Name: _____________________________ ( ) Class: _________ Date: __________

Open the URL http://www1.moe.edu.sg/edsoftware/ir/files/chem-mole/ and complete the worksheet below.

8.2 The Mole • One mole of particles contains ________________________________ particles.

( 6.02 X 1023 is also known as the Avogadro’s constant. )• Symbol of "mole" is __________________________.

• Definition of mole:

A mole is the _____________________________________________________________

(atoms, molecules or ions) as the number of atoms in 12 g of carbon-12

• ____ mole of water molecules is made up of _____ moles of hydrogen atoms and

____ mole of oxygen atoms.

• Conversion between number of moles and number of particles:

Number of particles

Number of moles = 6 X 1023

8.3 The Molar Mass

• The __________________________________________________________________ is

known as its molar mass.

• The unit for molar mass is ________________________________________ (g/ mol).

• Molar mass of an element = Relative atomic mass (Ar) of the element in grams.

Mass of element (g)

Number of moles of an element = Relative atomic mass of the element

Mass of compound (g)

Number of moles of a compound = Relative molecular mass

Mass of compound (g)

= Relative formula mass

Secondary 3 Express Science (Chemistry)Chapter 8: Counting Atoms – The MoleMole and Molar Masses

The Mole

Worksheet 1:Investigation 1 (Relationship between molar mass and relative atomic mass)

1. Complete columns A, B and D in the table below.

A B C DElement Chemical

SymbolRelative

atomic mass, Ar

Molar Mass(mass of 1

mole of substance)

No. of atoms in 1 mole of substance

(a)

Carbon

(b)

Aluminium

(c) Iron

(d)

Copper

(e)

Silver

(f) Gold

(g)

Mercury

(h)

Helium

2. Use the equipment in Prof’s Lab to determine the molar masses of the respective substances and record them into column C.

3. For each element existing as atoms , what do you observe about the values for its relative atomic mass (Ar) and its molar mass in g/mol?

Which of the following statements is correct?

(a) The molar mass (in g/mol) of an element that exists as atoms < its relative atomic mass (Ar).(b) The molar mass (in g/mol) of an element that exists as atoms = its relative atomic mass (Ar).(c) The molar mass (in g/mol) of an element that exists as atoms > its relative atomic mass (Ar).

( )4. Given 24 g of carbon, how many moles of carbon is that?

5. What is the mass of 0.5 mole of gold?

2

The MoleWorksheet 2:Investigation 2 (Relationship between molar mass and relative formula/molecular mass)1. Complete columns A, B and D in the table below.

A B C DElement / Compound

Chemical Formula

Relative Formula /

Molecular Mass, Mr

Molar Mass(mass of 1

mole of substance)

No. of molecules/

ions in 1 mole of

substance(a)

Hydrogen gas

(b)

Methane

(c) Ammonia

(d)

Oxygen gas

(e)

Carbon dioxide

(f) Bromine liquid

(g)

Sodium chloride

(h)

Sugar (Glucose)

2. Use the equipment in Prof’s Lab to determine the molar masses of the respective substances and record them into column C.

3. For each element (existing as molecules) or compound , what do you observe about the values for its relative formula/molecular mass (Mr) and its molar mass in g/mol?

Which of the following statements is correct?

(d) The molar mass (in g/mol) of an element (existing as molecules) or compounds < its relative formula/molecular mass (Mr).

(e) The molar mass (in g/mol) of an element (existing as molecules) or compounds = its relative formula/molecular mass (Mr).

(f) The molar mass (in g/mol) of an element (existing as molecules) or compounds > its relative formula/molecular mass (Mr).

( )4. Given 59.5 g of ammonia, how many moles of ammonia is that?

5. What is the mass of 1.5 moles of sugar (glucose)?

3

Practice Questions

1. How many moles of atoms are there in (a) 2.4 X 1024 atoms of sodium?

No. of moles of sodium atoms =

=

= _______________ mol

(b) 1X 1023 atoms of argon gas?

No. of moles of argon atoms =

= _______________ mol

2. How many(a) atoms are there in 0.5 mol of lead?

No. of lead atoms = No. of moles X Avogadro’s constant

= 0.5 X 6 X 1023

= ___________________________

(b) atoms are there in 2 moles of chlorine (Cl2) gas? (*Hint Refer to Example 8.7 on Pg. 119)

(c) water molecules are there in 36g of water molecules?

4

No. of sodium atomsAvogadro’s constant

2.4 X 10 24 6 X 1023

_________________

Note: Such shorts statements are needed in solving questions on

moles.

3. Calculate the mass of:(a) 4 moles of phosphorous atoms:

(b) 3 moles of oxygen molecules, O2

(c) 2 moles of magnesium chloride, MgCl2

(d) 1.5 X 1023 carbon atoms:

4. How many moles of (a) potassium atoms are contained in 8g of potassium atoms?

(b) calcium carbonate are contained in 20g of calcium carbonate (CaCO3)?

(c) oxygen atoms are contained in 64g of sulphur dioxide molecules?

5

What are some problems faced when doing the questions?

____________________________________________________________________________________

____________________________________________________________________________________