Atoms and Molecules

Q 1.

Give one major drawback of Dalton's atomic theory of matter.

Q 2.

Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.

Q 3.

What do we call those particles which have more or less electrons than the normal atoms ?

Q 4.

Explain with example that law of conservation of mass is valid for chemical reactions.

Q 5.

Who proposed Law of Definite Proportions (or Law of Constant Composition)?

Q 6.

(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.

Q 7.

Convert 12 g of oxygen gas into moles.

Q 8.

Fill in the blanks:
One mole of water contains ______________ molecules.

Q 9.

Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?

Q 10.

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 11.

If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.

Q 12.

What is the mass of 5 moles of sodium carbonate (Na$$₃CO₃) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)

Q 13.

State Law of constant proportions. Explain with an example.

Q 14.

Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.

Q 15.

Define 'formula mass' of a compound.

Q 16.

Calculate the mass of 3.011 x 10$24$atoms of carbon

Q 17.

Fill in the blanks:
Atoms can be observed using ____________ Microscope.

Q 18.

Name the international organization who approves names of elements.

Q 19.

Name one element each which forms diatomic and tetra atomic molecule.

Q 20.

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 (Na₂SO₃)?

Q 21.

How many moles are 3.6 g of water ?

Q 22.

(a) What is meant by 'a mole of carbon atoms' ?
(b)(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : A1 = 27 u ; Fe = 56 u)

Q 23.

(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al$$₂O₃(ii) co₂(iii) C1$$₂O₇ (iv) H$$₂SO₄(p)A1$$₂(S0₄)$$₃

Q 24.

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

Q 25.

What is the significance of a chemical symbol?

Q 26.

Fill in the blanks:
The chemical symbol of flourine is ________.

Q 27.

What is the molecular mass of a substance?

Q 28.

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 29.

Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.

Q 30.

How will you define chemical symbol?

Q 31.

Why do atoms of the most of the elements not exist independently?

Q 32.

What is relative atomic mass of an element? How it is related to atomic mass unit?

Q 33.

Define molecule. What are its important properties?

Q 34.

Fill in the blanks:
The chemical symbol of mercury is _________.

Q 35.

Give three examples of monoatomic molecules.

Q 36.

Give four examples of diatomic molecules.

Q 37.

What are ionic compounds?

Q 38.

Calculate the number of molecules of sulphur (S₈) present in 16 g of solid sulphur.

Q 39.

Calculate the molecular masses of the following compounds :
(a) Methanol, CH$$₃OH
(b) Ethanol, C$$₂H$$₅OH

Q 40.

Work out the formula for magnesium hydrogencarbonate.

Q 41.

Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO$$₄
(b) (NH$$₄)$$₂SO$$₄
(c)$Na$₂O
(d)Na$$₂CO$$₃
(e)CaCl$$₂

Q 42.

Calculate the number of molecules in 4 g of oxygen.

Q 43.

Who established the two important laws of chemical combinations?

Q 44.

Fill in the blanks:
___________ is the combining capacity of an element.

Q 45.

Fill in the blanks:
The mass of 5 moles of ammonia (NH₃) is __________.

Q 46.

(i) What is the chemical formula of Water molecule?
(ii) What is its atomicity?
(iii) Calculate the ratio of masses of atoms of elements present in water molecule.
(iv) Calculate the ratio by number of atoms of elements present in water molecule.

Q 47.

Write the chemical formulae of the following. Also identify the ions present.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate.

Q 48.

Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

Q 49.

Name one element which forms diatomic and triatomic molecule.

Q 50.

What is gram-atomic mass of an element?