Find out the theoretical yield of Magnesium Oxide, find the percentage yield of Magnesium Oxide identify any possible errors in the practical.

• When you have completed the whole experiment dispose of the Magnesium oxide in the chemical bins and not into regular waste bins.

• You must make sure that you do not lift the lid of the crucible when heating the magnesium strip; this will cause oxygen to reach within the crucible and inflaming the magnesium.

The equation for this is shown below:

2Mg(s)                        +                O2(g)                 →                2MgO(s)

Magnesium Metal                                Oxygen (Air)                        Magnesium Oxide

Procedure/ Method:

• Firstly you must cut a 10cm strip of magnesium metal from the roll of this material and make sure that it is 10cm, the experiment needs to be as accurate as possible.

• Clean the surface of the magnesium strip by using either the sand paper or the emery cloth, to clean the magnesium you must rub it gently with the                sand paper/ emery cloth until its clear and shiny at least.

• Then record the mass of the magnesium strip and write the results down in a table, you must also write down the mass results for the crucible and lid (empty), and the crucible and lid with the magnesium strip inside the crucible.

• Next you must calculate the mass of magnesium being used in the experiment (mass of crucible + lid) – (mass of crucible + lid + magnesium ribbon) this will give you the mass of the magnesium strip roughly.

• Then roll up the magnesium strip and put it into the crucible and then cover it with the lid making sure that there are no small gaps for oxygen to enter the crucible.

• Heat the crucible over the Bunsen burner for a maximum of ten minutes and every two minutes remove the Bunsen burner from underneath the crucible and lift the lid a slight bit to let in a fraction of air inside the crucible.

• Turn off the Bunsen burner and then allow the crucible to cool for at least fifth teen minutes, when its cooled down record the mass of the crucible + lid + magnesium oxide and then find out the mass of the magnesium oxide

(mass of magnesium oxide + lid + crucible) – (mass of crucible + lid).

Then write down the results in the table.

• Finally clean away all the apparatus and return them to where they belong.

Calculations:

1. Calculate the theoretical yield of Magnesium oxide in this redox reaction.

Theoretical Yield of MgO.

2Mg                +                O2              →                2MgO

Weight of 2Mg        =        24 x 2 = 48(g)

Because 24 is the relative atomic mass of Magnesium.

 

So 2 Moles of Magnesium = 48g

2 Moles of MgO =         48 + 32 = 80g of MgO

Because the relative atomic mass of oxygen is 32 and I added that to the relative atomic mass of Magnesium.

48g of Magnesium makes 80g of Magnesium Oxide.

I will now divide 80g with 48g

80                =        1.6   and I will now times 1.6 with 0.06 because 0.06 is the mass of my

48                                   Magnesium oxide.

1.6        x        0.06        =   0.096

Therefore my Theoretical Yield will be 0.096g

2. Calculate the % yield of Magnesium oxide.

Percentage Yield of MgO

% Yield        =        Actual                x        100

                 Theoretical

The Actual Yield is the mass of the MgO which I produced: 0.06g

To find the theoretical yield…

2Mg        +        O2        →        2MgO

2 Moles of Magnesium make two moles of Magnesium Oxide.

Weight of 2Mg        =        24        x        2        =        48g

Because 24 is the relative atomic mass of Magnesium

2 Moles of Magnesium = 48

2 Moles of MgO = 48                +        32        =        80grams of MgO

Because the relative atomic mass of oxygen = 32.

48 grams of Magnesium makes 80 grams of Magnesium Oxide.

To find one gram of Magnesium divide 48 with itself and therefore you have to do the same with 80 e.g.

48g of Mg ----------------------- > 80g of MgO

1g of Mg------------------------- > 1.6

I get 16 by dividing 80 with 48 which gave me 1.6.

I must now multiply them with my results from the table.

1        x        0.06        =        0.06                        1.6        x        0.06        =        0.096

So the percentage yield =                Actual                =           0.06        x 100 = 0.576

                                             Theoretical                       0.096

0.576 rounded up gives me 58 so it makes my percentage yield 58%

3. Can you identify any possible errors in this practical?

• I can firstly identify that there may have been a problem when cleaning the        magnesium strips, they may not of been cleaned with the sand paper good enough so this might have caused an miscalculation of some sort in the experiment.

• The magnesium strips may have been overheated and the experiment should’ve had an approximate time for the magnesium to be heated.

• When weighing the crucible, magnesium strip etc, I noticed that the results on the weighing scale kept on changing. I weighed the crucible and lid and the results on the weighing scale kept on switching from 21.47 to 21.49 so I just decided to go with 21.47g

• The tight spiral wasn’t much of a good support for the crucible and the crucible kept on tilting at odd angles because of this, which causes the lid to lift off a-bit and a-bit of the magnesium oxide ashes blew into the air.

4. Can you make any recommendations of how the yield for this reaction could be improved?

The yield for the reaction could have been improved probably if you was to use a longer length of magnesium strip or maybe if you was to heat the magnesium strip longer or shorter period of time.