Harcourt Essen Reaction

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Making up Hydrogen Peroxide

Volume required 250 cm3 and concentration required 0.1 moldm-3 Given concentration of H2O2 = 1.7 moldm¬-3

Number of moles (n¬¬¬¬¬¬¬¬¬¬¬) = Concentration (moldm-3) x Volume (dm-3) = 0.1 x 0.25
= 0.025 mol

Volume (dm-3) = Number of Moles (n)
X 1000 Concentration (moldm-3)

= (0.025/1.7) x 1000 = 14.7 cm3

Distilled water required: 250 cm3 – 14.7 cm3 = 235.3 cm3

1)Measure 14.7 cm3 of H¬2O2 using a 20 cm3 graduated pipette (with a pipette filler) and transfer to a 250 cm3 volumetric flask. 2)Rinse the pipette filler with distilled water and pour the washings into the volumetric flask. 3)To dilute the solution fill the flask with distilled water until it is 5mm below the calibration line. 4)Use a dropping to add the final quantity of distilled water until the bottom of the meniscus is level with the 250 cm3 mark. 5)Stopper the flask and invert it 10 times to ensure the solution is completely mixed.

The hydrogen peroxide should be stored in a dark and cool place to minimise decomposition, if possible a new solution should be mixed up every time.

Making up Sulphuric Acid

Volume required 250 cm3 and concentration required 0.1 moldm-3 Given concentration of H2SO4 = 4 moldm-3

Number of moles (n¬¬¬¬¬¬¬¬¬¬¬) = Concentration (moldm-3) x Volume (dm-3) = 0.1 x 0.25
= 0.025 mol

Volume (dm-3) = Number of Moles (n)
X 1000 Concentration (moldm-3)

= (0.025/4) x 1000 = 6.25 cm3

Distilled water required: 250 cm3 – 6.25 cm3 = 243.75 cm3

Water added to acid can cause an extremely violent reaction so the acid must always be added to the water. For this reason a ten-fold dilution will need to take place from 40 mol dm3.

n = c x v
= 10 X 0.25
= 2.5 mol

v = (n/c) x 1000
= (2.5/40) x 1000
= 62.5 cm3

1)Add 125 cm3 so as to half fill the volumetric flask.
2)Measure 62.5 cm3 of the H2SO4 using a 100 cm3 graduated pipette (with a pipette filler) and transfer to the 250 cm3 volumetric flask. 3)Rinse the pipette filler with distilled water and pour the washings into the volumetric flask. 4)To dilute the solution fill the flask with distilled water until it is 5mm below the calibration line. 5)Use a dropping to add the final quantity of distilled water until the bottom of the meniscus is level with the 250 cm3 mark. 6)Stopper the flask and invert it 10 times to ensure the solution is completely mixed. 7)Remove 25 cm3 of the 1 moldm3 H2SO4 solution using a graduated pipette (with pipette filler) and transfer to a new 250 cm3 volumetric flask half filled with distilled water (125 cm3). 8)Using the same steps as before, further dilute the solution up to the 250 cm3 mark with distilled water and invert 10 times ensuring is fully mixed. The new solution will be of the required 0.1 moldm3.

Making up Potassium Iodide

Volume required 500cm 3 and concentration required 0.1 moldm3 Given KI as a solid
Molar mass (mr) = 166

Number of moles (n¬¬¬¬¬¬¬¬¬¬¬) = Concentration (moldm-3) x Volume (dm-3) =0.1 x 0.05
=0.050 mol

mol (n) = Mass (g)
Molar mass

Mass (g) = mol (n) x Molar mass
= 0.050 x 166 = 8.30 g

1)Using a balance measure out 8.30g of KI in a weighing boat, ensure it is to 2 decimal places, as this will increase accuracy. 2)Next add the KI to a beaker with a small known volume of distilled water, when doing so wash out the weighing boat with distilled water to make sure all the KI has been transferred. 3)Mix the substance with a glass rod and heat with a Bunsen burner if necessary to ensure all of the KI has fully dissolved. 4)Transfer the contents of the beaker to the 500cm3 volumetric flask 5)Rinse out the beaker to ensure no residue has been left behind 6)To dilute the...
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