Marble Chips and Hydrochloric Acid.

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Marble Chips and Hydrochloric Acid

PLANNING

AIM

To find if changing the concentration of an acid will increase or decrease the rate of the reaction when marble is dissolved in hydrochloric acid. With the equation CaCO3 + 2HCl CaCl2 +H2O + CO2

HYPOTHESES

A reaction occurs when particles collide. This process is based on random particle movement. So therefore, the more particles you have in a space, the more likely they are to collide. Therefore making the reaction accelerate.

This theory can be proved if you compare the rates of reaction with marble in hydrochloric acid. 'If the acid is of a higher concentration, the reaction will be quicker.’

Also if the particles have more energy, they will be travelling faster, making them collide more frequently.

PREDICTION

When the concentration of acid increases, more gas will be given off faster. I know this from my trial experiments.

METHOD

Since I will be working with strong acid, I will wear safety goggles while conducting the experiment.

I will use Marble chips all of a small size. I can use a sieve to make sure they are all roughly similar size- about 7mm diameter.

The amount of acid I have decided on is 10ml. And so the amount of marble must be in excess - 3g.

I can measure the speed of the reaction by how much gas is given off. I can measure this in cm3 in a gas syringe. when the experiment takes place, I will take the reading every 10 second to get a good graph for the results. If the reaction goes very quickly, I will take the readings every five seconds.

I will use acid of 0.5, 1, 2, 3, and 4 molar concentrations. SInce I only have acess to acid of 1,2 and 4 molar concentrations, I will have to dilute some acids with de-ionised water to produce 0.5 and 3 molar concentration acid.

To be sure I can rely on my results I will repeat he experiment twice or three times if necessary, because there is chance of inaccurate results for many reasons.

I learnt from the trial experiments that it is quite hard to start a stopwatch, pour acid and stick a bung into a boiling tube all at the same time, so I will get someone to assist me while doing so.

If the experiment goes on for a ridiculous time, I will cut it off. I don't think it is necessary to have the experiment go over three minutes, so I will cut it off then. Also, if the amount of gas goes off the scale I will stop it there.

It is important to keep the starting temperatures constant for all the reactions as this can affect the results by giving the particles more energy (and making it faster).

Analysis of Results.

From the experiment, I have found that an increased concentration of acid increases the rate of the reaction.

I think that the best way of displaying these results is by drawing a line graph. In it, I have used the average of the two sets of results. The pattern I can see is that when the reaction first starts, the reaction is fastest, from then on, the reaction slows. We can see this because the gradient of the curve is steepest at the beginning.

The cause of this curve is that at the start of the reaction, there is the most ammount of acid molecules that are colliding with the marble. (I can draw this from my initial hypothesis)

OBTAINING EVIDENCE

TABLE of RESULTS

Concentrration of Acid. time 10 20 30 40 50 60 70 80

0.5 15 20 25 28 30 32 34 36 37 38

0.5 14 22 28 33 38 41 44 47 48 50

1 28 48 58 67 79 83 93 97 100 105

1 20 40 54 64 73 81 86 92 99 103

2 40 60 76 90 100

2 38 55 74 89 100

3 30 44 70 85 99 110

3 30 62 90 110

4 7 115

4 30 65 87 110

During the experiment, I kept the starting temperature constant at 23 degrees.

I stop watch to time the experiment.

I wore safety glasses.

Time is in seconds. Concentration is in molarity..

I repeated the experiment twice to make sur my results were reliable.

Hydrochloric Acid and Magnesium

Aim

The aim of this investigation is to find out the effect of concentration of acid, in the
reaction between dilute hydrochloric caid and magnesium ribbon. The rate of a chemical
reaction is a measure of how fast the reaction takes place. It is important to remember
that a rapid reaction is completed in a short period of time. Some reactions are very fast,
e.g (the formation of silver chloride precipitate when silver nitrate and hydrochloric acid
solutions are mixed.In this investigation we will test different concentrations of acid
reacting with magnesium.
HYPOTHESES

A reaction occurs when particles collide. This process is based on random particle movement. so therefore, the more particles you have in a space, the more likely they are to collide. Therefore making the reaction accelerate.

This theory can be proved if you compare the rates of reaction with marble in hydrochloric acid. 'If the acid is of a higher concentration, the reaction will be quicker.'.

Also if the particles have more energy, they will be travelling faster, making them collide more frequently.

PREDICTION

When the concentration of acid increases, more gas will be given off faster. I know this from my trial experiments.


RESULTS
The results for, the time taken for magnesium to disappear when it is placed in different
concentrations of acid are summarised below.

EXPERIMENT 1

From the results in the table and the graph we can see a steady increase in the rate of
reaction as the concentration of the acid decreaes. This complies with my prediction.
The graph shows that there is an increase in the rate of reaction as the concentration
increases because the graph has it´s largest gradient or it is steepest at this point.
When the graph was made into 1/time the result should have been a sraight line graph but
it did not turn out this way even though concentration~1/time. This 1/time graph could be
wrong because of inaccurate results so there seems to be no relationship between the
concentration graph and the 1/time graph. We can see from the rate of reaction graph that
when the concentration roughly doubles from (1.8 moles to 3 moles) the rate of the
reaction doubles (from 60 to 25 seconds). Also we can see that as the reaction continues
the concentration of the reactants decrease and so does the rate of the reaction as we can
see the decreasing gradient on the graph steadily falling and coming to a stop when the
reaction is complete and the magnesium has completely disappeared.

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CONCLUSION
I can conclude that if you double the concentration of the acid the reaction rate would
also double, this is because the ions are closer together in a concentrated solution. The
closer together they are, the more often the ions collide. The more often they collide, the
higher the chance of a reaction between the magnesium and the hydrochloric acid. Also
because there are more particles in the solution which would increase the likelihood that
they would hit the magnesium so the reaction rate would increase. The graph gives us a
good device to prove that if you double the concentration the rate of reaction doubles. ...

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4 Stars Response to the question The candidate has carried out a well-planned experiment to investigate the effect of changing concentration on rate of reaction. The experiment was well planned with a stated hypothesis, with clear direction on how this was to be tested. The reports conclusion is limited, with a evaluation used to look at laboratory procedures and improvements. The conclusion would be improved by linking it more closely to the aim of the experiment, stating the effect of concentration on rate of reaction. Although they have investigated the question well, they have failed to fully answer it in a well-balanced conclusion. Level of analysis The candidate has a good understanding of the rate of a chemical reaction and covers the majority of factors that effect it. The candidate used diagrams effectively to show both particles in solution and the effect of activation energy. The analysis of the data was of a good standard using specific references to results and stating the change in rates of reactions. It is well written however needs to link their results back to the scientific theory for rates of reaction. They could improve this by explicitly stating the effect of changing the concentration on particle numbers and therefore the probability of products being formed from successful collisions between particles. The method is described generally and should be improved by stating specifically how the experiment was set up and carried out. It should be possible to carry out the experiment again from these directions. They have evaluated their experimental method and suggested possible improvements, to develop this further they should include the impact of these changes on the experimental method and results. Some data that did not lie on the line of best fit was identified, however there was no evidence of these values being re-investigated to improve the reliability of the data. Quality of writing Their spelling and grammar is variable, there are a number of spelling errors and incorrect chemical formulae. The equation for the reaction is incorrect and not balanced and carbon dioxide is often written as carbon monoxide. There are some problems with the layout of the experimental report. The evaluation should have come before the conclusion. The method had a diagram however this should include labels. (the conclusion is 'hidden' within the analysis section). Despite these issues, they have described their investigation well.