Extra Questions with answers for Atoms and Molecules
Given below are the Extra questions with answers for Atoms and Molecules of Class 9 Science. These are important questions for examination also
(a) 1 Mark Questions
(b) Very Short Answer type
(c) Short answer questions
(d) Long answer questions
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1 Marks Questions
Question 1. Each Part Carry 1 Marks
(i) Name the body which approves the nomenclature of elements and compounds.
(ii) The symbol of sodium is written as Na and not as S. Give reason.
(iii) Name one element which form diatomic and one which form tetra atomic molecules.
Answer
(i) IUPAC (International Union of Pure and Applied Chemistry)
(ii) Latin name of sodium is Natrium. The first two letters (Na) of this name represents the symbol of sodium.
(iii) Oxygen forms diatomic molecules and phosphorus forms tetra atomic molecules.
Question 2. Each Part Carry 1 Marks
Write down the name of the following compounds:
(a)KNO3
(b)CaCO3
(c)Ca(HCO3)2
(d)AI2 (SO4)3
(e)CaCl2
(f)NaNO3
Question 3. Each Part Carry 1 Marks
write the symbol and Latin name of the following elements:
(a)sodium
(b)Potassium Question 4. Each Part Carry 1 Marks
Write atomicity of the following:
(a)Sulphur
(b)Phosphorus
(c)Oxygen
(d) Sodium
(e)Argon
(f) Neon
Answer
Atomicity is number of atoms in a molecule of an element.
(a)Atomicity of sulphur (S8) = 8
(b)Atomicity of phosphorous (P4) = 4
(c)Atomicity of oxygen (O2) = 2
(d)Atomicity of Sodium (Na) = 1
(e)Atomicity of Argon = 1
(f)Atomicity of neon (Ne) = 1
Question 5. Each Part Carry 1 Marks
Find the number of atoms present in:
(a)SO2 molecule
(b)SO4 ion
Answer
(a) 1 Sulphur and 2 Oxygen Atom ,Total 3 atoms
(b) 1 Sulphur and 4 Oxygen Atom ,Total 5 atoms
Question 6 Each Part Carry 1 Marks
Write formulas for ionic compounds formed from:
(a) Na and F
(b) Na and O,
(c) Mg and F
(d) AI and C Question 7 Each Part Carry 1 Marks
Write the chemical formulas for the following compounds:
(a) Copper (I) oxide
(b) Potassium peroxide
(c) Mercury (I) bromide
(d) Iron (III) carbonate
(e) Sodium hydrobromite.
Answer
(a)Cu2O
(b)K2O2
(c)Hg2Br2
(d)Fe2(CO3)3
(e) BrHNa
Question 8 Each Part Carry 1 Marks
Give the name for each of the following acids:
(a) HBrO3,
(b) HBr,
(c) H3PO4,
(d) HCIO
(e) HIO3
Answer
Very Short Answer type
Question 1.
What is meant by the term chemical formula? Question 2.
Name two scientists who established the laws of chemical combination? Question 3.
What is meant by a molecule? Give examples? Question 4.
Name the international organization which approves the names given to the elements?
Answer
IUPAC (International Union of Pure and Applied Chemistry)
Question 5.
What is the difference between an atom and a molecule? Question 6.
Define polyatomic ion? Question 7.
Write the chemical formulae for the chloride of magnesium? Question 8.
Define atomicity? Question 9.
Mention the difference between 2N and N2?
Answer
2N represents 2 atoms of Nitrogen, and it is not possible for it to exist independently.
N2represents an Nitrogen molecule which has two constituent Nitrogen atoms and this can exists independently
Question 10.
Nitrogen and Hydrogen combine in the ratio 14:3 by mass to form ammonia molecule. Find the formulae of ammonia molecule by calculating the molar ratio? Question 11
What is molecular weight? Explain with example.
Short Answer type
Question 1.
When 3.0g of magnesium is burnt in 2.00g of oxygen, 5.00g of magnesium oxide is produced. What mass of magnesium oxide will be formed when 3.00g magnesium is burnt in 5.00g of oxygen? Which law of chemical combination will govern your answer? Question 2.
‘Atoms of most elements are not able to exist independently’. Name two atoms which exist as independent atoms? Question 3.
Define atomic mass unit? State how do atoms exist? Question 4.
The atomic number of three elements A, B, and C are 9, 10, and 13 respectively. Which of them will form a cation? Question 5.
How would you differentiate between a molecule of element and a molecule of compound? Write one example of each type? Question 6.
Provide a difference between cations and anions, along with an example for each.
Answer
Cations are positively charged ions, e.g. Fe2+whereas, anions are negatively charged ions, e.g. F–
Question 7.
State the postulates of Dalton’s atomic theory which indicates the law of constant proportions? Question 8.
Calculate the number of molecules in 4g of methane? Question 9.
What formed the basis for John Dalton to formulate Dalton’s atomic theory? Question 10.
State the law of conservation of mass. Is this law applicable to the chemical reactions? Elaborate your answer with the help of an example? Question 11.
Compare relative molar mass and relative formula unit mass? Question 12.
Calculate the molar mass of HNO3. Compare it with its formula unit mass?
Answer
Molar mass =1+14+3×16 =63 grams /mole
Formula unit mass=1+14+3×16 =63 u
Molar Mass is the mass of 1 mole and Formula unit mass is mass of 1 unit
Long Answer type
Question 1.
Sodium is represented as $^{23}_{11}Na$
(a)What is its atomic mass?
(b)Write its gram atomic mass?
(c)How many atoms of Na will be there in 11.5 g of the sample?
Answer
(a) 23u
(b) 23g
(c) 23g contains $6.022 \times 10^{23}$ atoms
11.5 g will contains $3.011 \times 10^{23}$ atoms
Question 2.
Calculate the molar mass of the following compounds and identify the poly-atomic ions present in each of them:
(a)MgSO4
(b)Na2CO3
Question 3.
Define formulae unit mass of compounds. Calculate the formulae unit mass of :
(a)Na2CO3.10H2O
(b)CuSO4 Question 4.
How many atoms are present in:
(a)MnO2 molecule
(b)CO molecule
Answer
(a) 3
(b) 2
Question 5.
What is the mass of:
(a)1 mole of nitrogen atoms?
(b)4 mole of aluminium atoms?
(c)10 mole of sodium sulphite (Na2SO3)
(d) 0.2 mole of water
Answer
(a) Nitrogen Molar mass = 14 g/mol
Therefore 1 mole of nitrogen atoms=14g
(b) Aluminum Molar mass =26.982 g/mol
So, 1 mole of Aluminum atoms=26.982 g
Therefore
4 mole of Aluminum atoms=4*26.982=107.928 g
(c) Molar Mass of sodium sulphite=23*2 + 32+ 3*16=126 g/mol
Therefore 10 mole mass will be 1260 g
(d) Water Molar mass = 2 + 16=18 g
Therefore .2 mole of water mass will be =.2*18=3.6 g
Question 6.
A 0.48g sample of compounds of oxygen and boron was formed by analysis to contain 0.192 g of boron and 0.2888g of oxygen. Calculate the percentage composition of the compound by weight?
Answer
Percent composition of an element in a compound = total mass/mass of element * 100
% of boron = $\frac {0.48}{0.192} \times 100$=40%
% of oxygen =$\frac { 0.480}{.288} \times 100$=60%
Question 7.
State two examples in each case and write their chemical formulae:
(a)Molecules having one kind of atoms only.
(b)Molecules having two different kinds of atoms.
(c)Molecules having three different kinds of atoms. Question 8.
An element ‘Y’ forms an oxide whose chemical formulae is Y2O3
a)State the valency of Y.
b)Write the chemical formulae of its: (a) Sulphate and (b) Chloride? Question 9
(i) Distinguish between an atom and a molecule.
(ii) Differentiate between atom and ion.
