HCl Essay, Research Paper
Plan We
must produce a piece of coursework investigating the rates of reaction, and the
effect different changes have on them. The rate of reaction is the rate of loss
of a reactant or the rate of formation of a product during a chemical reaction.
It is measured by dividing 1 by the time taken for the reaction to take place.
There is five factors which affect the rate of a reaction, according to the
collision theory of reacting particles: temperature, concentration (of
solution), pressure (in gases), surface are (of solid reactants), and
catalysts. I have chosen to investigate the effect temperature and
concentration have on a reaction. This is because they are the most practical
to investigate ? it would take longer to prepare a solid in powdered and
unpowdered form, and it is difficult to get accurate readings due to the
inevitabilities of human errors, and as gas is mostly colourless it is difficult
to gauge a reaction changing the pressure, and if a substance is added to give
the gas colour, it may influence the outcome of the experiment. Similarly the
use of a catalyst complicates things, and if used incorrectly could alter the
outcome of the experiment.
Aim: –
To see the effects of a change in temperature and concentration on the rate of
a reaction. The reaction that will be used is:
Sodium Thiosulphate + Hydrochloric Acid
Na2S2O3 (aq) + 2HCl (aq)
Sodium Chloride + Water + Sulphur Dioxide +
2NaCl (aq) + H2O (l) + SO2 (g) +
Sulphur
S (s)
Two series of experiments will be carried out ? one changing the temperature
(while everything else remains constant) and one varying the concentration
(while keeping everything else constant). Both the sodium thiosulphate and the
Hydrochloric acid are soluble in water, so the concentration of either can be
changed. However I have chosen to vary the sodium thiosulphate as it is
available in larger amounts, and various concentrations are prepared. When the
temperature is constant room temperature will be used as the temperature as it
more practical and will not need to be monitored. When the temperature is being
varied a water bath will be used to heat up the acid and thiosulphate to the
necessary temperature.
I decided which temperatures and concentrations to use during my preliminary
series of experiments ?
1 mol/dm3 of HCl (acid concentration will be fixed)
10-35g/dm3 of sodium thiosulphate (all of these concentrations will be tested
in turn going up in steps of 5g/dm3)
20-70°C temperature (all of these temperatures will be used going up in steps
of 10°C)
Concentrations of 5, and 40 g/dm3 of thiosulphate were available to me but my
preliminary work showed that the 5 g/dm3 and 40g/dm3 were too slow and fast
respectively in reacting to be worth testing. Similarly any temperature below
20°C reacted too slowly, and 80°C and 90°C reacted too quickly to be worth
including in my final results.
Using my preliminary experiments I decided on using the following apparatus:
1 thermometer
1 beaker
2 measuring cylinders
1 conical flask
1 tripod
1 gauze
1 heatproof mat
1 stopwatch
1 Bunsen burner
X board
1 pair of tongs
1 pair of goggles
1 apron
Method: –
Experiment 1 – Changing the concentration
5 cm3 of HCl (at concentration 1 mol./dm3) and 15 cm3 of sodium thiosulphate
(at varying concentrations ? 10 to 35 g/dm3) are poured out into two measuring
cylinders and then poured into a conical flask, which is placed on top of a
board marked with letter X. The stopwatch will now be started. When the mixture
has turned sufficiently cloudy so that the letter X can no longer be seen the
stopwatch will be stopped and the time will be recorded. The experiment is
repeated with all the concentrations. The whole procedure is then repeated.
Experiment 2 ? Changing the temperature
5 cm of HCl (at concentration 1 mol./dm3) and 15 cm of sodium thiosulphate (at
varying concentrations ? 10 to 35 g/dm3) are poured out into two measuring
cylinders. A beaker is half filled with hot water from a tap. The water is
placed on top of a Bunsen on a blue flame and the two measuring placed inside
the water bath. The water is heated to the necessary temperature (30°C to 70°C)
then the two measuring cylinders are taken out and the contents of both are
poured into a conical cylinder. The time it takes for the X to disappear is
timed and recorded. The experiment is repeated using all the temperatures. The
entire procedure is the repeated.
Repeat results and averages will be taken to improve the credibility of the
findings, and present solid grounding for the final conclusion. The repeat
results will help to iron out any anomalies and the average will give a good
summary of the results of the experiment. However if one set of results is
entirely different to the other, a third experiment will be performed to
replace the anomalous set of results.
Safety ? A pair of goggles will be worn during the heating part of the
experiment in order to protect the eyes. An apron will also be worn to protect
the skin and clothing. When handling hot beakers and measuring cylinders a pair
of tongs will be used. A gauze and heatproof mat will be used while heating to
avoid any damage to the equipment.
Fair Test – In order for my findings to be valid the experiment must be a fair
one. I will use the same standard each time for judging when the X has
disappeared. I will make sure that the measuring cylinders for the HCl and
thiosulphate will not be mixed up. The amount of HCl will be 5 cm3 each time,
and the amount of thiosulphate will be fixed at 15 cm3. During the heating
stage of the experiment, a blue flame will be used throughout. Also the same
Bunsen burner and gas tap will be used to maintain continuity. All of these
precautions will make my final results more reliable and keep anomalies at a
minimum so thus make the entire investigation more successful.
Prediction ?
I predict that as the temperature is increased the rate of reaction will
increase. I also predict that as the concentration of the sodium thiosulphate
increases the rate of reaction will increase. This means that both graphs drawn
up in my analysis will have positive correlation, and will probably be curved
as the increase in rate of reaction will not be exactly the same as the concentration\temperature
is increased. This can be justified by relating to the collision theory. When
the temperature is increased the particles will have more energy and thus move
faster. Therefore they will collide more often and with more energy. Particles
with more energy are more likely to overcome the activation energy barrier to
reaction and thus react successfully. If solutions of reacting particles are
made more concentrated there are more particles per unit volume. Collisions
between reacting particles are therefore more likely to occur. All this can be
understood better with full understanding of the collision theory itself:
For a reaction to occur particles have to collide with each other. Only a small
percent result in a reaction. This is due to the energy barrier to overcome.
Only particles with enough energy to overcome the barrier will react after
colliding. The minimum energy that a particle must have to overcome the barrier
is called the activation energy, or Ea. The size of this activation energy is
different for different reactions. If the frequency of collisions is increased
the rate of reaction will increase. However the percent of successful
collisions remains the same. An increase in the frequency of collisions can be
achieved by increasing the concentration, pressure, or surface area.
Concentration ? If the concentration of a solution is increased there are more
reactant particles per unit volume. This increases the probability of reactant
particles colliding with each other.
Pressure – If the pressure is increased the particles in the gas are pushed
closer. This increases the concentration and thus the rate of reaction.
Surface Area ? If a solid is powdered then there is a greater surface area
available for a reaction, compared to the same mass of unpowdered solid. Only
particles on the surface of the solid will be able to undergo collisions with
the particles in a solution or gas.The particles in a gas undergo random
collisions in which energy is transferred between the colliding particles. As a
result there will be particles with differing energies. Maxwell-Boltzmann
energy distribution curves show the distribution of the energies of the
particles in a gas.
The main points to note about the curves are:
1. There are no particles with zero energy.
2. The curve does not touch the x-axis at the higher end, because there will
always be some particles with very high energies.
3. The area under the curve is equal to the total number of particles in the
system.
4. The peak of the curve indicates the most probable energy.
The activation energy for a given reaction can be marked on the distribution
curve. Only particles with energy equal or greater than the activation energy
can react when a collision occurs.
Although Maxwell-Boltzmann distribution curves are for the particles in a gas,
the same distributions can be used for the particles in a liquid or solid.
Effects of a temperature change – The graph below shows Maxwell-Boltzmann
distribution graphs for a fixed mass of gas at two temperatures ? T1 and T2,
where T2 is roughly 10°C higher than T1. The total area under the curve remains
the same, since there is no change in the number of particles present.
A small increase in temperature causes significant changes to the distribution
energies. At the higher temperature:
1. The peak is at a higher energy.
2. The peak is lower.
3. The peak is broader.
4. There is a large increase in the number of particles with higher energies.
It is the final change that results increase in rate, even with a relatively
small increase in temperature. A small increase in temperature greatly
increases the number of particles with energy greater than the activation
energy. The shaded areas on the energy distribution curves show this.
Effect of a catalyst – A catalyst works by providing an alternative reaction
pathway that has lower activation energy. A catalyst does not alter the
Maxwell-Boltzmann distribution. Because a catalyst provides a reaction route of
lower activation energy, however, a greater proportion of particles will have
energy greater than the activation energy.
Secondary Sources Used:
AS Level Chemistry Textbook (kinetics module)
The Internet
Dr. Jones?s Chemistry Lessons
Information sheets from Dr. Jones
Obtaining Evidence
Temp.(°C)???????? Time 1 (s)???????? Time 2 (s)??????? Average (s)
20??????????????????? 110.67????????????? 107.42????????????? 109.045
30??????????????????? 100.13????????????? 103.34????????????? 101.735
40??????????????????? 64.20?????????????? 65.92????? ??????????65.06
50??????????????????? 45.34?????????????? 37.73??????????????? 41.535
60??????????????????? 30.12??????????????? 33.18??????????????? 31.65
70???????????????????? 18.92?????????????? 16.34??????????????? 17.63
Concen.(g/dm3)???? Time 1 (s)?????? Time 2 (s)???? Average (s)
10???????????????????????? 222.63??????????? 224.38????????? 223.505
15???????????????????????? 150.90???????????? 147.03?????????? 148.965
20???????????????????????? 105.25??????????? 105.97?????????? 105.61
25??????? ?????????????????66.04?????????????
68.75??????????? 67.395
30???????????????????????? 55.63????????????? 56.1?????????????? 55.865
35???????????????????????? 27.32????????????? 25.96??????????? 26.64
Temp.(°C)? Rate of Reaction 1(s-1)?? Rate of Reaction 2 (s-1)? Average (s-1)
20???????????? 0.00904????????????????????????? 0.00931?????????????????????????? 0.00917
30???????????? 0.00999????????????????????????? 0.00968?????????????????????????? 0.00983
40???????????? 0.01558????????????????????????? 0.01517??????????????????????????? 0.01537
50????????????? 0.02206???????????????????????? 0.02650?????????????????????????? 0.02428
60????????????? 0.03320???????????????????????? 0.03014??????????????????????????? 0.03167
70????????????? 0.05285??????????? ?????????????0.06120??????????????????????????? 0.05703
Concen.(g/dm3)?? Rate of Reaction
1(s-1)?? Rate of Reaction 2 (s-1)?? Average (s-1)
10.00000??????????????? ?0.00449????????????
?0.00446 ???????????????????????0.00447
15.00000??????????????? ?0.00663 ?????????????0.00680 ???????????????????????0.00671
20.00000??????????????? ?0.00950????????????
?0.00944????????????????????? ??0.00947
25.00000 ????????????????0.01514 ?????????????0.01455???????????????????????? 0.01484
30.00000??????????????? ?0.01798 ?????????????0.01783?????????????????????? ??0.01790
35.00000??????????????? ?0.03660 ?????????????0.03852 ???????????????????????0.03756
Temp.(°C)??? Rate of Reaction 1(s)
x1000?? Rate of Reaction 2 (s)
x1000??? Average (s)
20????????????????? ????9.04????????????????????????????????????????????????? 9.31???????????????????????????? 9.17
30????????????????????? 9.99?????????????????????????????????????????????????
9.68???????????????????????????
9.83
40???????????????????? 15.58???????????????? ?????????????????????????????????15.17???????????????????????? 15.37
50??????????????????? 22.06?????????????????????????????????????????????????
26.50???????????????????????
24.28
60??????????????????? 33.20???????????????????????????????????????????????
??30.14???????????????????????? 31.67
70??????????????????? 52.85?????????????????????????????????????????????????
61.20???????????????????????
57.03
Concen.(g/dm)??? Rate of Reaction 1(s)
x1000??? Rate of Reaction 2 (s)
x1000? Average (s)
10???????????? ??????????????????????????4.49???????????????????????????????????????
4.46?????????????????????????
4.47
15??????????????????????????????????????
6.63??????????????????????????????????????? 6.80????????????????????????? 6.71
20???????????????????????????? ??????????9.50?????????????????????????????????????? 9.44?????????????????????????? 9.47
25??????????????????????????????????????
15.14????????????????????????????????????? 14.55???????????????????????? 14.84
30??????????????????????????????????????
17.98 ?????????????????????????????????????17.83???????????????????????? 17.90
35??????????????????????????????????????
36.60???????????????????????????????????? 38.52???????????????????????? 37.56
Analysis
In this experiment I have found that as the temperature and concentration is
increased the time taken for the reaction to take place decreases. This means
the rate of reaction increasers as it takes less time for a reaction to take
place, so more take place per second. In the temperature experiment the time taken
for a reaction to take place decreased by roughly 10 to 15 seconds for every
10°C increase in temperature, with the one anomaly being the 30°C reading.
There is also a trend in the increase in rate of reaction as the temperature
increases. The difference is always more or less 0.02 s-1, with the same
exception.
Using the graphs, with lines of best fit, I can draw a conclusion from my
experiment. Firstly I can see that with the ?time? graphs (that plot
temperature and concentration against time taken for the reaction to take
place) the graphs have negative correlation in both cases, meaning that as the
temperature\concentration increased the time taken for the reaction to take
place decreases. The time graph for the temperature experiment has a much
steeper curve than the one for the concentration experiment, meaning that the
decrease in time taken for the reaction was far more rapid.
Naturally, the above means that the both the graphs plotting rate against
temperature and concentration have positive correlation ? as the temperature
and concentration are increased so does the rate of reaction. This is because
when the temperature is increased the particles will have more energy and thus
move faster. Therefore they will collide more often and with more energy.
Particles with more energy are more likely to overcome the activation energy
barrier to reaction and thus react successfully, and when solutions of reacting
particles are made more concentrated there are more particles per unit volume.