Comprehensive chemistry notes for Ninth Class Chemistry

1. Chapter 2
Chemical Combinations
(You can neither stop nor save the time but
can make every moment historical if you
know the value of time)
Chemistry MCQs Dr. Sajid Ali Talpur

2.  Definitions
1. Atomic mass: - Atomic mass is defined as the
mass of one atom of the element compared with
the mass of one atom of C12 (the stable light
isotope of carbon).
2. Molecular mass: - It is defined as the sum of
atomic masses of the atoms of all the elements
present in a molecule shown by its molecular
formula.
3. Empirical formula mass/ formula mass: - It is
the sum of atomic masses as given in the
simplest (empirical) formula of ionic compound
4. Molecular formula: - The expression, showing
types and actual number of atoms present in a
compound, using symbols for component
elements and numerals for number of atoms of
each element per molecule, like C6H6 for
benzene.
5. Empirical formula: - A chemical formula that
indicates the relative proportions of the elements
in a compound rather than the actual number of
the atoms of the elements.
6. Mole: - One mole is gram atomic mass, gram
molecular mass or gram formula mass of any
substance (atoms, ions, molecules), which
contains 6.02*1023
elementary entities.
Chemistry MCQs Dr. Sajid Ali Talpur

3. 7. Molar mass: - The mass of one mole is called
molar mass.
8. Avagadro’s number: - The number of basic
quantities as present in 12 grams of C12
i.e
6.02*1023
 Multiple Choice Questions
1. Mass can not be created but can be destroyed.
a) true b) false
2. Landolt experiment is performed to verify:
a) law of conservation of mass
b) law of definite proportions
c) law of multiple proportions
d) law of reciprocal proportions
3. The empirical formula of glucose is:
a) CH b) CH2O
c) C3H6O6 d) C6H12O6
4. The empirical formula mass of benzene is:
a) 12 a.m.u b) 13 a.m.u
c) 78 a.m.u d) N.O.T
5. Molecular mass of sodium is:
a) 11 a.m.u b) 12 a.m.u
c) 23 a.m.u d) N.O.T
Chemistry MCQs Dr. Sajid Ali Talpur

4. 6. ______moles are there In 50 g of CaCO3.
a) 0.5 b) 1
c) 1.5 d) 1.5
7. 3 moles of Carbon are equal to:
a) 4g b) 36g
c) 132g d) 18.06*1023
8. Zn + HCl → ZnCl2 + H2. The reaction is an
example of:
a) decomposition reaction
b) addition reaction
c) single displacement reaction
d) double displacement reaction
e) combustion reaction
9. Chemical equation is a short hand method for
describing a compound.
a) true b) false
10. Combustion reaction consumes heat:
a) true b) false
The book MCQs
11. mass is neither created nor destroyed during a
chemical reaction is the statement of:
a) law of conservation of mass
b) law of definite proportions
c) law of multiple proportions
d) law of reciprocal proportions
Chemistry MCQs Dr. Sajid Ali Talpur

5. 12. a given compound always contains exactly the
same proportion of elements by mass is the
statement of:
a) law of conservation of mass
b) law of definite proportions
c) law of multiple proportions
d) law of reciprocal proportions
13. the average mass of natural mixture of isotopes,
which is compared to the mass of one atom of
C-12 a.m.u is called:
a) atomic number b) atomic mass
c) mass number d) molecular mass
14. a formula that gives only the relative number of
each type of atoms in a molecule is called:
a) empirical formula b) molecular formula
c) molecular mass d) formula mass
15. a formula that indicates actual number and type
of atoms in a molecule is called:
a) empirical formula b) molecular formula
c) molecular mass d) formula mass
16. the sum of atomic masses of all atoms in a
molecule is called:
a) empirical formula b) molecular formula
c) molecular mass d) formula mass
17. the sum of atomic masses of all atoms in a
formula unit:
a) empirical formula b) molecular formula
c) molecular mass d) formula mass
Chemistry MCQs Dr. Sajid Ali Talpur

6. 18. the mass of one mole of a substance expressed
in grams is called:
a) empirical formula b) molecular formula
c) molecular mass d) molar mass
19. 44 a.m.u of CO2 is equal to:
a) formula mass b) atomic mass
c) molecular mass d) molar mass
20. 5 moles of H2O are equal to:
a) 80g b) 90g
c) 100g d) 90a.m.u
Answer Key
1 B 2 A 3 B
4 B 5 D 6 A
7 B 8 C 9 B
10 B 11 A 12 B
13 B 14 A 15 B
16 C 17 D 18 D
19 C 20 D
Chemistry MCQs Dr. Sajid Ali Talpur

7. 18. the mass of one mole of a substance expressed
in grams is called:
a) empirical formula b) molecular formula
c) molecular mass d) molar mass
19. 44 a.m.u of CO2 is equal to:
a) formula mass b) atomic mass
c) molecular mass d) molar mass
20. 5 moles of H2O are equal to:
a) 80g b) 90g
c) 100g d) 90a.m.u
Answer Key
1 B 2 A 3 B
4 B 5 D 6 A
7 B 8 C 9 B
10 B 11 A 12 B
13 B 14 A 15 B
16 C 17 D 18 D
19 C 20 D
Chemistry MCQs Dr. Sajid Ali Talpur