This experiment will be an attempt to determine the molar mass of magnesium. For that we will have an experiment where we dissolve sulphur into hydrochloric acid. Then we measure the amount of gas created during the reaction. To get the molar mass itself we will have to make sure to record the conditions of the experiment such as the temperature or pressure.
The material used for the experiment was:
4. measuring cylinder (1000 cm3)
5. Stand with clamp
6. magnesium ribbon
7. hydrochloric acid
1. About 20mm of magnesium ribbon and weight it with the accuracy of 0.001g
2. Pour 5cm3 of HCl into the eudiometer. Then carefully filling the eudiometer with water above the HCl, without mixing the liquids.
3. Wind the magnesium ribbon around a piece of copper wire and let it hang down a little bit into the eudiometer. Make sure there is a hole into the rubber stopper and fill it with water.
4. Place a large measuring cylinder filled with water in the sink. Put a finger over the hole in the stopper and turn the eudiometer upside down into the cylinder.
5. Observe what happens with the hydrochloric acid and magnesium after a little while. When the reaction is complete wait at least 5 minutes so that the eudiometer reaches room temperature.
6. Arrange the eudiometer in the cylinder so that the gas into the eudiometer has the same pressure as the air pressure in the room. Note the air pressure and temperature in the room.
7. Calculate the molar mass of magnesium.
Before the experiment the magnesium was carefully weighted on a scale. After turning the eudiometer the HCl started to go down towards the magnesium through the water. Once it reached it a reaction took place creating bubbles of air that went up to the top and pushed the water level down. Once the reaction ended all the magnesium was gone. During the reaction the temperature was read of a thermometer and the pressure of a barometer to get the most accurate values. finally we measured the volume of air inside the eudiometer.
Conclusion and Evaluation:
When studding the results and comparing them with the book (24.31 ) one can see that the value received from the experiment () is very comparable. Percentage yield:
Despite that high percentage the experiment was not accurate enough to have the book value within the error range (≈).
The biggest two sources of error in this experiment are the instruments (systematic errors) and of course the human factor (random errors). Also the part of the experiment where one is supposed to turn the eudiometer and put it into water can impossibly be done without bigger or lesser errors since it’s such a complex movement. Then I would like to put extra attention on the thermometer and especially the barometer. The thermometer could only show whole degrees which is a great loss to precision.
Then the barometer seemed quite old and unstable and the need to convert the pressure to Pascal and finally reading from it was quite hard which in my opinion was altogether quite hard. Also these where only the conditions in the entire room. One cannot be sure if they where exactly the same in the tube. Especially the temperature of water could have been quite different. Then of course the amount mg could have impossibly been measured accurately and we can’t be sure if exactly all of it reacted. Also the unknown pureness of the reactants and the solvent could justify the error in the result.
My suggestions for improvements is to begin with is use of more precise instruments. Then a different method involving a more closed environment and a different method for gathering data.
1. “Standard Level Chemistry” Pearson Baccalaureate by Catrin Brown and Mike Ford