Question:
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Answer:
(i) sodium oxide: Na+ + O2- ➜Na2O
(ii) aluminium chloride: Al3+ + Cl- ➜ AlCl3
(iii) sodium suphide: Na+ + S2- ➜ Na2S
(iv) magnesium hydroxide: Mg2+ + OH- ➜ Mg(OH)2
Atoms and Molecules
Q 1.
What is the chemical symbol for iron?
Q 2.
Define 'formula mass' of a compound.
Q 3.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 4.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 5.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 6.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 7.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 8.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 9.
What is the atomic mass unit?
Q 10.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 11.
What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na
2SO
3)?
Q 12.
Magnesium is two times heavier than C-12 atom, what shall be the mass of Mg atom in terms of atomic mass units? (Given mass of C-12 atom = 12u)
Q 13.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 14.
Name one element each which forms diatomic and tetra atomic molecule.
Q 15.
What is gram-atomic mass of an element?
Q 16.
Define molecule. What are its important properties?
Q 17.
What is the molecular mass of a substance?
Q 18.
Define mole. What is its significance?
Q 19.
Convert 12 g of oxygen gas into moles.
Q 20.
What is gram-molecular mass of a substance?
Q 21.
Give one major drawback of Dalton's atomic theory of matter.
Q 22.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Q 23.
What are the postulates of Dalton's atomic theory?
Q 24.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 25.
What is the significance of a chemical symbol?
Q 26.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 27.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 28.
Name one element which forms diatomic and triatomic molecule.
Q 29.
How many atoms are there in 0.25 mole of hydrogen ?
Q 30.
What is the law of conservation of mass?
Q 31.
Who established the two important laws of chemical combinations?
Q 32.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 33.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 34.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 35.
Give four examples of diatomic molecules.
Q 36.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 37.
Find out number of atoms in 15 moles of He.
Q 38.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 39.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 40.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 41.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 42.
What are polyatomic ions? Give examples?
Q 43.
Write down the names of compounds represented by the following formulae:
(i) Al
2(SO
4)
3 (ii) CaCl
2 (iii) K
2SO
4 (iv) KNO
3 (v) CaCO
3
Q 44.
What are ionic compounds?
Q 45.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 46.
Convert into moles: (a) 12 g of oxygen gas (b) 20 g of water (c) 22 g of carbon dioxide
Q 47.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 48.
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(
Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
Q 49.
Calculate the molecular mass of ethanoic acid, CH
Q 50.
Calculate the molecular mass of chloroform (CHC1
