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Reagents 3

Reagents 3 — Calculating Amounts of Components

 
You know the (final) concentration of a component in a reaction mixture of a given volume, and are to calculate the amount of the component.
All the answers to the questions here are in µmoles, but the units of volume and concentration may vary.

Amount of component: µmol   
 
These calculations are best set out on a piece of paper (i.e. without a calculator). Do not try to use a formula — use the definition of molarity followed by logic involving simple proportion.
Example Question: How many μmol in 50 μl of 100 mM KCl?
Strategy:
  • Express mM as its definition — mmol per litre
  • Convert to μmol per litre because answer requires μmol
  • Convert to μmol per μlitre because volume is in μlitre
  • Convert to μmol per 50 μlitre (the volume in this case)
Worked Answer:
  • 100 mM = 100 mmol/litre
  • 100 mM = 100 x 103 μmol/litre
  • 100 mM = 100 x 103 x 10–6 μmol/μlitre
  • 100 mM = 50 x 100 x 103 x 10–6 μmol/50 μlitre
  • i.e. 5 μmol in 50 μlitre of 100 mM KCl
The three-stage version of these calculations illustrates this approach.