Question:
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Answer:
(a) 34 u (b) 76 u
Atoms and Molecules
Q 1.
What is gram-atomic mass of an element?
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.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 4.
What is the chemical symbol for iron?
Q 5.
Define 'formula mass' of a compound.
Q 6.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 7.
Who established the two important laws of chemical combinations?
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.
How many atoms are there in 0.25 mole of hydrogen ?
Q 10.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 11.
Write the formulae of the following compounds. Also name the elements present in them.
(a) Water
(b) Ammonia
(c) Methane
(d) Sulphur dioxide
(f) Ethanol
Q 12.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 13.
Name the international organization who approves names of elements.
Q 14.
Name one element each which forms diatomic and tetra atomic molecule.
Q 15.
Define molecule. What are its important properties?
Q 16.
Give four examples of diatomic molecules.
Q 18.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 19.
What is the significance of a chemical symbol?
Q 20.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 21.
What are the postulates of Dalton's atomic theory?
Q 22.
State Law of constant proportions. Explain with an example.
Q 23.
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 24.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 25.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 26.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 27.
Write down the names of compounds represented by the following formulae:
(i) Al
2(SO
4)
3 (ii) CaCl
2 (iii) K
2SO
4 (iv) KNO
3 (v) CaCO
3
Q 28.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 29.
How many atoms are present in a
(i) H
2S molecule and
(ii) PO
43- ion?
Q 30.
What are ionic compounds?
Q 31.
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Q 32.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 33.
Fill in the blanks:
Atomic radius is measured in __________.
Q 34.
Which element has the smallest atom in size?
Q 35.
What is the atomic mass unit?
Q 36.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 37.
What are polyatomic ions? Give examples?
Q 38.
What is the mass of
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?
(c) 10 moles of sodium sulphite (Na
2SO
3)?
Q 39.
Give one major drawback of Dalton's atomic theory of matter.
Q 40.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 41.
Calculate the molecular mass of chloroform (CHC1
Q 42.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 43.
Give an example to show Law of conservation of mass applies to physical change also.
Q 44.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 45.
How do we know the presence of atoms if they do not exist independently for most of the elements?
Q 46.
Name one element which forms diatomic and triatomic molecule.
Q 47.
Name the unit in which the radius of an atom is usually expressed.
Q 48.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 49.
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 50.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
