Rate Of Reaction Investigation
D. Crowley, 2008
Friday, November 04, 2011
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
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 Time for test tube to fill with H2 (sec)
Mg (g)
1 1 2 3 Average
2
3
4
5 etc…
Results - Volume
Volume Time for test tube to fill with H2 (sec)
HCl (cm3)
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
35
Time Taken For Test
Tube To Fill (sec)
30
25
20
15
10
5
0
0 1 2 3 4 5 6
Mass Mg (g)
Graph
Rate Of Reaction Between Mg + HCl
30
Time Taken For Test
Tube To Fill (sec)
25
20
15
10
5
0
0 10 20 30 40 50 60
Volume HCl (cm3)
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?