hydrochloric acid and magnesium concentration experiment

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4. Investigate the rate of reaction Apparatus and chemicals

Looking at how quickly magnesium reacts with dilute hyrdrochloric acid.

Part of Combined Science Prescribed practicals

Apparatus and chemicals

• 200 cm 3 of 2 mol/dm 3 hydrochloric acid and deionised water
• 10 x 3 cm strips of magnesium
• 100 cm 3 beaker, 250 cm 3 beaker, watch glass, measuring cylinder (25 cm 3 )
• Carefully collect 200 cm 3 of hydrochloric acid using the 250cm 3 beaker, and 10 strips of magnesium using a watch glass.
• Using the measuring cylinder, measure out 25 cm 3 of hydrochloric acid and add to the small beaker. Remember to use the measuring cylinder accurately.
• Drop the piece of magnesium ribbon into the beaker and start the stop watch, swirl once to ensure the magnesium is fully coated in the acid. Stop the watch when all the magnesium disappears.
• Repeat the experiment to ensure reliability of results.
• Repeat steps 2-4 except using a total of five different volumes of acid and water to ensure different concentrations of acid. The proportions you need to use are given in the results table:

Analysis of results

In this experiment we can use the times to calculate an approximate value for the rate of each reaction by using the formula:-

\(Rate~= \frac {1}{time}\)

Using your average times calculate the rate of reaction for each experiment:-

We can also calculate the percentage of acid used, or, since we know the original concentration of the acid is 2 mol/dm 3 , we can calculate the concentrate for each experiment:-

Finally, we can plot a graph of our Independent Variable (x-axis) against our Dependent Variable (y-axis). Your Independent Variable will be either % Acid, or Concentration. Your Dependent Variable will either be time or rate. Your teacher will instruct you on which to use.

More guides on this topic

• 1. Investigate the reactions of acids
• 2. Identify the ions in an ionic compound
• 3. Investigate the reactivity of metals
• 5. Determine the mass of water in hydrated crystals
• 6. Investigate the reaction of gases

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Rate of Reaction of Magnesium and Hydrochloric Acid

Introduction.

In acid-base chemical reactions, there are four main variables, which influence the rate of reaction. These include the presence or absence of catalyst, temperature, concentration, and surface area of reactants. Temperature influences the rates of reaction through kinetic energy, such that high temperatures increase the kinetic energy of reacting molecules therefore causing frequent collisions, which form products faster. High concentrations imply that more reacting molecules are at high proximity to each other therefore intermolecular collisions are frequent therefore forming products frequently. Reactants with high surface area provide a greater binding surface for other reacting molecules, and therefore increase the number of successful collisions at any moment.

To measure, the effect of each of above factors, one has to hold some factors constant during rate reaction experimentation. Therefore, this study intends to investigate the effect of concentration and surface area of reactants on the rate of chemical reactions.Magnesium metal (in form of a ribbon or powder) reacts with acids rapidly than water liberating hydrogen gas. For stance, magnesium metal reacts with hydrochloric to form magnesium chloride salt while displacing hydrogen from the acid as hydrogen gas. This is as shown in the equation below: 2HCl (aq) + Mg (s) => MgCl2 (aq) + H2 (g) Research Question: If magnesium ribbon is replaced with an equivalent weight of powered magnesium, does the rate of reaction between magnesium and hydrochloric acid double?

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Aims and objectives of the experiment

The aim of this experiment is to verify the effects of surface area of solid reactants and concentration of aqueous reactants on the rates of acid-base chemical reactions. Therefore, we sought to test the duration of reaction of equal lengths Magnesium ribbons with reducing concentrations of hydrochloric acid.

Similarly, the duration of reaction will be determined using equivalent weights of powdered Magnesium metal. The experiment will be carried at a room temperature 25 0C.

Study Variables

• The Dependent Variables: The measured duration of acid-metal reaction in seconds and the rate of gas bubbles.
• The Independent Variables:  The concentration of hydrochloric acid used and the surface area of the Magnesium metal used.

For the Magnesium ribbon, the lengths of the Magnesium ribbon used will be constant, while quantities of powdered Magnesium metal (in grams) will be equivalent to the weight of the length of magnesium ribbon used. The experiment will be carried out at room temperature (25 0C)

The study variables are summarized in the table below:

Table 1 A table of study variables and operationalization of the study variables Prediction Given that, powdered Magnesium metal has a high surface area than equivalent lengths of Magnesium ribbon, we predict that the former will have shorter duration of reaction with hydrochloric acid than the latter. We also predict that reaction of powdered Magnesium metal with highest concentration of hydrochloric acid will take the shortest duration of reaction. Hypothesis: Powdered Magnesium metal will reduce the reaction duration by a half if used in place of equivalent length of magnesium ribbon, when reacted with hydrochloric acid.

Equipment and Materials

Chemicals and Reagents The following chemicals and reagents were required in the experimentation:

• Magnesium ribbon
• Powdered Magnesium metal

0 M, 1.5M, 1.0 M and 0.5M )

• Distilled water

Apparatus and personal protection equipment

• 10 Conical flasks (100 cm 3 )
• 3 Measuring cylinders (100 cm 3 )
• Clamp stand
• Glass trough
• A Stopwatch
• Safety goggles
• Laboratory dust coat

Experimentation procedures

The experiment procedure was divided into two related investigations involving equal lengths of Magnesium ribbons and equal amounts of powdered Magnesium metal.

• First, repair your working bench by simply removing unnecessary materials. Make sure you put on your personal protective clothing and safety goggles.
• Clean the Magnesium ribbon using a sand paper to remove oxides coating its surface. This will reduce reaction errors related to impurities.
• Cut 5 equal sizes (10 cm) pieces of Magnesium from the fleshly cleaned Magnesium ribbon, weigh each of them using a digital weighing balance and record their weights.
• Wrap the magnesium pieces immediately in an aluminum foil to prevent them from being re-oxidized.
• Measure 40 ml of 3M HCl using a clean dry measuring cylinder and pour into a clean 100 ml conical flask.
• Add 40 ml of distilled water and label the conical flask with the concentration of the HCL poured.
• Repeat step 5 and 6 for 2M, 1.5M, 1M, and 0.5M HCL and keep all the acids ready on the working bench.
• Reset your stopwatch timer and prepare a gas delivery system including water bath as shown figure one below.
• Pick one piece of Magnesium ribbon drop in the first prepared acid in the conical flask and immediately start your stopwatch.
• Immediately cork the flask to the prepared gas delivery system.
• Monitor the reaction progress closely and stop your running stopwatch when the Magnesium ribbon completely dissolves in the acid and record the reaction duration in seconds in a data sheet.
• Reset your stopwatch, a repeat steps 9, 10 and 11 for the subsequent acids.
• Discard all the chemicals, wash, and rinse the conical flasks ready for another procedure.
• Repeat steps 5, 6 and 7 above.
• Add up the weights of the five 10 cm-long magnesium ribbons and obtain the average weight in grams
• Use the average weight as obtained in 15 above and weigh of an equivalent weight of Magnesium powder (for this case 0.102 grams) and pour into the first conical flask containing the 3 M HCl acid, start your stopwatch, and immediately cork the flask to the gas delivery system.
• Monitors the reaction progress and stop the stopwatch when the Magnesium powder dissolves completely in the acid.

5M HCL and clearly label your results.

• Clear your working bench.

Results and Observations

During the reaction, the water bath in the gas delivery system showed gas bubbles ascending to the gas cylinder.

At higher acid concentration, the rates of bubble forming were rapid than those in lower acid concentrations were. The most rapid gas bubbles were observed in the acid reactions with powdered Magnesium metal. The duration of reactions were recorded as shown in tables 2 and 3 below.

Table 2. A table of results showing HCl-Magnesium ribbon reaction duration (seconds) in reducing concentration

Table 3. A table of results showing HCl-Magnesium powder reaction duration (seconds) in reducing concentration

Processing and Presenting Data

Importantly, suitable acid-base indicators can be used to detect the end of the reaction accurately.

Retrieved March 8, 2012, from newton.dep.anl.gov: http://www.newton.dep.

anl.gov/askasci/chem00/

• chem00021.htm

Retrieved March 8, 2012, from chemguide.co.uk: http://www.chemguide.co.uk/physical/basicrates/surfacearea.

• Gallagher, R., & Ingram, P. (2001). Chemistry for higher tier: New coordinated science. New York: Oxford University Press. p137

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Reacting Magnesium With Hydrochloric Acid

GCSE   Science   Module   6   Coursework

Reacting   Magnesium   With   Hydrochloric   Acid

Planning   Experimental   Procedures

The aim of this experiment is to investigate how the surface area of a reactant can affect the rate of a reaction. The two reactants we will be using for this experiment are magnesium(Mg) and hydrochloric acid(HCl).

Investigation   Factors

I already know how the concentration of the hydrochloric acid can alter the rate of a reaction, as I carried out an experiment in a previous coursework assignment, in which the aim was to investigate the concentration factor. I also know how the mass of the magnesium and the temperature can affect the rate of a reaction, as I carried out some research in order to find this information out. Written below is a brief summary of the conclusion from my previous experiment, as well as some of the information I found during my research.

The   Concentration   Of   The   Hydrochloric   Acid

The more concentrated the reactants are, the greater will be the rate of reaction. This is because the higher the concentration of the hydrochloric acid is, the closer together the ions are and the closer together they are, the more often they will collide with each other. The more often the particles collide, the higher the chance will be of starting a reaction between magnesium and hydrochloric acid.

This also explains why the greatest rate of reaction is usually as soon as both the reactants are at their highest concentrations of the reacting substances decrease and the rate of reaction decreases.  

The   Temperature

An increase in temperature produces an increase in the rate of a reaction because, when a mixture of substances is heated, the particles move faster. This has two effects. Since the particles are moving faster they will travel at a 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 collision will exceed the activation energy and so the rate of reaction increases.

The   Mass   Of   Magnesium

The mass of the magnesium will affect the rate of reaction because the more magnesium there is, the more reactions will occur, due to there being a larger amount

of area for reactions to occur upon.

The   Surface   Area   Of   The   Magnesium This is the variable I have chosen to investigate. Increasing the surface area of the magnesium will result in an increased reaction rate. The reason as to why this happens is given below within my hypothesis.

Collision   Theory

Two things are needed in order to start a reaction. Firstly, the particles of the reacting substances must collide with each other and, secondly, a fixed amount of activation energy must be reached if the reaction is to take place. If a collision between a magnesium particle and a hydrochloric acid particle can produce sufficient activation energy, by colliding with sufficient velocity i.e. in the right direction and at the right speed, a reaction will take place. Not all collisions will result in a reaction, as some do not collide with sufficient velocity. A reaction is speeded up if the number of suitable collisions is increased.

My prediction for this experiment is that as the surface area of the magnesium  increases, so will the rate of reaction and the amount of hydrogen produced. I predict this because for a solid material, smaller particles have a larger total surface area than larger particles would, if the mass of the solid is the same. A simple way to visualise this is to take a loaf of bread and cut it into slices. Each time you cut a new slice, you get an extra surface onto which you can spread butter. The thinner you cut the slices, the more slices you get and so the more butter you can put on them. Similarly, the thinner you cut the magnesium pieces, the larger the surface area will be and so the more collisions there will be, due to an increased surface area for the reactants to react upon. This explains why increasing the surface area will cause an increase in the rate of reaction. Another way to explain why this happens is because the magnesium and hydrochloric acid molecules can only bump into each other at the liquid solid interface.

For the experiment we will use the following equipment/chemicals:

A test tube, a test tube rack, a delivery tube, a measuring cylinder, a timer, a tray, a thermometer, a gas syringe, a micrometer(to measure the thickness of the magnesium), a pair of scissors, a pair of safety goggles, water, magnesium and hydrochloric acid.

Safe   Testing

To ensure that the test is safe we will:

a) Carry out each of the basic safety procedures required before carrying out any experiment (tucking ties in, tying back long hair, wearing a pair of safety goggles etc.)

This is a preview of the whole essay

b) Hold the magnesium carefully and not let into go into the water/hydrochloric acid until we are carrying out the reaction.

c) Handle the hydrochloric acid very carefully, by using a pipette to transfer the hydrochloric acid from the bottle into the test tube.

Fair   Testing

To ensure that the test is fair we will:

a) Not let any air into the measuring cylinder when turning it upside down into the water.

b) Keep the temperature at 22 degrees celsius throughout the experiment.

c) Keep the volume of hydrochloric acid at 1.5cm 3.

d) Keep the concentration of the hydrochloric acid at 2%.

e) Keep the time for each reaction at 1 minute.

Collecting   Our   Results

I will be taking down results for five different surface areas(stated below). I will then be repeating the experiment two more times, in order to confirm that my results are accurate and precise. There are three different methods which I could use to collect my results:

a)We could use a timer to see how long it takes for magnesium to disappear.(We will not be using this method as it is inaccurate, and also too basic and would be used at a lower level.)

b)We could collect the hydrogen using a syringe and measure how much gas there is.(Although this would be the most accurate method, we will not be using this method as there may be a shortage of syringes if everyone was to use one.)

c)We could fill a beaker with water, attach a delivery tube, turn the measuring cylinder upside down and see how much gas is collected.(We will be using this method, as it is more accurate than the first method and we have the equipment required to use this method.)

Brief   Method   Plan(done before experiment)

Before I start the experiment I will make sure I have all the equipment required and will

prepare a results table to record my results into.

1) Get a pair of safety goggles, tie back long hair and tuck in ties(see safety section).

2)  Fill a tray up with water and place a test tube into a test tube rack. Collect all the equipment you will need.

3) Place into the test tube 1.5cm 3  of 2% concentrated hydrochloric acid.

4) Fill the measuring cylinder with water and turn it upside down into the water, making sure no air is let in. Get a delivery tube and attach one end to the measuring cylinder and the other end to the test tube.

5) Place the magnesium into the water, cover the top of the test tube with the end of the delivery tube and start the timer.

6) After the reaction has been going for 30 seconds, measure the amount of hydrogen collected so far and record it into your results table.

7) Measure the amount of hydrogen collected again at the end of the minute and record it once again into your table.

8) Repeat steps 2-7, keeping everything exactly the same, changing only the surface area of the magnesium by cutting one extra piece out of it.

9) Repeat steps 2-8 two more times, in order to make sure the results are accurate and precise.

Obtaining   The   Evidence

Calculating   The   Surface   Area   Of   The   Magnesium

I required a micrometer to calculate the thickness of the magnesium. In order to calculate the surface area of the magnesium I first had to calculate the area of faces A, B & C on the diagram shown below, and then add all three areas up and multiply them by two as there are six sides on the surface area. My calculations are shown below my diagram.

Area of face A=10 x 0.3=3cm 2

Area of face B=10 x 0.02=0.2cm 2

Area of face C=0.3 x 0.02=0.006cm 2

face A + face B + face C=3 + 0.2 + 0.006=3.206cm 2

Total surface area=3.206 x 2=6.412cm 2

Each time we then cut off another piece of magnesium, two extra areas will be created, with each one having the same area as the area of face C. Therefore, every time we cut another piece of magnesium, we will have to add onto the surface area the area of face C multiplied by two, which gives 0.012cm 2 (0.006 x 2).

Method   Used(done after experiment)

Firstly, before I started the experiment, I carried out the basic safety procedures listed above within the safety section, in order to decrease the chances of getting hurt. Next, I began to prepare for the experiment. Firstly, I collected a tray and filled it halfway up with water. Then I got some magnesium and cut off a 10cm strip. Then, I collected all the other equipment I needed for the experiment: a test tube, a test tube rack, a delivery tube, a measuring cylinder, a timer, a gas syringe and a pair of scissors. I was then ready to start the experiment.

I started by placing the test tube into the test tube rack, before filling the measuring cylinder up with water. I then covered up the top of the measuring cylinder with my hand, turned it upside down and placed it into the water. I did not let any air get into the measuring cylinder as this would have tampered with my results, making them inaccurate and I would have had to

repeat this step. I then measured out exactly 1.5cm 3  of 2% concentrated hydrochloric acid and poured it into the test tube. Then I put one end of the delivery tube into the measuring cylinder and I was then ready to start the reaction.

I dropped the magnesium into the test tube, quickly covered the top of the test tube with the other end of the delivery tube and started the timer. After the reaction had been going for 30 seconds, I measured the amount of hydrogen collected so far and recorded it in my results table, though I did not stop the reaction or the timer. After the reaction had been going for 1 minute I once again measured and noted, the amount of hydrogen collected.

I then repeated this process for each of the different surface areas of the magnesium. Each time I kept all the other factors the same, changing only the number of pieces/surface area of the magnesium, though keeping the mass the same each time.

Finally I repeated the whole process two more times to make sure my results were accurate and precise.

Results   Table (Analysis given below within ‘Analysis of Results’ section)

A   Graph   To   Show   How   The   Surface   Area   Affected   The   Rate   Of   A   Reaction

Volume Of Hydrogen Produced(cm 3 )

Surface Area Of Magnesium(cm 2 )

A   Graph   To   Show   How   The   Rate   Of   Reaction   Had   Been   Affected   Half   Way   Through   The   Reaction

An analysis of the graphs is given within the conclusion section.

Analysing   Evidence   And   Drawing   Conclusions

Summary   And   Explanation   Of   The   Reaction

The equation for the reaction between magnesium and hydrochloric acid is:

magnesium(s) + hydrochloric acid(aq)--------->magnesium chloride(aq) + hydrogen(g)

       Mg         +          2HCl               --------->           MgCl 2                +         H 2

A displacement reaction occurs when the magnesium reacts with the hydrochloric acid. The reason for this is because magnesium is higher in the reactivity series than hydrogen, so it displaces the hydrogen in the hydrochloric acid, forming magnesium chloride and hydrogen as the products of the reaction. Another example of this would be reacting aluminium with hydrochloric acid, where the aluminium would displace the hydrogen, forming aluminium chloride. Anything below hydrogen in the reactivity series(copper, silver, gold & platinum) would not react with hydrochloric acid as they are too unreactive, and anything above magnesium in the reactivity series(calcium, sodium & potassium)would be too dangerous to react with a strong acid.

Analysis   Of   Results

My results table shown above, shows that I carried out a fair test by keeping the temperature, time, and the volume and concentration of hydrochloric acid the same throughout the experiment. The table also shows that my prediction was correct, as the table proves that as you increase the surface area of the magnesium, the rate of reaction/amount of hydrogen produced increases.

Looking at the graphs, you can see that a pattern has emerged in my results. The pattern was that as the surface area of the magnesium increased, the amount of hydrogen produced also increased. The pattern in my results also agrees with my prediction. I received no anomalous results whilst carrying out the experiment. I have also included the results of my retest in the graphs.

Comparing the first graph to the second, you can see that the reaction began quite slowly before eventually increasing, as the majority of the collisions between particles occurred within the last 30 seconds of the reaction. The reason for this is because the reaction between magnesium and hydrochloric acid is an exothermic reaction. This means that as the reaction progresses the particles will heat up, and the hotter the particles are, the more energy they have and so the higher the rate of reaction will be, due to a larger number of collisions, because of an increase of energy within the particles.

Having analysed the results table and graphs, I can now conclude that as you increase the surface area of the magnesium, the rate of reaction also increases i.e. a larger volume of hydrogen bubbles are produced. The reason for this is because increasing the surface area gives a larger area for the acid particles to collide on, which will lead to more successful collisions, and also, the magnesium molecules and hydrochloric acid molecules can only collide with each other on the surface of the magnesium.

So, smaller particles of magnesium, lead to a larger surface area, which leads to more collisions, which leads to more successful collisions(collisions with sufficient velocity), which eventually leads to a higher rate of reaction.

My conclusion is also very similar to my hypothesis, as my hypothesis was about what I predicted my conclusion would be and as they are similar, this again proves my prediction was correct.

Evaluating   The   Evidence

Evaluating   Our   Choice   Of   Method

I think the method that we used to obtain our results was quite successful, although it could have been better. The most important thing to consider whilst selecting an appropriate method is that the method is accurate enough to give a valid conclusion, as this method did. Our results were more accurate than they would have been had we used the method of timing how long it took for the magnesium to disappear, as this would have been the most inaccurate method of the three main methods. There was a method which was more simple and also, more importantly, more accurate, than the method we chose. This method would have been to collect the gas using a syringe and then measure the amount of hydrogen produced. The reason we were unable to use this method was because there would have been a shortage of syringes, had everyone required one.

Although the results were not always exactly the same in each of the re-tests, I think, overall, the method was sufficient, as it provided me with a valid conclusion, as well as a reliable set of results, and it also gave no anomalous results.

Investigation   Extensions

The following investigations could be carried out in order to provide additional evidence to the conclusion:

-The experiment could be repeated, though this time using a wider range of surface areas, as the range of surface areas we used wasn’t very large.

-The experiment could be repeated with a different metal, other than magnesium, to ensure that the conclusion does not just apply to magnesium.

-The experiment could also be repeated changing the type of acid used, to ensure that the conclusion does not just apply to hydrochloric acid.

-The experiment could be repeated keeping all the factors, including the surface area, the same. My prediction would be that the rate of reaction would be the same. If it was, then this would again prove that the conclusion is correct.

Document Details

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• Page Count 9
• Subject Science

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