Determine the relative atomic mass of lithium.

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Introduction

Lithium (Li), is the first metal in group 1of the periodic table, the group also goes by the name of the alkali metal group, lightest of the solid elements.   It's the lightest of all the solid elements at room temperature and the least reactive metal in amongst the alkali metals, but nevertheless it is extremely reactive.  

Lithium has a white appearance and a very soft texture, you could probably be able to cut a piece of lithium in half with a butter knife.

Aim

The aim of this experiment is to determine the relative atomic mass of lithium.

Planning

I intend to use two different methods in trying to determine the relative atomic mass of lithium.  

When lithium reacts with water at room temperature it produces lithium hydroxide and hydrogen gas.  Here is a balanced formula for that -

 2Li(s) + 2H2O(l)            2LiOH(aq) + H2(g)

This knowledge can be used to help us de determine the relative atomic mass of lithium.  If a known mass of lithium is dissolved in water, the volume of hydrogen produced can be used to calculate the relative atomic mass of lithium.  This will be the basis of method 1.  The way it would work is that the mole of the hydrogen collected could be worked out, from that the mole of the lithium could be deduced.  From that the relative atomic mass of lithium could be worked out by using this formula –

      m = mr

                              n

The resulting solution of Lithium hydroxide is a base, this can be used in an acid base titration. This again will be the basis for method 2.

The acid base titration requires and acid and a base as the name suggests.  In this example the lithium hydroxide is the alkaline, and a suitable acid to use in the experiment would be hydrochloric acid.  The concentration of the acid must be known for the experiment to work.  As we do not know the concentration of the alkaline we must use the fact that the concentration of the acid is known to our advantage.  We can use the known concentration of the hydrochloric acid to work out the moles of hydrochloric acid used to neutralise the alkaline.  This is the formula that is to be used

The n represents the mole of the substance.  The c stands for the concentration of the substance and the v stands for the volume.  The number of moles present in the lithium hydroxide can be worked by using the ration of acid and base in the reaction.

As I’ve mentioned earlier when the titration process is carried out water and a salt is produced from the acid and alkaline, this is known as a neutralisation reaction.  The formula for the reaction is shown below.

 

Acid + Alkali         Salt + Water.

As it is a neutralisation reaction the outcome of the reaction would naturally be neither acidic or alkaline but neutral.  

When the lithium hydroxide is titrated it will be essentially neutralised with a known concentration of an acid, in this case that acid will be hydrochloric acid, this is the formula of the titration process -

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

Method 1 :  

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Apparatus

1 x Measuring cylinder (250cm³)

1 x Conical flask (250cm³)

1 x Rubber bung

1 x Tube

1 x Container

1 x Electronic scale

1 x Distilled water

1 x Lithium

1 x Goggles

1 x Gloves

1 x Lab coat

The apparatus should be set up like this –

Method

  1. Weigh a piece of lithium on the scale and record the weight.

  1. Clean the piece of lithium properly removing any oil from the

surface.

  1. Use the measuring cylinder to measure 100 cm³ of distilled

water ...

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