5.1 - Moles II

Question 1

in a lab what are volumes of gas usually measured in

Answer 1

cubic centimetres (cm^3)

Question 2

what more common unit is used in mole calculations for volume

Answer 2

cubic decimetres (dm^3)

Question 3

what is the scale factor to convert between cm^3 and dm^3

Answer 3

1000

Question 4

how do you get from cm^3 to dm^3

Answer 4

divide by 1000

Question 5

how do you get from dm^3 to cm^3

Answer 5

multiply by 1000

Question 6

what is the equation to calculate the moles of a gas

Answer 6

moles = volume (dm^3) / 24 dm^3

Question 14

what is the concentration of a solution

Answer 14

a measure of how much solute is dissolved per unit volume

Question 15

what is the concentration of a solution measured in

Answer 15

mol/dm^3

Question 16

what formula is used to calculate the concentration of a solution

Answer 16

concentration (mol/dm^3) = moles (mol) of solute / volume (dm^3) of solvent

Question 17

what is titration used to measure

Answer 17

the volume or ‘titre’ of acid needed to neutralise a particular volume of alkali or vice-versa

Question 18

what are the two special pieces of equipment used in titrations

Answer 18

volumetric pipette and burette

Question 19

what is a volumetric pipette

Answer 19

measures out 25cm^3 very accurately

Question 20

what is a burette

Answer 20

measures any volume to the nearest 0.05 cm^3

Question 21

how do you set up a titration

Answer 21

1. use a volumetric pipette to place 25cm^3 of the unknown alkali into a conical flask
2. add a few drops of phenolphthalein indicator to the flask
3. fill a burette with known acid and clamp it above the conical flask

Question 22

how do you use a titration

Answer 22

1. measure the initial volume of known acid on the burette, to the nearest 0.05 cm^3
2. use the burette to add acid into the conical flask drop-by-drop and swirling the flask
3. close the burette tap as soon as the colour in the conical flask changes
   — the start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise)
4. measure the final volume of known acid on the burette, to the nearest 0.05 cm^3
5. calculate titre (final volume - initial volume)
6. repeat to get concordant (within 0.2 cm^3) titres

Question 23

explain the process of doing a titration

Answer 23

1. use a volumetric pipette to place 25cm^3 of the unknown alkali into a conical flask
2. add a few drops of phenolphthalein indicator to the flask
3. fill a burette with known acid and clamp it above the conical flask
4. measure the initial volume of known acid on the burette, to the nearest 0.05 cm^3
5. use the burette to add acid into the conical flask drop-by-drop and swirling the flask
6. close the burette tap as soon as the colour in the conical flask changes
   — the start colour will be the alkaline colour, the end colour will be the acidic colour (because the last drop of acid always has a tiny amount more than is needed to neutralise)
7. measure the final volume of known acid on the burette, to the nearest 0.05 cm^3
8. calculate titre (final volume - initial volume)
9. repeat to get concordant (within 0.2 cm^3) titres