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.

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

Q 7.

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

Q 8.

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 9.

What is the chemical symbol for iron?

Q 10.

What are the postulates of Dalton's atomic theory?

Q 11.

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

Q 12.

Give four examples of diatomic molecules.

Q 13.

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

Q 14.

How many atoms are there in 0.25 mole of hydrogen ?

Q 15.

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 16.

(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 17.

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

Q 18.

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

Q 19.

What are polyatomic ions? Give examples?

Q 20.

What are ionic compounds?

Q 21.

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

Q 22.

What is meant by atomicity ? Explain with two

Q 23.

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

Q 24.

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

Q 25.

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 26.

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

Q 27.

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 28.

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 29.

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

Q 30.

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

Q 31.

What is the law of conservation of mass?

Q 32.

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

Q 33.

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

Q 34.

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

Q 35.

Name one element which forms diatomic and triatomic molecule.

Q 36.

Define mole. What is its significance?

Q 37.

What is molar mass?

Q 38.

Who introduced the term 'mole' in chemistry?

Q 39.

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

Q 40.

What are the building blocks of matter ?

Q 41.

What is meant by the symbol of an element ? Explain with examples.

Q 42.

Work out the formulae for the following compounds :
(a) Sodium oxide

Q 43.

What is the numerical value of Avogadro number ?

Q 44.

What name is given to the number 6.022 x 10$23$

Q 45.

What is the mass of 0.2 mole of oxygen atoms ?

Q 46.

How many moles of calcium carbonate (CaCO$$₃) are are present in 10 g of the substance ? (Ca = 40 u • C= 12 u-O = 16 u)

Q 47.

Calculate the number of molecules in 4 g of oxygen.

Q 48.

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

Q 49.

(a) What is meant by the 'molar mass'of a substance ? State the unit in which molar mass usually expressed.
(b) Calulate the molar masses of the following substances. Write the results with proper units
(1) Ozone molecule, O$$₃,(ii)Ethanoic acid,CH$$₃COOH

Q 50.

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