Free Atoms and Molecules 01 Practice Test - 9th Grade
Question 1
In a biogas plant, methane gas (CH4) is produced as a fuel. Find the mass ratio of carbon to hydrogen in methane.
3:1
2:1
1:3
4:2
SOLUTION
Solution : A
Mass of one carbon atom = 12u
Mass of each hydrogen atom = 1u
Mass of 4 hydrogen atoms = 4u
Mass ratio of carbon and hydrogen atoms in methane =12:4=3:1
Question 2
Which theory has provided an explanation for the law of conservation of mass and the law of definite proportions?
Dalton's atomic theory
Lavoisier's theory
J.J Thomson's atomic theory
Democritus atomic theory
SOLUTION
Solution : A
Daltons' atomic theory was based on the laws of chemical combinations i.e., law of conservation of mass and the law of definite proportions. The two postulates which supports the law of combinations are:
- Atoms combine in the ratio of small whole numbers to form compounds.
- Atoms are indivisible particles, which cannot be created or destroyed in a chemical reaction
Question 3
Which of the following is the chemical symbol for iron?
I
Fe
Zn
Na
SOLUTION
Solution : B
Fe is the chemical symbol for iron, I is the chemical symbol for iodine, Zn is the chemical symbol for zinc and Na is the chemical symbol for sodium.
Question 4
What does the abbreviation amu stand for?
Atomic molecular unit
Atomic mass unit
Atomic mole unit
Atomic measuring unit
SOLUTION
Solution : B
According to IUPAC recommendations, mass of the atom is expressed as atomic mass unit (amu) or unified atomic mass unit (u). 1 amu is defined as one-twelth the mass of a carbon-12 atom.
Question 5
Atomicity of oxygen molecule is 1.
True
False
SOLUTION
Solution : B
Atomicity means the number of atoms present in one molecule. Oxygen exists as O2. The atoms in one molecule of oxygen is 2. Hence, it is diatomic and the given statement is false.
Question 6
What is the number of oxygen atoms present in 126 g of HNO3?
SOLUTION
Solution : A
Molecular mass of HNO3 = atomic mass of hydrogen + atomic mass of nitrogen + 3× atomic mass of oxygen = 1 + 14 + (3 × 16) = 63 u.Number of moles = Given massGram molecular mass
∙ In 1 molecule of HNO3 we have 3 atoms of oxygen.
Moles of HNO3 = 12663 = 2 moles
∙ 1 mole of HNO3 contains 3 moles of oxygen atoms. So, in 2 moles of HNO3 we will have 6 moles of oxygen atoms.
∙ One mole of a substance contains 6.022×1023 particles. So, the number of atoms in 126 g of HNO3= 6×6.022×1023 = 36.132×1023 atoms.
Question 7
What is the mass of one atom of neon if its gram atomic mass is 20 grams?
SOLUTION
Solution : B
1 mole of an element contains 6.022×1023 atoms.
1 mole of a compound contains6.022×1023 molecules.Neon is monoatomic in nature.
It is given that the gram atomic mass of Neon is 20 gSo, 6.022×1023 atoms of Neon weigh = 20 grams
The mass of one atom
= 206.022×1023
= 3.32×10−23 g
Question 8
What is the term used for the molecular mass of ionic compounds?
SOLUTION
Solution : C
The word formula unit is used for the substances of which constituent particles are ions.
For example, magnesium chloride has a formula unit MgCl2
Its formula unit mass can be calculated as:
(1× Atomic mass of magnesium)+(2× Atomic mass of chlorine)
=(1×24)+(2×35.5)=95u
Question 9
Find the number of hydrogen atoms in 9.033×1023 molecules of water.
SOLUTION
Solution : A
The chemical formula of water is H2O.
One molecule of water has 2 hydrogen atoms.
9.033×1023 molecules of water will have 2×9.033×1023=18.066×1023 atoms of hydrogen.
Question 10
According to the Dalton, which element does the following symbol represent?
SOLUTION
Solution : A
Dalton was the first scientist to use the symbols for elements in a very specific sense. The symbols are the unique pictorial representation of each element. The given symbol was used for representing the element "hydrogen".