5. Formula and amounts (CONCENTRATION + TITRATION)

Question 1

What is an acid

Answer 1

a solution with a pH below 7 and is a proton donor - releases H+ ions

Question 2

What is a base

Answer 2

A proton accepter - accepts H+ ions

Question 3

What is an alkali

Answer 3

A base that has been dissolved in water

Question 4

What is the difference between a concentrated and a dilute solution

Answer 4

A concentrated solution fully ionises in aqueous solutions to give H+ ions and OH- ions
A dilute solution only partially ionises in aqeous solutions

Question 5

How to go from cm3 to dm3

Answer 5

divide by 1000

Question 6

How to go from cm3 to m3

Answer 6

Divide by 1000 000

Question 7

How to go from dm3 to m3

Answer 7

Divide by 1000

Question 8

What is 1 cm3 the same as

Answer 8

1 ml
–> so 1 dm3 is the same as one Litre

Question 9

Phenolphthalein in acid

Answer 9

Colourless

Question 10

Phenolpthalein in alkali

Answer 10

Pink

Question 11

Methyl orange in acid

Answer 11

Red (salmon pink)

Question 12

Methyl orange in alkali

Answer 12

Yellow

Question 13

What is the colour change involving methyl orange

Answer 13

Orange

Question 14

Why is it good to wash out pipette and burette with the acid / alkali before the titration

Answer 14

Ensures the titration is done with a known concentration of the acid / alkali
Also so water doesn’t dilute the solution

Question 15

Why must you remove the funnel from the top of the burette before the titration

Answer 15

Drops of acid could fall into the burette so then you don’t know how much was added

Question 15

During the titration the student washed the inside of the conical flask containing the alkali with some distilled water.
Suggest why this washing does not give an incorrect result.

Answer 15

Water does not change the number of moles of the alkali as water is a product of the titration

Question 15

What are concordant results

Answer 15

Results within 0.1 cm3 of each other

Question 16

Explain 4 actions you would take in a titration to ensure the end point is accurate just before the end point titration is reached

Answer 16

Add drop by drop to avoid ‘overshooting to the end point’
Swirl to ensure all acid and alkali react
Rinse the sides with deionised water between additions to rinse all reactants into the solution so all can react
Use a white tile to clearly see colour change

Question 17

What is a standard solution

Answer 17

A solution with a known concentration