TUISYEN IBNU SINA CHEMISTRY MODULE 3CHEMICAL FORMULAE AND EQUATION

Molecular formula and Empirical formula

1) Compound X contains 6 carbon atoms, 12 hydrogen atoms and 6 oxygen atoms. Write the

i) Molecular formula : ____________________

ii) Empirical formula : ____________________

2) 2.4 g of magnesium combine with 7.1 g of chlorine. Complete the following table [Relative molecular mass : Mg ,24; Cl, 35.5]

Element Magnesium ChlorineMass (g)

Number of moles

Ratio of number of moles

Empirical Formula = _________________

3) 1.08 g of P combine with 0.96 g of oxygen. Calculate the empirical formula for the oxide formed. [Relative atomic mass : P , 27; O, 16]

4) Sodium sulphate consists of 29.1 % sodium, 40.5 % sulphur and 30.4 % oxygen. What is the empirical formula of the substance? [Relative atomic mass : Na,23; S,32; O,16]

5) 7.8 g M reacts completely with 1.6 g oxygen to form a substance with empirical formula of M2O. Calculate the relative atomic mass of X. [Relative atomic mass: M,39;O,16]

6) An experiment was conducted to determine the empirical formula of magnesium oxide. The table below shows the data collected.

1

TUISYEN IBNU SINA CHEMISTRY MODULE 3CHEMICAL FORMULAE AND EQUATION

Mass(g)Mass os crucible + lid 18.00Mass of crucible + lid + magnesium oxide 22.00Mass of crucible + lid + magnesium 20.40[RAM , Mg,24 : O,16]

Calculate the empirical formula.

Module 3.2:

1. Diagram 1 shows the set-up of apparatus to determine the empirical formula of magnesium oxide.

Diagram 1

The following are the results of the experiment

Mass(g)Mass of crucible + lid 54.6Mass of crucible + lid + magnesium ribbon 59.4Mass of crucible + lid + magnesium oxide 62.6 [Relative atomic mass: Mg,24; O,16]

a) Calculate the mass ofi) Magnesium ii) Oxygen

b) Calculate the number of moles of i) Magnesium ii) Oxygen

c) Determine the empirical formula of magnesium oxide formed.

2

heat

TUISYEN IBNU SINA CHEMISTRY MODULE 3CHEMICAL FORMULAE AND EQUATION

d) Write the chemical equation between magnesium and oxygen in this experiment.

_________________________________________________________________________

e) Why must magnesium ribbon be cleaned with sandpaper?

_________________________________________________________________________

f) Explain why

i) the crucible must be closed immediately when the magnesium ribbon starts to burn?

_________________________________________________________________________

ii) the crucible lid must be opened at intervals during the experiment?

_________________________________________________________________________

g) How to make sure all the magnesium has reacted completely with oxygen?

_________________________________________________________________________

2. Diagram 2 shows the set-up of apparatus used to determine the empirical formula of oxide metal M.

Diagram 2

The following are the results of the experimentMass of combustion tube + asbestos crucible = 54.63 gMass of combustion tube + asbestos crucible + M oxide = 58.30 gMass of combustion tube + asbestos crucible + M = 56.70 g[Relative atomic mass: M,207; O,16]

a) Calculate the mass ofi) M ii) Oxygen

b) Calculate the mole ratio of atom M and oxygen

3

Asbestos crucible

Oxide of metal M

Dry hydrogen gas

TUISYEN IBNU SINA CHEMISTRY MODULE 3CHEMICAL FORMULAE AND EQUATION

c) Determine the empirical formula of M oxide

_________________________________________________________________________

d) Write the chemical equation for the reaction that occurs in the experiment.

_________________________________________________________________________

e) Suggest two substances to produce the hydrogen gas in this experiment

_________________________________________________________________________

f) Name the substance used to dry hydrogen gas

_________________________________________________________________________

g) The combustion tube must be filled up with hydrogen gas. Describe how to confirm that hydrogen gas has filled up the combustion tube.

_________________________________________________________________________

_________________________________________________________________________

f) Explain why the hydrogen gas is still passed through the apparatus during the cooling of the combustion tube.

_________________________________________________________________________

4