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Dilution

When you dilute a solution with water, the amount of substance is the same before and after. Concentration times volume is therefore constant. The volumes must have the same unit on both sides, for example millilitres in both places. You do not need to convert to litres as long as the unit is shared. Dilution lowers the concentration, and it can never become higher than the one you started with. Remember to mix well afterwards.

c1V1=c2V2c_1 V_1 = c_2 V_2dilution

Symbols

c1c_1concentration beforemol/L
V1V_1volume you takemL or L
c2c_2concentration aftermol/L
V2V_2final volumesame unit

Example

20 mL of a 0.50 mol/L solution is diluted to 100 mL.

c2=0.50⋅20/100=0.10c_2 = 0.50 \cdot 20 / 100 = 0.10 mol/L.

V2 is the total volume afterwards, not the volume of water you added.
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Part of Chemistry 1: Amount of substance and concentration.