Atoms and Molecules

Q 1.

What is gram-atomic mass of an element?

Q 2.

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

Q 3.

Define 'formula mass' of a compound.

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.

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

Q 6.

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 7.

(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 8.

State whether the following statements are true or false :
(a)A sodium ion has positive charge because it has more protons than a neutral atom
(b)A chloride ion has negative charge because it has more electrons than a neutral atom.

Q 9.

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

Q 10.

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

Q 11.

Fill in the blanks:
The atomicity of sulphur S₈ is ________.

Q 12.

What are the building blocks of matter ?

Q 13.

Name the unit in which the radius of an atom is usually expressed.

Q 14.

The molecular formula of glucose is C$$₆H₁₂O₆. Calculate its molecular mass. (Atomic masses : C = 12 u ; H =1 u ; O = 16 u)

Q 15.

Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS$$₂
(Atomic masses :H = lu;S = 32u;C = 12u)

Q 16.

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 17.

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

Q 18.

Fill in the blanks:
The _______________ of a compound is a symbolic representation of its composition.

Q 19.

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 20.

What is the chemical symbol for iron?

Q 21.

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

Q 22.

Fill in the blanks:
Hydrogen and oxygen combines to form H₂O and H₂O₂. These two compounds obey the law of ____________________.

Q 23.

What is an ion?

Q 24.

Who introduced the term 'mole' in chemistry?

Q 25.

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

Q 26.

Is it possible to see atoms these days ? Explain your answer.

Q 27.

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

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.

How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)

Q 31.

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

Q 32.

Calculate the mass m grams of 0.17 mole of hydrogen sulphide, H,S.(Atomic masses : H = 1 U/ S = 32 u)

Q 33.

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

Q 34.

What are the postulates of Dalton's atomic theory?

Q 35.

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

Q 36.

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

Q 37.

How will you define chemical symbol?

Q 38.

What is valency of an element?

Q 39.

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

Q 40.

'If 100 grams of calcium carbonate (whether in the form of marble or chalk) are decomposed completely,then 56 grams of calcium oxide and 44 grams of carbon dioxide are obtained'.Which law of chemical combination is illustrated by this statement ?

Q 41.

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

Q 42.

Calculate the molecular mass of ethanoic acid, CH$$₃COOH.
(Atomic masses :C = 12u;H = lu;0 = 16u)

Q 43.

An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?

Q 44.

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 45.

What are (ionic compounds, and (ii) molecular compounds ? Give two examples of each type of compounds.

Q 46.

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 47.

How many atoms are present in one gram atomic mass of a substance ?

Q 48.

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

Q 49.

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 50.

If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?