Rates of reaction

Expected qualitative observations:

• The colour of copper sulphate is blue and therefore it will change colour when a reaction takes place as it will get displaced.
• Copper will be displaced as a product of the reaction, thus, a brownish precipitate of copper will be formed as the reaction takes place.
• During any reaction if the beaker is touched, it will be warm since the reaction is exothermic. Moreover, it will be the hottest when the reaction between magnesium and copper sulphate takes place.
• The reaction between magnesium and copper sulphate will be very vigorous and therefore with temperature, one can also expect to see a lot of effervescence and also hear a fizzy noise.

Graph of expected results (rise in temperature):

The rise in temperature for each of the metal powders to be used is shown after a period of 2 minutes for each reaction. The graph above shows that the reaction with magnesium is the fastest whereas the reaction with iron is the slowest. This reaction started at about 27ºC. Moreover we also see that the reaction with magnesium took the shortest time to complete.

Variables:

Constant:

• Concentration of CuSO4 solution, therefore1 mol was kept constant by not diluting it and getting incorrect results.
• Surroundings (temperature at r.t.p, pressure) kept constant by performing all the trials in the same room and at the same place.
• Volume of CuSO4 solution i.e. 20cm3 kept constant by using a measuring cylinder for measuring out the amount used for each reading.
• Time interval to check the temperature rise i.e. 120 seconds
• Mass of the four metal powders i.e. 0.05g kept constant by measuring out the masses using a digital weighing scale reducing errors.

Independent variable:

• The Metal powders used i.e. Mg, Al, Zn and Fe.

Dependant variable:

• Temperature change when each of the metals reacts with copper sulphate in a given period of time.

Apparatus:

• 4 glass beakers (range 0-100ml)
• Aqueous Copper sulphate solution- 1mol/dm3, around 80ml.
• Analogue thermometer (range 0-110, uncertainty ± 0.1 oC)
• Pure magnesium powder- 0.1g
• Pure aluminium powder- 0.1g
• Pure zinc powder- 0.1g
• Pure iron powder- 0.1g
• Measuring cylinder (range 0-100cm3)
• Stopwatch (uncertainty: ±0.1s)
• Measuring cylinder (range 0-100cm3)
• Digital weighing balance

Fair Test:

• More reactive metal powders which react vigorously with oxygen should be kept away from air and they should be removed and weighed just before the reaction to prevent anomalies.
• All equipment should be dry before the reaction so that less anomalies occur.
• The thermometer should be immersed correctly in the copper sulphate so that inaccurate results are avoided.
• All readings should be taken at eye-level so that the reactions can be done accurately.

Safety precautions:

• Wear safety goggles to prevent any outside, harmful substances from entering the eye and damaging it.
• Some of the reactions are extremely vigorous and exothermic and therefore should be kept at safe distance from the reaction that is taking place.
• Use the glass equipment carefully since it is breakable.

Procedure:

• Measure out 20ml of copper sulphate in each of the four 100ml beakers using a measuring cylinder.
• Weigh out 0.1g of each of the four metal powders using the digital weighing scale.
• Measure the temperature of the aqueous copper sulphate solution before starting the reaction.
• Add the metal powder to the copper sulphate solution and start the stopwatch immediately.
• Record the temperature at intervals of 10seconds till 120 seconds. There should be 12 temperatures at the end of 120seconds.
• Repeat the procedure for each of four metal powders and record all the results in a table.
• Take 2 trials for each of the reactions for better accuracy.
• If any anomaly is seen, repeat the experiment to correct it and to get accurate results.

Qualitative analysis (observations):

General observations:

• The copper sulphate has a deep blue colour and is an odourless solution.
• Magnesium is a fine powder, it is blackish- grey and has a non- shiny appearance and has a very low density.
• Aluminium is a dark grey powder with a shiny appearance. It is not a fine powder and has a low density.
• Zinc is a fine grey powder with a non-shiny appearance. It is a dense substance
• Iron is a metallic grey powder with a shiny appearance. It is not a fine powder and has a high density.

Reaction 1: Mg  +  CuSO4 → MgSO4  +  Cu

• As seen the reaction was a very vigorous and exothermic.
• Vapours were given out during the reaction.
• There was a lot of effervescence and a fizzy noise was heard during the reaction..
• The colour of blue copper sulphate quickly changed to dark green.
•  When the beaker was felt after the reaction, it was very hot which tells us that the reaction was very exothermic.
• The reaction is highly exothermic and the mercury rose very fast in the analogue thermometer.
• The copper displaced cannot be seen at all since its colour is much lighter than that of magnesium sulphate.
• During the reaction there was a pungent colour coming out from the vapours.

Reaction 2: 2Al   +  3CuSO4  → Al2(SO4)3  +  3Cu

• There is evidence of a small rise in the temperature.
• When aluminium is poured into the beaker containing copper sulphate, a very slow reaction takes place.
• At the end of 120 seconds, the temperature drops again showing that the reaction has stopped.
• No effervescence or smoke can be observed during the reaction.
• There is no odour given out during the reaction.
• The reddish copper displaced floats on the surface of the beaker.
• Copper sulphate solution does not change its colour because it is not completely used up at the end of the 120 seconds.
• The aluminium has a layer of aluminium oxide which is heavy and settles down in the beaker.

Reaction 3:  Zn  +  CuSO4  → ZnSO4  +  Cu

• Although there is no smoke coming out, effervescence can be observed during the reaction.
• When the zinc powder is poured into the blue copper sulphate solution, a vigorous reaction takes place.
• The temperature starts rising as soon as the reaction begins. However, at the end of the reaction, it does not rise by a very high margin.
• The copper sulphate does not completely change colour at the end of 120 seconds since it is not completely used up.
• There is a slightly pungent odour given out during the reaction.
• Since zinc sulphate is white in colour, it is not visible in the copper sulphate solution.
• The beaker becomes very warm during the reaction showing that the reaction is exothermic.
• The copper displaced is reddish in colour and it floats on the surface of the beaker.

Reaction 4: Fe  +  CuSO4  → FeSO4   +  Cu

• The copper sulphate does not change colour since it is not completely used up at the end of 120 seconds.
• There is hardly any effervescence and there is no odour given out.
• The reaction of copper sulphate with iron is quite slow from the start.
• There is a slight rise in temperature at the end of 120 seconds and the beaker feels warm when touched during the reaction.
• The dark precipitate of ferrous sulphate settles down at the bottom of the beaker.
• There is no odour given out during the reaction.
• The copper produced is reddish in colour and floats on the surface of the beaker.

Results:

Reaction 1: Magnesium with copper sulphate

Reaction 2: Aluminium with copper sulphate

Reaction 3: Zinc with copper sulphate

Reaction 4: Iron with copper sulphate

Graphs:

Graph analysis:

The graph above shows us the different changes in temperatures with different metal powders. It is a representation of the experiment performed above. Therefore the higher the temperature rise the more reactive the metal is. Therefore we can see that the line of the magnesium reaction is the steepest and is therefore the most reactive. Whereas, the line of the reaction with aluminium is the least steepest and is therefore the least reactive. But practically it is seen that even the reaction with the aluminium should have been vigorous, but was not as it had a very slight rise in temperature. This could be because the aluminium had an aluminium oxide layer which prevented the reaction to take place. It was also shown that the zinc was more reactive than iron.

Evaluation:

There were certain errors, which led to certain anomalies and these errors could be:

• The more reactive metals were not kept in air tight containers and therefore could have reacted with the oxygen and caused major anomalies in the reaction.
• The analogue thermometer is not very sensitive and do not change due to temperature changes and therefore could cause certain anomalies.
• The stopwatch was not stopped exactly at 120 seconds thus causing some inaccuracy in the results obtained.
• The volume of copper sulphate was measured using a measuring cylinder instead of a burette for better accuracy.

Improvements:

• The metal powders should have been kept in air-tight containers so that they do not react with the oxygen in the air and therefore cause errors in the experiment.
• A digital thermometer could have been used instead of an analogue thermometer so that the temperature rises could have been recorded more accurately.
• The copper sulphate could have been poured into the beaker using a burette or pipette instead of a measuring cylinder to get a more accurate result.

Conclusion:

After performing the experiment it can be concluded that the rate of reaction increases as you go up the reactivity series. From the results shown above magnesium is the most reactive followed by zinc, iron, and then aluminium. Therefore my hypothesis is proved right which was that as you go down the reactivity series the rate of reaction decreases.