1.2.2: Avogadro’s Constant & The Mole

1.2.2: Avogadro’s Constant
& The Mole

Amount of Masses

The quantity whose unit is the mole.

Avogadro's constant

The number of atoms per mole of the carbon-12 isotope

Chemist use it as a means of counting atoms

6.02x10^23 mol^-1

Mole

The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of the Carbon-12 isotope

Molar Mass

The mass per mole of a substance.

The units of molar mass is g mol^-1

Relationship of Mass, Molar Mass and Moles

Moles = Mass ÷ Molar Mass

n (mol) = m (g) ÷ Mr (g mol^-1)

Calculating the Mass of a substance

Mass of 0.05 moles of Sodium Thiosulfate

O=8 (16.00)=128.00

H=10 (1.01)=10.1

S=2 (32.06)=64.12

Mr=248.20

Na=1(22.99)=32.06

Mass= Moles x Molar Mass

Mass= 0.05 x 248.20

Mass= 1.2x10^1 g (2sf)

Calculating the number of moles in a substance

Number of moles in 560g of ethene

H=4(1.01)=4.04

Mr=28.06

C=2(12.01)=24.02

Moles=Mass/Molar Mass

Moles= 2.00x10^1 mol (3sf)

Moles=560/28.06

Significant Figures

5.000 x 21.9= 109.5 = 110 (3sf)

When multiplying or dividing in scientific notation the result will always be to 3 significant figure as both factor are to 3 sig figs.

When multiplying or dividing the answer should be to the lowest number of significant figures of the factors

3.50x10^1 x 2.11x10^1 = 7.385x10^2 = 7.39x10^2 (3sf)