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.

(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.

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

Q 9.

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

Q 10.

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

Q 11.

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

Q 12.

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 13.

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

Q 14.

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

Q 15.

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

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.

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

Q 23.

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

Q 24.

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 25.

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 26.

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

Q 27.

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

Q 28.

What is the chemical symbol for iron?

Q 29.

How will you define chemical symbol?

Q 30.

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

Q 31.

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

Q 32.

What is gram-molecular mass of a substance?

Q 33.

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

Q 34.

What are the building blocks of matter ?

Q 35.

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

Q 36.

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

Q 37.

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

Q 38.

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

Q 39.

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

Q 40.

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 41.

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 42.

How many atoms are there in 0.25 mole of hydrogen ?

Q 43.

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

Q 44.

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

Q 45.

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 46.

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

Q 47.

Who established the two important laws of chemical combinations?

Q 48.

What are the postulates of Dalton's atomic theory?

Q 49.

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 50.

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