I am going to calculate the number of moles of hydrogen, H2 that I had collected:
No. of moles = V÷ 24000 V = amount of hydrogen collected
1: 173÷24000 = 0.0072083mols (Li) 2: 176÷24000 = 0.0073333mols (Li)
I will now deduce the number of moles of lithium that reacted:
2 x molls of H2
1: 0.0072083 x 2 = 0.0144166mols
2: 0.0073333 x 2 = 0.0146666mols
Now I have these results I will calculate the relative atomic mass of lithium.
RAM = mass of lithium ÷ no. of moles
1: 0.09 ÷ 0.0144166 2: 0.09 ÷ 0.0146666
= 6.24 (3s.f) = 6.14(3s.f)
Method 2
Titration of LiOH (aq) with 0.100mol dm3 of HCl
On average 25.0cm3 of LiOH requires 40cm3 of 0.100 mol dm-3 HCL
Treatment of results
The equation for neutralisation reaction and my titration is:
LiOH + HCl → LiCl +H2O
1 mole of LiOH + 1 mole of HCl give us 1 mole of LiCl + 1 mole of H2O
Now I’m going to calculate the no. of moles of HCl used in the titration:
No. of moles = ( m(0.100) x v (40) ) ÷ 1000 LiOH = 25 cm3
HCl = 0.100dm-3
= 4.0 ÷ 1000 = 0.004 moles
Now I will deduce the number of moles of LiOH used in the titration
This is the same number of moles of HCl used in the titration = 0.004
To calculate the number of moles of LiOH, I will have to calculate how many moles present in 100cm3 of the solution from method 1:
100cm3 → 0.004 x 4 = 0.016 moles
Now I am going to use the original mass of lithium and this result so calculate the relative atomic mass (RAM) of lithium:
RAM = 0.09 ÷ 0.016 = 5.625 g/mol
The actual RAM of lithium is 6.941 g/mol therefore the accuracy of my experiment wasn’t too good.
Hazards of the chemicals that I used during this experiment:
1: lithium hydroxide is quite fatal if swallowed, it is poisonous and corrosive if inhaled.
2: lithium chloride can affect the central nervous system when inhaled and can be fatal and can also attack the respiratory system if swallowed.
3: Hydrochloric acid is very corrosive and can cause the skin to burn and is fatal if swallowed.
Evaluation
The accuracy of my experiment wasn’t to good I ended up being 1.316 g/mol out so there was obviously so measurements that I read wrong because I have checked my calculations so it must have been in either the titration of the amount of hydrogen I collected. Whilst doing the experiment I encountered other problems as well:
: The oil that the lithium had soaked up could have affected the mass of the lithium/
2: The gas inside the measuring cylinder could have been released and therefore giving me the wrong amount and the wrong calculations.
3: during the titration stage I could have been more accurate by having some help to take down the readings while I stop the titration instead of me doing both.
4: The pipette is not 100% accurate in its measurements so that also gave me an in accurate reading.
