Rates of Reaction

• 2Moler concentrated Hydrochloric Acid of 10ml in a test tube
• Water in a water bath at temperature of 30°C, containing test tube to the level of acid
• A gas syringe held on a clamp stand connected to a tube, which on the other end will enclose the test tube after Magnesium, is inserted to the acid.

When the water was in correct temperature of 30°C we placed the test tube in the water bath. Then we organized a clamp stand to hold the gas barometer. We decided upon entering only 2 grams of Magnesium. As soon as we entered the magnesium, we enclosed the test tube with the other end of the tube connected to the gas barometer. One of the persons timed how long the reaction takes to give off gas until the barometer reached 50ml. The time measured 6 seconds approximately. The rate of reaction was too fast, so we decided to reduce the concentration of Hydrochloric Acid to 1Moler. We did the same experiment again; only difference was with the concentration of acid. The time measured 9 seconds. We carried out these practice experiments so we could decide upon concentration of acid, volume of acid, what temperatures to experiment on, etc…

Here is a table of our results for the preliminary experiments.

With the preliminary experiment we had experience on what the practical work will be like. Since this preliminary work was implemented we now have a better idea of how we will carry out our coursework experiment.  

PLAN

We are going to test the rate of reaction by measuring the amount of gas reaction given off when Magnesium reacts with Hydrochloric Acid. We will exercise 5 experiments, keeping 1 variable and five non-variables. We will keep the temperature as the one variable, practicing 20°C, 30°C, 40°C, 50°C and 60°C. The non-variables consist of: -

• Acid concentration – 1Moler
• Volume of acid – 10ml
• Mass of magnesium used – 0.5g
• Equipment used – Water bath, gas barometer, clamp stand etc…

We are going to measure: -

• The time to collect the selected volume of gas
• The set volume of gas – 50ml

We will keep the acid concentration by keeping 5ml of 2 molar acid and adding 5ml of water which will bring down the concentration of the acid to one 1 molar. As this is a non-variable we will repeat this process in each of the 5 experiments. The volume, will 10ml, as I said 5ml of 2 molar acid and 5ml of water. The mass of magnesium used will be 0.5 grams because in out practice experiments we found that mass of more than a gram of magnesium gives off a very fast reaction and therefore we will be recording results which are very close together. We chose 0.5 grams of magnesium so we could have spaced out set of results. This too is a non-variable so in each experiment it will be kept the same. The other non-variables consist of the equipment used, the water bath, the clamp stand, the test tube etc… The variable we kept is the temperature, and in each experiment we would try different temperatures, going up 10°C each time.

PREDICTION

I predict that as I increase the temperature, the rate of how much gas is given off (rate of reaction) will increase.

This I back-up with my background knowledge, as I said that temperature will excite the particles and make them more active, this will increase the chances of colliding and reacting therefore it will increase the rate of reaction.

APPARATUS & TECHNIQUES

Obviously to carry out my experiment I will require apparatus.

Here is a list of all the apparatus I used:

• A Water Bath
  This machine is quite a large device whereby one must load the device with a selected amount of water and then he/she can select a temperature to which the water bath will heat and keep the water the same temperature as selected for as long. I used this to heat the test tube properly, as it is safer to use than a Bunsen burner. It is also to an advantage because it keeps the water the same temperature. It is also capable of rising the water temperature to as much as 90°C.
• Test tube
  This was required to contain the acid and also, it was feasible enough to use as we could fit the end of the barometer into the tube.
• Barometer
  We used this piece of apparatus to collect the gas and keep a track of how much gas is being collected.
• Measuring Cylinder
  This was needed to measure the volume of acid, we first collected the acid up to 10ml in the measuring cylinder and until we obtained the required amount we poured it into the test tube.
• Clamp stand
  This was needed to hold the barometer.
• Stopwatch
  We used this piece of apparatus to record how long it took from the time the magnesium entered the test tube containing the 10ml of acid until the barometer contained exactly 50ml of gas given off from the reaction.
• Weighing scale
  We used a weighing scale to weigh the amount of magnesium. It was a small scale and measured quite accurately.

The apparatus is illustrated on the next page.

METHOD & FAIR TEST

Basically my method was described in the planning area.

Most of the equipment for my experiment will be obtained from the school and the prep room. Firstly I will collect the Hydrochloric acid of 2 molar strength and pour only 5ml into the measuring cylinder and then to make it 1 molar strength I will add another 5ml of water, which makes 10ml. This will all be done using the measuring cylinder. Subsequently it will be poured into a test tube.

Then with the test tube I will contain it in a test tube rack which will be inside the water bath filled with water. I will select the temperature of 20°C and the water bath will keep the temperature of the water at the selected. Since the test tube will be contained in the water, the acid inside will become the same temperature. When the temperature becomes stable, I will collect 0.5g of small fillings of magnesium. This will be weighed on the weighing scale. The magnesium will be contained in a small plastic plate. Then when everything is set, we will add the magnesium into the tube and immediately enclose the top of the test tube with the open-ended tube of the gas syringe with a whole. The syringe will be held by a clamp stand. Straight away we should expect the gas pushing the plunger outwards. As soon as the test tube is enclosed I will immediately start the stopwatch and stop it as soon as the plunger exceeds 50ml.

I also considered the factors which could affect my investigation. These are the factors that could effect my investigation:

• The water bath is quite old and it may not keep the water to the exact temperature selected. If the top is not placed on it when trying to achieve high temperature the water will not heat.
• The barometer should be flexible; I mean the plunger should be able to move in and out easily. If it is unable to move out smoothly then my results could get affected as it will give me the wrong timing.

I will obviously need to keep some factors the same through out my 5 experiments. These are: -

• The mass of magnesium
• The volume of acid
• The amount of gas to be collected
• The acid strength
• The equipment used

The only factor that will vary is the temperature, as this is the aim of my investigation to test the affects of a factor on the rate of reaction.

OBTAINING EVIDENCE

I carried out my five experiments and I recorded these results.

 

My trial run went well enough, which prepared me for my final run. I believe my final run and my results are excellent except for one irregular. The time taken for the rate of reaction when the temperature was 40°C was 11.69s.

ANALYSING EVIDENCE

With my results I realise that I can draw a chart which will make the results presentable. I will draw a line graph as this is most suitable to present the data I have obtained. Line graphs are usually used to present data which is vis-à-vis against another. In this case it is the Temperature against Time. This will also tell us if my prediction is correct. As I said, “that as I increase the temperature, the rate of how much gas is given off (rate of reaction) will increase.”

According to my prediction, this means that the time (seconds) should decrease (high to low, e.g. 5 seconds – 1 second).

Here is my graph.

As you can see, I have drawn the line of best fit on my graph. We do notice a slight pattern; the line goes down as the temperature increases. This means that as the temperature increases the rate at which gas is given off increases, this means that the time in seconds decreases.

Analysis

The longest amount of time was when the temperature was at 40°C, where it took 11.69 seconds. This is quite an irregular result. This we can tell because when the temperature was 20°C the time taken was lower than at 40°C, 7.97 seconds.

The shortest amount of time was, evidently at 60°C where the time taken was 5.1 seconds.

When temperature rises, air particles are given more energy and move around more excitedly. This increases the rate of collisions taking place. This means that the rate of reaction becomes higher. As the temperature rises the chances of collisions are higher, as I mentioned earlier the rate of collisions doubles every time the temperature increases by 10°C.  

My evidence does support my prediction as it precisely shows that as the temperature increases the rate of reaction increases. Meaning the time taken goes down and the plotted line of best fit shows exactly this.

EVALUATION

I believe my investigation and my practical work went overall quite well. The enthusiastic environment in which we were working made it quite pleasant. My practical work went quite well as it gave me a good set of reliable, consistent results, with exception of just one. Otherwise my set of results was quite good.  

I had only one unusual result from the original experiment. This was at 40°C where the time taken was 11.69 seconds. This is unusual because it is not between the two results, which come before and after 40°C. These were at 20°C where the time taken was 6.65 seconds and at 50°C where the time taken was 6.32 seconds. So clearly, the time taken at 40°C should be somewhere between 6.65 and 6.32 seconds.

I think we have this irregular result because I found there was a problem with one of the gas syringes. I remember that one of them had a bit of moisture in the syringe, which made the plunger to move in and out of the syringe in flexibility. This could be why we have one irregular result. One of the other reasons could be that the tubing was incorrectly attached to the test tube, which could have lead to the gas being exposed into the air and not through the tube.

I believe our experiment went well enough, but if it were possible I would make a few changes. For example: -

• I would carry out all the five experiments in one day, as this could have affected my results. The five experiments that we did were done at different timings, which know if the more AC’s could have been switched on at certain days. What if during one experiment 3 AC’s were on but during another experiment only 1 AC was on. This could have affected the temperature.
• I would make the volume lower or lower the mass of magnesium used. This is because I would like to have results that would be on a longer scale of time in seconds.