0.3 kg of NaOH is dissolved in 5 litres of water. It is used as
a titrant with 20.0cm3 of H2SO4 of a concentration of 0.5mol/dm3.
what is the volum eof NaOH solution that is required to neutralize
all the H2SO4?
For reference purposes, here's the equation for the
reaction:
2 NaOH + H2SO4 -> 2 H2O + Na2SO4
Find concentration of NaOH = 300/5
= 60g/dm3
No. of moles of of H2SO4 = concentration X volume
=0.5 X 0.02
=0.001 moles
Using mole ratio, no of moles of NaOH =0.01 X 2
=0.02 moles
Now change 60g/dm3 to mol/dm3
concentration of NaOH in mol/dm3 = 60 / 40
=1.5mol/dm3
concentration of NaOH (dm3) = no.of moles/vol of NaOH used
(manipulate with formula)
=
0.02/1.5
=
0.0133dm3 (answer)
2nd question.
5g of barium nitrate would react with 15cm3 of 0.3mol/dm3 of
sodium sulphate. Determine total mass of products formed from
reaction. (aint sure of how you do this. but i took a stab at the
question anyway. correct me where necessary)
Equation of reaction = Ba(NO3)2 + Na2SO4 -> BaSO4 +
2NaNO3
find No. of moles of sodium sulphate
concentration of sodium sulphate (mol/dm3) = no.of mol/vol of
solution
0.3 = no. of moles /0.015
manipulate with terms given and you get 0.0045 moles of
Na2SO4.
No. of moles needed for BaSO4 (use mole ratio) : 0.0045moles
No of moles needed for NaNO3 = 0.0045 * 2
= 0.0090moles
Mr of BaSO4 = 233
Mr of NaNO4 = 85
No of moles (BaSO4) = mass/Mr
Mass = 233 * 0.0045
= 1.0485g
No of moles of NaNO3 = mass/mr
mass : 85 *0.0090 = 0.765g
total mass = 1.0485 +0.765
= 1.81g (ans)
3rd question.
Bromine liquid is produced when chlorine gas is pumped into a
beaker filled with 100ml of 80g/dm3 of lithium bromide.
(a) find vol of chlorine gas needed to produce 4.5 g of bromine
liquid.
(b) determine amount of LiCl produced when 2g of bromione liquid
is also produced.
equation - 2 LiBr + Cl2 -> 2 LiCl + Br2
Find the no. of moles of bromine. (0.028moles)
compare using mole ratio.
(a)no. of chlorine moles needed is also
0.028moles.
0.027 = vol of gas(dm3) / 24dm3
vol. of Cl2 gas produced = 0.028 *24 = 0.672dm3(ans)
(b) Mr of Br2 = 80(2)
=160
No of moles of Br2 = mass/mr = 2/160 = 0.0125moles.
using mole ratio : 2*0.0125
= 0.025moles(ans)
lengthy post. thanks for going through the entire entry. please
help identify mistakes wherever necessary.