In quantitative analysis titration is used to determine the concentration of an unknown sample. A typical titration involves an erlenmeyer flask with the unknown sample – the analyte – and a buret filled with a reactant of a known concentration – the titrant – which will react with the unknown sample. A magnetic stirrer can be stirring the unknown sample and an indicator reagent such as phenolphthalein may be added. The volume of the titrant solution required to react completely with the unknown analyte will determine the concentration of the analyte. The equivalence point is the point at which the number of moles of titrant used equals the number of moles of analyte present. The endpoint will be indicated by a color change in the indicator. A pH meter can be used for acid base reactions; a sudden change in pH will be the endpoint of the titration. A sudden change in the working electrode potential will indicate the endpoint of a redox titration.