Question:
Name the international organization who approves names of elements.
Answer:
IUPAC (International Union of Pure and Applied Chemistry)
Atoms and Molecules
Q 1.
What is the chemical symbol for iron?
Q 2.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 3.
Define 'formula mass' of a compound.
Q 4.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 5.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 6.
What is the atomic mass unit?
Q 7.
What do we call those particles which have more or less electrons than the normal atoms ?
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:
One mole of water contains ______________ molecules.
Q 10.
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 11.
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 12.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 13.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 14.
Define molecule. What are its important properties?
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.
What is gram-atomic mass of an element?
Q 18.
Define mole. What is its significance?
Q 19.
Convert 12 g of oxygen gas into moles.
Q 20.
Give one major drawback of Dalton's atomic theory of matter.
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.
What are the postulates of Dalton's atomic theory?
Q 23.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 24.
What is the significance of a chemical symbol?
Q 25.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 26.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 27.
What is gram-molecular mass of a substance?
Q 28.
How many atoms are there in 0.25 mole of hydrogen ?
Q 29.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 30.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 31.
Name one element which forms diatomic and triatomic molecule.
Q 32.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Q 33.
Find out number of atoms in 15 moles of He.
Q 34.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 35.
What is the law of conservation of mass?
Q 36.
Who established the two important laws of chemical combinations?
Q 37.
How will you define chemical symbol?
Q 38.
Can atoms of an element exist independently? Give examples of elements which exist in atomic form. Give examples of elements that do not exist in atomic form.
Q 39.
Fill in the blanks:
An element has only one type of __________.
Q 40.
Based on type of substance, how molecules are classified?
Q 42.
Give four examples of diatomic molecules.
Q 43.
(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 44.
What are polyatomic ions? Give examples?
Q 45.
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 46.
How many moles are there in 4.6 gms of Sodium(Na)?
Q 47.
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 48.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 49.
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 50.
Calculate the number of molecules of phosphorus (P
4) present in 31 gram of phosphorus.
