Amount of Substance

Uncertainty / measured value x 100

C1V1 = C2V2

((Mass1 x Mr1) + (Mass2 x Mr2))/100

NH4⁺

n = m/Mr

PO4(3-)

Mr of desired product / Mr of all products x 100

CO3 (2-)

pV = nRT (R is usually 8.31 unless given)

HSO4-

NH3

Actual yield / Theoretical yield x 100

SO42-

• Weigh the sample bottle containing the solid on a (2 dp) balance. • Transfer solid to beaker and reweigh sample bottle. • Record the difference in mass. • Add distilled water and stir with a glass rod until all the solid has dissolved. • Transfer to a volumetric flask with washings. • Make up to the 250cm° mark with distilled water. • Shake flask. Common sources of errors Using anhydrous solid -make sure it is not too old -as it will have picked up water -hence mass values will not be as accurate Balance -usually gives to 0.01g (systematic error - same for each value that is recorded) -alternatively the known mass of solid in the weighing bottle could be transferred to beaker, washed and washings added to the beaker -remember to fill so the bottom of the meniscus sits on the line on the neck of the flask -dark liquids, e.g. potassium manganate (KMnO4) can be difficult to see the meniscus -so place a piece of white paper behind to make the marker clearer to see Reducing uncertainties in measuring mass -use a more accurate balance -use a larger mass -weighing sample before and after addition and then calculate difference (weighing by difference)