# 201 Chemistry/2.3

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# Introduction

Quantative chemistry is the study of 'how much'.

This unit is designed to prepare you for NCEA level 2 Achievement standard 90763: Solve simple quantitative chemical problems.

Before we start we need to remind ourselves of some definitions.

Scientific notation or standard form:

Significant figures:

# Outcomes

 By the end of this unit you should be able to: Calculate the molar masses of molecules from given molar masses of atoms and formulae. Calculate mole ratios from given molar masses of atoms and their formulae. Carry out calculations using the formulae: $n = \frac{m}{M}$ and $n = v \times c$ Calculate the percentage composition of a compound Determine the empirical and molecular formula of a compound. Calculate the number of water molecules in the formula of a hydrated salt.

# Preknowledge

 It is useful to be able to write balanced equations