CHEM1201 Lecture Notes - Lecture 18: Volumetric Flask, Sodium Hydroxide, Molar Mass
7 Jun 2018
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Chemical reactions:
- Observation of evidence:
o Let us know a chemical reaction has taken place
- Correlation of prior knowledge and experience:
o Allow deduction of both the types of products formed and the amounts
formed
- Describing the chemical reaction therefore involves writing a balanced chemical
equation
- Need to know:
o Correct chemical formulae for all the reactants and products
o Stoichiometry (relative amounts of each species)
- MgCl2(aq) + 2AgNO3(aq) → 2AgCl(s) + Mg(NO3)2(aq)
Definitions: atoms and molecules
- Atoms:
o Submicroscopic particles that are the fundamental building blocks of nature
- Molecules:
o Two or more non-metallic atoms which are covalently bond together
o Smallest unit of a substance that retains that chemical properties of that
compound
Definitions: moles
- Moles:
o A chemical unit of measurement that describes the amount of a substance
that otais Avogadro’s uer of partiles
o Must specify the nature of the particles
o Avogadro’s uer (NA) = 6.02 x 1023
o E.g. 1 mole of CO2 molecules:
▪ Contains 6.02 x 1023 CO2 molecules
▪ Contains 6.02 x 1023 C atoms
▪ Contains 2 x 6.02 x 1023 = 1.204 x 1024 O atoms
▪ Contains 2 moles of O
Can moles be directly measured? NO
- Moles can be calculated from other quantities that can be measured, e.g.
o Mass n = m/M
o Volume n = cV
o Concentration n = cV
Concentration of solutions:
- Number of moles of a substance in a given volume c = n/V
- Molarity = number of moles of solute per litre of solution
- 6M MgCl2 solution contains 6 moles of MgCl2 per litre of solution
o MgCl2(s) → Mg2+(aq) + 2Cl-(aq)
o 12M Cl-
Making solutions: e.g. 0.5L of 0.6M MgCl2
1. find the number of moles of solute (substance being dissolved) needed
o n = cV = 0.6x0.5 = 0.3 mol
2. find the mass of solute needed using the molar mass of the solute
o m = nM = 0.3 (95.21) = 28.56 g
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