The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction with Magnesium


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The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction with Magnesium

Aim:

To investigate the effect of concentration of hydrochloric acid on the
rate of reaction with magnesium

Prediction:

As the concentration of the hydrochloric acid increases, so will the
rate of reaction

Hypothesis:

In a reaction, particles of two different reactants react together to
form a product. The reaction only takes place on account of two
things, if the particles collide, and if the collision has enough
'activation energy'.

The two reactant particles, in this case magnesium particles and
hydrochloric acid particles, must collide with each other on the
correct 'collision course'. If this does not occur then no chemical
reaction will take place. The reaction must also have enough energy,
this can be affected by temperature, the more heat the particles have
the faster they move and so the more energy therefore more chance of
successful collisions. If there is not enough energy no reaction takes
place.

In a solution of 0.5M hydrochloric acid, there are less hydrochloric
acid particles compared to that of 2M hydrochloric acid, therefore,
there are less particles to react with magnesium particles thus
meaning less chance of collisions between the two reactants:

[IMAGE]

Therefore, as the concentration of the hydrochloric acid is increased,
the chances of collisions increase thus giving a faster rate of
reaction.

Apparatus:

Beaker

Hydrochloric acid

Distilled water

Measuring cylinder

Pipette

Test tubes

Test tube rack

Diagram:

[IMAGE]

Method:

Measure out 10cm3 of hydrochloric acid, as the concentration requires,
for each concentration its composition is:

Moles

Volume HCl

Volume Water

2M

10 cm³

0 cm³

1.5M

7.5 cm³

2.5 cm³

1M

5 cm³

5 cm³

0.5M

2.5 cm³

7.5 cm³

0M

0 cm³

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"The Effect of Concentration of Hydrochloric Acid on the Rate of Reaction with Magnesium." 123HelpMe.com. 26 Feb 2017
    <http://www.123HelpMe.com/view.asp?id=120948>.

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10 cm³

Pour the desired concentration of hydrochloric acid into a test tube.
Now add a 3cm strip of magnesium into the test tube. The mixture
should begin to effervesce. From the point the magnesium is added,
start the stopwatch, as soon as the effervescing stops, the reaction
is over:

Magnesium + hydrochloric acid à magnesium chloride + hydrogen

All variables of the concentration should be done at room temperature
for consistency.

Precautionary measures should be taken to ensure safety such as use of
goggles and special care undertaken when using acidic material.

Fair test:

To ensure the test is fair, the same amounts of magnesium and
hydrochloric acid shall be used throughout. The temperature will be
constant at that of the room, about 21 degrees Celsius.

Results:

volume HCl

volume water

moles

time /s

rate of reaction /s

10 cm³

0 cm³

2M

90

0.011111111

7.5 cm³

2.5 cm³

1.5M

126

0.007936508

5 cm³

5 cm³

1M

331

0.003021148

2.5 cm³

7.5 cm³

0.5M

1124

0.00088968

0 cm³

10 cm³

0M

1800+

0

Conclusion:

From the graph plotted from the results, it is apparent that the
general trend is that as the concentration of hydrochloric acid is
increased, so does the rate of reaction with magnesium.

The reaction can be summarized as:

Magnesium + hydrochloric acid à magnesium chloride and hydrogen

Mg + 2HCl à MgCl2 + H2

My hypothesis has been proven correct, in that beforehand I believed
increasing the concentration means that we have more particles in the
same volume of solution. This increases the chance of collisions
between reactant particles, resulting in more collisions in any given
time and a faster reaction. This can show us a general rule about
concentrations and rates of reactions:

The more concentrated a solution is à the faster the reaction

Concentration is measured in moles (M) per cubic decimetre; it shows
us how man particles there acre dissolved in a substance. Therefore,
1M of hydrochloric acid dissolved in one cubic decimetre of water is
the same concentration as 1M of sodium chloride dissolved in one cubic
decimetre of water. If the amount of moles per cubic decimetre doubles
from 1M to 2M, then so does the concentration double.

Evaluation:

I believe my experiment was quite accurate, but there are some
noticeable wrong points, mainly in that, as the concentration doubles,
so should the rate of reaction,(as there are double the amount of
hydrochloric particles) but we find that as concentration doubles from
1M to 2M, the rate more than triples. This therefore could be
considered anomalous in that it does not fit with scientific
principles, but it does go with the trend of things in that the rate
of reaction has increased.

I think it could also have been improved in the way it was measured,
that instead of through the time taken for the magnesium to disappear
completely, through the amount of hydrogen produced for each
concentration, as it relies upon the judgment of the individual for
when the magnesium has completely reacted, therefore for each reading,
it will be measured to a different extent because you may think it has
gone when it has gone when it has not etc, thus leading to
inaccuracies. A more suitable method for this may have been along the
lines of some form of indicator that would turn a certain colour when
all the hydrogen had been released from its compound.

And it could have been improved by the repetition of each
concentration 3 times, instead of the one time I was able to conduct,
to eliminate all anomalous results. As from 3 sets of readings, an
average can be calculated which will provide a more reliable result as
it is based upon 3 readings, not just the one reading which may be
wrong.


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