Unit 5 - Formulae, Equations and Amounts of Substance
Institution
Pearson (PEARSON)
A comprehensive in-depth, specification led, revision booklet of the 2015 spec chemistry AS level course. Written during AS studies by an AS student, meaning it is written in an easily comprehensible stance for any student wishing to find extra resources to revise from.
Unit 5 - Formulae, Equations and Amounts of Substance
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A Cook 2016
Chemistry Spec Led Revision
Chapter 5 - Formulae, Equations and Amounts of Substance
1. Know that the mole (mol) is the unit for amount of a substance
The Mole:
A mole is the amount of substance that contains the same amount of atoms as 12g of of the 12C
isotope.
2. Be able to use the Avogadro constant, L, (6.02 × 1023 mol-1) in calculations
Avogadro Constant:
Avogadro's constant is 6.02 x 1023, which allows us to scale up small numbers of atoms into grams
- which are easier to visualise.
Calculations using Avogadro constant:
1) Calculate the number of particles in a given mass of a substance
2) Calculate the mass of a given number of particles of a substance
Example 1 -
How many H2O molecules are there in 1.25g of water?
Equation: Moles = Mass / Mole Mass
Moles = 1..0 = 0.0694 mol
0.0694 x (6.0 x 1023) = 4.18 x 1022
Example 2 -
What is the mass of 100 million atoms of gold
Equation: Moles = Mass / Mole Mass
Moles = 100 x .02 x 1023 = 1.66 x 10-16 mol
Mass = 1.66 x 10-16 mol x 197.0 = 3.27 x 10-14 g
3. Know that the molar mass of a substance is the mass per mole of the substance in g mol-1
Molar mass is the mass per mole of any substance (molecular or ionic), and it has the units g mol-1
(grams per mole).
Amount in mol = Mass of substance in g / Molar Mass in g mol-1 or n = m / M
Substance O2 CH4 H 2O NH4NO3
Mass in g 5.26 4.0 100 14.7
Molar Mas in g mol-1 32.0 16.0 18.0 80.0
Amount in mol 0.16 0.25 5.6 0.18
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