The aim of this investigation is to find out the effect of concentration of acid, in thereaction between dilute hydrochloric caid and magnesium ribbon.

GCSE Science

Aim The aim of this investigation is to find out the effect of concentration of

acid, in thereaction 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.

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 essaybank.co.uk explains why

the greatest rate of reaction is usually as soon as the reactants have been

mixed,i.e they are both at thier 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 wwee eew eseeees ayee eeba nee kcee eeuk.

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 wwac acw esacacs ayac acba nac kcac acuk:

use, the less time it takes for the magnesium to disappear and so the rate

reaction

increases. The concentraton of HCL you use is the independant 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 dependant variable because it depends upon the

concentration of wwdd ddw esdddds aydd ddba ndd kcdd dduk.

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 effect the 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 wwdg dgw esdgdgs aydg dgba ndg kcdg dguk.

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 HCL is poured into beaker with

the

magnesium in it. 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 axSEHVi3 Visit essaybank bg co bg uk bg for more bg Do not

bg redistribute axSEHVi3

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 testube 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 wwgf gfw esgfgfs aygf gfba ngf kcgf gfuk.

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 exceedly

exothermic wwed edw esededs ayed edba ned kced eduk.

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 effects the rate but b) is a minor effect which effects

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(3 mole)

Water(to dilute acid)

10ml testube

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

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

1mole 2moles 1mole 1mole

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

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long) and wwga gaw esgagas ayga gaba nga kcga gauk.

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 ...

This is a preview of the whole essay

long) and wwga gaw esgagas ayga gaba nga kcga gauk.

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 wwfe few esfefes ayfe feba nfe kcfe feuk.

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.

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

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started the 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. wwaa aaw esaaaas ayaa aaba naa kcaa aauk!

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 wwda daw esdadas ayda daba nda kcda dauk!

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 wweb ebw esebebs ayeb ebba neb kceb ebuk!

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 tk4 from tk4 essay tk4 bank tk4 co tk4 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 wwcb cbw escbcbs aycb cbba ncb kccb cbuk.

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

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Magnesium ribbon is just another form of magnesium metal. This reacts with hydrochloric acid

(and virtually all other acids) to form the acid salt of magnesium and hydrogen: Mg + 2HCl =

MgCl2 + H2 Hydrogen is a gas and will be seen as bubbles. However, it is also very explosive,

so do not have any flames around when you do it, unless you know exactly what you are doing!

Magnesium chloride is soluble, so the magnesium ribbon will slowly disappear into solution.

'''This chemistry coursework requires an investigation to see how long it takes for magnesium

ribbon to be eaten away by hydrochloric acid.

Before starting the investigation, I decided to do some research about magnesium and

hydrochloric acid.

Magnesium is a light, shiny grey metallic element, symbol Mg, atomic number 12, found in group

two in the periodic table. It is quite reactive giving vigorous reactions towards acids. It is one of

the alkaline earth metals, and the lightest of the commonly used metals. It is used in alloys, flash

photography, flares, fireworks and flash bulbs because it burns vigorously in air with a bright

white light. Magnesium reacts with steam to release hydrogen and it also burns in carbon

dioxide gas.

Hydrochloric acid, HCl, is a solution of hydrogen chloride (a colourless acidic gas) in water.

The concentrated acid is about 35% hydrogen chloride and is corrosive. The acid is a typical

strong, monobasic acid forming only one series of salts, the chlorides. Like most acids, it

releases hydrogen ions when it is added to water and certain metals, and has a pH of less than

7. Hydrochloric acid is a common laboratory acid.

Extracts from: a chemistry coursework from an Internet source and

The HUTCHINSON Dictionary of SCIENCE second edition.

Before looking at the factors that can alter the rate of reaction, we must consider what happens

when a reaction take place.

First of all, the particles of the reacting substances must collide with each other and, secondly,

they need a certain amount of energy to break down the bonds of the particles and form new

ones. This energy is called the activation energy or Ea. If a collision between particles can

produce sufficient energy (i.e. if they collide fast enough and in the right direction) a reaction will

take place. Not all collisions will result in a reaction. essaybank.co.uk

The investigation could be done using one variable and therefore have a set of results which

were related in some way. The variables that could be used are:

1. Concentration

2. Particle size/surface area

3. Pressure (for reactions involving gas)

4. Temperature

5. Light

6. Presence of a catalyst.

These variables can be used because:

1. The more concentrated the reactants, the greater the rate of reaction will be. This is because

increasing the concentration of the reactants increases the number of collisions between particles

and, therefore, increases the rate of reaction. wweg egw esegegs ayeg egba neg kceg eguk!

2. When one of the reactants is a solid, the reaction must take place on the surface area of the

solid. By breaking up the solid into smaller pieces, the surface area is increased, giving a greater

area of collisions to take place and so causing an increase in the rate of reaction. wwfd fdw

esfdfds ayfd fdba nfd kcfd fduk!

3. When one or more of the reactants are gases an increase in pressure can lead to an increased

rate of reaction. The increase in pressure forces the particles closer together. This causes more

collisions and increases the rate of reaction.

4. An increase in temperature produces an increase in the rate of reaction. A rise of 10º C

approximately doubles the rate of reaction. When a mixture of substances is heated, the

particles move faster. This has two effects. Since the particles are moving faster they will travel

greater distance in a given time and so will be involved in more collisions. Also, because the

particles are moving faster a larger proportion of the collisions will exceed the activation energy

and so the rate of reaction increases. wwad adw esadads ayad adba nad kcad aduk!

5. The rates of some reactions are increased by exposure to light. Light has a similar effect as

temperature because it produces heat.

6. A catalyst is a substance, which can alter the rate of a reaction but remains chemically

unchanged at the end of the reaction. Catalysts usually speed up a reaction. A catalyst, which

slows down a reaction, is called a negative catalyst or inhibitor. Catalysts speed up reactions by

providing an alternative pathway for the reaction, i.e. one that has much lower activation energy.

More collisions will, therefore, have enough energy for this new pathway. wweg egw esegegs

ayeg egba neg kceg eguk.

Extracts from: Letts Study Guide, GCSE CHEMISTRY.

All this information is relevant to my investigation, as I now know what would happen to the

molecules when using different variables. It also makes it easier to decide what variable I am

going to use in this circumstance.

I decided to use the concentration of acid as my variable. I used 5 different strengths of

hydrochloric acid. These strengths would determine the rates of reactions. I decided to measure

the acid in millilitres. I predicted that the higher the concentration of the acid, the faster the

reaction between magnesium ribbon and the hydrochloric acid. This would be because there

were more acid molecules to react with the magnesium ribbon. I decided that I would do 5

experiments and the different concentrations of hydrochloric acids were: L1SJ7Op Visit

essaybank eb co eb uk eb for more eb Do not eb redistribute L1SJ7Op

v 1.0 molar

v 1.25 molar

v 1.50 molar

v 1.75 molar

v 2.0 molar

Before doing the actual experiment I decided to do some preliminary work. These were to tell

me the details that I would need to know for my investigation to be successful. I saw from these

preliminary investigations that the magnesium ribbon started to react with the hydrochloric acid

the moment that I dropped it in. I decided that it would be a good idea to start timing the

second that I dropped it in. When the ribbon had been eaten away by the acid, it stopped

fizzing. I decided that I would stop timing the second that the fizzing stopped. I discovered from

my preliminary experiments that when I used a low concentration of hydrochloric acid, for

instance, 0.25 molar, it took a long time for the magnesium ribbon to be eaten away. I decided

that it would be impractical to spend time on the following strengths of hydrochloric acid: wwgc

gcw esgcgcs aygc gcba ngc kcgc gcuk!

v 0.25 molar

v 0.50 molar

v 0.75 molar

This was because they were the three slowest strengths of acids available to react with the

magnesium ribbon over a period of time. I also learnt from my preliminary experiments that it

was sometimes quite difficult to stop timing on the exact moment that the fizzing stopped. I

decided therefore that I would carry out each of the 5 experiments three times and find the

average time as this would result in a more accurate figure. wwcc ccw esccccs aycc ccba ncc

kccc ccuk.

When the magnesium ribbon reacts with the hydrochloric acid, magnesium chloride is formed. I

wrote down the equation to show this:

Magnesium + Hydrochloric acid = Magnesium Chloride + Hydrogen

Mg + 2HCl = MgCl + H

The equipment I needed for the investigation were:

v Magnesium ribbon- 15 pieces, 1cm long and weighed 0.01g

v Hydrochloric acid – 30 ml of 1.0 molar

30 ml of 1.25 molar

30 ml of 1.50 molar

30 ml of 1.75 molar

30 ml of 2.0 molar

v Test tubes – 5

v Test tube rack

v Stop clock

v Pipette

v Measuring Cylinder

v Thermometer

v Safety goggles

I decided to do 5 experiments, three times each, using all the information that I gained while I

was doing my preliminary experiments.

To ensure a safe experiment and working environment I needed to have at least 1 meter

squared of working space around me, wear safety goggles at all times when using acid, use a

test tube rack instead of holding the test tubes, secure all equipment and make sure that all the

equipment were fully functional and not damaged.

To make the experiment a fair test I used the same amount of acid for all experiments, only

changing the concentrations. I used the same size of magnesium ribbon and weight

(approximately 0.01g). I also started the stop clock when the magnesium touched the acid and

stopped it when the magnesium stopped fizzing for each experiment. I always washed out the

test tubes when an experiment had finished so the different concentration wouldn´t get mixed

together causing strange results.

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First I measured out the amount of hydrochloric acid using the measuring cylinder. I used a

pipette to pour the acid into the measuring cylinder as to be accurate. I needed 10 ml of acid in

the cylinder and poured it into a test tube. I then put a thermometer into the test tube for 1

minute to check the temperature. I did this to see if the experiments with the same strength of

acids affected the rate of reaction if there was a change in temperature. I then got a piece of

magnesium ribbon about 1 cm long weighing 0.01g and dropped it into the acid and started

timing the moment that the magnesium ribbon touched the acid solution. When the magnesium

ribbon stopped fizzing, I stopped the clock and recorded the number of seconds (rounded up to

nearest second) taken for the reaction from start to finish. wwab abw esababs ayab abba nab

kcab abuk.

I made a table to record my results in. The table is shown below.

Experiment Strength of hydrochloric acids in 10 ml No. of Mg ribbon pieces (0.01g) Test 1

secs. Temp Test 2 secs. Temp Test 3 secs. Temp AverageSecs.

1 1.0 molar 1 151.0 18 ºc 141.0 18 ºc 117.0 18.4ºc 136.3

2 1.25 molar 1 81.0 17 ºc 76.0 17.5ºc 74.0 18 ºc 77.0

3 1.50 molar 1 58.0 17.5ºc 56.0 18 ºc 56.0 18 ºc 56.3

4 1.75 molar 1 50.0 18 ºc 41.0 18º c 31.0 18 ºc 40.7

5 2.0 molar 1 20.0 19 ºc 22.0 19 ºc 16.0 21 ºc 19.3

To calculate the average time that it took for the magnesium to be eaten away by the acid, I did

the following calculation:

Test 1 + Test 2 + Test 3 = Average time

As I already have mentioned, I used a measuring cylinder to make the measurements and used a

pipette for further accuracy. I did each experiment three times so I would be able to calculate

averages and thereby get more accurate results. I recorded the results in seconds instead of

minutes in order to obtain more precise results. I used a stop clock instead of a 24-hour clock

so I could look at the milliseconds and round it up to the nearest second, which made the results

more exact.

It was noticeable, when looking at the results table, that the more concentrated acid had a faster

rate of reaction than the less concentrated acid. This was probably because there are more

particles in a concentrated acid and therefore more collisions will occur. For instance, 1.0

molars´ average time, 136.3 seconds, is longer than 2.0 molars´ average time, which was 19.3

seconds.

I made a graph to show the results.

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The graph above supports my original prediction of: the more concentrated the acid the faster

the rate of reaction because it shows the time difference between the different strengths of acids.

In a higher concentration there are more acid particles to react with the magnesium ribbon and

therefore it is eaten away faster.

I conclude that changing one factor does have a significant effect on the rate of reaction as we

have seen.

Looking at the set of results obtained, you can clearly see that they all follow the expected

pattern. This is pattern suggests that the reaction rate increase when the concentration of the

acid increases because if you increase the concentration of the acid you are introducing more

particles into the reaction which will in turn produce a faster reaction because there will be more

collisions between the particles which is what increases the reaction rate. wwcf cfw escfcfs aycf

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The evidence I have been able to gather from this investigation seems to lead to a quite firm

conclusion. I might not have been able to find the exact speed of the reactions but the pattern

seems to be correct as I have repeated readings three times and as it agrees with the information

I have researched.

I used the variable of concentration, which seemed to be of a good choice as it would show the

results of how more acid molecules reacting with magnesium, would result in a faster reaction.

There will always be ways in which you can improve your investigations and the same thing goes

to my investigation.

I found it very hard to measure out the exact number of millilitres for the acid even though I used

a pipette and I was also in a hurry. If I was to redo this investigation I would put some more

effort into measuring the acid. I could have used the wrong concentration of acid by accident

and that would have affected the speed because there would have been fewer or more acid

particles to react with the magnesium ribbon. Next time I do this experiment I would try to

remember which acid I am using so it doesn´t get mixed up. Every time I washed a test tube or

a measuring cylinder, I did not dry it before using it. This may have affected the rate of reaction,

as water would dilute the acid. To improve my results, I could dry the test tubes and the

measuring cylinder after they are washed to prevent diluted acids. The size and weight of the

magnesium would have affected the rate of reaction. The experiment could be improved by

measuring, adjusting and weighing the magnesium ribbons so they all are the same size and

weight. I also found out from background information, that the magnesium ribbon is covered

with a whitish deposit. This deposit was magnesium oxide where the magnesium had reacted

with the air. I would imagine that some pieces had only a little of this oxide and some had a lot.

The pieces of magnesium ribbon that did not have much oxide on them reacted faster than those

with a lot. To improve my results, I could clean the magnesium oxide of all the magnesium

pieces using some sandpaper, and this would mean that the acid would not have to eat through

the magnesium oxide before reacting with the magnesium. In my investigation I also measured

the temperature to see if there would be any change in the rate of reactions. From my results it

was noticeable to look at each experiment and see how the temperature had affected the rates

of reactions. For instance, if we refer back to the table on page 5 and look at experiment 5, test

three is slightly faster than test 1 or test 2 because it has a temperature of 21º, where as the

other two tests both have a temperature of 19º. To improve my investigation I could assure that

the temperature was constant all the time. I could also do more readings to get nearer to a more

accurate result.

The aim of this investigation is to find out the effect of concentration of acid, in thereaction between dilute hydrochloric caid and magnesium ribbon.

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