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#Post#: 32--------------------------------------------------
Chemistry CA - Rates of Reaction
DIR By: Dietrech
Date: October 30, 2014, 8:35 am
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What is this for?
To check if the strength of Hydrochloric acid will affect the
speed of the
rate of reaction when reacting with Magnesium Ribbon.
I want to find out whether the strength of Hydrochloric acid
will
affect the speed of the rate of reaction when reacting with
Magnesium
Ribbon.
Variables
There are two important independent variables in my
investigation the
first of which is the concentration of the Hydrochloric Acid
used
during the investigation. The concentration of the acid will
partly
determine how fast the reaction takes place, if we put some of
the
magnesium ribbon into the HCL at 2molar then it might have
simply
dissolved within a few seconds and then I would not have had
time to
record down any decent enough results to plot a graph with. The
other
important independent variable that will affect the speed of the
rate
of reaction is the length of magnesium ribbon. We need to put
enough
Mg Ribbon into the HCL so that it doesn’t run out straight away
but
also so that the experiment stops by itself once the gas syringe
has
filled up.
The reasons for choosing these two independent variables are
that it
would be too hard to try and find a catalyst for this
experiment; a
catalyst is a substance that increases the rate of a chemical
reaction
without being consumed in the reaction. Finding a catalyst for
this
particular experiment could take months never mind the amount of
time
we have been given for our experiment.
The independent variable that I will change is going to be the
hydrochloric acid, we will use 50ml of HCL at the following
molarity
concentrations; 2molar, 1.6molar, 1.2molar, 0.8 molar and 0.4
molar. I
have decided to experiment with these different strengths of
molar
because I think it will give a wide set of results to put into a
graph.
The dependant variable I shall be measuring will be the time it
takes
for the magnesium to completely react with the hydrochloric
acid, I
shall record the times for each concentration of hydrochloric
acid
three times so that it makes it a fair test.
To ensure the investigation is fair we will use the same length
of
magnesium ribbon for all the different strengths of hydrochloric
acid
and the length will be the one that we picked out from the
preliminary
experiments. Another way in which we will keep the investigation
fair
will be to carry out an experiment at each concentration of
hydrochloric acid three times so that we can then get hopefully
around
the same outcome from each experiment, and if there are any
anomalies
we can try to explain why they happened.
The final way in which we will try to keep our experiment fair
will be
to use the same gas syringe each time therefore we will not have
one
which glides smoothly for one experiment and one that sticks and
jumps
for a different experiment. Although we cannot always guarantee
that
the experiments will be fair because we will not always get the
same
bottle of hydrochloric acid because there will not be enough to
carry
out all the experiments with just the one bottle so the
different
bottles could be at ever so slightly higher or lower
concentrations of
hydrochloric acid which will affect the outcome never the less.
Prediction
I think that my results will show that the hydrochloric acid
with a
molarity of 2 will finish reacting the quickest because it is
the
strongest hydrochloric acid and I predict that the slowest
experiment
to finish reacting will be the 0.4 molar strength of
hydrochloric
acid. I think that the results will go slower and slower the
nearer
they are to the 0.4 strength of hydrochloric acid. The reason
that the
experiment with hydrochloric acid at 2 molar will dissolve the
magnesium ribbon faster is because it is of a stronger
concentration
and so the molecules in the hydrochloric acid move faster and so
react
with the magnesium ribbon quicker.
Preliminary Experimental Work
I have carried out two preliminary experiments, the first reason
that
I carried out these were to see which of the two would be
easiest and
most accurate to carry out in the actual experiment. Then once I
had
picked one of the two to take forward I then went on to try to
get
some good measurements and molar strengths to use in the actual
experiment.
[tt]Burette Method
Equipment [/tt]
Conical Flask, Bung, Connecting Pipe, Burette, Large Measuring
Jug.
For this method we first set up the equipment needed to carry
out the
burette experiment as shown below;
The burette method consists of the Magnesium ribbon being put
into a
conical flask with 50ml of hydrochloric acid quickly put the
bung in
once the magnesium ribbon has been put in, then the gas will go
up and
around the pipes and go into the burette which will be filled
with
water as air bubbles. This method was hard to take down results
because every time a bubble of the gas released went through the
burette it would simply stop and start, for example just as I
was abut
to take a reading a bubble shifted the reading down 7ml and so
this
gives the results a certain degree of inaccuracy. We took down
measurements in 5 second intervals. The burette has a volume of
50ml³.
[tt]Gas Syringe Method[/tt]
Equipment
Conical Flask, Bung, Connecting Pipe, Gas Syringe, Hydrochloric
Acid,
Magnesium Ribbon, Clamp, Stand.
For this method we set up the equipment as follows;
The first to do is to gather together all equipment, then once
that is
done get the conical flask and put the bung into the top of it.
Then
connect the pipe from the bung to the gas syringe, making sure
that it
is air tight. Then once everything is set up get the stop clock
ready,
measure out the 50ml of hydrochloric acid and pour it into the
conical
flask and again the same as the burette method simultaneously
put the
magnesium into the conical flask, put the bung into the top of
the
flask and start the timer. We took down measurements in 5 second
intervals. The gas syringe has a volume of 100ml³.
GRAPH
This is another disadvantage of the gas burette method because
it will
only measure up to 50ml³ we will not be able to get the full
reading
for the experiment. Another disadvantage is that the burette
method
changes readings in stages going from 9 to 17 instantly as soon
as an
air bubble reaches the surface; this can make the experiment
inaccurate because if you about to take a reading and an air
bubble
comes to the top and the reading drops then it will not be
scientifically accurate.
Gas Syringe Method
GRAPH
This is another example of an advantage of the gas syringe
method as
it can hold up to 100ml³ of gas. Another advantage of the gas
syringe
method is the accuracy that this method allows us to have
because the
gas is constantly passing into the gas syringe the reading is
steadily
and constantly going up so when the time comes you can take an
accurate reading.
How did the preliminary Experiments help with my decisions for
the
actual experiment?
The preliminary experiments helped me to make a lot of decisions
and
the most important decision of all which was with which method I
would
carry out the actual experiment? I have decided to do the
experiment
using the gas syringe method; I made this decision using several
things from the preliminary experiments the first was the fact
that
the gas syringe method was quiet a lot more accurate than the
burette
method. This means that it would be a good idea to use this
method
because it is more accurate when taking down the results and so
should
therefore give us a more accurate rate of reaction. Other things
that
pushed me towards making the decision to use the gas syringe
method
was that it was a lot easier to take down the results because
the
readings on the side of the gas syringe can be set to any angle
whereas the readings on the side of the burette will always have
to be
upside down and so this makes it a lot harder to try and read
out the
readings when the time comes.
Equipment
Conical Flask, Bung, Connecting Pipe, Gas Syringe, Hydrochloric
Acid,
Magnesium Ribbon, Clamp, Stand, Measuring tube and Stop clock.
The accuracy of the conical flask will go up in sets of 25ml,
but we
will first use the measuring tube to measure out the quantities
of
both the acid and the water we will use to dilute the acid. The
measuring tube is accurate down to 1ml. The accuracy of the gas
syringe is also down to 1ml but this is down to 1ml³.
Risk Assessment
The acid that we are using in this experiment is of 2 molar
strength,
which is strong enough to at least cause irritation to the skin
if
spilled on it, the hydrochloric acid would also cause irritation
to
the eyes and mouth if ever spilled into those. Another risk is
that
magnesium is flammable especially if in powder form, but we are
using
it in a ribbon form and we are not using any flames in any part
of the
experiment. The gas which is given off from the reaction between
Hydrochloric acid and Magnesium ribbon is Hydrogen which is a
flammable gas.
We will reduce the risk of these hazards by wearing protective
eyewear
for example laboratory goggles, we will also measure out the
hydrochloric acid pouring away from the body, over the sink. We
will
not be using flames in our experiment so the risk is reduced
from the
hydrogen and magnesium but still other experiments could be
using
flames so we will still have to be careful and make sure to stay
away
from any other experiments using flames.
Method
Above is a labeled diagram of my equipment which has been set
up.
The first thing that we shall do is to prepare our work area
where we
will be doing the experiment, clear anything that could cause an
obstruction or any risk. The next thing to do is to simply
gather
together, and not set up, all equipment that we shall need. When
getting the hydrochloric acid we shall take one container full
and if
we need anymore we merely ask for some more, and we shall only
get the
magnesium ribbon when we need it, this is not only for safety
reasons
but also we shall be able to measure out the desired amount
there and
then. Next we will set up the equipment that we have just
gathered
together, as the diagram above shows.
Once this is done we will take the measuring tube and measure
out our
first strength of hydrochloric acid, once measured out
accurately we
shall then put it into the conical flask. Then we shall measure
out
the 10cm of magnesium ribbon and gently fold it into a smaller
shape.
Then this is where a moment of inaccuracy could enter into the
experiment we now have to put the magnesium ribbon into the
conical
flask, whilst at the same time put the bunk into the top and
start the
stop watch, but this is impossible so we just have to do it as
fast as
we can whilst still being safe in what we are doing.
Once we have done this we then record results every 5 seconds
until
the experiment runs out of either hydrochloric acid or magnesium
ribbon and so cannot carry on. I will take measurements ranging
from
1ml³ to 100ml³, as this is the largest amount of gas that the
gas
syringe will hold. I will check that my results are reliable by
firstly checking that everything went as predicted in which the
weakest solution took the longest time in order to give off all
the
gas and that the strongest solution would finish reacting the
quickest.
Another way which we will check that the results are reliable
will be
to check the results against the preliminary experiment. I shall
make
sure that my results are accurate by keeping some aspects of the
experiment the same. The things that are going to be kept the
same are
the amount of hydrochloric acid and water, there will always be
50ml
no matter what the concentration, The length of the magnesium
ribbon
will not change either; there will always be 10cm of that and
the
temperature at which the experiment will take place will always
be
near enough the same because we shall carry it out at room
temperature
and although we cannot always control this we will always do the
experiment in the same room as to try to lessen this possible
change.
We will change however the concentration of the hydrochloric
acid.
GRAPH GRAPH GRAPH GRAPH
One of the key calculations that I used was the calculation of
how to
work out the rates of reactions which was, you have to take the
amount
of gas given off after the first 5 seconds and divide it by 5.
For Example: At 2 Molarity strength of hydrochloric acid set of
results; 1.
The volume of gas was 64cm², divide this by 5 which was the
amount of
time that elapsed for this much gas to be given off and you get
12.8cm²/second. Now to carry on working this out for the rest of
this
set you have to find the difference between 64cm² which was the
amount
given off after 5 seconds and the amount of gas released after
10
seconds which was 88cm², the difference is 24cm² and so we again
divide that by 5 and we then get 4.4cm²/second which is the
correct
rate of reaction for this time period.
Conclusion
The most obvious trend that I can see is that the higher the
strength
of the hydrochloric acid then the larger the rates of reaction
will.
This is proven in the first and last sets of results, which are
for
hydrochloric acid strengths of 2molar and 0.4molar. The highest
rate
of reaction for any set of result in the 2molar is 14cm²/second
whereas the highest rate of reaction for hydrochloric acid
strength of
0.4 is 1cm²/second which is a difference in rates of reaction of
13cm²/second. Another pattern that I saw was that no matter the
strength of the hydrochloric acid the volume of gas will always
increase and never decrease, it may stay exactly the same for a
few
seconds but it should still increase. This will always happen
because
this particular experiment is an irreversible reaction. This
means
that once the magnesium has reacted with the hydrochloric acid
and the
gas is given off then there is no way to get the magnesium back.
My
results are agree totally with my original predictions, which
was that
the 2molar experiments would react a quicker than the
hydrochloric
acid that was 0.4molar. My prediction also said that as the
hydrochloric acid became nearer and nearer to 0.4molar then the
reaction would take place slower and slower. The only
abnormality that
there was in the whole experiment was with hydrochloric acid
strength
of 1.2molar, results set 3 the first rate of reaction result was
7cm²/second, which was a 4 cm²/second increase on the other 2
sets of
results.
Evaluation
I think my results were very accurate as the results for the gas
given
off was accurate down to the nearest cm² thanks to the gas
syringe and
the rates of reaction results were accurate down to the nearest
tenth
of a cm²/second and that was down to how I worked out those
particular
results. I had one odd results which didn’t match my prediction
and
that was set of results 3 for with a molar strength of 1.2molar.
This
result was 7cm²/second over the other 2 sets of results. One
explanation for this odd result could possibly be that we put
the bung
into the top of the conical flask too late and didn’t start the
stop
clock at the same time. My results I think are very accurate
because
the volume of gas measured from the gas syringe and taken down
were
accurate to the nearest cm² and the rates of reaction was
accurate
down to the nearest tenth of a cm²/second. I think that my
results are
good enough and accurate enough to give a firm conclusion that
the
stronger the molarity of the hydrochloric acid is then the
faster the
magnesium ribbon is going to dissolve. I think this because my
results
show it, the starting strength which was 2molar took less than
half a
minute whereas the finishing strength which was 0.4molar took 5
and a
half minutes, this was the longest results set out of all
strengths of
hydrochloric acid. There are a few ways in which I could make my
reaction more accurate and reliable and the most obvious would
be that
I would have to find a way to hang the magnesium above the
hydrochloric acid so that as soon s the bung goes in the acid
drops
and the stop clock starts, this would therefore eliminate any
possible
abnormalities. I think a way in which I could make this
experiment
last longer and to give extra evidence would be to do the same
experiment only using smaller gaps in strengths of the
hydrochloric
acid, in other words do the experiment again only use
hydrochloric
acid of 2molar, 1.8molar, 1.6molar, 1.4molar…and so on until you
got
down to 0.2molar. This would give you a much more wider set of
results
especially if you did all of those strengths 3 times as we have
done
in this experiment. That is another way of making the experiment
more
accurate, by repeating it more than 3 times to so that we had
enough
sets of results for each strength to rule out any abnormalities.
#Post#: 50--------------------------------------------------
Re: Chemistry CA - Rates of Reaction
DIR By: Karenza
Date: May 25, 2015, 4:24 am
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The way forward has not always been smooth.
#Post#: 77--------------------------------------------------
Re: Chemistry CA - Rates of Reaction
DIR By: Jonathan
Date: February 8, 2018, 1:01 am
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These are good information you should read.
#Post#: 83--------------------------------------------------
Re: Chemistry CA - Rates of Reaction
DIR By: Monaliyo
Date: May 14, 2018, 5:20 am
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#Post#: 87--------------------------------------------------
Re: Chemistry CA - Rates of Reaction
DIR By: Minicode
Date: May 28, 2018, 3:45 am
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It is very good content to find information for me.
#Post#: 90--------------------------------------------------
Re: Chemistry CA - Rates of Reaction
DIR By: Schaeffer
Date: May 28, 2018, 5:09 am
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Get to know the full without any parts that are well written it.
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