Welcome to my presentations on the likely calculations for the volumetric analysis for 2023
Alternative B chemistry practical
Note the following points:
(1)I used VA of 24.60cm³which is the theoretical value for all the calculations here (use yours)
(2)Acid=E, Base=F, VA=VE,
VB=VF, CA=CE, CB=CF and so on (All the formulas remains the same)
(3)The values I used in all the questions here can be changed
(4)The base is an alkali not a carbonate so no need for calculations on volume of CO₂ gas evolved
Question 1. For % purity and % impurity
E is a solution of HCl containing
0.0812mol/dm³
F is a solution of impure
NaOH containing 5.4g/dm³
(a)Put E into the burette and titrate with 25.0cm³ or 20.0cm³ portions of F using methyl orange
as indicator.
Repeat the titration to obtain
concordant titre values. Tabulate your results and calculate the
average volume of acid used.
The equation for the reaction is
HCl + NaOH ---> NaCl + H₂O
(b)From your results and
the information provided
above, calculate the:
(i)concentration of F in mol/dm³
(ii)concentration of F in g/dm³
(iii)% purity of NaOH in F
(iv)% impurity of NaOH in F
Solution
CE=0.0812moldm³
Molar mass of HCl=36.5g/mol
Mass concentration of
impure NaOH=5.4g/dm³
Molar mass of NaOH=40g/mol
VE=24.60cm³,VF=25.0cm³, nA=1, nB=1
(i)Concentration of F in mol/dm³
Formula
CEVE/CFVF=nE/nF
Therefore
CF=(CEVEnF)/(VFnE)
CF=(0.0812×24.60×1)/(25×1)
CF=(1.99752)/(25)
CF=0.0799008
to 3 significant figures
CF=0.0799mol/dm³
(ii)Concentration of F in g/dm³
Formula
Massconcentration=
Molar concentration×Molar mass
Mass concentration=0.0799×40
Mass concentration=3.196
to 3 significant figures
Mass concentration =3.20g/dm³
(iii)% purity of NaOH in F
Formula
%purity=
(Mass concentration of pure/Mass concentration of impure)×100/1
%purity=(3.20/5.4)×100
%purity=(0.592)×100
%purity=59.2
to 3 significant figures
%purity=59.2%
(iv)%impurity of NaOH
Formula
%impurity=(100)-(%purity)
%impurity=(100)-(59.2)
%impurity=40.8
to 3 significant figures
%impurity=40.8%
Question 2: For unknown equation and to get mole ratio of acid and base
E is a solution of a mineral acid containing 0.0812mole of the acid per dm³ of solution.
F is a solution containing 0.08mol/dm³ NaOH
(a)Put E into the burette and titrate with 25.0cm³ or 20.0cm³ portions of F using methyl orange
as indicator. Repeat the titration to
obtain concordant titre values. Tabulate your results and calculate the average volume of acid
used
(b)From your results and
the information provided
above, calculate the
(i)number of mole of acid in the average titre
(ii)number of mole of base in
the volume of F
(iii)mole ratio of acid to base
(iv)write the equation for the reaction
Solution
CE=0.0812mol/dm³
CF=0.08mol/dm³
VE=24.60cm³ and VF=25.0cm³
(i)number of moles of acid in the average titre
Formula
Concentration=mole/volume in dm³
Therefore
nE=(CE)×(VE in dm³)
nE=(0.0812)×(24.60/1000)
nE=(0.0812)×(0.0246)
nE=0.00199752
to 3 significant figures
nE=0.002mole
(ii)number of mole of base in
the volume of F
Formula
Concentration=mole/volume in dm³
Therefore
nF=(CF)×(VF in dm³)
nF=(0.08)×(25/1000)
nF=(0.08)×(0.025)
nF=0.002
to 3 significant figures
nF=0.002mole
(iii)mole ratio of acid to base
nE=0.02mole
nF=0.002mole
Divide by the smallest value
nA=(0.002/0.002)=1
nB=(0.002/0.002)=1
nA=1 and nB=1
Mole ratio=1:1
(iv)write equation for the reaction between acid and base that will give nA=1, nB=1
Question 3: For unknown acid
and molar mass of the acid
E is a solution of a monobasic acid HX
F is a solution containing
3.2g/dm³ of NaOH solution
(a) Put E into the burette and titrate with 25.0cm³ or 20.0cm³ portions of F using methyl orange
as indicator. Repeat the titration to
obtain concordant titre values
Tabulate your results and calculate the average volume of acid used
The equation for the reaction is:
HX + NaOH --> NaX + H₂O
(b)From your results and
the information provided
above, calculate the:
(i)concentration of F in mol/dm³
(ii)concentration of E in mol/dm³
(iii)molar mass of the acid, given that 500cm³ of solution E contained 1.48g of the acid
(iv)relative atomic mass of X
Solution
Mass concentration of F=3.2g/dm³
VE=24.60cm³
VF=25.0cm³
Molar mass of NaOH=40g/mol
Mass concentration of E
=(1.48/500)×(1000)
=(0.00296)×(1000)
=2.96g/dm³
nA=1 and nB=1
(i)concentration of F in mol/dm³
Formula
Mass concentration=
Molar concentration × Molar mass
Therefore
Molar concentration
=Mass concentration/Molar mass
Molar concentration=3.2/40
Molar concentration=0.08
to 3 significant figures
Molar concentration of F=
0.0800mol/dm³
(ii)Concentration of E in mol/dm³
Formula CEVE/CFVF = nE/nF
Therefore
CE=(CFVFnE)/(VEnF)
CE=(0.08×25×1)/(24.60×1)
CE=2/24.60
CE=0.081300813
to 3 significant figures
CE=0.0813mol/dm³
(iii)Molar mass of the acid
Formula
Mass concentration=
Molar concentration × Molar mass
Therefore
Molar mass=
Mass concentration/
Molar concentration
Molar mass =2.96/0.0813
Molar mass = 36.40836408
to 3 significant figures
Molar mass of E=36.4g/mol
(iv)Relative atomic mass of X
Formula
HX=Molar mass of the acid
HX=36.4
1+X=36.4
X=36.4-1
X=35.4
to 3 significant figures
X=35.4
Question 4: For unknown base and molar mass of the base
E is a solution
containing 0.0812mol/dm³ of
HCl solution F contains 1.6g of XOH in 500cm³
(a)Put E into the burette and titrate with 25.0cm³or 20.0cm³portions
of F using methyl orange as indicator. Repeat the titration to
obtain concordant titre values. Tabulate your results and calculate the average volume of acid
used.
(b)From your results and
The information provided
above, calculate the:
(i)concentration of F in mol/dm³
(ii)molar mass of XOH
(iii)relative atomic mass of X
(iv)% by mass of X in XOH
Solution
•CE=0.0812mol/dm³
Molar mass of HCl=36.5g/mol
Mass concentration of F=
(1.6/500)×1000
=0.0032×1000
=3.2g/dm³
VE=24.60cm³
VF=25.0cm³
nA=1, nB=1
(i)concentration of F in mol/dm³
Formula
CEVE/CFVF=nE/nF
Therefore
CF=CEVEnF/VFnE
CF=(0.0812×24.60×1)/(25×1)
CF=1.99752/25
CF=0.0799008
to 3 significant figures
CF=0.0799mol/dm3
(ii)Molar mass of XOH
Formula
Mass concentration=
molar concentration × molar mass
Therefore
Molar mass=mass concentration/molar concentration
Molar mass=3.2/0.0799
Molar mass=40.05006
to 3 significant figures
Molar mass=40.1g/mol
(iii)relative atomic mass of X
Formula
XOH=molar mass
X+16+1=40.1
X+17=40.1
X=(40.1)-(17)
X=23.1
to 3 significant figures
x=23.1
(iv)% by mass of X in XOH
Formula
(X/XOH) × 100/1
=(23.1/23.1+16+1)×100
=(23.1/40.1)×100
=(0.576)×100
=57.6
to 3 significant figures
% of mass of X in XOH=57.6%
Question 5: For mass of salt formed and mass of sodium ion
E is 0.0812mol/dm³ HCl
F is a solution containing Xg/dm³of NaOH
(a)Put E into the burette and titrate with 25.0cm³ or 20.0cm³portions of F using methyl orange
as indicator.
Repeat the titration to
obtain concordant titre values. Tabulate your results and calculate the average volume of acid
used
The equation for the reaction is
HCl + NaOH ----> NaCl + H₂O
(b)From your results and
the information provided
above, calculate the
(i)concentration of F in mol/dm³
(ii)value of X
(iii)mass of salt formed when 500cm³ of F is completely neutralized by E
(iv)mass of sodium ion (Na⁺) in 1dm³ of F
Solution
CE=0.0812mol/dm³
Molar mass of HCl=36.5g/mol
Molar mass of NaOH=40g/mol
VE=24.60cm³
VF=25.0cm³
nA=1 and nB=1
(i)Concentration of F in mol/dm³
Formula
CEVE/CFVF = nE/nF
Therefore
CF=CEVEnF/VFnE
CF=(0.0812×24.60×1)/(25×1)
CF=1.99752/25
CF=0.0799008
to 3 significant figures
CF=0.0799mol/dm³
(ii)Mass concentration of F
Formula
Mass concentration=
Molar concentration×Molar mass
Mass concentration=0.0799×40
Mass concentration=3.196
to 3 significant figures
Mass concentration=3.20g/dm³
(iii)Mass of salt formed when 500cm³ of F is completely neutralized by E
Mass of salt formed=
(CF)×(volume in dm³)×(molar mass of the salt NaCl)
Mass of salt formed=
(0.0799×(500/1000)×(23+35.5)
=(0.0799)×(0.5)×(58.5)
= 2.337075
to 3 significant figures
Mass of salt formed= 2.34g
(iv)mass of sodium ion (Na⁺) in 1dm³ of F
Mass of Na⁺=
(CF×subscript of Na in the base) × (volume given in dm³) × (molar mass of Na)
Mass of Na⁺= (0.0799×1)×(1)×(23)
Mass of Na⁺ = (0.0799)×(1)×(23)
Mass of Na⁺ = 1.8377 to 3 significant figures
Mass of Na⁺ = 1.84g
Question 6: For number of hydrogen ion in E
E is a solution of hydrochloric acid.
F is a solution containing 3.2g/dm³ of sodium hydroxide
(a)Put E into the burette and titrate with 25.0cm³ or 20.0cm³ portions of F using methyl orange
as indicator. Repeat the titration to obtain concordant titre values. Tabulate your results and
calculate the average volume of acid used.
The equation for the reaction is:
HCl + NaOH --> NaCl + H₂O
(b)From your results and the information provided above, calculate the:
(i)concentration of F in mol/dm³
(ii)concentration of E in mol/dm³
(iii)number of hydrogen ion in 1dm³ of E
Solution
Molar mass of HCl=36.5gmol
Mass concentration of F=3.2g/dm³
VE=24.60cm³, VF=25.0cm³, nA=1 and nB=1
Molar mass of NaOH=40g/mol
(i)concentration of F in mol/dm³
Formula: Mass concentration=Molar concentration×Molar mass
Therefore
Molar concentration=
Mass concentration/Molar mass
Molar concentration=3.2/40
Molar concentration=0.08
to 3 significant figures
Molar concentration=0.0800 mol/dm³
(ii)Concentration of E in mol/dm³
Formula: CEVE/CFVF = nE/nF
Therefore
CE=(CFVFnE)/(VEnF)
CE=(0.08×25×1)/(24.60×1)
CE=2/24.60
CE=0.081300813 to 3 significant figures
CE=0.0813mol/dm³
(iii)Number of hydrogen ion in 1dm³ of E
Formula
Number of H⁺ =
(Avogadro's number)×(Basicity of the acid)×(CE)
Number of H⁺ =
(6.02×10²³)×(1)×(0.0813)
Number of H⁺ =
4.89426×10²²
to 3 significant figures
Number of H⁺ = 4.89×10²² ions