Does Concentrated Acid or Diluted Acid React Faster?
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I am going to carry out a reaction between Magnesium ribbon and
Hydrochloric acid. The aim of this investigation is to work out which
reacts faster, concentrated acid or diluted acid. I will judge if the
reaction is fast or slow by observing the bubbles which occur during
the reaction and also observe if the Magnesium has disappeared. Only
the concentration of the acid will be changed - the Magnesium is a
Magnesium + Hydrochloric Acid Magnesium Chloride + Hydrogen
Mg(s) + 2HCl(aq) MgCl(aq) + H2 (g)
There are four main factors which may affect rate of reaction. These
4. Surface area
CONCENTRATION- if the concentration of the acid is increased, the rate
goes faster. In a concentrated acid there are more particles in it
this means that there is a more chance of successful collisions
occurring. If the acid was diluted, there are not many acid particles,
which means that there is not much chance of an acid particle hitting
a magnesium atom. At the start, there are plenty of Magnesium atoms
and acid particles but they get used up during successful collisions.
After, a time there a fewer Magnesium atoms and the acid is less
concentrated so the reaction slows down. This graph shows this: -
volume of hydrogen
Time Diluted Acid Concentrated Acid
= Acid particle = water molecule = Magnesiumatom
TEMPERATURE - at low temperatures the particles of reacting substances
don't have enough energy. So if the substances were heated this would
mean the particles take in energy. This causes them to move faster and
collide vigorously very often. Also making more successful collisions.
Therefore the rate of reaction increases.
CATALYST - using a catalyst can speed up reactions. If there is a
catalyst in the reaction then the collision needs less energy in order
to be successful. This results into more collisions becoming
successful, so the reaction goes faster, catalysts are very important
in industry. Reactions are speeded up at low temperatures, which means
less fuel is needed so money is saved.
SURFACE AREA - if the Magnesium had a large surface area the atoms in
the outer layer will only collide with the acid particles but if the
metal was powdered, many more atoms are exposed, so there is a greater
chance of successful collisions.
Concentrated Acid = Acid particle = water molecule = Magnesium atom
The Collision Theory is used to predict the rate of reaction. The
Theory is based on the fact that for a reaction to take place, it is
essential for the reacting particles to collide with each other with
enough Activation Energy to break or form new bonds also known as to
be successful collisions. If they do collide and there is not enough
energy the bonds will not break and will just bounce of each other,
causing an unsuccessful collision.
Collision has enough energy for the Hcl to split up
Not enough energy so particles bounce back unchanged
The apparatus that I will be using are standard laboratory equipment.
He items which I will be using are: -
· Measuring cylinders
· Glass rod ( to mix water with the acid)
I will produce to the maximum of ten reactions. If the results
collected are not accurate then I will repeat the experiment to obtain
To keep the experiment a fair test I will keep the surface area the
same for each test at 2cm. If the lengths of the ribbon were different
then the reaction will produce greater or lesser collisions. This will
make my experiment carry anomaly results.
I will also keep the temperature the same by changing the acid after
each reaction as it may be warmed up by the reaction. I will only vary
the concentration because this will show if concentrated acid will
produce quicker reactions and more successful collisions than diluted
As we are using acid in this experiment I will have precaution on
wearing goggles. But we are using a maximum of 2 molars of
concentration; the acid will irritate my skin.
I predict that my first set of results, which includes 2 molars of
acid, will react quickest. This is because there are more acid
particles in the reaction causing more successful collisions.
Gradually when I start diluting the acid by adding water, the time of
the reaction will increase. This is because there are not many acid
particles I the reaction making the chance of an acid particle hitting
a magnesium atom very small.
The volume of the concentration will be 50ml3. The concentration of
acid will decrease by 5ml which will be replaced with 5ml of water.
Making dilute acid. The concentration of acid will be measured in
molars. I will be using 7 different concentrations and will be
repeated twice. I will also get another set of results from another
group which will make the total of results to three.
Firstly I collected my apparatus. I also collected 200ml3 of
Hydrochloric acid and around 20 cm of Magnesium ribbon.
Secondly I cut up the magnesium ribbon into 2cm pieces. Then measured
50ml3 of Hydrochloric acid into a beaker then added the 2cm Magnesium
piece. I then started to time the reaction until no [i]Magnesium was
For the next concentration I diluted the acid with 5ml of water whilst
taking out 5ml of acid. Leaving 45 ml of acid remaining. Add the
Magnesium, time the reaction using a stopwatch and record the time. I
kept on adding 5ml of water and taking out 5ml of acid. I produce 7
different sets of concentrations.
I used books such as Cambridge Chemistry book, which had vital
information and diagrams on how different factors changed rate of
reactions. I also used the Internet, especially the website
www,bbc,co,uk/gcsebitesize. This also had important information on
collision theories and rates of reactions. These resources helped me
produce an outcome on which factor I chose and also what I predict
Results which have been collected after 7 experiments which has been
processed twice and a third set of results taken from another group.
The results which I have collected are not what I have expected in my theory and in my prediction.
The rate with the concentration of acid, the
line is not a smooth curve. There has been an anomaly result, which
has not made the line a smooth curve. This may have occurred during
the experiment carried out by me or the set of results from another
group. This anomaly result may have come from a few reasons.
Firstly, the acid and the water might have not been mixed properly so
there may have been more successful collisions or unsuccessful
collisions. For successful collisions to occur, there should may more
acid particles (concentrated acid) colliding with the atoms in the
outer layer of the Magnesium. But unsuccessful collisions may have
occurred where there a fewer number of acid particles (diluted acid)
in the experiment.
Other reasons may have been that other factors such as the surface
area of the magnesium or the temperature of the acid may have affected
the rate of reaction.
All three lines do not
have a smooth curve making the whole outcome not as predicted. My
results and the graphs show the same procedure. Odd results which make
the graph not a smooth curve and consistent.
The results which I have collected are not what I
have expected in my theory and in my prediction.
I have identified a few anomalies which shows the results
of the experiment. They have occurred in each set of results and in my
average time especially. You can also see anomaly results in the table
which I have produced.
The quality of my evidence is not really sufficient for me if I am
trying to find out what I predicted which is that an increased
concentration will have a quicker reaction rate. These results would
not be suitable for anyone finding out how the concentration of acid
affects the rate of reaction.
I think I have chosen a suitable method. Very simple and easy to do.
But the results, which were not accurate, may have occurred by the
other factors, which may have changed the rate of reaction, such as
temperature or surface area of the magnesium.
The improvements which I may consider are to are to do more
experiments which show a pattern and are much more accurate. I will
also consider making changes to the surface area of Magnesium which
may also give me more accurate results.