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Y 10 Chem Solving Moles Problems 1
Contributed by: Chang
[ Relative atomic mass:
Relative Atomic Mass
FIRST STEP:
Mass
1.
Calculate the number of atoms in
1.28 g of copper?
Find the
 Cu = 64; NA = 6 x 1023 mol-1 ]
Number of MOLES
=
using 1.28g
NEXT
mol
Relative Molecular Mass
[ Relative atomic mass:
Mass
2.
FIRST STEP:
Calculate the number of
in 4.4g of vitamin C, C6H8O6
Find the
 H = 1; C = 12; O = 16;
 NA = 6 x 1023 mol-1 ]

Number of MOLES
molecules
=
using 4.4g
NEXT
mol
use 0.6 g to find the number of moles of NH3
[ Relative atomic mass:
Use NA to find the number of atoms of NH3
3.
in 0.6g of NH3 gas evolved during an experiment
FIRST STEP?
What is the
Calculate the number of
 N = 14 ; H = 1; O = 16;
 NA = 6.02 x 1023 mol-1 ]

atoms
NEXT
Relative Molecular Mass
[ Relative atomic mass:
Mass
4.
FIRST STEP:
in 0.6g of NH3 gas evolved during an experiment
Calculate the number of
use 0.6 g to Find the
 N = 14 ; H = 1; O = 16;
 NA = 6.02 x 1023 mol-1 ]

atoms
Number of MOLES
=
0.035
NEXT
mol
use RMM to find the number of atoms of H2O2
use 10 g to find the number of moles of H2O2
[ Relative atomic mass:
What is the first step?
is used, find the mass of  oxygen released?
5.
FIRST STEP:
If 10 g of hydrogen peroxide
Hydrogen peroxide decomposes as below
2H2O2
 H = 1; O = 16; ]
2H2O + O2
NEXT
Mass
Relative Molecular Mass
FIRST STEP:
[ Relative atomic mass:
is used, find the mass of  oxygen released?
6.
If 10 g of hydrogen peroxide
Hydrogen peroxide decomposes as below
use 10g to Find the
2H2O2
 H = 1; O = 16; ]
2H2O + O2
Number of MOLES
=
0.147
NEXT
mol
The 2nd STEP
mole=
mole =
mole=
22.4 dm3(STP)
No. atom
24dm3 (room t)
vol
vol
NA
mole=
mole=
RAM/RMM/RFM
the problems
use the correct
FORMULA
mass
No. molecule
NA
to solve
NEXT
[ Relative atomic mass:
FIRST STEP:
SECOND STEP:
8.
Calculate the number of atoms in
1.28 g of copper?
use 1.28g to  Find the
USE THE FORMULA
 Cu = 64; NA = 6 x 1023 mol-1 ]
Mole =
No of Atoms
N
Number of MOLES
A
NEXT
[ Relative atomic mass:
What is the
 number of mole =number of atoms x NA
 number of mole = number of atoms  ÷ NA
9.
Calculate the number of atoms in
1.28 g of copper?
use the formula
SECOND STEP ?
 Cu = 64; NA = 6 x 1023 mol-1 ]
NEXT
Number of C6H8O6 Molecules=
[ Relative atomic mass:
SECOND STEP:
From the first step, the number of moles of C6H8O6 is
Number of MOLES
0.025 mol
10.
Calculate the number of
in 4.4g of vitamin C, C6H8O6
Use the formula
=
 H = 1; C = 12; O = 16;
 NA = 6 x 1023 mol-1 ]

number of molecules
molecules
N
X
6X1023mol-1
A
NEXT
First: use 0.6g to find the number of moles of NH3,
SECOND: use formula of mole=No. of atoms ÷ NA
[ Relative atomic mass:
11.
first: Use numbers of atoms x NA , then
Second step: find the number of moles of NH3
What is the step of solving this?
in 0.6g of NH3 gas evolved during an experiment
Calculate the number of
 N = 14 ; H = 1; O = 16;
 NA = 6.02 x 1023 mol-1 ]

atoms
NEXT
First: use 3.4g to find the number of moles of NH3,
SECOND: use formula of mole=No. of atoms ÷ NA
[ Relative atomic mass:
first: Use the formula of mole x NA , then
Second step: find the number of moles of NH3
12.
What is the step of solving this?
in 3.4g of NH3 gas evolved during an experiment
Calculate the number of
 N = 14 ; H = 1;
 NA = 6 x 1023 mol-1 ]

atoms
NEXT
Step 1:
Step 2:
Now use the 
[ Relative atomic mass:
13.
in 3.4g of NH3 gas evolved during an experiment
Calculate the number of
No. of NH3
No. of Moles of NH3=
ANSWER
molecules
to find the no. of
 N = 14 ; H = 1;
 NA = 6 x 1023 mol-1 ]

NA
atoms
mol-1
=
NH3
X
mol-1
molecules
X 1023
NEXT
Step 2:
Step 1:
Step 3:
[ Relative atomic mass:
14.
we  want to  find number of 
in 1 molecule of NH3
how many atoms
in 3.4g of NH3 gas evolved during an experiment
No. of NH3
No. of Moles of NH3=
Calculate the number of
No. of NH3
molecules =
 ATOMS
3.4
17
0.2 mol-1
 N = 14 ; H = 1;
 NA = 6 x 1023 mol-1 ]

=
=
=
0.2
X
Atoms
atoms
6 X 1023
mol-1
x
0.2 mol-1
X1023
of NH3
atoms
x 6 x1023
NEXT
Step 3:
Step 2:
Step 1:
[ Relative atomic mass:
15.
of hydrated copper (II) sulphate CuSO4.5H2O
Calculate the mass of
Relative Formula Mass
No. of Moles of CuSO4.5H2O=
Mass
of CuSO4.5H2O =
= mole x RFM
=
x
 O = 16 ; H = 1;
 S = 32; Cu = 64 ]

0.3
g
=
mol
g
no need to find
g
mol
NEXT
given
Step 3:
Step 2:
Step 1:
[ Relative atomic mass:
16.
of Sulphur trioxide SO3
Calculate the mass of
Relative Formula Mass
No. of Moles of SO3=
Mass
of SO3 =
= mole x RFM
=
x
 O = 16 ;  S = 32  ]
0.5
g
=
mol
g
g
mol
NEXT
given
Step 2:
Step 1:
Step 3:
[ Relative atomic mass:
17.
of Sulphur trioxide SO3
Calculate the number of atoms
1 molecule of SO3
No. of atoms of
1.5 M of SO3
No. of Moles of SO3=
 O = 16 ;  S = 32;
NA=6.02 x 1023  ]

 =
=
atoms of S, O,O,O
x
mole x Avogadro
in 1.5
x
mol
mol
NEXT
given
x1023
Step 2:
Step 1:
Step 3:
[ Relative atomic mass:
18.
which has 3.01 x 1023
Calculate the mass
RFM  of CO2
Mass of CO2
No. of Moles of CO2=
=
=
 O = 16 ;  C = 12;
NA=6.02 x 1023  ]

molecules
of carbon dioxide CO2
 =
g
No of molecules
mole x RFM
g
NA
x
in  STP
NEXT
mol
[ Relative atomic mass:
From the equation, 1 mol of  Oxygen O2 used
19.
when S + O2 → SO2 and the O2 used is 67.2 dm3 at STP?
produce
Calculate the
S      +    O
mole of SO2
volume
 O = 16 ;  S = 32;
NA=6.02 x 1023  ]

of sulphur dioxide SO2
SO2
NEXT
Moles:
molar gas volume=22.4 dm3 STP 
Volume:
No. of moles

=Vol ÷ 22.4
when S + O2 → SO2 and the O2 used is 67.2 dm3 at STP?
20.
Calculate the
[ Relative atomic mass:
S    +  O2    
1
 67.2
volume
1
dm3
  SO2
of sulphur dioxide SO2
1
?
 O = 16 ;  S = 32;
NA=6.02 x 1023  ]

=
=
Volume of SO2
X
dm3
NEXT
dm3
Step 2:
Step 1:
Step 3:
21.
at STP
Calculate the
Find the RMM
Divide  mass of C2H6 by RMM
use the mole  x molar gas volume=vol
[ Relative atomic mass:
 H = 1 ;  C = 12;
molar gas volume=22.4 dm3 STP  ]

volume
of 0.75g of ethane gas C2H6
NEXT
Step 2:
Step 1:
Step 3:
22.
at STP
Calculate the
No. of  mole  of C2H6
Volume of C2H6
RMM of C2H6=
[ Relative atomic mass:
 H = 1 ;  C = 12;
molar gas volume=22.4 dm3 STP  ]

volume
=
=
of 0.75g of ethane gas C2H6
dm3
 =
g
dm3 x
mol
mol
NEXT
Step 2:
Step 1:
Step 3:
23.
at room temperature
Calculate the
Get mole=Divide  vol of C3H6 by Molar gas vol
use the mole  x RMM =mass
Find the RMM
mass
 H = 1 ;  C = 12;
molar gas volume=24 dm3 R.T.  ]

of 6.72 dm3 of propene gas C3H6
[ Relative atomic mass:
NEXT
Step 2:
Step 1:
Step 3:
24.
at room temperature
Calculate the
No. of  mole  of C3H6
Mass of C3H6
RMM of C3H6=
mass
 H = 1 ;  C = 12;
molar gas volume=24 dm3 R.T.  ]

=
of 6.72 dm3 of propene gas C3H6
=
[ Relative atomic mass:
g
 =
g
g x
mol
mol
NEXT
Moles:
Step 1:
No. of
Moles
when 0.5 dm3 of     mole of

25.
so
Calculate the
Study the balanced equation
0.5
2H2O2  → 2H2O + O2 .
2
1
2
volume
of oxygen gas O2 produced
1
H2O2
decomposed
1 x 0.5 ÷ 2
NEXT
To find Volume of O2 :
Step 2:
Volume:
when 0.5 dm3 of       mole of

26.
Calculate the
given
2000÷4
the volume
0.5
volume
2000 cm3
500
2H2O2  → 2H2O + O2 .
2
of oxygen gas O2 produced
H2O2
÷ 4
=
decomposed
24000 cm3
1
x
X
NEXT
no. of
moles
mol
Moles:
No. of
moles

when 200 cm3 of 0.5 mol of

 
27.
2H2O2  → 2H2O + O2 .
Calculate the
[ Relative atomic mass:
2H2O2       
0.5
volume
2H2O
 + O2
of oxygen gas O2 produced
H2O2
 O = 16 ;  H = 1;
24dm3 at room tem  ]

decomposed
NEXT
when 200 cm3 of 0.5 mol of

 
28.
2H2O2  → 2H2O + O2 .
Volume
No. of
moles

Moles
Calculate the
2000 cm3
[ Relative atomic mass:
2H2O2       
0.5
2
volume
2H2O
2
 + O2
0.25
of oxygen gas O2 produced
1
H2O2
 O = 16 ;  H = 1;
24dm3 at room tem  ]

cm3
decomposed
NEXT
when 200 cm3 of 0.5 mol of

 
29.
2H2O2  → 2H2O + O2 .
Volume
÷10
No. of
moles

Moles
Calculate the
2000 cm3
[ Relative atomic mass:
2H2O2       
0.5
2
cm3
volume
2H2O
2
24000
 + O2
0.25
of oxygen gas O2 produced
1
H2O2
 O = 16 ;  H = 1;
24dm3 at room tem  ]

cm3
cm3
decomposed
=
=
Volume of O2
x
cm3
cm3
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