Introduction to Moles

Introduction to Moles

By S Fergusson

Masses of an atom

​Atomic Mass

The mass of an atom is the sum of the neutrons and protons.

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Masses of an Atom

Relative ​Atomic Mass

The ratio of the average mass of one atom of the element compared ​to 1/12 the mass of one atom of carbon

​Calculating Relataive Atomic Mass

​Calculate the Relative formula mass of Chlorine which has two isotopes​

Chlorine-35 with a percentage of 75.5 %

Chlorine 37 with a percentage of 24.5 %​

​

​

​Relative atomic mass = ( 75.5/100 x 35 ) + (24.5/100 x 37) = 35.5

​

Determine the relative atomic mass for

neon-20 (90.9%), neon-21 (0.3%), and neon-22 (8.8%)​

Calculating Relative Atomic Mass of Neon

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( 90.9/100 x 20)​ +( 0.3/100 x 21) + (8.8/100 x 22) = 20.1

NOTE - THE RELATIVE ATOMIC MASS HAS NO UNITS .​

​RELATIVE FORMULA MASS OR MOLECULAR MASS

​The relative formula mass is the sum of the relative atomic masses of each atom in the compound

EXAMPLE 1: Calculate the relative formula mass of ammonia: NH₃

N = 14 x 1 = 14

H =1 x 3 = 3

Relative formula mass NH₃= 17 ​

Multiple Choice

The relative atomic mass is the average mass of one atom of an element compared to

• carbon -12 atom

• the mass of a hydrogen atom

• $$\frac{1}{12}$$  the mass of a hydrogen atom

• $$\frac{1}{12}$$  the mass of a carbon-12 atom

Multiple Choice

What is the unit of the relative atomic mass

• kilograms

• groms

• there are no units

• pounds

Multiple Choice

THe relative atomic mass of an element is the

• average of the atomic number and mass number of the element

• Weighted average masses of the isotopes of the element

• total mass of the isotopes of the element

• the sum of the subatomic particles in the nucleus.

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Calculate the relative formula mass of HCl

(H = 1; Cl = 35.5)

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Calculate the relative formula mass of NaOH

(Na = 23 ; O = 16 ; H = 1)

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Calculate the relative formula mass of MgCl₂

(Mg = 24 ; Cl = 35.5)

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Calculate the relative formula mass of sulphuric acid H₂SO₄

(H = 1; S= 32 ; O = 16 )

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Calculate the relative formula mass of potassium carbonate K₂CO₃

(K =39 ; C = 12 ; O =16)

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Calculate the relative formula mass of ammonium sulphate (NH₄)₂SO₄

(N=14 ; H =1 ;S =32 ;O =16 )

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calculate the relative formula mass of magnesium nitrate. Mg(NO₃)₂

(Mg = 24 ; N = 14; O = 16)

THE MOLE

Definition of the mole

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A mole is the The amount of substance​ that contains 6.02 x 10²³ particles

Calculation Involving Moles

​How many sodium atoms are in 2 mols of Na

Standard Statement : 1 mols of Na atoms contain 6.02 x 10²³

​This is also the unitary statement. Always start with what you have and end with what you want

2 mols of Na atoms contain : (6.02 x 10²³ atoms∕ 1mole) x 2 moles

​ = 1.20 x 10^24` atoms

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Multiple Choice

Find the number of atoms in 0.5 mole of aluminium.

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 3.01x10²³

• 3.01x10²²

• 6.02x10²³

• 6.02x10²²

Multiple Choice

Find the number of molecules in 1.2 moles of hydrogen gas.

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 7.224x10²³

• 7.224x10²⁴

• 3.612x10²³

• 5.02x10²³

Multiple Choice

How many moles of water contain 3.01x10²² water molecules?

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 0.05 mol

• 0.25 mol

• 0.75 mol

• 0.35 mol

Multiple Choice

A beaker contains a sample of 0.5 mole of potassium bromide, KBr.

Calculate the total number of ions present in the beaker.

[Avogadro constant, N_A: 6.02x10²³]

• 3.01x10²³

• 6.02x10²³

• 1.204x10²⁴

• 1.204x10²²

Multiple Choice

A beaker contains a sample of 0.5 mole of potassium bromide, KBr.

Find the number of formula units of KBr in the beaker.

[Avogadro constant, N_A: 6.02x10²³mol^-1]

• 3.01x10²³

• 1.204x10²⁴

• 8.31x10²¹

• 8.31x10^-25

Multiple Choice

How many atoms of iodine are in a mole of iodine?

• 53
• 63.55g
• 126.9
• 6.02 x 10²³

Multiple Choice

How many moles are 2.85 x 10²⁰ atoms of iron?

• 4.73 x 10^-4 moles
• 1.72 x 10⁴ moles
• 1.72 x 10^-42 moles
• 4.73 x 10⁴ moles

Multiple Choice

The number 6.02 x 10²³ is called...

• Obama's number
• Bohr's number
• Trump's number
• Avogadro's number

Multiple Choice

How many moles of copper are 4.57 x 10¹⁵ atoms of copper?

• 7.59 x 10^-9 moles
• 2.75 x 10^-33 moles
• 7.59 x 10⁹ moles
• 2.75 x 10³³ moles

Multiple Choice

Determine the amount of moles in 4.50 x 10²³ atoms of fluorine.

• 9.03 x 10⁴⁶ moles
• 0.757 moles
• 4.73 moles
• 0.0131 moles

Multiple Choice

How many molecules of of methane are there if there are 24 x 10²³ atoms of H? (MCH₄ = 16)

• 4
• 1
• 24 x 10²³ / 16

Multiple Choice

In 53g of Na₂CO₃ (M(Na₂CO₃) = 106,  M(O) =16), what is the mass of O?

• 53 /106
• 53/106 x 16
• 53 /106 x 3 x 16

Multiple Choice

How many atoms of H in 4.5g of H₂O?  M(H₂O) =18 ?

• 4.5 / 18
• 18/4.5 x 6 x 10²³
• 0.25 x 6 x 10²³

Multiple Choice

What is the mass of O in 100g of CaCO₃ (M (CaCO₃ = 100)

• 1
• 100/48
• 100/16
• 3

Multiple Choice

How many moles of H in 32g of methane (CH₄).  M(CH₄) = 16

• 32/16
• 32 x 16
• 32 /16 x 4
• 32/16  x 4

Multiple Choice

How many atoms of Cl in  35.5g of Cl₂ molecules (M(Cl) = 35.5)

• 35.5/35.5 x 6 x 10²³
• 71 x 6 x 10²³
• 71/35.5 x 6 x 10²³

Multiple Choice

How many moles of lead in 42g of Na (M=23)?

• 42/23
• 23/42
• 42 x 6 x 10²³

Multiple Choice

How many moles of lead in 42g of Na (M=23)?

• 42/23
• 23/42
• 42 x 6 x 10²³