CPAC 02

Question 1

Outline the method to make a standard solution of sulfamic acid

Answer 1

• add between 2.3 and 2.4g of sulfamic acid to weighing boat and weigh
• transfer as much of the acid as possible of to clean beaker and reweigh weighing boat
• add 100cm3 of deionised water to beaker and stir until all sulfamic acid has dissolved
• remove stirring rod and wash any remaining contents on stirring rod with wash bottle
• place funnel on volumetric flask and pour solution in
• rinse beaker several times with wash bottle and transfer rinsings to flask
• add deionised water to the flask and make it up to the 250cm3 graduation mark exactly- measuring at bottom of meniscus
• stopper flask and invert it several times to make uniform solution

Question 2

What is the weighing by difference technique?

Answer 2

• method to weigh substances accurately

- mass of substance= mass of weighing dish and substance- mass of weighing dish after substance has been transferred

Question 3

What is the procedure for the titration?

Answer 3

• rinse conical flask with deionised water and place on white tile
• using pipette filler, rinse pipette with deionised water and then with sodium hydroxide solution
• use pipette to transfer 25cm3 of sodium hydroxide solution to the conical flask
• add around 3 drops of methyl indicator
• rinse burette with deionised water and then some sulfamic acid solution
• fill burette with sulfamic acid solution and set up in stand above conical flask
• record burette reading
• add sulfamic acid to conical flask until it just changes colour and record burette reading
• empty and rinse conical flask with deionised water and repeat titration until concordant results obtained

Question 4

What are concordant results?

Answer 4

within 0.1cm3 of each other

Question 5

What should the burette readings be measured to?

Answer 5

0.05cm3

Question 6

Why should the pipette be rinsed with sodium hydroxide solution after washing it with water?

Answer 6

water left in the pipette will dilute the sodium hydroxide used so changing the moles

Question 7

Why is it not necessary to dry out the conical flask after washing it between trials?

Answer 7

the water will not change the number of moles of sodium hydroxide as its volume is measured before it is put in the flask

Question 8

What colour change takes place in this titration for methyl orange?

Answer 8

methyl orange goes from yellow to red

Question 9

What other indicator could be used?

Answer 9

phenolphthalein goes from pink to colourless

Question 10

What are the hazards with sulfamic acid?

Answer 10

can be toxic if ingested