Atoms and Molecules

Q 1.

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

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 is gram-atomic mass of an element?

Q 4.

Define 'formula mass' of a compound.

Q 5.

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

Q 6.

(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 7.

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

Q 8.

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

Q 9.

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

Q 10.

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

Q 11.

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 12.

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

Q 13.

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

Q 14.

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

Q 15.

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

Q 16.

What is the chemical symbol for iron?

Q 17.

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

Q 18.

What is gram-molecular mass of a substance?

Q 19.

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

Q 20.

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

Q 21.

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

Q 22.

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

Q 23.

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 24.

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

Q 25.

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 26.

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 27.

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 28.

Calculate the number of moles in 12.044 x 10$23$ atoms of phosphorus

Q 29.

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

Q 30.

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

Q 31.

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 32.

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

Q 33.

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

Q 34.

How will you define chemical symbol?

Q 35.

Define molecule. What are its important properties?

Q 36.

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

Q 37.

(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 38.

What is an ion?

Q 39.

Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide

Q 40.

What is the molecular mass of a substance?

Q 41.

How do we know the presence of atoms if they do not exist independently for most of the elements?

Q 42.

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

Q 43.

Calculate the number of molecules of phosphorus (P₄) present in 31 gram of phosphorus.

Q 44.

What are the building blocks of matter ?

Q 45.

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

Q 46.

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

Q 47.

Convert 12 g of oxygen gas into moles.

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.

Give an example to show Law of conservation of mass applies to physical change also.