The determination of the Ar of Lithium.

There were 0.0155 moles of Lithium.

        Moles of Hydrogen x 2 = Moles of Lithium

        0.00775 x 2 = 0.0155 moles of Lithium

From this I can deduce that the Ar of Lithium in this experiment was 6.452

(Actual Ar of Lithium is 6.941)

        Mass                 = Ar

        Number of moles

        0.10g  = 6.452

        0.0155

Titration

        LiOH(aq) + HCl(aq) → LiCl(aq) +H2O(l)

In the Titration there were 0.0139 moles of HCL (Hydrochloric Acid).

        Concentration x Litres = Number of moles

0.1 x 0.139 = 0.0139 moles

There were 0.0139 moles of LiOH (Lithium Hydroxide).

        Concentration x Litres = Number of moles

1. x 0.139 = 0.0139 moles  

In 100cm3 of the solution from method 1 there were 0.139 moles of LiOH

(Lithium Hydroxide) Present.

        Number of Moles = Moles Present in Solution

        Concentration

        0.0139 = 0.139 moles

           0.1

Using these results I can calculate that the Ar of Lithium in this experiment was 7.194

(Actual Ar of Lithium is 6.941)

        Mass                 = Ar

        Number of moles

        0.10g = 7.194

        0.0139

Evaluation

The experiment was simple enough to carry out in school, but was not suitable for a proper scientific experiment needing precise results.

My first attempt at titration produced an anomalous result. I chose to exclude this result from my average because it was a rough attempt to get an idea how much Hydrochloric Acid was needed to neutralise the Lithium Oxide.  However the second two attempts were much more accurate and they provided me with an average.  Repeating the experiment more than three times can counteract this problem and provide a good average.

In the first experiment I collected 186cm3 of Hydrogen, this recording is vital to the mole calculations and needs to be as accurate as possible.  We used a Bees Hive in a water bath and a 250cm3 measuring cylinder to collect the gas.  The measuring cylinder is not exact so the amount of gas produced could be slightly more or less than recorded.  Using a 250cm3 gas syringe would allow me to record results with much greater accuracy.

When the Lithium in the first experiment oxidised the results may not have been accurate, this is because when I weighed my Lithium the scale may have been wrong.  Vibrations through the table my have changed the reading.  The Lithium may have also been partially oxidised because only the side of the Lithium that has been cut will be fresh.  Next time I would make sure that all the sides have been freshly cut and use a very accurate scale in another room to cut down on vibrations.