The pH of a variety of substances were tested. They were diluted with water so they
became less concentrated. Five substances were chosen that had a pH of 4.5, 6.0, 7.0, 7.5 and 8.5. These substances were
orange juice, eno, water, pond water and egg white.
Five identical, small broccoli plants in small pots were purchased. There heights
were measured and recorded.
The five plants were labeled with the pH it would be watered with.
A measuring cylinder was used to measure 10mL of each substance, which were then placed
in separate identical plastic cups. The plastic cups were labeled with the pH and substance it contained inside (the same
cup was used for the same substance throughout the experiment).
A measuring cup was used to measure 50mL of water which was added to each substance. This
diluted each substance.
Each substance was watered with its matching broccoli plant.
Steps 4, 5 and 6 were repeated every two days. The heights of each plant was also measured
and recorded at the same time.
Digital photos of each plant were taken twice a week.
Repeat the experiment. This will be trial two. Compare the results from both trials for
a more accurate result.
When doing this
experiment it’s vital that you make sure that variables are controlled properly throughout the entire experiment. Any
changes could alter the result, therefore giving you an inaccurate result. The controlled variables that need to be kept the
same while conducting this experiment are:
plants: They all must be of
the same kind eg broccoli plants. As well as this they must all be in pots of relatively the same size as it may change the
outcome of the experiment. Also each plant has a specific pH it is being watered with. This cannot change during the experiment;
it must stay the same. For example if one plant is being watered with the substance that has a pH of 4.5, a week later it
cannot be watered with the substance that has a pH of 6.0. If this happens there is no point at all to the experiment. How
is it possible to draw conclusions from it?
substances: Once the five substances
have been chosen they are the ones that must be used. Substances cannot be changed half way through the experiment as the
results will change entirely and accurate conclusions cannot be drawn.
quantity of the substances:
Each plant must be watered with exactly the same amount of each substance (50mL of water and 10mL of each particular substance).
the plants are watered: Each
plant should be watered at the same time. The time between each watering should be kept the same eg every two days. This must
be kept constant throughout the experiment.
measuring cup: The same measuring
cup should be used during the experiment so that you can be sure the amount of substance each plant is being watered by is
exactly the same. Some measuring cups or beakers may be not be accurate and if more then one is used during this experiment
the amount of substance used on each plant may be altered slightly each time they are watered. This too will change the results
of the experiment.
cups: The cups used to water
each plant should be kept the same throughout the experiment. Each cup should have the same substance put in it each time.
For example the substance with a pH of 4.5 should be placed in the same cup each time the plants are being watered. This is
because when the plants are watered a small amount of the substance is usually left in the cup, if another substance is put
in there, the pH may change, altering the experiment.
measuring tape: The same measuring
tape must be used to ensure accurate results.
way the plants are measured:
The way the plants are measured needs to be done exactly the same each time (measuring their height from the top of the soil
to the tallest leaf).
The position of the plants: Each plant must stay in the same spot from the beginning to the end of the experiment, especially if more then one trial is done. If they are moved they may grow differently depending
on the amount of sunshine they receive and precise results cannot be drawn.
The length if each trial: The length
of each trial must be kept the same eg 3 weeks.