Chapter 8 Solutions — Nature of Matter: Elements, Compounds, and Mixtures

Keep the Curiosity Alive

1. 1.
   Consider the following reaction where two substances, A and B, combine to form a product C: A + B → C Assume that A and B cannot be broken down into simpler substances by chemical reactions. Based on this information, which of the following statements is correct?

   • (i) A, B, and C are all compounds and only C has a fixed composition.
   • (ii) C is a compound, and A and B have a fixed composition…
2. 2.
   Assertion: Air is a mixture. Reason: A mixture is formed when two or more substances are mixed, without undergoing any chemical change.

   • (i) Both Assertion and Reason are true and Reason is the correct explanation for Assertion.
   • (ii) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion.
   • (iii) Assertion is true, but Reason is false.
   • (iv) Assertion is false…
3. 3.
   Water, a compound, has different properties compared to those of the elements oxygen and hydrogen from which it is formed. Justify this statement.
4. 4.
   In which of the following cases are all the examples correctly matched? Give reasons in support of your answers.

   • (i) Elements — water, nitrogen, iron, air.
   • (ii) Uniform mixtures — minerals, seawater, bronze, air.
   • (iii) Pure substances — carbon dioxide, iron, oxygen, sugar.
   • (iv) Non-uniform mixtures — air, sand, brass, muddy water.
5. 5.
   Iron reacts with moist air to form iron oxide, and magnesium burns in oxygen to form magnesium oxide. Classify all the substances involved in the above reactions as elements, compounds or mixtures, with justification.
6. 6.
   Classify the following as elements, compounds, or mixtures in Table 8.3. Carbon dioxide, sand, seawater, magnesium oxide, muddy water, aluminium, gold, oxygen, rust, iron sulfide, glucose, air, water, fruit juice, nitrogen, sodium chloride, sulfur, hydrogen, baking soda. Also identify pure substances amongst these and list them.
7. 7.
   What new substance is formed when a mixture of iron filings and sulfur powder is heated, and how is it different from the original mixture? Also, write the word equation for the reaction.
8. 8.
   Is it possible for a substance to be classified as both an element and a compound? Explain why or why not.
9. 9.
   How would our daily lives be changed if water were not a compound but a mixture of hydrogen and oxygen?
10. 10.
    Analyse Fig. 8.24. Identify Gas A. Also, write the word equation of the chemical reaction. (Fig. 8.24 shows iron filings reacting with dilute hydrochloric acid, producing a gas collected above.)
11. 11.
    Write the names of any two compounds made only from non-metals, and also mention two uses of each of them.
12. 12.
    How can gold be classified as both a mineral and a metal?