Science - Class 9

Q38. Give the names of the elements present in the following compounds.

(a) Quick lime

(b) Hydrogen bromide

(c) Baking powder

(d) Potassium sulphate.

 

Q39. Compute the difference in masses of 10³ moles each of magnesium atoms and magnesium ions. (Mass of an electron = 9.1×10^–31 kg)

 

Q40. You are provided with a fine white coloured powder which is either sugar or salt. How would you identify it without tasting?

 

Q41. Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

 

Q42. State the number of atoms present in each of the following chemical species

(a) CO₃^2–

(b) PO₄^3–

(c) P₂O₅

(d) CO

 

Q43. Which of the following represents a correct chemical formula? Name it.

(a) CaCl (b) BiPO₄ (c) NaSO₄ (d) NaS

 

Q44. Write the cations and anions present (if any) in the following compounds

(a) CH₃COONa

(b) NaCl

(c) H₂

(d) NH₄NO₃

 

Q45. Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?

 

Q46. Raunak took 5 moles of carbon atoms in a container and Krish also took 5 moles of sodium atoms in another container of same weight. (a) Whose container is heavier? (b) Whose container has more number of atoms?

 

Q47. Write the chemical formulae of the following.

(a) Magnesium chloride

(b) Calcium oxide

(c) Copper nitrate

(d) Aluminium chloride

(e) Calcium carbonate

 

Q48. Which of the following symbols of elements are incorrect? Give their correct symbols

(a) Cobalt CO

(b) Carbon c

(c) Aluminium AL

(d) Helium He

(e) Sodium So

 

Q49. Classify each of the following on the basis of their atomicity.

(a) F₂ (b) NO₂ (c) N₂O (d) C₂H₆ (e) P₄ (f) H₂O₂

(g) P₄O₁₀ (H) O₃ (i) HCl (j) CH₄ (k) He (l) Ag

 

Q50. What is the SI prefix for each of the following multiples and submultiples of a unit?

(a) 10³ (b) 10^–1 (c) 10^–2 (d) 10^–6 (e) 10^–9 (f) 10^–12

 

Q51. Write down the names of compounds represented by the following formulae:

(i) Al2(SO₄)₃

(ii) CaCl₂

(iii) K₂SO₄

(iv) KNO₃

(v) CaCO₃

 

Q52. Calcium chloride when dissolved in water dissociates into its ions according to the following equation.

CaCl₂ (aq) ‑> Ca₂+ (aq) + 2Cl– (aq)

Calculate the number of ions obtained from CaCl₂ when 222 g of it is dissolved in water.

 

Q54. If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?

 

Q55. 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?

 

Q56. The mass of one steel screw is 4.11g. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth (5.98 × 10²⁴kg). Which one of the two is heavier and by how many times?