Rate Of Reaction Investigation

D. Crowley, 2008

Rate Of Reaction Investigation

Your task is to investigate what affects the rate of reaction between magnesium ribbon and hydrochloric acid

As you complete this experiment you need to think how you can make this test a fair one, how you can be accurate and precise, and how you can ensure the results are reliable

Wednesday, April 19, 2023

Initial Experiment

Set up an experiment with 5ml hydrochloric acid in a test tube

Add a small amount of magnesium ribbon to this, and place your thumb over the top

Finally take you thumb off the top, and quickly place a lit splint over top of the test tube

Initial Experiment

What caused the squeaky pop?

Can you write a word / symbol equation for the reaction?

Many metals react with acids – producing the gas hydrogen

A burning splint is the test for this, producing a squeaky pop when it ignites

Magnesium + Hydrochloric Acid → Magnesium Chloride + Hydrogen

Mg + 2HCl → MgCl2 + H2

Balloon

Many metals react with acids – producing the gas hydrogen

A burning splint is the test for this, producing a squeaky pop when it ignites

Watch the balloon hydrogen demo…

Initial Questions

Different reactions can happen at different rates: - Reactions that happen slowly have a low rate of reaction Reactions that happen quickly have a high rate of reaction

Initially you need to brainstorm what could affect the rate of reaction between the magnesium and the hydrochloric acid: - What does the reaction need to take place (what are the

reactants) How could you compare the rate of reaction if you

changed some of the independent variables

Initial Questions

The rate of a reaction can be measured by measuring the rate that a reactant is used up, or by measuring the rate that a product is formed

Temperature, concentration, pressure of reacting gases, surface area of reacting solids and the use of catalysts are all factors which affect the rate of a reaction

*A catalyst changes the rate of a reaction, without being used up itself

Key Words

During your investigation you will come across some key words: -

Accurate: a measurement that is close to the true value (accuracy can be increased by controlling the key variables)

Precision: this is a more precise measurement, which can be achieved by using a smaller scale

Reliability: the experiment needs to be repeatable – if someone else did the experiment then they should get exactly the same results: this comes from repeating your experiment

Dependent variable – what is changed by the experiment (what you are going to measure)

Independent variable – what you change

Control variable(s) – what you are going to keep the same, making the experiment more accurate

Introduction

Initially write you introduction for the rate of reaction investigation

Note your aim (what we are doing); why we are doing it and what tests which will carry out and why

I.e. What does the reaction need to take place (what are the

reactants)? How could you compare the rate of reaction if you

changed some of the independent variables? What is it you are going to measure?

Method

Your task is to now consider what methods you are going to use to measure the rate of reaction between the Mg + HCl

How are you going to make your experiment: - Accurate (as close to the true value as possible) Reliable (so someone else can repeat this experiment and get similar

results) Precise (how many readings are going to be taken and how can you ensure

each repeat is completed in the same way)

Complete a step-by-step guide to completing your experiment

Note your independent variable (thing you change) and how you will change this

Note your dependent variable(s), and how you will measure this

What data are you collecting / recording

Method

You need to complete two experiments: initially changing the mass of magnesium (experiment 1) and then changing the amount of hydrochloric acid (experiment 2)

Submerge a test tube in a tub of water, ensuring the test tube is filled completely

Measure the mass of magnesium (keeping all other factors the same) and add this to a conical flask with the delivery tube going into the test tube

Record how long it takes for the test tube to fill up with hydrogen gas, and then repeat…

For the second experiment keep everything the same (including a known mass of magnesium) but this time add different volumes of hydrochloric acid to the conical flask

Prediction

What do you expect will happen when you change the independent variable

Can you explain what will happen, and why you think this

E.g. I think that when I change the… the… will… because…

We should find a difference in the rate of reaction based on the mass of magnesium / volume of hydrochloric acid – both an increased mass and volume should increase the rate of reaction, if these are currently limiting factors

Apparatus Order Form

Finally, you will need to order all the apparatus your require to carry out this experiment

Ensure you have thought of everything, and just as importantly you must identify how much equipment you need – e.g. 5g magnesium ribbon; 1x conical flask; 50cm3 1M hydrochloric acid etc…

Your apparatus form must be signed off before it will be given to the laboratory technicians

Results

Produce a results table for the two experiments (how mass of magnesium and volume of hydrochloric acid affects the rate of reaction)

Remember to include your units and how many repetitions you will be doing

Results - Mass

Mass of Mg (g)

Time for test tube to fill with H2 (sec)

1 1 2 3 Average

2

3

4

5 etc…

Results - Volume

Volume HCl (cm3)

Time for test tube to fill with H2 (sec)

10 1 2 3 Average

20

30

40

50 etc…

Experiment

You have this lesson to complete your experiments

Remember to be as accurate and precise as possible, repeating an appropriate amount of times and recording your results

You will also need to calculate all the averages this lesson for your results

Conclusion

Your task is to graph your results – one graph for the mass and one for the volume changes

A scatter graph is most suitable – mass of Mg / volume of HCl on the x axis, and time taken for the test tube to fill (seconds) on the y axis

Remember to add a title; units etc…

Once you have drawn your graphs you need to complete an analysis – what do the results show you / why do you think this is?

Graph

Rate Of Reaction Between Mg + HCl

0

5

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35

0 1 2 3 4 5 6

Mass Mg (g)

Tim

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Fil

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ec)

Graph

Rate Of Reaction Between Mg + HCl

0

5

10

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0 10 20 30 40 50 60

Volume HCl (cm3)

Tim

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Evaluation

Finally you need to complete an evaluation – were there any anomalous results?

What errors may have caused these: - Random error (happens occasionally) Systematic error (same mistake occurred every time (likely due to you

measuring this incorrectly)

How accurate was your experiment – did you consistently get the same results?

Was your method fair allowing you to collect accurate results?

Do you have enough reliable evidence to support the conclusion that you have made

What improvements would you do if you could repeat this experiment?