Video Transcript
An investigation is carried out to
see the effect of different concentrations of sulfuric acid in the reaction with
calcium metal. Using an excess of sulfuric acid,
different concentrations are added to different masses of calcium. The table below shows how long it
takes for the mass of calcium to completely disappear in the conical flask. In which of the following
experiments is the strongest concentration of acid used?
In the question, an experiment is
described in which calcium metal is reacted with sulfuric acid. Different masses of calcium and
different concentrations of acid are used. The time it takes for the calcium
metal to completely disappear is recorded in the table. We need to use this information to
determine which experiment used the strongest concentration of acid. So we need to determine the
relationship between the concentration and the speed of a chemical reaction.
The speed at which a chemical
reaction takes place is known as the rate of reaction. Rate of reaction measures how
reactant or product concentration, mass, or volume changes per unit of time. The table provided does not give us
the rate of reaction for each experiment. But we do know the amount by which
the mass of calcium changed and how long that change took to occur. We can use these pieces of
information to calculate the rate of reaction for each experiment.
Let’s clear some space so we can
determine the rate for each experiment. We can calculate the average rate
of reaction by dividing the change in mass by the change in time. Since we are told in the question
that the mass of calcium completely disappears, we can simplify the equation to say
that the average rate of reaction for this experiment will be equal to the mass of
calcium used divided by the time recorded. So the rate of reaction for
experiment one will be equal to 0.5 grams divided by 50 seconds, or 0.01 grams per
second. The rate of reaction for experiment
two is one gram divided by 40 seconds, or 0.025 grams per second. The rate of reaction for experiment
three is 0.008 grams per second. The rate of reaction for experiment
four is 0.008 grams per second. And the rate of reaction for
experiment five is 0.005 grams per second.
Now that we know the rates of
reaction, we need to know how concentration would affect the rate. Concentration is a measure of the
amount of a substance in a particular volume. A solution with a higher
concentration will have more particles in the same amount of volume. So how does this affect the rate of
reaction? Well, reactions occur when
particles successfully collide with one another, but not all of the collisions which
occur are successful. Increasing the concentration of a
substance means that more total collisions are occurring, and the likelihood of a
successful collision increases. So increasing the concentration
increases the frequency of collisions, which increases the rate of reaction.
Looking at the rates, we can see
that experiment two had the highest rate of reaction. So this experiment must have used
the highest concentration of acid. Another way to say highest
concentration is strongest concentration. So the experiment that used the
strongest concentration of acid was experiment two.
