The acid restricts the number of collisions.
PRELIMINARY EXPERIMENT No.1
Investigating the effect of changing the concentration of hydrochloric acid.
EQUATION:
2HCL + CaCO3 »» CaCl2 + CO2 + H2O
(aq) (aq)
We measured the volume of carbon dioxide produced every 10 seconds for 120 seconds. We measured 10cm3 of acid (100%) 5cm3 acid with 5cm3 water (50%) 2.5 cm3 acid with 7.5cm3 of water (25%)
Results of preliminary experiment.
Concentration of acid
Time (secs) 100% 50% 25%
10 3 1 0
20 5 2 0
30 7 4 0
40 10 5 0
50 13 7 0
60 17 10 0
70 21 13 0.5
80 25 16 1
90 28 19 1
100 32 21 1.5
110 35 23 2.5
120 39 25 4
These results support the prediction as the concentration of HCL acid decreases so does the rate of reaction.
PRELIMINARY EXPERIMENT No.2
To investigate the effect of changing the concentration of Sodium Thiosulphate on the rate of reaction between sodium Thiosulphate and HCL.
NA2S2O3 + 2HCL »» S + 2NaCl + SO2 + H2O
PREDICTION: the higher the concentration of sodium Thiosulphate the quicker the rate of reaction
Apparatus
Conical flask 250ml
Stopwatch
Paper with cross drawn on it inside a plastic wallet
50ml measuring cylinder
10ml measuring cylinder
Pipette
Thermometer
Safety
Tuck in tie
Hair tied back
Stools and bags tucked under tables
Wear goggles
METHOD:
- Set up apparatus as shown in diagram above.
- Put the correct concentration of s.thio in flask. As you add 10cm3 of HCL to flask start stopwatch.
- Watch for the solution to cloud over. When the cross disappears stop the stopwatch.
- Record results and repeat 1-3 times for other concentrations.
3 concentrations of sodium Thiosulphate were investigated
solution time
thio : water 1 2 average
50:0 26.06 26.06
25:25 53.63 52.75 53.19
10:40 3.00.72 180.72
rate = 1/time to get an easier number to plot multiply this by 100
Time taken for cross to disappear
As the concentration of sodium Thiosulphate decrease the time taken for the cross to disappear increases. This is an inverse relationship.
This is what a graph would look like if the results for this were plotted
Rate = concentration of Thiosulphate / time
From my preliminary experiments I have learned that I can improve my method and improve the accuracy of my results.
I have found that my range of concentrations doesn’t give me good enough results to back up my prediction. I only used 3 concentrations and only repeated them once each. In the final experiment I will use a range of 5 concentrations and repeat each 3 times. This will allow me to plot more points on any graphs I make from the results.
Also the accuracy of measurements may be the cause of poor results. To gain precise volumes I use a pipette and the right size-measuring cylinder.
Also the temperature of the room can affect the rate of reaction. To see this I can take the temperature at the beginning and end of the experiment.
To investigate the effect of changing the concentration of sodium Thiosulphate on the rate of reaction between sodium Thiosulphate and hydrochloric acid.
Apparatus and diagram (see preliminary experiment No.2)
Safety
Wear goggles to prevent damage to eyes from splashes
Tie back hair and tuck in tie
Bags and stools under tables to prevent falling over.
Report spillages and breakages to a teacher
Concentrations that are going to be used:
Vol : vol ratio
Thio : Water
50 : 0
40 : 10
30 : 20
25 : 25
20 : 30
10 : 40
0 : 50
Method:
- Set up apparatus as in preliminary experiment.
- Record the temperature of the room.
- Add the first of the concentrations of sodium Thiosulphate to the flask. As you add 10cm3 of HCL and start the stopwatch
- Watch the solution as it clouds over. Once the cross has disappeared stop the clock.
- Record the time in a results table
- Repeat the above steps for the other concentration of sodium Thiosulphate. Repeat the experiment 3 times for each of the concentrations.
- Record all results in a table and work out the rate by dividing 1 by the average time for each.
Variables
Concentration of thio
Temperature
Stirring
Volume of reactants HCL (10cm3) = thio (50cm3)
Catalyst + or –
Height of eye above cross
Same person to watch over cross each time
Precision of measurements
Constant variables
Volume of reactants
Height of eye above cross
Stirring
Results (see table)
Graphs
Graph 1 shows that as the concentration increase so does the rate of reaction. This is a directly proportional relationship. As one increases so does the other. The graph is quite accurate. The points plotted lie on or are close to the line of best fit.
Graph 2 shows that as the concentration on Sodium Thiosulphate increase the time taken for reaction to take place decreases. This is an inverse relationship.
Conclusion
As the concentration of Sodium Thiosulphate increases the rate of reaction does so too and the time taken for a reaction decreases. This is because as the concentration increases you are increasing the number of reactions that can take place in a certain time. The increase in the number of Thiosulphate particles results in more particles to collide and react with the acid. This means more product is made in a shorter time( see particle theory in plan) the conclusion does agree with my prediction made. My experiment wasn’t as accurate as others as the equipment did not include things such as a light sensor. Overall the experiment proved a success and the results support my answer. I was able to produce graphs and draw a line of best fit.
Evaluation
I data I obtained from the experiment was as accurate as it could be and was fairly reliable. My method could have been made more reliable by using a light sensor.
You find out at what light level the sensor records when solution is completely clouded over. You then do the experiment and record the time taken for it to reach this point and repeat for all concentrations.
My results could be slightly off due to bad measuring. I tried to use cylinders of correct sizes for each volume, as it would be stupid to use a 10cm3-measuring cylinder to measure 50cm3. Water would be lost or trapped and so the accuracy would be poor. For measuring a 50cm3 you would use a 50cm3-measuring cylinder.
My graphs were accurate and all points were close to or on the line of best fit. I had no clearly anomalous results. This could be due to good measuring and the consistency of fixed variables. The temperature of the room could also effect them as heat can speed up reaction times. To check for changes I recorded the room temperature at the beginning and end of the experiment. There was no considerable different between them. The temperature of the water could also make a difference. I didn’t measure it but it could be an improvement I could make in future. The water was from the tap and may alter in temperature. To prevent this I could use a beaker with water in so that the water would be room temperature or use a thermometer controlled water bath.
My results weren’t very reliable because on each repeat of the concentration I got a different time outcome. None of the readings were exactly matched but then there weren’t any clear anomalous results. The end point of was hard to judge so we tried to prevent this each time by using the same person to watch the solution. I could have used a light sensor to improve this further.
I used a clean dry flask for each of the repeat and concentration as water droplets may dilute the solution more preventing accurate results. Ideally I would repeat the experiment again with the improvements in place and use higher concentration range of 8 concentrations. This pattern in the data supports my prediction.
