Amount of Substance Flashcards
% uncertainty formula
Uncertainty / measured value x 100
Dilution formula
C1V1 = C2V2
Formula for isotopic abundance
((Mass1 x Mr1) + (Mass2 x Mr2))/100
Formula of an ammonium ion
NH4⁺
Equation that links Mr, mass and moles
n = m/Mr
Phosphate ion
PO4(3-)
Atom Economy
Mr of desired product / Mr of all products x 100
Formula of carbonate ion
CO3 (2-)
Ideal Gas Equation
pV = nRT (R is usually 8.31 unless given)
Hydrogen sulfate ion
HSO4-
Formula of an ammonia molecule
NH3
Percentage Yield
Actual yield / Theoretical yield x 100
Sulfate ion
SO42-
Titration method from markscheme
Common source of errors:
Reducing uncertainties in measuring mass
- 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.
-if using anhydrous solid, make sure it is not too old as it will have picked up water and therefore 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
-with dark liquids like potassium manganate (K,MO,) it can be difficult to see the meniscus, so placing a piece of white paper behind to make the marker clearer to see
-use a more accurate balance
-use a larger mass
-weighing sample before and after addition and then calculate difference (weighing by difference)
