Question:
Name the elements water is made of. What are the valencies of these elements ? Work out the chemical formula for water.
Atoms and Molecules
Q 1.
Define 'formula mass' of a compound.
Q 2.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 3.
What is the chemical symbol for iron?
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.
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 8.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 9.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 10.
What is the atomic mass unit?
Q 11.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 12.
Define molecule. What are its important properties?
Q 13.
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 14.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 15.
What is the molecular mass of a substance?
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.
Convert 12 g of oxygen gas into moles.
Q 20.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 21.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 22.
What is gram-molecular mass of a substance?
Q 23.
Define mole. What is its significance?
Q 24.
Give one major drawback of Dalton's atomic theory of matter.
Q 25.
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 26.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 27.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 28.
How many atoms are there in 0.25 mole of hydrogen ?
Q 29.
What is the law of conservation of mass?
Q 30.
Who established the two important laws of chemical combinations?
Q 31.
What are the postulates of Dalton's atomic theory?
Q 32.
What is the significance of a chemical symbol?
Q 33.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 34.
Give four examples of diatomic molecules.
Q 35.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 36.
What are ionic compounds?
Q 37.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 38.
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 39.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 40.
Based on type of substance, how molecules are classified?
Q 41.
(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 42.
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 43.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 44.
Find out number of atoms in 15 moles of He.
Q 45.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 46.
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 47.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 48.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 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
Q 50.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
