# [Solution]Online assessment: COVID-19

Complete Tasks 1 – 4. Tasks 1 and 2:  To be able to determine concentration of sodium hydroxide by using two different methods: Task 1: …

Tasks 1 and 2:  To be able to determine concentration of sodium hydroxide by using two different methods:

Task 1:  By using the mass of the substance and volume of the solution

Task 2:  By using data from the titration procedure

Method 1:  A student weighed accurately  2.70 g of potassium hydroxide and dissolved it a 300cm3 volume if distilled water in a volumetric flask

1.  Use the mass of potassium hydroxide from above to calculate the concentration of the standard solution and record the result

(2)   Method 2:

2a)  A student filled the burette with 0.150 M hydrochloric acid (HCl)

2b)  A student measured 30cm3 of potassium hydroxide prepared in method 1  and pour it into a conical flask

2c)  A student added four drops of phenolphthalein indicator to the conical flask containing potassium hydroxide

2d)  A student added the HCl acid from the burette until the indicator just changes from lilac colour to colourless

2e)  A student repeated titration until two concordant results were obtained.  (results are concordant in this experiment if they are within 0.1cm3 of each other)

The recorded results from the titration procedure are presented here:

Run 1:

Initial titre:  2.5 cm3

Final titre: 35.5 cm3

Run 1 titre =      cm3

Run 2:

Initial titre: 2 cm3

Final titre: 33.5 cm3

Run 2 titre =     cm3

Run 3:

Run 2:

Initial titre: 6.6 cm3

Final titre: 39.6 cm3

Run 2 titre =     cm3

Create a suitable table to present result of the titration procedure Calculate the mean titre Use the mean titre to calculate the concentration of the potassium hydroxide solution determined by the titration procedure Calculate the percentage difference between the values of the concentration of potassium hydroxide solution obtained in method 1 and method 2.

Show all equations used and calculations here in detail.

Task 1:  Use the mass of potassium hydroxide from above to calculate the concentration of the standard solution and record the result

1 A) To find out  number of moles in 2.70 g of potassium hydroxide (KOH)

Number of moles = mass / molecular mass

Mass =

Molecular mass = K (   ) + O (    ) + H (     ) =

Number of moles = mass / molecular mass =     /      =      moles

B)  Concentration = molarity (M)

Concentration (M) = number of moles / volume

Number of moles  =       (see 1A)

Volume  = 300 ml  =     L

Concentration (M) = number of moles / volume =    moles /    L =   moles  / L

Create a suitable table to present result of the titration procedure. Calculate the mean titre. Use the mean titre to calculate the concentration of the potassium hydroxide solution determined by the titration procedure. Calculate the percentage difference between the values of the concentration of potassium hydroxide solution obtained in method 1 and method 2.

Titres to be used for calculations are run 1 and 3.

Mean titre =        /      =      cm3

2.3.  Equation to be used:

Macid x Vacid = Mbase x Vbase

moles / L = Molarity of base

2.4.

Percentage difference  =

Percentage difference  =        %