Question:
Define molecule. What are its important properties?
Answer:
The smallest particle of matter (element or compound) which can exist in a free state is called a molecule.
Atoms of the same element or of different elements can join together to form molecules.
Properties:
- Molecules of any given substance are similar.
- Molecules of different substances are different.
- The properties of a substance are the properties of the molecule of that substance.
- Each molecule is described by its chemical formula.
Atoms and Molecules
Q 1.
Fill in the blanks:
The atomic mass of sodium is 23. The gram atomic mass of sodium is _________.
Q 2.
What is the chemical symbol for iron?
Q 3.
What is gram-atomic mass of an element?
Q 4.
Define molecule. What are its important properties?
Q 5.
Define 'formula mass' of a compound.
Q 6.
Name the international organization who approves names of elements.
Q 7.
Write the chemical symbols of the following:
(i) Gold
(ii) Iron
(iii) Chlorine
(iv) Mercury
Q 8.
Name one element each which forms diatomic and tetra atomic molecule.
Q 9.
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 10.
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 11.
Give four examples of diatomic molecules.
Q 13.
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 14.
How many atoms are there in 0.25 mole of hydrogen ?
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.
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 17.
Fill in the blanks:
According to law of definite proportions, in a chemical substance the elements are always present in __________ proportions by mass.
Q 18.
Convert 12 g of oxygen gas into moles.
Q 19.
Who established the two important laws of chemical combinations?
Q 20.
(i) State the law of constant proportions.
(ii) Show that water illustrates the law of constant proportions.
Q 21.
Fill in the blanks:
The mass of 5 moles of ammonia (NH
3) is __________.
Q 22.
How will you define chemical symbol?
Q 23.
Fill in the blanks:
The chemical symbol of mercury is _________.
Q 24.
Based on type of substance, how molecules are classified?
Q 25.
Fill in the blanks:
Hydrogen and oxygen combines to form H
2O and H
2O
2. These two compounds obey the law of ____________________.
Q 26.
What are polyatomic ions? Give examples?
Q 27.
Name the element having following Latin names
(i) Stibium
(ii) Cuprum
(iii) Argentum
(iv) Natrium
(v) Stannum
(vi) Wolfram
(vii) plumbum
(viii) Kalium
Q 28.
What is the significance of a chemical symbol?
Q 29.
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 30.
(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 31.
What is valency of an element?
Q 32.
If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?
Q 33.
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 34.
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 35.
Find out number of atoms in 15 moles of He.
Q 36.
Calculate the molecular masses of the following compounds :
(a) Methanol, CH
Q 37.
Write down the formulae for the following compounds :
(a) Calcium oxide
(b) Magnesium hydroxide
Q 38.
(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 39.
Who proposed Law of Definite Proportions (or Law of Constant Composition)?
Q 40.
State Law of constant proportions. Explain with an example.
Q 41.
Magnesium and oxygen combine in the ratio of 3 : 2 by mass to form magnesium oxide. How much oxygen is required to react completely with 12 g of magnesium?
Q 42.
Fill in the blanks:
Atomic radius is measured in __________.
Q 43.
Fill in the blanks:
The mass of 1 mole of a substance is called its _____________.
Q 44.
Fill in the blanks:
Atoms can be observed using ____________ Microscope.
Q 45.
What is relative atomic mass of an element? How it is related to atomic mass unit?
Q 46.
Fill in the blanks:
An element has only one type of __________.
Q 47.
Fill in the blanks:
The atomicity of sulphur S
8 is ________.
Q 48.
Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium suphide
(iv) magnesium hydroxide
Q 49.
How many atoms are present in a
(i) H
2S molecule and
(ii) PO
43- ion?
Q 50.
What is the molecular mass of a substance?
