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Science Do as directed; [Che-1 M]

Atoms and Molecules · CBSE STD 9 (CBSE - English Medium). 75 questions.

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Do as directed; [Che-1 M]

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Question 11 Mark
Write the symbols/ formulae of two simple ions and two compound ions (or polyatomic ions).
Answer
Write the symbols/ formulae of two simple ions and two compound ions (or polyatomic ions).
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Question 21 Mark
Write the relation between nanometer and metre.
Answer
$1 \text{ nanometre} = \frac{1}{109}\text{metre}$
or
$1 \text{ nanometre} = 10^{-9}\text{ metre}$
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Question 31 Mark
Write the full form of IUPAC.
Answer
The full form of IUPAC is International Union of Pure and Applied Chemistry.
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Question 41 Mark
Write down the formulae for the following compounds:
Magnesium hydroxide
Answer
Magnesium hydroxide: Mg(OH)2
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Question 61 Mark
Work out the formula for sulphur dioxide.
(Valencies: S = 4; O = 2)
Answer
$\ \text{Symbols}:\ \ \ \ \ \text{S}\ \ \ \ \ \ \ \ \ \text{O}\\ {\text{Valencies}}:\ +4\ \ \ \ -2$
Chemical formula of sulphur dioxide is SO2
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Question 71 Mark
Work out the formula for magnesium hydrogencarbonate.
Answer
$\ \text{Symbols}:\ \ \ \ \ \text{Mg}\ \ \ \ \ \ \text{HCO}_3\\ {\text{Valencies}}:\ \ +2\ \ \ \ \ \ \ -1$
Thus, the resulting compound is Mg(HCO3)2
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Question 81 Mark
Work out the formulae for the following compounds:
Sodium oxide.
Answer
Sodium oxide:

$\ \text{Symbols}:\ \ \ \ \ \text{Na}\ \ \ \ \ \ \ \text{O}\\ {\text{Valencies}}:\ +1\ \ \ \ -2$

Thus, the formula of sodium oxide is Na2O

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Question 91 Mark
Work out the formulae for the following compounds:
Calcium carbonate.
Answer
Calcium carbonate:

$\ \text{Symbols}:\ \ \ \ \ \text{Ca}\ \ \ \ \ \ \ \ \ \text{CO}_3\\ {\text{Valencies}}:\ \ +2\ \ \ \ \ \ \ \ -2$

Thus, the resulting compound is CaCO3

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Question 101 Mark
Which particular atom of the above element is used for this purpose?
Answer
Atom with 6 neutrons and 6 protons in its nucleus so that its mass number is 12.
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Question 151 Mark
What name is given to the amount of substance containing 6.022 × 1023 particles (atoms, molecules or ions) of a substance?
Answer
A mole.
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Question 171 Mark
What is the name of a particle which contains 10 electrons, 11 protons and 12 neutrons?
Answer
Its Na+, the sodium ion.
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Question 181 Mark
What is the mass of 0.2 mole of oxygen atoms?
Answer
Mass of 0.2 moles of oxygen atoms = 0.2 × 16 = 3.2g
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Question 191 Mark
What is the difference between 2H and H2?
Answer
2H represents two separate atoms of hydrogen and H2 represents one molecule of hydrogen.
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Question 201 Mark
What is meant by saying that ‘the atomic mass of oxygen is 16’?
Answer
It means that one atom of oxygen is 16 times heavier than 1/ 12 of a C-12 atom.
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Question 211 Mark
What is meant by ‘a mole of carbon atoms’?
Answer
A mole of carbon atoms means a carbon sample weighing 12g and containing 6.022 × 1023 carbon atoms.
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Question 221 Mark
What is meant by 'a mole of carbon atoms'?
Answer
The amount of substance, whose mass in grams is numerically equal to its atomic mass, is called gram atomic mass of that substance. Gram atomic mass of oxygen is 16g.
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Question 271 Mark
What do we call those particles which are formed:
By the loss of electrons by atoms?
Answer
Cations are formed by the loss of electrons by atoms.
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Question 281 Mark
What do we call those particles which are formed:
By the gain of electrons by atoms?
Answer
Anions are formed by the gain of electrons by atoms.
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Question 291 Mark
What do the symbols, H2, S and O4 mean in the formula H2SO4?
Answer
H2 represents two atoms of hydrogen, one atom of sulphur and four atoms of oxygen.
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Question 311 Mark
The radius of an oxygen atom is 0.073nm. What does the symbol ‘nm’ represent?
Answer
The symbol 'nm' in 0.073nm (radius of an oxygen atom) represents the unit of atomic radius, i.e. nanometre.
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Question 321 Mark
The molecular formula of glucose is C6H12O6. Calculate its molecular mass. (Atomic masses: C = 12 u; H = 1 u; O = 16 u)
Answer
Molecular formula of glucose = C6H12O6
Molecular mass of glucose = (6 × C) + (12 × H) + (6 × O) = 72 + 12 + 96 = 180u
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Question 331 Mark
Stat the chemical symbols for the following elements:
Sodium, Potassium, Iron, Copper, Mercury, Silver.
Answer
Elements
Symbols
Sodium
Na
Potassium
K
Iron
Fe
Copper
Cu
Mercury
Hg
Silver
Ag
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Question 341 Mark
State whether the following statement is true or false:
The symbol of element cobalt is CO.
Answer
False. The symbol for the element Cobalt is Co, as the second letter of the symbol of an element has to be in the lower case.
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Question 351 Mark
  1. In what form does oxygen gas occur in nature?
  2. In what form do noble gases occur in nature?
Answer
  1. Oxygen gas occurs as a diatomic molecule in nature.
  2. Noble gases occur as mono atomic gases in nature.
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Question 361 Mark
Name the unit in which the radius of an atom is usually expressed.
Answer
The radius of an atom is usually expressed in nanometre (nm).
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Question 371 Mark
Name the scientist who gave:
Law of constant proportions.
Answer
Law of constant proportions was proposed by Joseph Proust.
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Question 381 Mark
Name the scientist who gave:
Law of conservation of mass.
Answer
Law of conservation of mass was proposed by Antoine Lavoisier.
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Question 391 Mark
Name the scientist who gave atomic theory of matter.
Answer
John Dalton proposed the atomic theory of matter.
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Question 401 Mark
Name the particle which has 18 electrons, 18 neutrons and 17 protons in it.
Answer
Its Cl-, the chloride ion.
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Question 411 Mark
Name the law of chemical combination:
Which was given by Proust.
Answer
The law of chemical combination proposed by Proust is well known as the law of constant proportions.
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Question 421 Mark
Name the law of chemical combination:
Which was given by Lavoisier.
Answer
The law of chemical combination proposed by Lavoisier is well known as the law of conservation of mass.
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Question 431 Mark
Name the element used as a standard for atomic mass scale.
Answer
Carbon is used as a standard for atomic mass scale.
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Question 441 Mark
Name the elements represented by the following symbols:
Hg, Pb, Au, Ag, Sn.
Answer
Symbols
Elements
Hg
Mercury
Pb
Lead
Au
Silver
Ag
Silver
Sn
Tin
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Question 451 Mark
If the valency of hydrogen is 1 and that of nitrogen is 3, work out the formula for ammonia.
Answer
$\ \text{Symbols}:\ \ \ \ \ \text{H}\ \ \ \ \ \ \ \ \ \text{N}\\ {\text{Valencies}}:\ +1\ \ \ \ -3$
So, chemical formula of ammonia is NH3
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Question 461 Mark
If the valency of carbon is 4 and that of sulphur is 2, work out the formula of the compound formed by the combination of carbon with sulphur. What is the name of this compound?
Answer
$\ \text{Symbols}:\ \ \ \ \ \text{C}\ \ \ \ \ \ \ \ \ \text{S}\\ {\text{Valencies}}:\ +4\ \ \ \ -2$
Name and formula of the resulting compound is Carbon disulphide, CS2
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Question 501 Mark
How many atoms are present in one gram atomic mass of a substance?
Answer
One mole of atoms (6.002 × 1023 atoms)
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