Find out the effect of concentration of acid, in the reaction between dilute hydrochloric acid and magnesium ribbon.

Aim

The aim of this investigation is to find out 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 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.

Prediction

I predict 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.

Linking prediction to theory

Reaction rate and concentration.

The collision theory describes how the rate of reaction increase (the time taken for the magnesium ribbon to disappear when it is reacted with hydrochloric acid) when the concentration of HCL increases. The theory states that if, the more concentrated the reactants, the greater the number of collisions between particles increase. This also explains why the greatest rate of reaction is usually as soon as the reactants have been mixed, i.e. they are both at their highest concentrations. As the reaction continues, the concentration of the reacting substances decrease and so does the rate of reaction. We must consider what happens when a reaction takes place. First of all the particles of the reacting substances must collide with each other, and secondly a fixed amount of energy called activation energy (Ea) must be reached if the reaction is to take place. If the particles can produce the right amount of energy (i.e. if they collide fast enough and in the right direction) a reaction will take place. The reaction is speeded up if the number of collisions is increased. In this investigation we must consider the topic of variables. Clearly, the time taken for the magnesium to disappear when it is placed in different concentrations of HCL is related in some way. The higher the concentration of HCL you use, the less time it takes for the magnesium to disappear and so the rate reaction increases. The concentration of HCL you use is the independent variable because it will vary, and the time taken for the rate of reaction to take place (i.e. the magnesium to disappear) is the dependent variable because it depends upon the concentration of hydrochloric acid. Other variables throughout the investigation, which will vary are the volume of water used, and the volume of hydrochloric acid. The variables, which will remain unchanged, are the temperature (room temperature) will stay the same in order for it to be a fair test, because if the temperature changes it will affect the rate of reaction between the reactants, either by speeding it up if the temperature rises because the particles move faster and travel a greater distance in a given time and so will be involved in more collisions. Or the temperature may slow the reaction down due to particles moving slower. The amount of magnesium used will stay the same (2cm long), so that it is a fair test. The time it takes for the magnesium to disappear will be measured accurately using a stop clock as soon as the magnesium is dropped into the HCL in the beaker. This way most results will be accurate. It is important to keep the reactants separate while setting up the apparatus so that the starting time of the reaction will be measured accurately. Factors, which may not be easy to control, are, how well the solution is mixed when it is diluted, to get the correct concentration. A way to come around could be (stirring the test tube twice, or shaking the test tube twice). This factor is quite important because it determines exactly what the concentration of the solution is each time it is mixed, if the stirring factor is not carefully controlled it could lead to inaccurate results if the concentration of the acid solution is not what we calculated it to be. During a chemical reaction the particles have to collide with enough energy to first break the bonds and then to form the new bonds and the rearranged electrons, so it´s safe to say that some of the particles don´t have enough energy to react when they collide. The minimum amount of energy that is required to break the bonds is called activation energy (Ea). 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. An example of low (Ea) would be in explosives when they only need a small input of energy to start their exothermic reactions. A change in concentration is a change in the number of particles in a given volume. If we increase the volume

a) The particles are more crowded so they collide more often.

b) Even though the average amount of energy possessed by a particle does not change, there are more particles with each amount of energy - more particles with the activation energy. a) Is a major effect, which affects the rate, but b) is a minor effect, which affects the rate only slightly. In this experiment we are not concerned with whether the reaction is exothermic or endothermic because we are interested with the activation needed to start and continue the reaction.

Apparatus/method

Hydrochloric acid (2 mole)

Water (to dilute ...

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a) The particles are more crowded so they collide more often.

Apparatus/method

Hydrochloric acid (2 mole)

Water (to dilute acid)

magnesium(2cm long)

stop clock(sensitivity 1/10s)

beaker

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) + 2HCL(aq)>Mgcl2(aq) + H2(g)

So we can say that one mole of magnesium reacts with 2 moles of hydrochloric acid.

We know that the concentration of hydrochloric acid that we start with is 3 moles.

Throughout the experiment, we diluted the acid solution using water, as we did this the

concentration of the acid decreased. We put the acid(3 moles) into the 10ml testube and

then poured the solution into the beaker with the magnesium ribbon init(2cm long) and wwfe few esfefes ayfe feba nfe kcfe feuk.

then measured the time taken for the magnesium ribbon to disappear, using the stop

clock. Next, we diluted the acid by placing 9ml of acid and 1ml of water into the testube

and then poured it into the beaker with the magnesium and measured the time taken for

the magnesium ribbon to disappear using the stop clock. Then 8ml of acid and 2ml of

water solution on the magnesium, measured time taken for magnesium to disappear using

stop clock . Then 7ml of acid and 3ml of acid, repeated as above . Then 6ml of acid and

4ml of water, repeated as above. We repeated the experiment 3 times to get a fair test by wwec ecw esececs ayec ecba nec kcec ecuk!

proving that all results are accurate, if they were inaccurate we repeated the experiment

again, or ignored wrong results. We tabulated the results in a clear table as soon as each experiment was completed, in case we lost them and to check for possible errors or gaps in our results and it helped us to spot patterns in the results. We calculated the different, concentrations of the acid throughout the experiment using the method below as in the table. When we did the experiment, we made sure that we started the stop clock, at exactly the same time as the acid was poured onto the magnesium, to measure the start of the reaction to the finish of the reaction where the equivalent care was taken to stop the clock at the point the magnesium disappeared which was at the end of the reaction. While we set up the apparatus we kept the reactants separate so that the starting time of the reactants could be measured accurately and for it to be a fair test. We wore safety goggles when we did the experiment, to protect our eyes from the very harmful acid. We considered the factors in the reaction, and decided how we were going to control them. We kept our eyes on the experiment so that we could see exactly when we should´ve stop clock and stopped the clock. This way the rate of reaction (the time taken for the magnesium to disappear) was measured accurately for a fair test. We made sure the amount of magnesium used stayed the same in all the experiments (2cm long).

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. wwgd gdw esgdgds aygd gdba ngd kcgd gduk;

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 wwgc gcw esgcgcs aygc gcba ngc kcgc gcuk.

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 wwgc gcw esgcgcs aygc gcba ngc kcgc gcuk.

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 magnesiums physical properties silvery

white metallic element), the activation energy of a particle gets higher with heat, the fwz7A3 from fwz7A3 essay fwz7A3 bank fwz7A3 co fwz7A3 uk

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.

EVALUATION

There are many reasons why our results for the 1/time graph did not prove the point that wwga gaw esgagas ayga gaba nga kcga gauk:

concentration~1/time,such as

1)When the reaction takes place bubbles of H2 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 effects the results.

2)We could have controlled factors in the investigation better (e.g the stirring of the

solution because if this is´nt done properly it can lead to incorrect results).

3)using larger concentrations of acid would give a bigger more accurate conclusion

instead of just using 10ml testubes use 1litre testubes, this way graphs would be more

spaced out and give an accurate form or curve

Find out the effect of concentration of acid, in the reaction between dilute hydrochloric acid and magnesium ribbon.

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