5.1 - Moles II

Question 1

How to covert from centimetres to decimetres?

Answer 1

divide by 1000

Question 2

How can we calculate moles with only a value for volume?

Answer 2

moles = volume (decimetres) / 24

Question 3

When can we use the moles and volume equation?

Answer 3

for gas volumes

Question 4

What does concentration mean?

Answer 4

The concentration of a solution is a measure of how much solute is dissolved per unit volume. It is measured in mol/dm3 and in the lab it usually varies between 0.1 and 2.0

Question 5

What is the equation including concentration moles and volume?

Answer 5

conc. = moles / volume (decimetres)

Question 6

What is a tritation?

Answer 6

Titration is a practical method used measure the volume (or ‘titre’) of acid needed to neutralise a particular volume of alkali, or vice-versa.

Question 7

What equipment do we need to use when calculating a titration?

Answer 7

Volumetric pipette
Burette

Question 8

What is the role of a volumetric pipette?

Answer 8

Measures out 25 cm3 very accurately.

Question 9

What is the role of a burette?

Answer 9

Measures any volume to the nearest 0.05 cm3

Question 10

What setup is needed when carrying out a titration to find an unknown alkali?

Answer 10

1. Use a volumetric pipette to place 25 cm3 of the unknown alkali into a conical flask.
2. Add a few drops of either methyl orange or phenolphthalein indicator to the flask.
3. Fill a burette with known acid and clamp it above the conical flask.

Question 11

How do we use the setup to carry out a titration?

Answer 11

4. Measure the initial volume of known acid on the burette, to the nearest 0.05 cm3.
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.
7. Measure the final volume of known acid on the burette, to the nearest 0.05 cm3
8. Calculate titre (final volume − initial volume).
9. Repeat to get concordant (within 0.2 cm3) titres/

Question 12

What is a concordant result?

Answer 12

within 0.2 cm3