moles II 5.1

Question 1

1 dm3 =

Answer 1

1000 cm3

Question 2

1000 cm3 =

Answer 2

1 dm3

Question 3

how do you calculate moles of a gas?

Answer 3

moles = volume (DM3 - must be in dm3) / 24dm3

Question 4

how do you calculate volume in dm3 of a gas?

Answer 4

volume = moles x 24 dm3

Question 5

what is the concentration of a solution?

Answer 5

is a measure of how much solute is dissolved per unit volume

Question 6

what is concentration measured in?

Answer 6

mol/dm3

Question 7

how do you work out concentration of a solution?

Answer 7

concentration (mol/dm3) = moles / volume (dm3)

Question 8

how do you work out moles in a volume of concentration?

Answer 8

moles = volume (dm3) x concentration (mol/dm3)

Question 9

what is a titration?

Answer 9

a practical method used to measure the volume of acid needed to neutralise a particular volume of alkali

Question 10

what are the two pieces of equipment used in a titration?

Answer 10

volumetric pipette
burette

Question 11

what’s the use of a volumetric pipette?

Answer 11

measures out 25cm3 very accurately

Question 12

what’s the use of a burette?

Answer 12

measures any volume to the nearest 0.05cm3

Question 13

where does the acid and the alkali go in the titration experiment?

Answer 13

acid is known so in the burette

alkali unknown to in conical flask

Question 14

how do you set up a titration?

Answer 14

• use a volumetric pipette to place 25cm3 of unknown alkali into a conical flask
• add a few drops of methyl orange or phenolphthalein (pink)
  universal indicator doesn’t work as it changes colour too gradually
• fill a burette with known acid and clamp above conical flask

Question 15

how do you use/ carry out a titration?

Answer 15

• measure initially volume of known acid on the burette to nearest 0.05 cm3
• use burette to add acid into the conical flask drop by drop and swirling the flask
• close the burette tap as soon as the colour of the liquid in the conical flask changes (start colour is the alkaline colour and end is the acidic colour)
• measure final volume to nearest 0.05 cm3
• calculate final trite (final - initial vol)
• repeat to get concordant writes (within 0.2 cm3)

Question 16

how to work out mean titre?

Answer 16

get concordant titres (within 0.2cm3)
find the mean

Question 17

what colour is phenolphthalein in an acidic solution?

Answer 17

colourless

Question 18

what colour is phenolphthalein in an alkaline solution?

Answer 18

pink

Question 19

what colour is methyl orange in an acidic solution?

Answer 19

red

Question 20

what colour is methyl orange in an alkaline?

Answer 20

yellow