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) 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 compound4. 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.7. Molar mass: - The mass of one mole is called molar mass.8. Avagadros 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) CHb) CH2O

c) C3H6O6d) C6H12O6

4. The empirical formula mass of benzene is:

a) 12 a.m.ub) 13 a.m.u

c) 78 a.m.ud) N.O.T

5. Molecular mass of sodium is:

a) 11 a.m.ub) 12 a.m.u

c) 23 a.m.ud) N.O.T

6. ______moles are there In 50 g of CaCO3.a) 0.5b) 1

c) 1.5d) 1.5

7. 3 moles of Carbon are equal to:a) 4gb) 36g

c) 132gd) 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) trueb) false

10. Combustion reaction consumes heat:

a) trueb) falseThe book MCQs11. 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

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 numberb) atomic mass

c) mass numberd) molecular mass

14. a formula that gives only the relative number of each type of atoms in a molecule is called:

a) empirical formulab) molecular formula

c) molecular massd) formula mass

15. a formula that indicates actual number and type of atoms in a molecule is called:

a) empirical formulab) molecular formula

c) molecular massd) formula mass

16. the sum of atomic masses of all atoms in a molecule is called:

a) empirical formulab) molecular formula

c) molecular massd) formula mass

17. the sum of atomic masses of all atoms in a formula unit:

a) empirical formulab) molecular formula

c) molecular massd) formula mass

18. the mass of one mole of a substance expressed in grams is called:

a) empirical formulab) molecular formula

c) molecular massd) molar mass

19. 44 a.m.u of CO2 is equal to:

a) formula massb) atomic mass

c) molecular massd) molar mass

20. 5 moles of H2O are equal to:

a) 80gb) 90g

c) 100gd) 90a.m.u

Answer Key

1B2A3B

4B5D6A

7B8C9B

10B11A12B

13B14A15B

16C17D18D

19C20D

Chemistry MCQs Dr. Sajid Ali Talpur