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CourseworkHelp
:An Investigation into the factors affecting the rate of reaction between magnesium and hydrochloric acid
- Planning
* Hypothesis
I predict that as the temperature increases, the speed of the reaction will
increase therefore the gas will be produced faster. I believe this because most
chemical reactions happen faster when the temperature is higher. At higher
temperatures molecules mover around faster, which makes it easier for them to
react together. Usually, a rise of 10OC will double the rate of reaction.
Chemical reactions take place by chance. Particles need to collide with enough
velocity so that they react. As the temperature is increased the particles move
faster since they have more energy. This means that they are colliding more
often and more of the collisions have enough velocity to cause a reaction.
Since there are more collisions the chemical reaction takes place faster.
* Pilot Experiment
To decide on the best volume and concentration of hydrochloric acid and best
mass of magnesium a number of calculations were done and a pilot experiment
conducted.
The equation for the reaction is:
Magnesium(s) + Hydrochloric Acid(l) Magnesium Chloride(l) + Hydrogen(g)
Mg(s) + 2HCL(l) MgCl2(l) + H2(g)
We were advised to use 0.1g of magnesium ribbon (found to be 10.9 cm long). The
Relative Molecular Mass (RMM) of magnesium is 24, therefore the moles of
magnesium to be used was:
Moles= 0.1
24
Moles= 0.00416
In the reaction above, 1 mole of magnesium reacts with 2 moles of hydrochloric
acid. The concentration of acid was 1mol/dm3. Therefore the volume of
hydrochloric acid used was:
Volume = 0.00416 * 2
1
Volume = 0.0083dm3
Volume = 8.3cm3
It was decided to use an excess of hydrochloric acid to ensure all the
magnesium reacted, therefore 10cm3 of acid was used in the pilot experiment. At
room temperature 10cm3 of hydrochloric acid was added to 0.1g of magnesium and
the gas was collected (see fig 1). The volume of gas produced was measured
every 15 seconds. It was found that the reaction was too rapid to be effectively
measured, therefore 10cm3 of water was added to halve the concentration of the
acid.
* Investigation Experiment
I am going to investigate how temperature affects the rate of reaction between
magnesium and hydrochloric acid. The procedure for the experiment is as
follows;
* Using a measuring cylinder, measure 10cm3 of water and pour it into the side
arm tube.
* Measure 10cm3 of hydrochloric acid (1 mol/ dm3) and add it to the water.
* Place the side arm tube in a water bath at 20OC, set up the apparatus below.
* Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs
0.1g.
* Coil the ribbon around a pencil and then drop it into the side arm tube and
quickly put a bung on the side arm tube (this must be done quickly to prevent
gas escaping).
* Every 15 seconds measure the volume of gas produced until less than 1cm3 of
gas is produced every 15 seconds.
* Repeat experiment two more times (for accuracy) and record all results in a
table.
* Repeat the experiment for temperatures of 30 OC, 40 OC, 50 OC and 60 OC
It is important that only the temperature is changed since this is what is
being investigated.
Method
* Apparatus
I have chosen to use a 10cm3 measuring cylinder to measure the volumes of
substances used since it is more accurate than a pipette. I will use an
electronic water bath for maintaining the mixture at a temperature since the
temperature is more accurate than a water bath above a Bunsen burner.
A 100cm3 gas syringe should be appropriately accurate for measuring the gas
produced since it is accurate to 1cm3 of gas. I will use a three figure balance
to measure the mass of magnesium to be used since it is vital that as close to
0.1g of magnesium is used as possible.
* Variables
I have chosen to repeat the experiment 3 times because it therefore allows me
to calculate an average rate of reaction. This will ensure that there are no
abnormal results and it will increase accuracy. I have decided to start
readings at 20OC and increase by 10OC each time until 60OC is reached, since it
will allow me to see the increase in rate of reaction and 5 results should be
enough to identify any trends.
* Rates of Reaction
Increasing the temperature increases the speed of the particles. The faster the
particles move, the greater the number of collisions, and therefore the rate of
the reaction increases. A 10OC rise in temperature almost doubles the rate of
most reactions.
Chemical reactions take place by chance. Particles need to collide with enough
velocity so that they react. As the temperature is increased the particles move
faster since they have more energy. This means that they are colliding more
often and more of the collisions have enough velocity to cause a reaction.
Since there are more collisions the chemical reaction takes place faster.
Analysing Evidence
First three graphs were drawn (one for each time the whole experiment was
carried out). So that the graphs did not become over crowded the curves were
drawn on separate pieces of see through OHP film and overlaid each graph. Note:
They have been attached all overlaid their appropriate graph but should be
viewed one at a time overlaid the appropriate graph. A tangent was drawn at the
beginning of each curve and its gradient calculated, the gradients are shown in
the table below.
The average gradient was calculated and then the gradients plotted on a graph.
As the temperature increases so does the rate of reaction. Increasing the
temperature increases the speed of the particles. The faster the particles
move, the greater the number of collisions, and therefore the rate of the
reaction increases.
Chemical reactions take place by chance. Particles need to collide with enough
velocity so that they react. As the temperature is increased the particles move
faster since they have more energy. This means that they are colliding more
often and more of the collisions have enough velocity to cause a reaction.
Since there are more collisions the chemical reaction takes place faster.
In my design I predicted that as the temperature increased the rate of reaction
would increase. I predicted that for every 10OC increase in temperature the
rate of reaction would double. I was correct that as the temperature increases
so does the rate of reaction however the rate of reaction does not double for
every 10 OC increase in temperature although it is a linear relationship.
Evaluating Evidence
I believe that the experiment was successful but some of the results were
unexpected/unreliable. The lines on the graphs for 20OC and 30OC cross, this doesn’t
affect my results since I am only concerned with the initial rate or reaction
but it was unexpected. In graph 3 the rate of reaction for 60OC is lower than
that of 50OC - this result is anomalous and has been ignored in this
investigation.
I believe that the experiment was designed well but there were a few problems.
Although the initial rate of reaction (which is what I am concerned with in
this investigation) seemed to fit a trend, the rate of reaction curves of some
temperatures on the graphs crossed. This could have been because some of the
magnesium had corroded forming a magnesium oxide layer which would have
affected the rate of reaction.
Other factor which could have given me unreliable results could have been that
the gas syringes were wet causing them to jam and so not giving correct results
or that the bung was not placed on the top of the side arm tube fast enough
which allowed gas to escape. I conducted all three experiments for each
temperature at the same time to save time. An error in my graphs (plotting,
drawing curves or calculating gradients) could have also affected the
calculated rates of reaction.
To improve the experiment I would find a way of attaching and releasing the
magnesium inside the side arm tube above the acid (with a bung at the top of
the side arm tube) so that the magnesium could be dropped into the acid without
any gas being lost.
Additional work, which could be carried out, is to repeat the experiment using,
a wider range of temperatures. The investigation could also be extended to
investigate other factors affecting the rate of reaction such as catalysts,
concentration of the acid or particle size of the magnesium.
Introduction
In the reaction between hydrochloric acid and magnesium ribbon, the
hydrochloric acid will dissolve the magnesium and produce hydrogen gas.
All chemical reactions involve reactants which when mixed may cause a chemical
reaction which will make products.
In my case the reactants are hydrochloric acid and magnesium ribbon. The
chemical reaction takes place when the magnesium ribbon is dropped into the
hydrochloric acid. The products that are formed during this reaction are
hydrogen gas and magnesium chloride. The formula equation for this experiment
is:
Mg + 2HCl ® MgCl2 + H2
Magnesium + Hydrochloric acid ® Magnesium Chloride + Hydrogen
( s ) ( aq ) ( aq ) ( g )
Magnesium will react with hydrochloric acid, because it is higher in the
reactivity series that hydrogen. When the two chemicals react a displacement
reaction will take place and the magnesium will displace the hydrogen in the
hydrochloric acid forming magnesium chloride and hydrogen gas.
Reactivity Series
K (potassium)
Na (sodium
Li (lithium) all to dangerous to react with a strong acid
Ba (barium)
Ca (Calcium)
..
Mg (magnesium) –
Al (aluminium) manageable metals
Zn (zinc) these metals will react with hydrochloric acid as they
Fe (iron) they are higher in the reactivity series than hydrogen
Sn (tin) and so a displacement reaction will take place
Pb (lead) ¯
..
H (hydrogen)
..
Cu (copper)
Hg (mercury) none of these metals will react with hydrochloric
Ag (silver) acid as they are all lower in the reactivity series than
Al (gold) hydrogen, therefore a displacement reaction will not
happen
Depending on certain factors the rate that this reaction will take place will
either increase or decrease. The factors that may affect the rate of reaction
are as follows:
· Temperature of the Hydrochloric Acid
· Mass of the magnesium ribbon used
· Concentration of the Hydrochloric acid
· Surface area of the magnesium ribbon used
All of these factors will change the rate of reaction because of the Collision
Theory. This is a theory that is used to predict the rate of a reaction. The
Collision Theory is based on the idea that for a chemical reaction to take
place, it is necessary for the reacting particles to collide with each other
with enough energy to break or form new bonds between the other particles,
which is called a successful collision. If when they collide and they do not
have enough energy to break or form new bonds then they will simple bounce of
each other, causing an unsuccessful collision.
Ways that I could record my experiment
There are several way which I could record my experiment. The possible ways are
as follows:
Amount of gas evolved
I could use a gas syringe to collect the gas that will evolve from my
experiment. I could use these results to calculate the initial rate of
reaction.
The weight before and after the experiment
I could put the conical flask with the chosen volume of hydrochloric acid onto
a set of accurate electronic scales and record the weight of it. I could then
drop a piece of magnesium into the conical flask and measure the decrease in
weight at chosen intervals. The weight of the experiment will decrease because
as the hydrogen in the hydrochloric acid is being displaced it is being
released and will float up and out the conical flask, the weight change will
not be very big, but there will be one.
How long the magnesium takes to dissolve
I could measure the length of time it takes for the magnesium to dissolve. The
only problem with recording my experiment this way is that I could only
calculate the average rate of reaction and not the initial rate of reaction
Ways to measure the rate of the reaction:
Average rate of reaction
Initial rate of reaction
I will be using the initial rate to calculate the rate of reaction as it can
calculate the true rate and not the average rate of reaction.
Factors
The factors that could affect the rate of reaction of my experiment are as
follows:
· Concentration of acid
This could affect the rate of reaction because the higher the concentration of
the acid then the more acid particles per 100cm3 so more collisions per second
and then there will be more successful collisions per second.
· Temperature of the acid
If the starting temperature of the acid is different each time the speed at
which the acid particles collide with the magnesium ribbon will increase more
the higher the temperature goes. This means the acid particles move with more
energy, which means they will collide with the magnesium with more energy,
which will give more successful collisions per second.
· Surface area of the magnesium
If the magnesium had a bigger surface area each time the experiment was done,
then the acid particles will have a bigger area to collide with, so more
collisions will occur every second and the more collisions per second than the
more successful collisions per second.
· Type of acid used
If you changed the type of acid then the rate of reaction would change.
Hydrochloric, Sulphuric and Nitric acid all would produce a different rate of
reaction, so if I do change the type of acid then all three kinds would produce
a different set of results.
Key factor
I have chosen to use the concentration of the acid as my factor that I will
change. I chose this because several different concentrations can be made up
before the experiment by the lab technicians and they will be able to make them
accurately.
There will be several different concentrations of acid, which will give me a
wide range of results, which will be reliable and reproducible.
Question
My question is to see that if I change the concentration of the Hydrochloric
acid for each experiment I will see an increase or decrease in the rate of
reaction between Hydrochloric acid and Magnesium ribbon.
Prediction
My prediction is that the higher the concentration of the acid then the higher
the rate of the reaction will be. I am saying this because of the collision
theory. The higher the concentration of acid then the higher the number of acid
particles present per 100cm3 of acid. This means that there will be more
collisions per second, which means there will be more successful collisions per
second, so the rate of reaction will increase.
If I double the concentration of the acid from 1M hydrochloric acid to 2M
hydrochloric acid then I will expect to see the rate of the reaction double.
This is because there are twice as many acid particles in 2M hydrochloric acid
than in 1M hydrochloric acid, so there will be twice the amount of collisions
per second and because there are twice the amount of collisions per second then
there will be twice as many successful collisions per second, increasing the
rate of reaction.
Plan
I am intending to react a chosen length of magnesium ribbon with a chosen
volume of hydrochloric acid. I will measure the rate of reaction by collecting
the hydrogen gas that is produced in a gas syringe that will be connected, via
a piece of rubber tubing and a rubber bung to the conical flask that the
reaction will take place. I will quickly drop the length of magnesium into the
flask and connect the rubber bung to it. I will then start the stop clock and
record the volume of gas evolved every 5 seconds for 15 seconds. I have chosen
these times because I only need three results as I am going to measure the
initial rate of reaction and not the average. I will repeat each experiment so
that my results are reliable and reproducible.
Fair Test
In order to keep my experiment a fair test I will have to make sure that I keep
the following factors the same:
· Starting temperature of the acid
· Volume of acid used (cubic centimetres)
· Surface area of the magnesium
· Clean the magnesium with emery paper before experiment
· Length of magnesium
I will also have to make sure that the gas syringe is correctly connected and
that it is placed quickly and tightly enough so that no hydrogen gas escapes.
The following factor that I will change is:
· The concentration of the acid
Apparatus and chemicals used
The apparatus and chemicals used during my experiment are as follows:
Chemicals
· 1M hydrochloric acid
· 1.5M hydrochloric acid
· 2M hydrochloric acid
· 2.5M hydrochloric acid
· 3M hydrochloric acid
· 3.5M hydrochloric acid
· Distilled water
Apparatus
· Measuring cylinder (100ml, 50ml, 25ml and 10ml)
· Conical flask (250ml and 100ml)
· Safety glasses
· Beakers (200ml and 90 ml)
· Test tubes
· Test tube rack
· Gas syringe
· Tile
· Paper boat
· Ruler
· Thermometer
· Scissors
· Glass rod
Safety
The things that I will need to do to keep my experiment a safe one for myself
and other students around me are as follows:
· Wear safety goggles as I am using concentrated hydrochloric acid
· Care to eyes and the skin besides all the other people is always vital and
necessary
· Care in using glassware since it is sharp when broken and can cut skin
· Safe disposal of reagents and laboratory chemicals
· Care when returning all used glassware and equipment at the end of the
experiment
Preliminary work
The preliminary work that I will be conducting is to find out the optimum
length of magnesium ribbon and the optimum volume of hydrochloric acid.
To do this I will be measuring out a volume of hydrochloric acid and a length
of magnesium ribbon and reacting them together. If there is still some
magnesium left over when it has stopped effervescing then I will have to
increase the volume of hydrochloric acid.
If the reaction takes too long to finish then I will have to shorten the length
of magnesium that I use, however if the reaction is too short then I will have
to do the opposite and increase the length of magnesium that I use. The optimum
rate that I am trying to find is a reaction that isn‚t too short but isn‚t too
long, so I can get enough results to plot a good graph. I need to find the
optimum volume of hydrochloric acid so that it is in excess after the reaction
is over.
Apart from trying to find the optimum rate of reaction I also have to find out
how to keep the temperature change down. This is because as the reaction is
taking place the temperature will rise because the reaction is exothermic, and
this could cause my results to be inaccurate as the temperature change will
heat up the acid and give the acid particles more energy so they will move
faster and collide with the magnesium with greater force causing more
successful collisions per second.
To show that the hydrogen gas is not being given of from the water in the
hydrochloric acid I will have to conduct a control experiment. This is when I
will react magnesium ribbon with distilled water to show that there is no
reaction between magnesium ribbon and water and that the hydrogen gas is
evolving from the hydrochloric acid when it is being broken down into magnesium
chloride and hydrogen.
Preliminary results
After my preliminary experiments I discovered that if I used 50cm3 of
hydrochloric acid with 3 cm of magnesium ribbon then I could obtain some good
results.
Also with these quantities the temperature change is kept to a minimum
Time (seconds) 5 10 15
Gas evolved for 1M hydrochloric acid (cm3) 4 7 11
Gas evolved for 2M hydrochloric acid (cm3) 18 24 24
Starting temperature (oC) End temperature (oC) Temperature change (oC)
22 25 3
As these results produced a reasonable volume of gas in a reasonable time these
were the quantities of chemicals that I used.
I also used these quantities of chemicals because it kept the temperature
increase to a minimum.
Method
1. Put on safety goggles
2. Collect clamp stand, clamp and boss
3. Collect conical flask and measuring cylinder
4. Collect stop clock
5. Measure out 50 cm3 of 0.0M hydrochloric acid with the measuring cylinder
6. Pour hydrochloric acid into the conical flask
7. Collect thermometer
8. Measure the starting temperature of the hydrochloric acid
9. Measure 3cm of magnesium ribbon
10. Clean the surface of the magnesium with the sandpaper
11. Drop the magnesium into the conical flask
12. Quickly place the rubber bung into the conical flask
13. Start timing with the stop clock
14. Record the amount of gas evolved every 5 seconds for 15 seconds
15. Measure the temperature of the solution after the reaction is over and
measure the temperature change
16. Repeat steps 5 to 12 changing the concentrations of the acid
17. Repeat steps 5 to 15 to make sure that my results are reliable and
reproducible
Results
Raw results
A table to show the results for test 1
Time (seconds) 0 5 10 15
Concentration (Molar)
0.0 0.0 0.0 0.0 0.0
1.0 0.0 4.0 7.0 11.0
1.5 0.0 10.0 20.0 26.0
2.0 0.0 18.5 24.0 24.0
2.5 0.0 29.0 29.0 29.0
A table to show the results for test 2
Time (Seconds) 0 5 10 15
Concentration (Molar
0.0 0.0 0.0 0.0 0.0
1.0 0.0 4.0 8.0 11.0
1.5 0.0 10.0 20.0 26.0
2.0 0.0 15.0 21.0 21.0
2.5 0.0 25.0 26.0 26.0
Processed results
Gas evolved in test 1 (cm3) Gas evolved in test 2 (cm3) Average gas evolved
(cm3) Initial rate of reaction (cm3/s)
Concentration (Molar)
0.0 0.0 0.0 0.0 0.0
1.0 4.0 4.0 4.0 0.8
1.5 10.0 10.0 10.0 2.0
2.0 18.5 15.0 16.7 3.3
2.5 29.0 25.0 27.0 5.4
My processed results contain the results for the amount of gas that had evolved
in 5 seconds for both tests then the mean average for both of them and then I
calculated the initial rate of reaction.
Conclusion
My results table and graph show me that when I increase the concentration of
the hydrochloric acid, the initial rate of reaction also increases.
Altogether I tested 5 different concentrations of hydrochloric acid. 0.0M,
which was the lowest concentration of acid that I used, there was no reaction.
2.5M hydrochloric acid, which was the highest concentration that I used,
produced the fasted rate of reaction. I repeated all 5 concentrations twice to
be sure that they were reliable results and in all cases the higher the
concentration the higher the rate of reaction. I had stated this in my
prediction.
However I also stated in my prediction that if I doubled the concentration from
1M to 2M hydrochloric acid then the rate of reaction will also double. I have
discovered that this is not the case.
Concentration (Molar) Test 1 Test 2
1.0 4.0 4.0
1.5 10.0 10.0
2.0 18.5 15.0
As you can see from this table as the concentration doubles then the rate of
reaction approximately quadruples. My graph also shows that as the
concentration doubles then the initial rate of reaction approximately
quadruples.
When the concentration is 1M the rate = 4 = 0.8 cm3/second
5
When the concentration is 2M the rate = 16.7 = 3.3 cm3/second
5
I therefore conclude that:
1. The initial rate of reaction increase as the concentration of the acid
increases
2. There is a fourfold increase in the rate of reaction as the concentration
increases
3. As the concentration doubles the initial rate of reaction is approximately
squared
My original prediction was that the initial rate of reaction would double as
the concentration doubles. This was incorrect because it was not based on
experimental evidence.
Evaluation
Was I precise in my measurements?
I feel that I was precise and accurate in recording measurements.
I measured the acid accurately by measuring the acid when the bottom of the
liquid meniscus just touched the line on the measuring cylinder.
Liquid Meniscus
Measuring cylinder
I accurately cut the magnesium ribbon to the nearest millimetre with the ruler
provided.
I measured the starting and the end temperature accurately with a thermometer
to the nearest .5OC.
I accurately measured the volume of gas evolved to the nearest .5cm3.
I accurately measure the time that had elapsed to the nearest second with the
stop clock.
Did I take enough readings?
Not enough concentrations were used for a good graph. I should have used
concentration 3M acid ought to have been done but it was not known then that it
was necessary and required.
The results that I did collect were reliable as I repeated the experiments
twice to obtain good average results. My results were not only reliable they
were reproducible.
Anomalous results
I obtained two anomalous results.
For concentration 2M there was 18.5cm3 of gas produced in test one, and in test
two there was 15.0cm3, which is a 3.5cm3 difference:
= 23% error
For concentration 2.5M acid there was 29.0cm3 gas produced in test one, in test
two the was 25cm3 gas produced, which id a difference of 4cm3:
= 16% error
These errors both occurred in the first run, when the technique and practical
skill had not been perfected over a large number of experiments. The more times
an experiment is preformed then the more accuracy and skill the student
acquires. At higher concentrations there is more heat evolved which gives a
larger volume error, since gases have a larger volume at higher temperature.
Another reason for these anomalous results is that the plunger on the syringe
may have been sticking on the barrel after a lot of runs, which would have
given me lower readings.
Improvements to my procedure
Improvements to my experiment are that I could stop the syringe plunger
sticking by applying a thin coating of Vaseline to it.
I could also use a monometer to be sure that the atmospheric pressure inside
the syringe is the same as the pressure outside of the syringe.
Monometer Gas Syringe
To be sure that the pressure is the same inside the syringe as outside the
syringe the water levels in the monometer must be level.
The last improvement to my procedure is that I should check for gas leakages
where the bung is placed into the conical flask, a smear of Vaseline would help
me do this.
Further work
There are several things that I could do for further work. The first is to find
out what the initial rate of reaction would be for concentrations 1.25M
hydrochloric acid and 1.75M hydrochloric acid as it would be interesting to see
how the rate increases compared to 1M hydrochloric acid.
Another experiment that I could do is change the type of acid that I use.
I could use sulphuric acid. This is a dibasic acid and its molecular build-up
is H2SO4 and hydrochloric acid is 2HCL, because of this I would obtain
different results. I could also use phosphoric acid, which is a tribasic acid,
and its molecular build-up is H3PO4, I would also obtain different results if I
used this type of acid. Nitric acid is a monobasic acid but its molecular
build-up is HNO3, which is very similar to the molecular build-up of
hydrochloric acid so the results that I would obtain from using this acid would
be similar to the ones I already have, so I would not use this for any further
experiments. The reason I could use a different type of acid for any further
work is to find if the is a difference between them if their molecular build up
is different.
I could also use the less reactive metals of the reactivity series (zinc,
aluminium, iron and lead) that way I could find the initial rate of reaction at
5 seconds for the higher concentrations of acid like 3.0M or 3.5M and I could
find there relative activity.
Bibliography
I obtained most of the information that I needed for my experiment form my
teacher and exercise book. I also obtained information from several science
textbooks and computer encyclopaedias. I obtained a small amount of information
from the Internet.
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