Question:
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 (Na2SO3)?
Answer:
(a) 1 mol of nitrogen (N) atoms = gram atomic mass of N = 14g
(b) mass = molar mass × number of moles
1 mol of Aluminium (Al) = gram atomic mass of Al = 27g
mass of 4 mols of Al = 4 × 27 = 108g
(c) mass = molar mass × number of moles
molecular mass of sodium sulphite (Na2SO3) =
= 2 × Atomic mass of Na + 1 × Atomic mass of S + 3 × Atomic mass of O
= 2 × 23u + 1 × 32u + 3 × 16u = 46u + 32u + 48u
= 126u
mass of 1 mol of sodium sulphite (Na2SO3) = gram molecular mass or molar mass = 126g
mass of 10 moles of Na2SO3 = 10 × 126g = 1260g
Atoms and Molecules
Q 1.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 2.
What is gram-atomic mass of an element?
Q 3.
Define 'formula mass' of a compound.
Q 4.
What is the mass of 5 moles of sodium carbonate (Na
) ?(Atomic masses : Na = 23 u ; C = 12 u ; O = 16 u)
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 chemical symbol for iron?
Q 7.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 8.
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.
Q 9.
Give four examples of diatomic molecules.
Q 10.
Who established the two important laws of chemical combinations?
Q 11.
Define molecule. What are its important properties?
Q 12.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 13.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 14.
How many atoms are there in 0.25 mole of hydrogen ?
Q 15.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 16.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 17.
What is the significance of a chemical symbol?
Q 18.
Dalton's atomic theory says that atoms are indivisible. Is this statement still valid ? Give reasons for answer.
Q 19.
Write the formulae of the following compounds. Also name the elements present in them.
(a) Water
(b) Ammonia
(c) Methane
(d) Sulphur dioxide
(f) Ethanol
Q 20.
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 21.
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 22.
What are the postulates of Dalton's atomic theory?
Q 23.
Name the international organization who approves names of elements.
Q 24.
Fill in the blanks:
The chemical symbol of flourine is ________.
Q 26.
Name one element each which forms diatomic and tetra atomic molecule.
Q 27.
What is the numerical value of Avogadro number ?
Q 28.
Fill in the blanks:
Atomic radius is measured in __________.
Q 29.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Q 30.
What are ionic compounds?
Q 31.
Give one major drawback of Dalton's atomic theory of matter.
Q 32.
State Law of constant proportions. Explain with an example.
Q 33.
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 34.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 35.
Which element has the smallest atom in size?
Q 36.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 37.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 38.
How many atoms are present in a
(i) H
2S molecule and
(ii) PO
43- ion?
Q 39.
An element X has a valency of 4 whereas another element Y has a valency of 1. What will be the formula of the compound formed between X and Y ?
Q 40.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Q 41.
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 42.
Give an example to show Law of conservation of mass applies to physical change also.
Q 43.
Explain with example that law of conservation of mass is valid for chemical reactions.
Q 44.
Calculate the molecular mass of chloroform (CHC1
Q 45.
What is an ion ? How is an ion formed ? Explain with the help of two examples of different ions.
Q 46.
Calculate the mass in grams of 0.17 mole of hydrogen sulphide, H
Q 47.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 48.
Fill in the blanks:
According to Dalton's atomic theory, atoms of different elements differ in ______, size and chemical properties.
Q 49.
What are polyatomic ions? Give examples?
Q 50.
Give examples of triatomic molecules.
