Controlled Variable
The equation for the reaction can be seen below;
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
I will be controlling many of the variable which affect the volume of hydrogen which is produced.
Temperature – The temperature will be controlled because if the temperature was to be changed this could affect the dependent variable. To control this the experiment shall be done in the same lab with no heating and no cooling will be done while the temperature will also be maintained using a thermometer.
Volume – In this investigation the volume of the hydrochloric acid that will be used will always be the same to maintain a fair test. The volume will always be 50 cm3.
Surface Area – The surface area will be maintained throughout the experiment as changing the surface area can affect the rate of reaction. To do this the same length of magnesium will be used which will be 2cm. This will ensure that the test will be fair
As I am using the same length and same coil of magnesium the mass should always be kept constant.
Mass – The mass of the magnesium will be kept constant throughout the experiment as the length and coil of magnesium is always kept constant.
Other ways in which the experiment will be controlled is by using the same conical flask and gas syringe. I will also be using the same measuring equipment to measure out the hydrochloric acid and the water for all the concentration while also using the same ruler
Method
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Measure out the 50 cm3 of the 2 mol dm-3 hydrochloric acid using one of the measuring cylinders. Once measured out pour the 50 cm3 hydrochloric acid into the 100 cm3 conical flask.
- Set up the apparatus as shown in the diagram in the page before, ensuring that the gas syringe is secure so that no hydrogen gets lost.
- Cut the magenesium ribbon so that it is 2cm in length.
- Place the 2cm magnesium ribbon into the conical flask ensuring that the bung is put back into the fask as quickly as possible to ensure that no hydrogen is lost, and start the stop watch.
- Record the volume of hydrogen gas given off every 30 seconds for 5 minuted. O nce finisged wash out the conical flask and repeat 3 times for every concentration. Below isa table showing how each concnntration can be made up.
- To work out the rate of reaction all you have to do is use the following equation;
Volume of Hydrogen Produced
Time Take to Produce Volume of Hydrogen
For example if 15 cm3 was produced after 30 seconds, to work out the rate of reaction you will need to divide 15 by 30 so the rate of reaction will be 0.5 cm3 per second. To find out how the rate of reaction progresses throughout the experiment work out the rate of reaction for the volume of hydrogen produced every 30 seconds for 5 minutes .
Safety
When handling the hydrochloric acid make sure that care is taken. Avoid contact with the eyes or skin as it can cause serious permanent damage. If contact is made with the eye, immediately flush the eye with water for ten minutes then seek medical help, while if contact is made with the skin, wash area with plenty of water and remove any contaminated clothing. If swallowed drink plenty of water and seek medical help. Always wear safety glasses when handling hydrochloric acid.
Apparatus
2M Hydrochloric Acid
Water
Magnesium Ribbon
Clamp Stand
Delivery Tube + Single holed bung
Gas Syringe
100cm3 Conical Flask
2x 100cm3 Measuring Cylinder
Ruler
Stop Watch
