Rate of Reaction- P&D
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Name: Jamal Dow Class: L6’O Date: 15/04/16 Title: Rate of Reaction- Plan and Design Problem Statement: You went to the hairdresser and noticed that the hydrogen peroxide was kept in the refrigerator. Suggest a hypothesis for the storage of the hydrogen peroxide and design an experiment to test tour hypothesis.
Hypothesis: The decomposition of hydrogen peroxide increases with increase in temperature.
Aim: To investigate the effect of temperature on the rate of decomposition of hydrogen peroxide and where it should be stored.
Theory: The rate of a chemical reaction can be regarded as the change in concentration of the reactant or product for the reaction with respect to time. The graph that shows the change in concentration over time is therefore known as a rate curve. The rate of the reaction at any instant in time is given by the gradient of the curve at that instant. The gradient of the curve is found by drawing the tangent to the curve at that point and taking its gradient. The tangent at time zero is called the initial rate. The gradient of this tangent is steepest of any taken along the rate curve; this means the reaction is fastest at the start. The rate of a reaction can be affected by pressure, size of the solid particles, temperature, catalyst and other factors. Equation for the decomposition of hydrogen peroxide is shown as: 2H2O2(aq) 2H2O(l) + O2(g) However, hydrogen peroxide is somewhat unstable. It decomposes at room temperature to yield oxygen. Peroxides are sensitive to heat and the rate of decomposition is greatly accelerated by substances including acids, bases and transition metal ions. For example, hydrogen peroxide decomposes very slowly by itself to form water and oxygen, however, in the presence of manganese (IV) oxide, the reaction is very rapid; it provides a different reaction path with lower activation energy hence the rapid occurrence. Lower activation energy then leads to a greater proportion of the particles colliding successfully and therefore reacting. The volume of gas given off in a reaction can be measured at various time intervals using a gas syringe. The volume of oxygen produced from the decomposition of hydrogen peroxide could be used to monitor changes in the rate of this reaction.
Materials/Apparatus: 2 moldm-3 hydrogen peroxide solution, powdered manganese (IV) oxide, distilled water, stopwatch, spatula, (4) 250cm3 conical flask, rubber bongs with delivery tube, graduated gas syringe, electronic scale, thermometer, water bath, Bunsen burner, (4) 500cm3 beakers.
Figure 1.0: Apparatus set up to determine the effect of temperature on the rate of decomposition of H2O2(as).
Method: 1. Pour 100cm3 of distilled water into the beaker and gently heat until the temperature of the water bath reaches 20 ℃ . 2. Add 25cm3 of the hydrogen peroxide in a conical flask. Place the conical flask in the water bath then add 1g of powdered manganese (IV) oxide to the hydrogen peroxide and mix. 3. Immediately connect the gas collecting apparatus as shown in figure 1.0 and start stopwatch. 4. Record the volume of gas collected in the syringe at 10 second intervals from the start of the reaction until 8 sets of readings are obtained. 5. Use the results to plot a graph of volume of gas evolved against time. 6. Repeat steps 1-5 at 30 ℃ , 40 ℃ and 50 ℃ . 2
Variables: Controlled: Concentration and volume of the hydrogen peroxide, mass of Manganese (IV) oxide added. Manipulated: Temperature. Responding: Initial rate of reaction.
Expected Results: Table 1.0: Showing the volume of oxygen gas produced during the course of the experiment with increase in temperature. Temperature/ oC o
20 C Time/ s
Vol. of gas/ cm3
30 C Time/ s
Vol. of gas/ cm3
Vol. of gas/ cm3
50 oC Time/ s
Vol. of gas/ cm3
Treatment of Results: Plot a graph of volume of gas produced vs time for each temperature. A curve ought to be obtained when the graphs are plotted. Find the gradient of the curve by drawing a tangent to the curve. The initial rate is equal to gradient (cm3s-1). Compare the initial rates for the decomposition of hydrogen peroxide at 20 ℃ , 30 ℃ , 40 ℃ and 50oC. Hence determine where the hydrogen peroxide should be stored.
If the initial rate increases with increasing temperature, then the rate of decomposition of hydrogen peroxide increases with increasing temperature and the hypothesis is valid. If the initial rate decreases with increasing temperature, then the rate of decomposition of hydrogen peroxide decreases with increasing temperature and the hypothesis is invalid.
Assuming enough catalyst is added to produce a measurable amount of oxygen gas within time frame allotted and the temperatures at which the decomposition is taking place is enough to give
Sources of Error:
When the conical flask containing hydrogen peroxide is added to the water bath (at a higher temperature) the decomposition may begin and some gas may be lost. As a result, the initial rate calculated may not be very accurate.
As the temperature at which the experiment is being increased so does the evaporation of the water being produced, thereby unavoidably increasing the volume of gas collected in the syringe with respect to time (rate). Therefore, giving a ‘false’ increase of the rate of decomposition.
Ensure the rubber bung or stopper is firmly corks the top of the conical flask to prevent minimal escape of gas.
References: “Rates of Reactions” in Chemistry for Cape by Maraj S. and Arnold Samai pg.116, Caribbean Educational Publishers 2009. Definitions- “Rates of Reaction” in AS and A Level Chemistry by Lewis E. and Martyn Berry pg. 292, Pearson Education Limited 2000 Chemistry A Caribbean Examinations Council Study Guide (2012 Edition), Publisher- Nelson Thornes Ltd., Location- Cheltenham, United Kingdom, AuthorsRoger Norris, Leroy Barrett, Annette Maynard-Alleyne and Jennifer Murray. PAGE 77, 80 and 81.