Question:
How many moles are there in 34.5 g of sodium ? (Atomic mass of Na = 23 u)
Atoms and Molecules
Q 1.
Give one major drawback of Dalton's atomic theory of matter.
Q 2.
What do we call those particles which have more or less electrons than the normal atoms ?
Q 3.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 4.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 5.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 6.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 7.
Convert 12 g of oxygen gas into moles.
Q 8.
If 16 g of oxygen contains 1 mole of oxygen atoms, calculate the mass of one atom of oxygen.
Q 9.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 10.
Fill in the blanks:
One mole of water contains ______________ molecules.
Q 11.
State Law of constant proportions. Explain with an example.
Q 12.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
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.
Define 'formula mass' of a compound.
Q 15.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
Q 16.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 17.
Name one element each which forms diatomic and tetra atomic molecule.
Q 18.
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 19.
Calculate the mass of 3.011 x 10
atoms of carbon
Q 20.
(a) What is meant by 'a mole of carbon atoms' ?
(b)(b) Which has more atoms, 50 g of aluminium or 50 g of iron ? Illustrate your answer with the help of calculations.
(Atomic masses : A1 = 27 u ; Fe = 56 u)
Q 21.
In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water
Q 22.
Name the international organization who approves names of elements.
Q 23.
What is the significance of a chemical symbol?
Q 24.
Why do atoms of the most of the elements not exist independently?
Q 25.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 26.
What are ionic compounds?
Q 27.
Calculate the number of molecules of sulphur (S
8) present in 16 g of solid sulphur.
Q 28.
Name the following compounds. Also write the symbols/formulae of the ions present in them :
(a) CuSO
Q 29.
How many moles are 3.6 g of water ?
Q 30.
Calculate the number of molecules in 4 g of oxygen.
Q 31.
(a) Define gram atomic mass of a substance.How much is the gram atomic mass of oxygen ?
(b) How many moles of oxygen atoms are present in one mole of the following compounds ?
(i)Al
(ii) co
2(iii) C1
(iv) H
(p)A1
Q 32.
How will you define chemical symbol?
Q 33.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 34.
Based on type of substance, how molecules are classified?
Q 35.
Give three examples of monoatomic molecules.
Q 36.
Give four examples of diatomic molecules.
Q 37.
What is the molecular mass of a substance?
Q 38.
An element Z has a valency of 3. What is the formula of oxide of Z ?
Q 39.
Work out the formula for magnesium hydrogencarbonate.
Q 40.
If one mole of nitrogen molecules weighs 28 g, calculate mass of one molecule of nitrogen in grams.
Q 41.
How many atoms are there in 0.25 mole of hydrogen ?
Q 42.
Who established the two important laws of chemical combinations?
Q 43.
If 12 g of carbon is burnt in the presence of 32 g of oxygen, how much carbon dioxide will be formed?
Q 44.
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 45.
A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
Q 46.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 47.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 48.
Define molecule. What are its important properties?
Q 49.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 50.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
