Atoms and Molecules

Q 1.

What is gram-atomic mass of an element?

Q 2.

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

Q 3.

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

Q 4.

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

Q 5.

Define 'formula mass' of a compound.

Q 6.

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

Q 7.

Which of the following statements is NOT true about an atom?
(a) Atoms are the building blocks from which molecules and ions are formed.
(b) Atoms cannot exist independently.
(c) Atoms are neutral in nature
(d) Atoms combine together to form matter that we can see, feel or touch.

Q 8.

What is the chemical symbol for iron?

Q 9.

If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?

Q 10.

Give four examples of diatomic molecules.

Q 11.

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

Q 12.

How many atoms are there in 0.25 mole of hydrogen ?

Q 13.

Show by means of calculations that 5 moles of CO, and 5 moles of H$$₂O do not have the same mass. How much is the difference in their masses ?

Q 14.

What are the postulates of Dalton's atomic theory?

Q 15.

Fill in the blanks:
Atomic radius is measured in __________.

Q 16.

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

Q 17.

Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium

Q 18.

What are polyatomic ions? Give examples?

Q 19.

What are ionic compounds?

Q 20.

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

Q 21.

What is meant by atomicity ? Explain with two

Q 22.

(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 23.

What is the law of conservation of mass?

Q 24.

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

Q 25.

Fill in the blanks:
_________ are building block of all matter.

Q 26.

What is Formula Unit Mass? How it is different from molecular mass?

Q 27.

Define mole. What is its significance?

Q 28.

Who introduced the term 'mole' in chemistry?

Q 29.

What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?

Q 30.

What are the building blocks of matter ?

Q 31.

Calculate the molecular mass of nitric acid,HNO$$₃.
(Atomic masses :H =lu; N = 14u;0 = 16u)

Q 32.

Calculate the molecular mass of hydrogen bromide (HBr).
(Atomic masses: H=1; Br= 80 U)

Q 33.

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 34.

What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.

Q 35.

What is the difference between a cation and an anion ? Explain with examples. Using this information, write down the formulae of:
(i) Sodium sulphide
(ii) Copper nitrate

Q 36.

Fill in the following blanks :
(a)1 mole Contains...........atoms- molecules or ions of a substance
(b)A mole represents an..........number of Particles of a substance.
(c)60 g of carbon element are...........moles of carbon atoms.
(d) 0.5 mole of calcium element has a mass of..........
(e) 64 g of oxygen gas contains..........moles of oxygen atoms.

Q 37.

If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.

Q 38.

Calculate the number of molecules in 4 g of oxygen.

Q 39.

Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H$$₂S.

Q 40.

Calculate the mole ratio of 240 g of calcium and 240 g of magnesium. (Ca = 40 u ; Mg = 24 u)

Q 41.

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

Q 42.

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 43.

When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combination will govern your answer?

Q 44.

Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?

Q 45.

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

Q 46.

Who proposed the chemical notation based on first two letters of the name of the element?

Q 47.

Name the international organization who approves names of elements.

Q 48.

What is the significance of a chemical symbol?

Q 49.

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

Q 50.

Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.