In this post you will find answers of questions of Worksheet -3 NIOS class 10 science (Code-212) Chapter 3- Atoms and Molecules with complete explanation.
Atoms and Molecule Worksheet 3 Answers
Q1.
Pure water contains 11.11% of hydrogen and 88.89%
of oxygen by mass. What will be the composition of compounds such as ammonia,
carbon dioxide, sodium chloride and hydrogen sulphide.
Percentage
of elements by mass in Ammonia
Mass
of nitrogen (N)=14
Mass
of hydrogen (H)= 1 ×3 =3
Total
mass 17g/mol
Percentage
of elements by mass in CO2
Mass
of Carbon (C) = 12
Mass
of oxygen (O) = 16 ×2 =32
Total
mass = 44g/mol
Percentage
of elements by mass in NaCl
Mass
of sodium (Na) = 23
Mass
of chlorine (Cl) =35.5
Total
mass =58.5g/mol
Percentage
of elements by mass in H2S
Mass
of hydrogen (H)= 1×2 =2
Mass
of sulphur (S) = 32
Total
mass = 34g/mol
Q2.
Analyse if everything is made of atoms. How could
scientists be sure that there was not anything smaller than an atom? Explain by
using your knowledge of chemistry.
Answer
Everything
is made up of atoms
Yes, all matter (solid, liquid and gas) is
made up of tiny particles called atoms. According to Dalton’s atomic theory-
Atom is the smallest particle and is basic building block of matter.
Scientists
thought atoms were indivisible
The
word ‘Atom’ comes from Greek word ‘ Atomos’ which means indivisible.
John
Dalton proposed atomic theory:
1. Atoms are the smallest indivisible particles.
2. They cannot be created or destroyed in
chemical reaction.
Discovery
of smaller particles than atoms
J.J.
Thomson discovered electrons and Rutherford discovered positively charged
particles in the nucleus of atom. James Chadwik discovered neutrons in the
nucleus.
Q3.
Atoms were thought to be indivisible, later as per
studies, we know that they are made of smaller particles, can we still consider
them as building blocks of matter. Give reasons in support of your answer.
Answer
Yes,
atoms are still considered the basic building blocks of matter. We know atoms
are divisible and made-up smaller particles – electrons, protons and neutrons.
Reasons
1. Atoms
are divisible into subatomic particles but these particles cannot take part in
chemical reaction and does not show chemical properties.
2. Atoms
combine in fixed ratio to form molecules but subatomic particles cannot do.
3. Structure
of substance (solid, liquid and gas) depends upon arrangement of atoms.
So,
atoms are divisible into smaller subatomic particles but they are fundamental
units of matter.
Q4.
Nitrogen and hydrogen combine in the ratio 14:3 by
mass of form ammonia molecule. Find the formulae of ammonia molecule by
calculating the molar ratio?
Answer
Mass
ratio of Nitrogen: Hydrogen =14:3
Atomic
mass of Nitrogen = 14u
Atomic
mass of Hydrogen = 1u
Moles
of each element
Molar
ratio
Nitrogen
: Hydrogen = 1:3
Chemical
formula of ammonia
1
atom of nitrogen and 3 atoms of hydrogen combines to form 1 molecule of ammonia
NH3
Q5.
C6H12O6 is the
formula for Glucose. What information do you get from this formula?
Answer
We can get following information through the chemical formula(here C6H12O6):
(i) Elements present: Glucose is made up of carbon(C), Hydrogen(H) and oxygen(O) atoms.
(ii) Number of atoms of each element: In glucose , carbon has 6 atoms, hydrogen has 12 atoms and oxygen has 6 atoms.
(iii) Molecular composition: Atoms are combined in fixed ration 6:12:6 or 1:2:1
(iv) Molar mass of glucose:
Carbon = 12 × 6=72 g
Hydrogen = 1 ×12=12 g
Oxygen = 16 × 6 =96 g
Total mass = 72 + 12+ 96 =180g/mol
(v) Nature of compound: Glucose is an organic compound and it is a primary source of energy in living beings.
So,
a formula provide the above information about a substance.
Q6.
As we know our body constituted approximately 80%
of water. Calculate the number of water molecules which are present in the body
of a young person whose weight is 62 kg.
Answer
Mass
of water in the body
Mass of water = 80% of total mass of the body
Convert
kg to grams
49.6
kg= 49600g
Find
moles of water
Molar mass of water = 18g/mol
Calculate
number of molecules
Avogadro’s
number (NA) = 6.022 × 1023 molecules/mol
Number
of molecules = moles× NA
= 2755.56× 6.022
× 1023
= 1.66 ×1027
molecules
So,
1.66 ×1027 water molecules which are present in the body of a young
person whose weight is 62 kg.
Q7. Calculate the molecular mass of the following compounds: MgO. CaO, NH3, H2SO4.
Answer
1.
Molecular mass of Magnesium oxide (MgO)
Mg= 24.3u
O = 16u
Molecular mass = 24.3+ 16 = 40.3 u
2.
Molecular mass of Calcium oxide (CaO)
Ca= 40.1 u
O= 16 u
Molecular mass
= 40.1+ 16 = 56.1 u
3. Molecular
mass of Ammonia (NH3)
N= 14 u
H = 1× 3 =3u
Molecular mass = 14 + 3 = 17u
4. Molecular
mass of Sulphuric Acid (H2SO4)
H= 1 ×2 = 2u
S= 32.1u
O = 16 ×4 =64
Molecular mass = 2 + 32.1 + 64 = 98.1u
|
Compound
|
Molecular mass |
|
MgO |
40.3 u |
|
CaO |
56.1 u |
|
NH3 |
17u |
|
H2SO4 |
98.1 u |
Q8.
These are different forms of oxygen ie 2O, O2
and O3. What is the difference between 2O, O2 and O3.
Answer
|
Features
|
2 O |
O2 |
O3 |
|
Composition
|
2
separate atoms |
Two
atoms bonded |
Three
atoms bonded |
|
Stability
|
Extremely
low |
High
|
Moderate
|
|
Reactivity
|
High |
Moderate
|
Very
high |
|
Occurrence
|
Upper
atmosphere |
Everywhere
|
Ozone
layer |
|
Role
|
Initial radical chemistry |
Respiration,
combustion |
UV
absorption |
Q9.
Atomic number of uranium is 92. If uranium has
three isotopes having 141, 143 and 145 neutrons in their nucleus. How would
they be the symbol of the isotopes? How does isotopes different form isobars?
Answer
Find
mass number of isotopes
Mass
number (A)= Number of protons(Z) + Number of neutrons(N)
Since
uranium’s atomic number id 92
Isotope
1: mass number = 92 +141=233
Isotope
2: mass number = 92+143 =235
Isotope
3: mass number = 92 +145 =237
Symbols
of isotopes
, 
, 
Difference between isotopes and isobars
|
Isotopes
|
Isobars
|
|
Atoms
of same elements having similar atomic number but different mass numbers |
Atoms
of different elements having same mass number but different atomic numbers. |
|
|
|
Q10.
“A sample of a pure substance always consists of
the same elements combined in the same proportion by mass”. Which law has
proposed this? Explain the law in details.
Answer
This
is the Law of constant Proportion (law of definite proportion)
This
law was proposed by Joseph Proust. According to this law ‘ If a compound is
pure, the mass ratio of its constituent elements remains constant.’
Example
– H2O
Mass of hydrogen =1×2=2g
Mass
of oxygen = 16g
Ration
by mass = 2 : 16 or 1:8
This
ration is always 1:8, whether water is from rain, river or sea.
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