moles 2

Question 1

what unit is volume measured in

Answer 1

-dm3
- sf of 1000 between cm and dm

Question 2

how to calculate the moles of gas ?

Answer 2

moles= volume(dm3) / 24dm3

the denominator is 24dm3 for every gas

Question 3

what is the concentration of a solution ?

Answer 3

a measure of how much solute is dissolved per unit volume
it is measure in cm3/dm3 and is usually between 1 and 2

Question 4

what is the formula to find concentration

Answer 4

concentration = moles of solute/ volume of solvent

Question 5

what is titration

Answer 5

a practical method used to measure the volume (or titre) of an acid needed to neutralise a particular volume or alkali

Question 6

what are the two special pieces of equipment used in titrations

Answer 6

• volumetric pipette (measures out 25cm3 very accurately )
• burette (measures volume to nearest 0.05)

Question 7

what is the procedure of a titration

Answer 7

• the acid is known, so it goes into the burette
• the alkali is unknown, so it goes into the conical flask

Question 8

describe the setup of a titration

Answer 8

1)- use a volumetric pipette to place 25cm3 of the unknown alkali into a conical flask
2)- add a few drops of either methyl orange or phenolphthalein indicator to the flask
- universal indicator doesn’t work because it changes colour to gradually
3)- fill a burette with known acid and clamp it above the conical flask

Question 9

usage of titration

Answer 9

4) measure the initial volume of the known acid on the burette, to the nearest 0.05cm3
5) use the burette to add acid to 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 acid colour
7) measure the final volume of the known acid on the burette, to the nearest 0.05cm3
8) calculate titre (final volume - initial volume)
9) repeat to get concordant (within 0.2 cm3) titres

Question 10

with your titration results what do you need to convert and what ratio do you use ?

Answer 10

• use the mole ratio in the balancing numbers from the reaction equation
• from moles of a substance you know lots about (e.g the known acid)
• to moles of a substance you dont know much about (e.g the unknown alkali)