The purpose of this experiment is to to prepare a solution of primary standard of potassium hydrogenphthalate C8H5O4K, which can be used to standardise water-soluble bases such as sodium hydroxide solution.
n= m/M and c= n/V
Many common reagents are supplied in an impure state or they can easily pick up moisture from the atmosphere, or may be supplied as concentrated solutions of an uncertain concentration. As a consequence, solutions made from such substances must be stanardised against a substance of known purity. We call them primary standards.
ï¿½ Potassium hydrogenphthalate (C8H5O4K)
ï¿½ top loading balance (weighing scale)
ï¿½ weighing bottle
ï¿½ volumetric flask
ï¿½ We started by weighing 5 g of potassium hydrogenphthalate accurately in a weighing bottle.
ï¿½ I poured the content of the weighing bottle into a beaker and i reweighed the the weighing bottle. I also made sure that no residue of the chemical was left in the weighing bottle.
ï¿½ I added about 100 ml of distilled water to the beaker and stired it until it dissolved the hydrogenphthalate.
ï¿½ I transferred the solution from the beaker to a 250 cm3 voumetric flask. i washed the beaker several times and poured the content into the volumetric flask just to make sure that no residue of the chemical was left in the beaker.
ï¿½ I put in more distilled water in the volumetric flask until the volume was 250 cm3 and mixed it thoroughly.
ï¿½ I labeled my flask with my initials, date and content.
Weight of weighing bottle and hydrogenphthalate: 5.964 g
Volume of solution: 250 cm3
mass of weighing bottle and content: 5.96 +_ 0.01g
mass of weighing bottle: .96 +_ 0.01 g
mass of C8H5O4K :uncertainity : 0.01+0.01= +_0.02
molar mass of potassium hydrogen phtalate: 0.01g/mol
molar mass of potassium hydrogenphthalate.
204.286 g/mol +_ .2 +_ .089 %
mass of weighing bottle and contents, m1
5.964 g +- .001
mass of weighing bottle, m2
0.962 g ï¿½+_ .001
mass of potassium hydrogenphthalate m=m1-m2
5.002 g +_ .002 +_ 0.385%
amount of potassium hydrogenphthalate, n= m/M
0.024 moles +_0.475%
We also know the volume of the solution to be 25 dm3, so putting all these values in the formula. uncetainty for volume: +_ 0.0005%
c = n/V
so concentration of potassium hydrogenphthalate c= 0.09612 mol/dm3
% uncertainty :0.00012%+0.475%= .47512%
Tap water contains chemicals and other impurities and is not suitable for making up solutions so we should always use distilled water for making solution. i have also noted margin of error of different appratus and all calculations have been made keeping in mind the margin of error.