Atoms and Molecules – Science – (NCERT Solutions for Class 9)
- In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.
Sodium carbonate + ethanoic acid →sodium ethanoate + carbon + dioxide + water
- 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?
- Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
- Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
- Define the atomic mass unit.
- Why is it not possible to see an atom with naked eyes?
- Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium sulphide
(iv) magnesium hydroxide
- Write down the names of compounds represented by the following formulae.
- What is meant by the term chemical formula?
- How many atoms are present in a (i) H2S molecule and (ii) PO43−ion?
- Calculate the molecular masses of H2, O2, CL2, CO2, CH4, C2H6, C2H4, NH3, CH3OH.
- Calculate the formula unit masses of Zn0, Na20, K2C03. Given atomic masses of Zn = 65 u, Na = 23 u, K = 39 u
C = 12 u and 0 = 16 u.
- If one mole of carbon atoms weighs 12 grams, what is the mass (in grams) of 1 atom of carbon?
- Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56u) ?
- A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g .of oxygen. Calculate the percentage composition of the compound by weight.
- When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen?
Which law of chemical combination will govern your answer?
- What are polyatomic ions? Give examples.
- Write the chemical formulae of the following.
(i) Magnesium chloride
(ii) Calcium oxide
(iii) Copper nitrate
(iv) Aluminium chloride
(v) Calcium carbonate
- Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate
- Calculate the molar mass of the following substances.
(a) Ethyne, C2H2
(b) Sulphur molecule, S8
(c) Phosphorus molecule, P4(Atomic mass of phosphorus = 31)
(d) Hydrochloric acid, HCl
(e) Nitric acid, HNO3
- 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 (Na2SO3)?
- Convert into mole.
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide.
- What is the mass of
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
- Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur
- Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
[Hint The mass of an ion is the same as that of an atom of the same element. Atomic mass of AI= 27 u.]