Report Repo rt on a Facto actor r Infl Influe uenc ncin ing g the the Posi Positi tion on of Chem Chemic ical al Equilibrium Research Question: How does the temperature affect the position of chemical equilibrium Independent variable: The temperature of the solution Dependent variable: The position of chemical equilibrium Controlled variable: ·The concentration of the dilute hydrochloride hydrochloride acid ·The surface area of reactants ·The pressure and temperature of the room ·The mass of the zinc ·The time for the reaction to take place How to control: Concentration of HCl: keep 1.0M Surface area: use zinc granule for f or reactants Press Pressur ure: e: the lab’s lab’s press pressur ure e won’t won’t change change enough enough to affect affect the reaction rate Mass of the zinc: 2.0 g each time The apparatus and chemicals: ·100 ml cylinders ·Dilute hydrochloride hydrochloride acid (1.0M) ·Zinc granule ·Delivery tube, trough, water, measuring cylinder (100 mL), cork, frosted glass plate. ·Gas collecting bottle, round bottom flask ·Electronic-weighting ·Electronic-weighting system ·Alcohol burner, iron pedestal, asbestosed wire gauze ·Timer Hypothesis: The reaction which used zinc powder will react more quickly than the reaction by using the zinc piece. Chemical equation: Zn(s)+2HCl(aq Zn (s)+2HCl(aq)) → ZnCl2(aq)+ H2 (g) Procedure: 1. Set up the apparatus as the graph shows. 2. Measure the total volume of the round bottom flask. 2. Use electronicelectronicweight system to get the 2g zinc powder.
3. Put the zinc powder into a conical flask. 4. Use 100 ml measuring cylinder to measure 30ml 1.0M HCl (which is in excess) 5. Enkindle the alcohol burner and heat the root of the conical flask which placed on the asbestosed wire gauze a. 6. Drop the 30mL of dilute hydrochloride (excess) acid into the conical flask. 7. Connect the delivery tube to the measuring cylinder which is the same and full of water. At the same time, use the timer to count time. 8. Stop timer until it shows four minutes. 9. Repeat steps 1-7 for another two times. 10. Repeat step 3-8 with the same mass of zinc pieces and zinc granule. 11. Collect the data into the table and process with the data.
Trai T(Time) l s ±0.2s 1 2 200. 3 0 Trai T(Time) l s ±0.2s 4 5 200.0 6 Trai l
T(Ti me)s ±0.2 s
1 2
200. 0
3 Trai l
T(Ti me)s ±0.2 s
M(Zn) powd er ±0.00 2g 2.011
Raw Data V1(HCl) M(Zn) V2(original V3(Water ml granule Water)ml rest) ±1ml ml±1ml ±1ml ±0.002g 2.011 113 2.011 110 30 150 2.011 109 V1(HCl) M(Zn) V2(original V3(H2) ml ml powder Water)ml ±2ml ±1ml ±1ml ±0.002g 2.017 49 2.017 59 30 150 2.017 66 Processed Data V1(origi V2 V3(H2 r(React Δr Perce nal (Water ) ml ion ml/s ntage Water)m rest) ml ±2ml rate ) of Δ r l ±1ml ±1ml ml/s ml/s 113
37
0.185
2.011
110
40
0.2
2.011
109
41
0.205
V3(H2 ) ml ±2ml
r(React ion rate ) ml/s
150
M(Zn) powd er ±0.00
V1(origi nal Water)m l ±1ml
V2 (Water rest) ml ±1ml
0.00 8 0.00 8 0.00 8 Δr ml/s
5% 4% 4% Perce ntage of Δ r ml/s
4
2g 2.017
101
49
0.245
0.00 3% 9 200. 150 5 2.017 91 59 0.295 0.00 2% 0 9 6 2.017 89 66 0.33 0.00 2% 9 The uncertainties of the Time and the Mass of the Zn are the reading errors, so we chose the half of the minimum of the measuring. And the volume of the H2 is the difference form V1 and V2, and the r is the radio of the V3 and Time. Example of Calculation 2.073g zinc granule reacts with 30ml HCl solution which concentration is 1M in four minutes. V3=V1-V2=150ml±1ml-113ml±1ml= 37ml±2ml Reaction rate=Δc/t=ΔV/t=V3/t= (37ml±2ml)/(200s±0.2s)= 0.185 ml/s±0.008 ml/s The Percentage of the reaction rate= (1ml/150ml+1ml/113ml) =5% ：
Conclusion and Evaluation: In this experiment above, the surface area of the zinc increase, the reaction rate increase. During the experiment: 1. There are differences in the mass of the Zinc. Because it was hard to control the amount of zinc powder and zinc granule when weighing, so that would also affect the surface area of the zinc and the reaction rate. Improvement: It was hard to control the mass of the zinc powder and granule totally the same, but we may try measure them several more times to achieve more accuracy. 2. We used the 1-100Ml measuring cylinder to measure the volume of the HCl (30ml), it would decrease the accuracy of the data. 3. The powder of the zinc sticks with the paper when we poured it into the container. Improvement (2-3): If there is enough apparatus in the lab we should use 1-50Ml measuring cylinder instead. 4. Some of the zinc powder combine together and became smaller particles when we put them into the round- bottom flask, it would affect the surface area of the zinc powder which would become smaller. 5. When we pour the HCl solution in to the container, some of the solution wasn’t poured into the container because we did it
hurriedly, so some spilled out or still left in the measuring cylinder. Improvement: DON’T do the experiment in a hurry, try to complete every step in a fine way. 6. After finish one reaction, we poured the wasting into the wasting cup, and cool down the container with the cold water. However, as we used the alcohol burner during the experiment, the temperature of the surrounding got higher, it would increase the reaction rate slightly, and so we can see the reaction rate of the zinc powder or zinc granule increase as the process of the experiment. Improvement: We need prepare more than 2 or 3 container in order to keep the initial temperature of the container and reactant the same. And also we should open the door, the window and the electrical fan in order to cooler the temperature in the room and won’t affect the result of the experiment too much, or we can increase the time between we change one experiment to the other. 7. When we did the trail 4, the previous alcohol burner was running out, and the flame became weaker. So we can suppose that this time the reactants didn’t receive the same amount of heat as the previous ones. It caused the amount of the rest of the water was much smaller than the others. Improvement: Use another alcohol burner contains full alcohol instead of the original one to keep the reactant receive almost the same amount of heat. The design of the experiment: At first we used the apparatus which the graph showed below for the reaction to occur, but we found there were only few bubbles through the delivery tube in four minutes and it would affect the result. So we changed our design and decided to increase the temperature for each time the reaction occurring. Then we could make more bubbles successfully and the data were more accurate.
During the Calculation: 1. We use the ratio of the volume of the H2 formed (instead of the concentration change of the H2) and time taken to compare the reaction rate.
