Page 38 - Chemistry ICSE Class IX

26 ICSE Chemistry – 9
7. What are molecular compounds
8. Why do we call the formula of an ionic compound as stoichiometric formula/chemical formula and not the
molecular formula
9. Identify the cation and anion present in the compound potassium aluminium sulphate.
10. Why are Dalton’s symbols not used in chemistry
11. De ne the term symbol of an element.
12. How is an ion formed from an atom of any element
13. (a) What are valence electrons
(b) How many valence electrons are there in an atom of chlorine (atomic number 17)
14. De ne molecular formula.
15. What is meant by the atomicity of a molecule Give two examples.
16. How is a chemical equation written
17. Why is it necessary to balance a chemical equation
18. Write the two postulates of Dalton’s atomic theory which are modi ed in the light of modern researches.
19. What is the signi cance of a symbol
20. (a) What is meant by variable valency
(b) Explain how does it occur.
21. The molecular formula of hydrogen is H . What does it mean
2
22. (a) What is the signi cance of molecular formula
(b) What does the formula CO signify
2
23. Why is it not correct to write the molecular formula of an element forming a covalent network solid
24. Valencies or the charge numbers of some ions are given below:
Aluminium ion 3+ Magnesium ion 2+ Potassium ion 1+
Nitride ion 3– Sulphate ion 2– Fluoride ion 1–
Using the above information, write down the chemical formulae of the following:
(a) Aluminium nitride (b) Magnesium nitride (c) Aluminium sulphate
(d) Potassium uoride (e) Magnesium uoride (f) Potassium nitride
25. By what common name are the substances on the left of the arrow (o) in a chemical equation called
26. What condition must be satis ed by a balanced chemical equation
27. How will you provide information regarding the reaction conditions in a chemical equation
28. State the law which must hold good for a balanced chemical equation.
(a) Balance the chemical equation, H + O o H O
2
2
2
(b) Balance the chemical equation, HNO + H S o NO + H O + S
2
2
3
2
29. Write the balanced chemical equation for the reaction between calcium carbonate and hydrochloric acid to form
calcium chloride, carbon dioxide and water.
30. In what way are the chemical equations useful to us
31. What is a balanced chemical equation
32. Write the balanced chemical equations for the following reactions:
(a) Zinc and hydrochloric acid react to give zinc chloride and hydrogen.
(b) Sodium metal reacts with water to give sodium hydroxide and hydrogen gas.
(c) Carbon dioxide when passed through limewater gives white turbidity due to the formation of calcium
carbonate.
(d) Phosphorus burns in air to give phosphorus pentoxide.
(e) Magnesium ribbon burns in air to give a white powder of magnesium oxide.