Core practical 2. Make up a volumetric solution and carry out a simple acid–base titration

Question 1

What is the procedure for Core practical 2: Find the concentration of a solution of
sodium hydroxide?

Answer 1

1. Weigh an empty test tube. Scoop approximately 2.5 g of sulfamic acid into the test tube.
2. Reweigh the test tube and its contents accurately.
3. Dissolve the sulfamic acid in approximately 100 cm3 of water in a beaker.
4. Transfer the solution, including the washings, into a 250 cm3 volumetric flask and make the solution up to the mark with deionised water.
5. Prepare your apparatus for the titration. The burette will contain the acid and the conical flask will contain the sodium hydroxide solution.
6. Pour a 25.0 cm3 aliquot of sodium hydroxide solution of unknown concentration into the 250 cm3 conical flask.
7. Add four drops of methyl orange indicator to the conical flask.
8. Titrate the contents of the flask against the sulfamic acid solution you prepared. (Burette readings should be to the nearest 0.05 cm3)
9. Continue to conduct titrations until you have 2 concordant titres.

Question 2

What is the objective of core practical 2?

Answer 2

To make a solution of a known concentration of acid and use it to find the concentration of a solution of sodium hydroxide

Question 3

Notes on safety

Answer 3

● Wear goggles.
● Sulfamic acid can be toxic if it is ingested.
● Acids and alkalis are corrosive (at low concentrations acids are irritants).
● Wear eye protection and gloves.
● If spilled immediately wash affected parts after spillage

Question 4

Equipment needed for core practical 3

Answer 4

● burette clamp and stand
● solid sulfamic acid
● sodium hydroxide solution of unknown concentration
● methyl orange indicator
● 250 cm3 conical flask
● 25 cm3 volumetric pipette plus safety filler
● 100 cm3 beaker for transfer of solutions
● funnel for filling burette
● 250 cm3 beaker
● 250 cm3 volumetric flask
● mass balance (2 d.p.)
● eye protection (goggles)

Question 5

Equation for number of moles in full volume

Answer 5

full volume/volume in which you know the number of moles

Question 6

Possible errors in core practical 2

Answer 6

● Be careful not to lose any solid when transferring from the weighing boat to the
beaker.
● When weighing out the solid, weigh by difference and then calculate the mass of a
solid in a beaker:
mass of (weighing bottle + beaker) - (mass of the bottle after emptying solid)
● Remember to fill so the bottom of the meniscus sits on the line on the neck of the flask

Question 7

How do you make a standard solution?

Answer 7

● Weigh by difference, using a balance, to get the mass of solid required
● dissolve this in approximately 100 cm3 of deionised water in a beaker.
● use a glass rod to stir the contents of the beaker until all of the solid has dissolved.
● Using a funnel, pour the contents of the beaker into a 250 cm3
volumetric flask. Wash out the beaker with deionised water to transfer the washings as well.
● Make the volumetric flask up to the graduated mark with deionised water.
● add a stopper to the volumetric flask and invert it to mix the contents.