Question:
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Answer:
J.L. Proust 1799 (French Chemist)
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.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 5.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 6.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
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.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 9.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Q 10.
What is the atomic mass unit?
Q 11.
Fill in the blanks:
One mole of water contains ______________ molecules.
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.
Define molecule. What are its important properties?
Q 14.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 15.
Name one element each which forms diatomic and tetra atomic molecule.
Q 16.
What is gram-atomic mass of an element?
Q 17.
What is the molecular mass of a substance?
Q 18.
Name one element which forms diatomic and triatomic molecule.
Q 19.
Define mole. What is its significance?
Q 20.
Convert 12 g of oxygen gas into moles.
Q 21.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 22.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 23.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 24.
What is gram-molecular mass of a substance?
Q 25.
Give one major drawback of Dalton's atomic theory of matter.
Q 26.
How many atoms are there in 0.25 mole of hydrogen ?
Q 27.
What is the law of conservation of mass?
Q 28.
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 29.
What are the postulates of Dalton's atomic theory?
Q 30.
What is the significance of a chemical symbol?
Q 31.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 32.
Calculate the molecular masses of the following compounds :
(a) Hydrogen sulphide, H2S
(b) Carbon disulphide, CS
Q 33.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 34.
Who established the two important laws of chemical combinations?
Q 35.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 36.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 37.
Give four examples of diatomic molecules.
Q 38.
What are ionic compounds?
Q 39.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 40.
Find out number of atoms in 15 moles of He.
Q 41.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 42.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
Q 43.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 44.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 45.
Fill in the blanks:
An element has only one type of __________.
Q 46.
Based on type of substance, how molecules are classified?
Q 48.
(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 49.
What are polyatomic ions? Give examples?
Q 50.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
