The concentration can be increased or decreased to effect the rate of reaction. The higher the concentration, the more particles, therefore a higher rate of reaction.
The surface area of magnesium can effect the rate of reaction. The larger the surface area, the faster the reaction will be as the particles of the magnesium are more accsessable and more spread out therefore there are more frequent collisions.
The temperature can effect the rate of reaction. A higher temperature gives the particles more energy, therefore the rate of collisions becomes more frequent.
Addind a Catalyst can also effect the rate of reaction. Adding a catalyst to a reaction will speed it up without adding or taking anything away from it.
Variables
The independant variable is the thing in the experiment that we will be changing in order to get the results. The independant variable for this experiment is the concentration. Therefore the other variables need to stay the same. The length of the magnesium will be kept the same at 4cm, this can be made accurate every time by measuring it with a ruler. The amount of acid will also be kept the same by measuring it in a measuring cylinder. The surface area will stay the same as we are using a Magnesium strip each time. I will not use a catalyst in the reaction as the reaction would go too quickly. It will be hard to keep the temperature the same as the reaction is exothermic which means the solution will heat itself through the reaction. To try and keep the temperature at one level i will measure the temperature before and after and check that the increase in temperature each time is the same.
Prediction
I think the rate of reaction will be much faster in a higher concentration as there are more particles in a level of higher concentration, so therefore more successful collisions. If i use 2 Molar instead of 1 Molar the rate of reaction will also be faster as there are twice the amount of particles in 2 Molar.
Concentration Values
The concentration values i am going to use are:
Upper Limit
Lower Limit
Length of Magnesium: 4 Cm
Concentration of Hcl Acid: Start with 20cm3
To get 1.75m add 2.5 cm3 of water
To get 1.5m add 5cm3 of water
To get 1.25m add 7.5cm3 of water
To get 1.0m add 10cm3 of water
To get 0.75m add 12.5cm3 of water
I am going to measure the amount of Hydrogen produced every: 10 seconds
Tables of Results
Time Volume of gas cm3 Average Concentration = 1.75
1 2 3 Start Temp = 29°
10 15 30 19 17 End Temp = 31°
20 35 45 35 35
30 50 48 46 48
40 52 55 53
50 60
60
70
Time Volume of gas cm3 Average Concentration = 1.5
1 2 3 Start Temp = 30°
10 30 7 15 11 End Temp = 33°
20 40 28 34 31
30 60 40 48 44
40 65 43 55 49
50 65 51 59 55
60 70 53 63 58
70
Time Volume of gas cm3 Average Concentration = 1.25
1 2 3 Start Temp = 30°
10 19 12 10 End Temp = 33°
20 38 35 29
30 54 45 41
40 65 53 46
50 72 58 53
60 61
70
Time Volume of gas cm3 Average Concentration = 1.0
1 2 3 Start Temp = 28°
10 10 15 8 End Temp = 32°
20 20 23 21
30 32 33 32
40 43 44 43
50 55 53 52
60 54 54 54
70 56 56 56
Time Volume of gas cm3 Average Concentration = 0.75
1 2 3 Start Temp = 29°
10 2 0 2 End Temp = 31°
20 8 4 6
30 13 6 7
40 12 8 10
50 12 12 12
60 13 13 13
70 14 15 15
From my results i have found out that the 1.75 acid affected the rate of reaction the most as compared to the other times it was much quicker. When I plotted my graphs using these results it proves my prediction was correct and that a higher concentration speeds up a reaction. I can see this as the higher the concentration the steeper the gradient.
The rate of reaction can be worked out using this equation:
Measure rate at 10seconds = Volume of gas made in 10seconds
10seconds
Gradient = Y
X X = First 10 Seconds
Evaluation
My results prove to be very reliable. I can see this by using the grapght that i have plotted using my results. The results, when plotted onto a graph show that as time goes on, the amount of gas increases. The results form a curv which also proves that the results are reliable. Also the points plotted onto the graph group arounf the line of best fit. The tables which i wrote the results into also show that the results are reliable as they are similar.
There were some sources of error in the experiment. One of these was the measurments of the gas. In our preliminary work we used 2cm of Mg, this made the experiment too fast, we also used 2cm Acid but that too was too fast.
The temperature effected the experiment. The temperature cannot be controlled completelt and changes automatically on its own. The increase in temperature during a reaction causes the rate of reaction to increase.
Overall the experiment went well and the results i found were reliable, but there could have been a few changes to the experiment which could of made it a little bit more accurate. The magnesium strips could have been made pure by scraping the impurities from them so that we are left with just pure magnesium also the measurments of gas could have been more accurate with the use of a gas siringe which measures out an exact amount of gas. The readings could have also been made more accurate if we got down at eye level with the tube and got the exact readings at teh time needed.
