Question:
(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.
Answer:
(i) Water molecule: (H2O)
(ii) It is triatomic i.e. 2 atoms of H + 1 atom of O = 3 atoms of water molecule.
(iii) Mass of 1 H-atom = 1 u
Mass of two H-atoms = 2u
Mass of O atom = 16u
Mass ratio of H:O = 2u:16u = 1:8
(iv) Number of atoms ration H:O = 2:1
Atoms and Molecules
Q 1.
What is the chemical symbol for iron?
Q 2.
Define 'formula mass' of a compound.
Q 3.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 4.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 5.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 6.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 7.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 8.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 9.
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 10.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 11.
What is the atomic mass unit?
Q 12.
Magnesium is two times heavier than C-12 atom, what shall be the mass of Mg atom in terms of atomic mass units? (Given mass of C-12 atom = 12u)
Q 13.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 14.
What is the molecular mass of a substance?
Q 15.
Define molecule. What are its important properties?
Q 16.
Name one element each which forms diatomic and tetra atomic molecule.
Q 17.
Name one element which forms diatomic and triatomic molecule.
Q 18.
What is gram-atomic mass of an element?
Q 19.
Define mole. What is its significance?
Q 20.
What is the law of conservation of mass?
Q 21.
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 22.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 23.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 24.
What is gram-molecular mass of a substance?
Q 25.
Convert 12 g of oxygen gas into moles.
Q 26.
What is the significance of a chemical symbol?
Q 27.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 28.
Give one major drawback of Dalton's atomic theory of matter.
Q 29.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 30.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 31.
How many atoms are there in 0.25 mole of hydrogen ?
Q 32.
What are the postulates of Dalton's atomic theory?
Q 33.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 34.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 35.
Give four examples of diatomic molecules.
Q 36.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 37.
Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?
Q 38.
Find out number of atoms in 15 moles of He.
Q 39.
Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(
Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
Q 40.
Who established the two important laws of chemical combinations?
Q 41.
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 43.
What are ionic compounds?
Q 44.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 45.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 46.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 47.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 48.
Fill in the blanks:
___________ is the combining capacity of an element.
Q 49.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 50.
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.
