add H2O to the side that already has oxygen, OH- to opposite side and then electrons to balance charge
Combining half equations - multiply one or both equations so that the number of electrons on each side is the same and they can cancel out
Concordant titre results are within 0.20 cm3 of each other
MnO4- to Mn2+ = purple to palepink
CrO7 2- to 2Cr3+ = orange to green
Fe2+ to Fe3+ = pale green to pale yellow
I2 to 2I- = brown to colourless (blue-black to colourless if starch is added)
1 mole of Cu2+ = 1 mole of S2O3 2-
To determine concentration of Cu2+ ions
1st reaction - 2 moles of Cu2+ form 1 mole of brown I2
2nd reaction - add thiosulfate ions to reduce I2 to I-, starch indicator to determine end point (blue black to colourless) 1 mole of I2 react with 2 moles of S2O3 2-
Therefore 1 mole of Cu2+ is equivalent to 1 mole of S2O3 2-