APPURATUS USED
I am going to investigate how temperature affects the rate of reaction between magnesium and hydrochloric acid. The procedure for the experiment is as follows;
* Using a measuring cylinder, measure 10cm3 of water and pour it into the side arm tube.
* Measure 10cm3 of hydrochloric acid (1 mol/ dm3) and add it to the water.
* Place the side arm tube in a water bath at 20OC, set up the apparatus below.
* Measure 10.9 cm of magnesium ribbon and check on the balance that it weighs 0.1g.
* Coil the ribbon around a pencil and then drop it into the side arm tube and quickly put a bung on the side arm tube (this must be done quickly to prevent gas escaping).
* Every 15 seconds measure the volume of gas produced until less than 1cm3 of gas is produced every 15 seconds.
* Repeat experiment two more times (for accuracy) and record all results in a table.
* Repeat the experiment for temperatures of 30 OC, 40 OC, 50 OC and 60 OC
It is important that only the temperature is changed since this is what is being investigated.
- Apparatus
I have chosen to use a 10cm3 measuring cylinder to measure the volumes of substances used since it is more accurate than a pipette. I will use an electronic water bath for maintaining the mixture at a temperature since the temperature is more accurate than a water bath above a Bunsen burner.
A 100cm3 gas syringe should be appropriately accurate for measuring the gas produced since it is accurate to 1cm3 of gas. I will use a three figure balance to measure the mass of magnesium to be used since it is vital that as close to 0.1g of magnesium is used as possible.
* Variables
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Equipment:
Test Tube Rack
2 Measuring Cylinders
5 Magnesium Strip
Hydrochloric Acid
Test Tubes
Sand Paper
Stop Clock
Water
I have chosen to repeat the experiment 3 times because it therefore allows me to calculate an average rate of reaction. This will ensure that there are no abnormal results and it will increase accuracy. I have decided to start readings at 20OC and increase by 10OC each time until 60OC is reached, since it will allow me to see the increase in rate of reaction and 5 results should be enough to identify any trends.
HOW WILL YOU CARRY OUT THE EXPERIMENT
Method:
Firstly I will collect all of the equipment and cut 5 magnesium strips (10cm) the same size. After that, using the sandpaper, I will sand any Magnesium Oxide layer (rust) off the magnesium strips. I will then collect the hydrochloric acid and measure out 10ml in the measuring cylinder and pour it into the test tube. I will then put test tube in the test tube rack. After that is done I will measure 8ml of hydrochloric acid and 2ml of water in the other measuring cylinder, and then pour in another test tube, again place in the test tube rack. I will then measure 7ml of hydrochloric acid and 3ml of water and pour into another test tube. Place tube in test tube rack. After that I will measure 6ml of hydrochloric acid and 4ml of water and pour into another test tube and then place in the test tube rack. Finally I will measure 5ml of hydrochloric acid and then 5ml of water and pour it into the last clean test tube, and then place in the test tube rack. By using the stop clock, collect one strip of magnesium and drop it in the first test tube. As soon as the strip touches the acid start the stop clock. Observe what happens to the strip and note down any observations you can see. As soon as the strip is invisible stop the stop clock, and note down the time. I will do the same with the four concentrations.
8. To make the experiment a fair test repeat two times. Collect observations/results.
Plan
I am intending to react a 10cm length of magnesium ribbon with a chosen volume of hydrochloric acid.
I will measure the rate of reaction by collecting the hydrogen gas that is produced in a gas syringe that will be connected, via a piece of rubber tubing and a rubber bung to the conical flask that the reaction will take place. I will quickly drop the length of magnesium into the flask and connect the rubber bung to it. I will then start the stop clock and record the volume of gas evolved every 5 seconds for 15 seconds. I have chosen these times because I only need three results as I am going to measure the initial rate of reaction and not the average. I will repeat each experiment so that my results are reliable and reproducible.
Fair Test
To make sure my experiment was a fair test, I double-checked the measurements of all my solutions. To gain a set of accurate results I did the experiment again. I assured that the volume of the concentration was always the same-10ml. By carrying out the following my experiment was fair.
In order to keep my experiment a fair test I will have to make sure that I keep the following factors the same:
· Starting temperature of the acid
· Volume of acid used (cubic centimetres)
· Surface area of the magnesium
· Clean the magnesium with emery paper before experiment
· Length of magnesium
I will also have to make sure that the gas syringe is correctly connected and that it is placed quickly and tightly enough so that no hydrogen gas escapes.
Safety
The things that I will need to do to keep my experiment a safe one for myself and other students around me are as follows:
· Wear safety goggles as I am using concentrated hydrochloric acid
· Care to eyes and the skin besides all the other people is always vital and necessary
· Care in using glassware since it is sharp when broken and can cut skin
· Safe disposal of reagents and laboratory chemicals
· Care when returning all used glassware and equipment at the end of the experiment
Preliminary work
The preliminary work that I will be conducting is to find out the optimum length of magnesium ribbon and the optimum volume of hydrochloric acid.
To do this I will be measuring out a volume of hydrochloric acid and a length of magnesium ribbon and reacting them together. If there is still some magnesium left over when it has stopped effervescing then I will have to increase the volume of hydrochloric acid.
If the reaction takes too long to finish then I will have to shorten the length of magnesium that I use, however if the reaction is too short then I will have to do the opposite and increase the length of magnesium that I use. The optimum rate that I am trying to find is a reaction that is not too short but is not too long, so I can get enough results to plot a good graph. I need to find the optimum volume of hydrochloric acid so that it is in excess after the reaction is over.
Apart from trying to find the optimum rate of reaction I also have to find out how to keep the temperature change down. This is because as the reaction is taking place the temperature will rise because the reaction is exothermic, and this could cause my results to be inaccurate as the temperature change will heat up the acid and give the acid particles more energy so they will move faster and collide with the magnesium with greater force causing more successful collisions per second.
To show that the hydrogen gas is not being given of from the water in the hydrochloric acid I will have to conduct a control experiment. This is when I will react magnesium ribbon with distilled water to show that there is no reaction between magnesium ribbon and water and that the hydrogen gas is evolving from the hydrochloric acid when it is being broken down into magnesium chloride and hydrogen.
2
How long the magnesium takes to dissolve
Seeing as though I have chosen to measure the length of time it takes for the magnesium to dissolve - the only problem is with recording my experiment this way is that I could only settle on the average rate of reaction and not the initial rate of reaction. Therefore I will be using the initial rate to analyse the rate of reaction as it can calculate the true rate and not the average rate of reaction.
Factors
The factors that could affect the rate of reaction of my experiment are as follows:
Concentration of acid
This could affect the rate of reaction because the higher the concentration of the acid then the more acid particles per 100cm3 so more collisions per second and then there will be more successful collisions per second.
· Temperature of the acid
If the starting temperature of the acid is different each time the speed at which the acid particles collide with the magnesium ribbon will increase more the higher the temperature goes. This means the acid particles move with more energy, which means they will collide with the magnesium with more energy, which will give more successful collisions per second.
