C3

Question 1

Percentage mass of an element in a compound=

Answer 1

(element mass/compound mass) × 100

element mass – Mass of the element in one mole of the compound; and
compound mass – Mass of one mole of the compound or its molar mass.

Question 2

Number of moles=

Answer 2

mass in g (of an element or compound)
———————————————————
Mr (of the element or compound)

Question 3

Conservation of mass

Answer 3

The law of conservation of mass states that in a chemical reaction mass is neither created nor destroyed.

Question 4

What is a limiting reactant?

Answer 4

The limiting reagent is the reactant that is completely used up in a reaction, and thus determines when the reaction stops.

Question 5

Concentration(g/dm3) =

Answer 5

mass of solute (g)
———-————————-
volume of solvent (dm3)

Question 6

Neutralisation reaction-

Answer 6

acid + base ——> salt + water

Question 7

Neutralisation reaction-

Answer 7

acid + base ——> salt + water

Question 8

Strong acids:

Answer 8

-ionise completely in water
-all acid particles dissociate to release H+ ions

Question 9

Weak acids:

Answer 9

-do not fully ionise in solution
-only a small proportion of acid particles dissociate to release H+ ions.

Question 10

PH is a measure of…?

Answer 10

Concentration of hydrogen ions

Question 11

Suggest why the mass of a reaction vessel might decrease during a reaction.

Answer 11

If the products are gases, they can’t be ‘contained’ in the reaction vessel.

Question 12

What is the state symbol of an aqueous substance?

Answer 12

(aq)
Dissolved in water