{"id":4962,"date":"2023-03-16T07:22:13","date_gmt":"2023-03-16T07:22:13","guid":{"rendered":"https:\/\/theexampillar.com\/ncert\/?p=4962"},"modified":"2023-03-28T06:13:06","modified_gmt":"2023-03-28T06:13:06","slug":"ncert-solutions-class-9-science-chapter-3-atoms-and-molecules","status":"publish","type":"post","link":"https:\/\/theexampillar.com\/ncert\/ncert-solutions-class-9-science-chapter-3-atoms-and-molecules\/","title":{"rendered":"NCERT Solutions Class 9 Science Chapter 3 Atoms and Molecules"},"content":{"rendered":"

NCERT Solutions Class 9 Science\u00a0<\/span><\/h2>\n

The NCERT Solutions in English Language for Class 9 Science Chapter – 3 (Atoms and Molecules) <\/strong>has been provided here to help the students in solving the questions from this exercise.<\/span><\/p>\n

Chapter – 3 (Atoms and Molecules)<\/span><\/h2>\n

Questions <\/strong><\/span><\/p>\n

1. In a reaction, 5.3g of sodium carbonate reacted with 6 g of acetic acid. The products were 2.2 g of carbon dioxide, 0.9 g of water and 8.2 g of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.
\n<\/strong>Sodium carbonate + acetic acid \u2192 Sodium acetate + carbon dioxide + \u00a0water
\n<\/strong><\/span>Answer –<\/strong>
\nSodium carbonate (5.3g) + acetic acid (6g) \u2192 Sodium acetate (8.2g) + carbon dioxide (2.2g) + \u00a0water (0.9g)
\nN<\/span>a<\/span>2<\/span><\/span><\/span><\/sub>\u200b<\/span><\/span><\/span><\/span><\/span>C<\/span>O<\/span>3 <\/span><\/span><\/span><\/sub>\u200b <\/span><\/span><\/span><\/span><\/span>+\u00a0 <\/span><\/span>C<\/span>H<\/span>3<\/span><\/span><\/span><\/sub>\u200b<\/span><\/span><\/span><\/span><\/span>C<\/span>O<\/span>O<\/span>H <\/span>\u2192 C<\/span>H<\/span>3<\/span><\/span><\/span><\/sub>\u200b<\/span><\/span><\/span><\/span><\/span>C<\/span>O<\/span>O<\/span>N<\/span>a + <\/span><\/span><\/span>C<\/span>O<\/span>2 <\/span><\/span><\/span><\/sub>\u200b <\/span><\/span><\/span><\/span><\/span>+\u00a0 <\/span><\/span>H<\/span>2<\/span><\/span><\/span><\/sub>\u200b<\/span><\/span><\/span><\/span><\/span>O <\/span>
\n<\/span><\/span>Mass of reactants\u00a0=<\/span><\/span>5<\/span>.<\/span>3 <\/span>+ <\/span><\/span>6 <\/span>= <\/span><\/span>1<\/span>1<\/span>.<\/span>3<\/span>\u00a0<\/span>g<\/span>m
\n<\/span><\/span><\/span><\/span>Mass of products\u00a0= <\/span><\/span>2<\/span>.<\/span>2 <\/span>+ <\/span><\/span>0<\/span>.<\/span>9 <\/span>+ <\/span><\/span>8<\/span>.<\/span>2 <\/span>= <\/span><\/span>1<\/span>1<\/span>.<\/span>3<\/span>\u00a0<\/span>g<\/span>m
\nThis shows, that during a chemical reaction, the mass of reactant = mass of the product.
\n<\/span><\/span><\/span><\/span><\/span><\/p>\n

2. Hydrogen and oxygen combine in a 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?
\n<\/strong><\/span>Answer –<\/strong>\u00a0 \u00a0We know hydrogen and water mix in a ratio 1 : 8.
\nThis means that 1g of Hydrogen reacts with 8g of Oxygen to form. H2<\/sub>O<\/span>
\n1g Hydrogen \u2192 8g Oxygen <\/span>
\n3g Hydrogen \u2192 3 \u00d7 8g Oxygen <\/span>
\n= 24g Oxygen<\/span>
\nThus, 24g of oxygen gas would be required to react completely with 3 g of hydrogen gas.<\/span><\/p>\n

3. Which postulate of Dalton\u2019s atomic theory is the result of the law of conservation of mass?
\n<\/strong><\/span>Answer – <\/strong>The postulate of Dalton\u2019s Atomic theory which is a result of the law of conservation of mass is, \u201cAtoms are indivisible particles, which can neither be created nor be destroyed\u201d.<\/span><\/p>\n

4. Which postulate of Dalton\u2019s atomic theory can explain the law of definite proportions?
\n<\/strong><\/span>Answer –<\/strong> The postulate of Dalton’s atomic theory that can explain the law of definite proportions is – the relative number and kinds of atoms are equal in given compounds.<\/span><\/p>\n

Questions<\/strong><\/span><\/p>\n

1. Define the atomic mass unit.
\n<\/strong>Answer – <\/strong>An atomic mass unit is a unit of\u00a0mass used to express the weight subatomic particles, where one unit is equal to exactly one-twelfth the mass of a carbon-12 atom.<\/span><\/p>\n

\n

2. Why is it not possible to see an atom with the naked eyes?
\n<\/strong>Answer –<\/strong> It is not possible to see an atom with naked eyes because an atom is a very small particle. For example, the radius of a hydrogen atom is 10-10<\/sup>\u00a0metre.<\/span><\/span><\/p>\n<\/div>\n

Questions<\/strong><\/span><\/p>\n

1. Write down the formulae of
\n<\/strong>(i) <\/strong>sodium oxide
\n<\/strong>(ii) <\/strong>aluminium chloride
\n<\/strong>(iii) <\/strong>sodium sulphide
\n<\/strong>(iv) <\/strong>magnesium hydroxide
\nAnswer –<\/strong> \u00a0The following are the formulae:
\n(i)<\/strong> sodium oxide \u2013 Na2<\/sub>O
\n(ii)<\/strong> aluminium chloride \u2013 AlCl3
\n<\/sub>(iii)<\/strong> sodium sulphide \u2013 Na2<\/sub>S
\n(iv)<\/strong> magnesium hydroxide \u2013 Mg (OH)2<\/sub><\/span><\/p>\n

2. Write down the names of compounds represented by the following formulae:
\n<\/strong>(i) <\/strong>Al2<\/sub>(SO4<\/sub>)3<\/sub>
\n<\/sub><\/strong>(ii) <\/strong>CaCl2
\n<\/sub>(iii)<\/strong> K2<\/sub>SO4<\/sub>
\n<\/sub><\/strong>(iv) <\/strong>KNO3<\/sub>
\n<\/sub><\/strong>(v) <\/strong>CaCO3<\/sub>
\n<\/strong>Answer –<\/strong> \u00a0The names of the compounds for each of the following formulae:
\n(i)<\/strong> Al2<\/sub>(SO4<\/sub>)3<\/sub>\u00a0\u2013 Aluminium sulphate
\n(ii)<\/strong> CaCl2\u00a0<\/sub>\u2013 Calcium chloride
\n(iii)<\/strong> K2<\/sub>SO4<\/sub>\u00a0\u2013 Potassium sulphate
\n(iv)<\/strong> KNO3\u00a0<\/sub>\u2013 Potassium nitrate
\n(v)<\/strong> CaCO3<\/sub>\u00a0\u2013 Calcium carbonate<\/span><\/p>\n

3. What is meant by the term chemical formula?<\/strong>
\nAnswer –\u00a0 <\/strong>The chemical formula is the symbolic representation of a chemical compound.
\nExample:<\/strong> Chemical formula of sodium chloride is\u00a0N<\/span>a<\/span>C<\/span>l<\/span><\/span><\/span><\/span><\/span><\/p>\n

4. How many atoms are present in a
\n<\/strong>(i) <\/strong>H2<\/sub>S molecule and
\n(ii) <\/strong>PO4<\/sub>3-<\/sup>\u00a0ion?
\nAnswer –<\/strong> \u00a0The number of atoms present is as follows:
\n(i)<\/strong> H2<\/sub>S molecule has 2 atoms of hydrogen and 1 atom of sulphur hence 3 atoms in total.
\n(ii)<\/strong> PO4<\/sub>3-<\/sup>\u00a0ion has 1 atom of phosphorus and 4 atoms of oxygen hence 5 atoms in total.<\/span><\/p>\n

Questions<\/strong><\/span><\/p>\n

1. Calculate the molecular masses of H2<\/sub>, O2<\/sub>, Cl2<\/sub>, CO2<\/sub>, CH4<\/sub>, C2<\/sub>H6<\/sub>, C2<\/sub>H4<\/sub>, NH3<\/sub>, CH3<\/sub>OH.
\n<\/strong>Answer –<\/strong> \u00a0The following are the molecular masses:<\/span><\/p>\n