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.

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

Q 7.

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

Q 8.

(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 9.

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

Q 10.

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

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.

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

Q 13.

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 14.

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

Q 15.

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

Q 16.

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

Q 17.

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

Q 18.

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

Q 19.

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 20.

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 21.

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

Q 22.

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 23.

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

Q 24.

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

Q 25.

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 26.

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 27.

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

Q 28.

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

Q 29.

What is the chemical symbol for iron?

Q 30.

How will you define chemical symbol?

Q 31.

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

Q 32.

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

Q 33.

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

Q 34.

What is gram-molecular mass of a substance?

Q 35.

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

Q 36.

What are the building blocks of matter ?

Q 37.

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

Q 38.

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

Q 39.

An element Z has a valency of 3. What is the formula of oxide of Z ?

Q 40.

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

Q 41.

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

Q 42.

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 43.

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 44.

How many atoms are there in 0.25 mole of hydrogen ?

Q 45.

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

Q 46.

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

Q 47.

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

Q 48.

Who established the two important laws of chemical combinations?

Q 49.

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 50.

What are the postulates of Dalton's atomic theory?