Moles

Question 1

Equation relating moles, volume (dm^3) and 24

Answer 1

Moles = volume (dm^3)/24

Question 2

Equation relating moles, pressure (Pa), volume (m^3), gas constant (8.314JK^-1mol^-1) and temperature (K)

Answer 2

n = PV/RT

PV = nRT

Question 3

What are the two units for pressure?

Answer 3

Nm^-2

Pa

Question 4

How to covert volume in cm^3 to m^3

Answer 4

x 10^-6

Question 5

How to convert volume in dm^3 to cm^3

Answer 5

x1000

Question 6

How to work out temperature in K

Answer 6

°C + 273

Question 7

Atom

Answer 7

The smallest unit of an element that can exist

Question 8

Molecule

Answer 8

The smallest part of an element or compound which can exist alone under normal conditions

Question 9

Ion

Answer 9

An atom or group of atoms possessing a charge

Question 10

Element

Answer 10

A substance containing only one type of atom

Question 11

Compound

Answer 11

A substance containing two or more different elements that have been chemically combined

Question 12

Empirical formulae

Answer 12

Simplest ratio showing the different types of atom present in a substance

Question 13

Molecular formulae

Answer 13

Actual numbers of each type of atom in a molecule of the substance

Question 14

Avogadro’s constant (L)

Answer 14

• the number of particles in 1 mole of substance

* 6.02 x 10^23

Question 15

Molar mass

Answer 15

• mass per mole of substance

* gmol-1

Question 16

To find molecular formula…

Answer 16

… you must divide molecular mass by empirical mass

Question 17

To find molecular formulae from masses…

Answer 17

… divide masses of elements by RAM, find the ratio of the elements and then calculate as above

Question 18

Mole

Answer 18

Unit for amount of substance

Question 19

Volume α

Answer 19

Moles x temperature

Moles/pressure

This is the universal gas constant (R)

Question 20

Titrations - basics

Answer 20

Method of finding out how much of one substances will react with how much of another

Question 21

Titration - process of rough reading

Answer 21

1) add a pipette-filler to a glass pipette
2) draw some of the solution into the pipette. Tilt the pipette and rotate it
3) discard the rinsing solution
4) draw the solution into the pipette until the bottom of the meniscus is on the mark
5) release the solution into a clean conical flask
6) when no more solution emerges from the burette, touch the lip of the burette against the side of the conical flask. Some of the liquid will remain in the tip
7) a suitable indicator added to the flask
8) place the flask on a white tile under the burette
9) hold the flask in the dominant hand and swirl
10) add the solution from the burette until the indicator changes colour. Note the reading on the burette- rough reading

Question 22

Why tilt and rotate the pipette?

Answer 22

All of the surfaces are rinsed in solution

Question 23

It does not matter if the conical flask…

Answer 23

… is wet

Question 24

Why is it okay for liquid to remain in the tip of the pipette?

Answer 24

It is calibrated to take this into account

Question 25

How should the burette tap be controlled?

Answer 25

* by the non-dominant hand * first and second fingers behind the tap * thumb in front of it

Question 26

Titration - process after rough reading

Answer 26

1) discard the contents of the flask and rinse it with two water and then distilled water 2) repeat the process, adding the solution from the burette fairly slowly with continual stirring. As the level of the burette approaches that of the rough reading, add the solution drop by drop. When one drop changes the colour of the indicator, allow the solution to drain down the sides of the burette before taking the reading 3) reading should continue to be taken in this way until one rough and two accurate readings are within 0.20cm^3 of each other; concordant readings are obtained 4) calculations should be based on the mean average of the two accurate concordant readings

Question 27

Accurate burette readings should be taken to...

Answer 27

... two decimal places, the second decimal being either 0 or 5

Question 28

Error is caused by the fact that...

Answer 28

... all apparatus used to take measurements have uncertainties associated with them

Question 29

Error is dependent on...

Answer 29

... the measuring device, and the amount being measured

Question 30

In general, most apparatus few be read to...

Answer 30

... half a scale division

Question 31

Percentage error

Answer 31

[(Apparatus uncertainty) / (amount being measured)] x100

Question 32

The larger the quantity being measured

Answer 32

* the less the percentage error * increase volume by dilution * increase mass

Question 33

Measuring pipette uncertainties

Answer 33

+- 0.1^cm3

Question 34

Measuring burette uncertainties

Answer 34

+-0.05cm^3

Question 35

If two readings are taken...

Answer 35

... the uncertainty occurs twice, so the value doubled

Question 36

Doubling concentrations...

Answer 36

* doubles percentage error | * burette reading would be half the original

Question 37

Percentage atom economy

Answer 37

[ (molar mass of useful product) / (total molar mass of starting materials) ] x 100