.
Data table
Graph
Conclusion
The hypothesis was correct – it can be seen that the tums with the larger surface
area reacted with the hydrochloric acid faster and the time taken for the phenol red
to turn yellow was small. The crushed tums (large surface area) took 42 seconds
and the whole tums (small surface area) took 4 minutes and 30 seconds. These
results are due to the fact when a reaction occurs a collision between the reactants
must occur and when there is a large surface area there is a greater area for these
collisions to occur. Therefore there will be more collisions and more reactions so the
products will be created much faster.
Evaluation
The experiment was fairly reliable as the results achieved were close to others in
the class and was what was expected. One error could have come from the
uncertainty of when exactly the phenol red had reached the correct shade of yellow
for the stopwatch to be stopped. This could have been improved by using a yellow
piece of paper that could have been used to reference the correct shade.
Furthermore, when the tums was emptied from the mortar a small amount stayed
on the edge. To improve this we could have used a scale to measure the mass of the
tums to ensure it was constant.