P2 2f acids, alkalis and titrations

Question 1

what are the three indicators for acids and alkalis?

Answer 1

litmus, phenolphthalein, methyl orange

Question 2

what colour does litmus turn when an acid is present?

Answer 2

red

Question 3

what colour does phenolphthalein turn when an acid is present?

Answer 3

colourless

Question 4

what colour does methyl orange turn when an acid is present?

Answer 4

red

Question 5

what colour does litmus turn when an alkali is present?

Answer 5

blue

Question 6

what colour does phenolphthalein turn when an alkali is present?

Answer 6

pink

Question 7

what colour does methyl orange turn when an alkali is present?

Answer 7

yellow

Question 8

what is litmus not suitable for?

Answer 8

for titrations as the colour change is not sharp, making it difficult to determine an endpoint

Question 9

what is universal indicator not suitable for?

Answer 9

for an acid-base titration, as a sharp colour change is required to identify an end-point

Question 10

what happens when acids are added to water?

Answer 10

they form positively charged hydrogen ions (H+)

Question 11

what happens when alkalis are added to water?

Answer 11

they form negative hydroxide ions (OH-)

Question 12

when does a neutralisation reaction occur?

Answer 12

when an acid reacts with an alkali, the ions react to produce water

Question 13

why is neutralisation important?

Answer 13

in the treatment of soils to raise the pH as some crops cannot tolerate levels below 7

Question 14

what are titrations used for?

Answer 14

a method of analysing the concentration of solutions
they can also determine exactly how much alkali is needed to neutralise a quantity of a acid
also to prepare salts

Question 15

method for titration?

Answer 15

• use a pipette and a pipette filler and place exactly 25cm3 of sodium hydroxide solution into the conical flask
• place the flask on a white tile, the tip of the burette over the opening
• add a few drops of a suitable indicator to the solution
• preform a rough titration by taking the burette reading, swirl vigorously
• quickly close the tap when the end-point is reached, record the volume
• now repeat the titration with a fresh batch of sodium hydroxide
• then add the solution drop-wise, until he indicator just changes colour
• record volume
• repeat until you get very similar results