Rate Of Reaction Investigation

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					Rate Of Reaction Investigation

                                 D. Crowley, 2008
                                                 Friday, June 22, 2012

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
   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
        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

       Independent variable – what you change

       Control variable(s) – what you are going to keep the same, making the experiment
        more accurate
   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
          How could you compare the rate of reaction if you
           changed some of the independent variables?
          What is it you are going to measure?
   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
      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
   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

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

   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



5 etc…
Results - Volume

 Volume     Time for test tube to fill with H2 (sec)
HCl (cm3)

   10       1           2             3         Average



50 etc…
   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

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

                                    Rate Of Reaction Between Mg + HCl

Time Taken For Test
  Tube To Fill (sec)

                            0   1           2           3          4    5   6
                                                   Mass Mg (g)

                                 Rate Of Reaction Between Mg + HCl

Time Taken For Test
  Tube To Fill (sec)

                            0   10       20         30           40   50   60
                                              Volume HCl (cm3)
   Finally you need to complete an evaluation – were there any anomalous

   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

   Was your method fair allowing you to collect accurate results?

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

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

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