Chemistry Class 9 Chapter 1
Fundamentals of Chemistry Important Numericals
1. What is the mass of 5 moles of ice?
SOLUTION
Given no. of mole of ice =5 moles
Molecular mass of ice (H2O)= (2×1)+(1×16)=2+16
Molecular mass of ice =18 amu
Number of moles = Mass in gram ÷ Molecular mass
Rearranging the formula
Mass in gram =number of moles × Molecular mass
Mass of ice in grams = 5 × 18 = 90 grams
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2. During thunder storms, oxygen is transformed into ozone O3. Determine the mass of ozone if a storm produces 9.05 moles of ozone.
Ozone is a molecular substance. Determine its molar mass and use it to convert moles to mass in grams.
9.05 moles of O3 ⎯→? g of O3
Solution:
1 mole of O3 = 16 x 3 = 48 g
1 mole of O3 = 48 g
So, 9.05 moles of O3 = 48 g x 9.05
= 434.4g of O3
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3. When methane is burned, carbon dioxide is produced. How much CO2 is created when 0.25 moles of CO2 are produced?
SOLUTION
Molar mass of CO2 = 12 + 16 x 2 = 44g
1 mole of CO2 = 44g of CO2
So, 0.25 moles of CO2 = 44 x 0.25 = 11g of CO2
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4. Calculate the moles of each of the following
A. Balloon filled with 5g of hydrogen
B. A block of ice that has mass of 100g
SOLUTION
a) Molar mass of H2 = 1.008 x 2 = 2.016g
1 mole of H2 = 2.016g
So, 2.016g of H2 = 1 mole of H2
1g of H2= 1/2.016 moles of H2
5 gram of H2 =1÷2.016×5
5 gram of H2 = 2.48 Moles of H2
b) 1 Mole Of H2O =2×1.008+16
1 Mole of H2O =2.016+16
1Mole of H2O=18.016g
so
1 gram of H2O = 1÷18.016 moles
100 Gram of H2O= 1÷18.016×100 moles
100 grams of H2O=5.55 Moles of H2O
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5. Zn is a metal used to prevent corrosion by galvanizing steel. How many atoms are in 1.25 moles of zinc?
SOLUTION
1 mole of Zn contains = 23 6.022 x 1023 atoms
1.25 moles of Zn contains = 6.022 x 1023 x 1.25 = 7.53 x 1023 Zn atoms
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6. Methane is one of the principal constituents of natural gas. Determine how many moles are in 0.5 moles of a pure methane sample.
SOLUTION
1 mole of CH4 contains = 6.022 x 1023 molecules
So, 0.5 moles of CH4 will contain = 6.022 x 1023 x 0.5 = 3.011 x 1023 molecules
7. Titanium is a metal that is used in rockets. Calculate the number of moles in a sample containing 3.011×1023atoms
SOLUTION
6.022 x 1023 atoms = 1 mole
3.011 x 1023Atoms →? mole
6.022×1023 atoms = 1 mole of Ti
1 Ti atom =1÷6.022×1023 moles of Ti
3.011×1023 Ti atoms = 1 ÷ (6.022×1023) ×3 .011×1023 moles of Ti
=0.5 moles of Ti
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8. Determine the number of moles in 60 grams of carbon dioxide.
SOLUTION
Mass of CO2 =60 g
The molar mass of CO2= 12g+2(16)g
=12g+32g
=44g/mol
Number of moles of CO2=Mass in grams ÷ molar mass
Number of moles of CO2=60/44
=1.364 moles
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9. How many moles of hydrogen are there in 8.9×1023 hydrogen atoms
SOLUTION
Number of atoms of hydrogen =8.9×1023
Avagadro number = NA=6.023×1023
Number of moles of hydrogen =Number of atoms or molecules /Avogadro number
Number of moles of hydrogen =8.9×1023 ÷6.023×1023
=1.48 moles
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10. Determine the molar masses of water, sodium, nitrogen, and sucrose
SOLUTION
a) Molecular mass of H2O
= 1 X 2 + 16 = 18
Therefore, mass of 1 mole of water = 18 g
b) 1 mole of sodium ( Na) = 23g
c ) Nitrogen occurs as diatomic molecules.
Molecular mass of nitrogen (N2 )= 14 x 2
= 28amu
Therefore, mass of 1 mole of N2 = 28 g
d ) Molecular mass ofC12H22O11
= 12×12 + 1×22 + 16×11
= 144 + 22 + 176
Therefore, mass of 1 mole of sucrose = 342g
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11. Calculate the number of moles of butane (C4H10) in 151g of butane?
SOLUTION
Mass= 151 g
Molecular mass of butane= (12×4) + (1×10) = 58amu
Number of moles = Mass ÷ Molecular mass
Number of moles =151÷58
Number of moles = 2.63 moles
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12. Calculate the mass of 6.68 ×1023molecules of PCl3
SOLUTION
Number of molecules =6.68 ×1023molecules
Avogadro number= 6.023×1023
Molecular mass of PCl3= (1×30.97)+(3×35.5)
Molecular mass of PCl3=30.97+106.5=137.47 amu
First Calculating moles
Number of moles = Number of molecules/ Avogadro number
Number of moles =6.68 ×1023molecules ÷6.023×1023
Number of moles =1.10 mol
Mass in gram =Number of moles × molecular mass
Mass in gram =1.10×137.47
Mass in gram =151.62g
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13. Determine the number of molecules in 6.50 moles of CH4
SOLUTION
Number of moles = 6.5 moles
Avogadro number =6.023×1023
Number of moles = Number of molecule / Avogadro’s number
Number of molecules= No of moles × Avogadro’s number
Number of molecules =6.50×6.023×1023
Number of molecules =39.14×1023
Number of molecules =3.914×1024
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