Rate Of Reaction Investigation

1. Rate Of Reaction Investigation D. Crowley, 2008

2. 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

3. 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

4. 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 popwhen it ignites Magnesium + Hydrochloric Acid→ MagnesiumChloride + Hydrogen Mg + 2HCl→MgCl2 + H2

5. Balloon • Many metals react with acids – producing the gas hydrogen • A burning splint is the test for this, producing a squeaky popwhen it ignites • Watch the balloon hydrogen demo…

6. 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

7. 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

8. 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

9. 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?

10. 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

11. 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

12. 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

13. 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

14. 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

15. Results - Mass

16. Results - Volume

17. 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

18. 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?

19. Graph

20. Graph

21. 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?