Rates of reactions between HCL and magnesium ribbon

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Rates of reactions between HCL and magnesium ribbon

Aim

I plan to investigate the effect of concentration of acid, in the reaction between dilute hydrochloric acid and magnesium ribbon. The rate of a chemical reaction is a measure of how fast the reaction takes place. It is important to know that a rapid reaction is completed in a short period of time. Some reactions are very fast, for example; the formation of silver chloride precipitates when silver nitrate and hydrochloric acid solutions are mixed. In this investigation I will test different concentrations of acid reacting with magnesium.

/Plan




To investigate what effect concentration of sodium thiosulphate has on the rate of reaction. The volume of HCL needs to be kept at 10cm constantly each time. Start with 60cm of sodium thiosulphate. Last reaction will have only 10cm of sodium thiosulphate.

Reactions will be completed when the x disappears, for the timing to stop. Three reactions will be made for each test; this is done to gain the different averages.

Introduction

I will be conducting an experiment on the rate of reaction for my GCSE coursework. I will be doing this coursework for a period of two weeks. We will be reacting sodium thiosulphate with hydrochloric acid. I will be investigating the effects had on rate of reaction.

When sodium thiosulphate and hydrochloric are mixed, a yellow precept of sulphur is produced. The solution becomes increasingly difficult to see through as more and more sulphur is formed.

Prediction

My prediction is that as the concentration of the hydrochloric acid increases, the time taken for the magnesium to disappear decreases. I predict that when the concentration of the hydrochloric acid doubles, the rate of the reaction doubles.

Background Knowledge

Rate is a measure of how fast or slow something is. For example, Silver Chloride precipitating (this is a very fast reaction) and Concrete setting (it may take a couple of days for concrete to harden). Rate is a measure of the change that happens in a single unit of time. Any suitable unit of time can be used - a second, a minute, an hour and even a day.

To find the rate of reaction, you should measure The amount of reactant used up per unit of time or the amount of a product produced per unit of time.

We are going to do an experiment on the rate of reaction. We are using acid and magnesium strips to test the rate of reaction.

Rates of reaction can be varied by a number of factors

? The concentration of the acid in which the magnesium is placed,

? The temperature of the acid and

? The size of the surface area of the magnesium strip.

Why rate changes with concentration If the concentration of the acid is increased, the reaction goes faster.

1

- Acid Particle

- Water Molecule

- Magnesium Atoms

1. In dilute acid, there are not so many acid particles. This means there is not much chance of an acid particle hitting a magnesium atom.

. Here the acid is more concentrated - there are more acid particles in it. There is now more chance of a successful collision occurring.

The more successful collisions there are the faster the reaction.

This idea also explains why the reaction between magnesium and hydrochloric acid slows down as time goes on

1

- Acid Particle

- Water Molecule

- Magnesium Atoms

1. At the start, there are plenty of magnesium atoms and acid particles. But they get used up during successful collisions.

. After a time, there are fewer magnesium atoms, and the acid is less concentrated. So the reaction slows down.

Why rate changes with the temperature At low temperatures particles of reacting substances do not have much energy. However, when the substances are heated, the particles take in energy. This causes them to move faster and collide more often. The collisions have more energy, so more of them are successful. Therefore the rate of reaction increases.

Why rate increases with surface area The reaction between the magnesium and acid is much faster when the metal is powdered

1

- Acid Particle

- Water Molecule

- Magnesium Atoms

1. Acid particles can collide only with magnesium atoms on the outside of the metal.

. When the metal is powdered, many more atoms are exposed. So there is a greater chance of successful collisions.

For my experiment my independent variable will be the concentration of the acid. I chose this as my independent variable as I feel this is the safest and easiest way to carry out the experiment. If I was to choose the temperature of the acid as my independent variable, and if I were to heat the acid too much it may boil and produce a corrosive gas, which would life threatening. It would be difficult to work out an accurate reading of the surface area if I was to choose the surface area as my independent variable.

Linking prediction to theory

Reaction rate and concentration.

The collision theory describes how the rate of reaction increases (the time taken for the magnesium ribbon to disappear when it is reacted with hydrochloric acid) when the concentration of HCL increases. As the reaction continues, the concentration of the reacting substances decreases and so does the rate of reaction. The reaction is speeded up if the number of collisions is increased. The higher the concentration of HCL you use, the less time it takes for the magnesium to disappear and so the rate reaction increases. If the activation energy is high only a small amount of particles will have enough energy to react so the reaction rate would be very small, however the activation energy is very low the number of particles with that amount of energy would be so high, so start, so the reaction rate would be higher.

Apparatus

Hydrochloric acid( mole)

Water(to dilute acid)

10ml testube

magnesium(cm long)

stop clock(sensitivity 1/10s)

beaker

In order to conduct any type of experiment, you need equipment. The equipment I used was a

Measuring Cylinder

Small measuring cylinder

Flask

beakers

Pad (marked with black cross) white cross

Timer

Method

To get the amount of magnesium and the amount of hydrochloric acid to use in the situation, we have to use an excess of acid so that all of the magnesium disappears.

An equation for the reaction

Magnesium + hydrochloric acid magnesium chloride + hydrogen

Mg(s) + HCL(aq)Mgcl(aq) + H(g)

1mole moles 1mole 1mole

So we can say that one mole of magnesium reacts with moles of hydrochloric acid. Throughout the experiment, we diluted the acid solution using water, as we did this the concentration of the acid decreased. Then 8ml of acid and ml of water solution on the magnesium, measured time taken for magnesium to disappear using stop clock. Then 7ml of acid and ml of acid, repeated as above. This way the rate of reaction(the time taken for the magnesium to disappear) was measured accurately for a fair test.

Results

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

Analysis of results

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 decreases. 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 its largest gradient or it is steepest at this point. When the graph was made into 1/time the result should have been a straight 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 moles) the rate of the reaction doubles (from 5 to 60 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.

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. If you increase the number of particles in the solution it is more likely that they will collide more often. In the reaction, when the magnesium hit the acid, it fizzed and produced many bubbles it was silver in colour (which is one of magnesiums physical properties silvery

white metallic element), the activation energy of a particle gets higher with heat, the particles which have to have the activation energy are those particles which are moving, in the case of magnesium and hydrochloric acid, it is the hydrochloric acid particles which have to have the activation energy because they are the ones that are moving and bombarding the magnesium particles to produce magnesium chloride. The graph for 1/time had the form of an s curve and it did have some relationship with the other graph.

Conclusion

The experiments made were very successful and we had managed to complete the experiment fully and fairly.

The fastest reaction made was with no water, 60 cm of sodium this sulphate and 10 cm acid. This reaction is very fast with a time average of 44.1 seconds. The slowest reaction made was with 50 cm of water, 10 cm of sodium thiosulphate and 10-cm acid. This reaction was very slow with a time of 4,4.5 minutes in average. But this average time has mainly been made with the one anomalous result in a certain reaction. The reaction was stopped at 61.46, but the reaction was still not finished. It seemed that the chemicals in the flask had only reacted halfway, then it just stopped reacting.

Evaluation

There are many reasons why our results for the 1/time graph did not prove the point that concentration~1/time, such as

1. When the reaction takes place bubbles of H are given off, which might stay around the magnesium, which therefore reduces the surface area of the magnesium and so the acid cannot react properly so this affects the results.

. We could have controlled factors in the investigation better (e.g. the stirring of the solution because if this is not done properly it can lead to incorrect results).

. Using larger concentrations of acid would give a bigger more accurate conclusion instead of just using 10ml test tubes use 1litre test tubes, this way graphs would be more spaced out and give an accurate form or curve.

Interpretation and Evaluation

In this experiment I found out that many different factors including; Concentration, Temperature and Surface Area affect the rate of reaction. For the experiment I found out that the higher the concentration of the acid the quicker it takes to dissolve the magnesium. I know this because the more acid molecules that is in the beaker there is more chance of a successful collision to take place. Another factor that I learned is that the rate is constantly changing during the reaction because as time goes on there are fewer acid molecules. There are fewer acid molecules because when the acid reacts the same particle cannot react again, so there are less to end with than there are to start with. As time goes on the number of acid particle decrease so there is less chance of a successful reaction to take place.

Before I started the experiment I made up a prediction. I predicted that the more concentrated the acid solution the faster the magnesium and hydrochloric acid will react. I thought that this would happen because when there are more acid particles in the test tube the more chance there is of a successful collision. I was right in my prediction but I did not predict that the rate of reaction slows down as time goes on which did happen in my experiment.

Improvements

The experiments were handled fairly but it could have been even more fair. Because The reaction was finished when the black cross on the pad dissapeared and this is only seen by the naked eye. With the whole class doing this with different eye types, there is no exact fairness in the experiment.

Fairness in this issue can be found by using devices such as a light sensor. The light sensor will pass through the flask, of were an reaction is taking place to a reciever. When the light sensor can not reach the reciever, the timing will be stopped automatically. This will bring fairness to experiments to test all similar to rate of reaction.

Variables

INDEPENDANT VARIABLE My independent variable is the concentration of the acid.

CONTROLLED VARIABLE My controlled variables are the temperature of the acid, the size of the surface area of the magnesium, the volume of the acid/water solution and the length of the magnesium strip.

DEPENDANT VARIABLE My dependant variables are the volume of the magnesium and the mass of the magnesium.

Apparatus

Stop Clock - Water -

Acid - Test Tube rack -

Test Tube - Magnesium -

Ruler - Scissors -

Beaker - Measuring Cylinder -

Safety

Safety is a very important part of this experiment as we are working with a corrosive chemical that is very dangerous. When carrying out the experiment, be sure to wear safety goggles as we are working with acid. When measuring out the different concentrations of acid, be careful not to spill it onto your hands or clothing.

Method

To begin with, set up all the apparatus in a safe position. Then make up the different concentrations of acid. To do this, add a quantity of water to the acid.

Water (cm) Acid (cm) Molarity Total (cm)

0 5 1 5

5 0 0.8 5

10 15 0.6 5

15 10 0.4 5

0 5 0. 5

Pour 5cm of each molarity of acid into a test tube. Then drop in a cm strip of magnesium. As soon as the magnesium strip drops, start the stop clock. When the magnesium is no longer visible, stop the stop clock and record the time. When the magnesium strip is dropped in a gas appears and it gives off a hissing noise. We can work out the name of this gas by solving a simple equation

Hydrogen Chloride + Magnesium = Magnesium Chloride + Hydrogen

HCL + Mg = MgCL + H

Or collect this gas and test it with the POP� test to identify it as Hydrogen.

Do this with each of the different molarities and repeat this again at least two more times to ensure that an accurate result is achieved.

BOILING TUBE

ACID OF DIFFERENT

MOLARITIES

MAGNESIUM

STRIP (CM)

BOILING TUBE

MAGNESIUM CHLORIDE

(THE MAGNESIUM HAS REACTED

WITH THE ACID AND HAS

DISSAPPEARED)

I will record the results in a table under the following headings

Molarity Volume (cm) Size of

Magnesium (cm) Time Taken

(sec) Rate of Reaction

1

0.8

0.6

0.4

0.

I will record the results in a graph under the following headings

T

I

M

E

(S

E

C)

MOLARITY OF SOLUTION

Prediction

I predict that the more concentrated the acid solution the faster the magnesium and hydrochloric acid will react. I think that this will happen because when there are more acid particles in the test tube the more chance there is of a successful collision

1

- Acid Particle

- Water Molecule

- Magnesium Atoms

1. The particles in the liquid move around continually. Here an acid particle is about to collide with a magnesium atom.

. If the collision has enough energy, reaction takes place. Magnesium chloride and hydrogen are formed.

. If the collision does not have enough energy, no reaction occurs. The acid particle bounces away again.

Results

1st results;

Molarity Volume (cm) Size of

Magnesium (cm) Time Taken

(sec) Rate of Reaction

1 5 5

0.8 5 6

0.6 5 11

0.4 5 516

0. 5 117

nd results;

Molarity Volume (cm) Size of

Magnesium (cm) Time Taken

(sec) Rate of Reaction

1 5 4

0.8 5 40

0.6 5 6

0.4 5 67

0. 5 NO TIME

rd results;

Molarity Volume (cm) Size of

Magnesium (cm) Time Taken

(sec) Rate of Reaction

1 5 6

0.8 5 8

0.6 5 61

0.4 5

0. 5 NO TIME

In some of the tests we had no time to complete them.

I also made a table for my average results;

Molarity Volume (cm) Size of

Magnesium (cm) Time Taken

(sec) Rate of Reaction

1 5 5

0.8 5 8

0.6 5 85

0.4 5 8

0. 5 117

I only recorded this result once because we had only enough time to test it once.



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