Chapter 3

Question 1

Formula including moles, Mr and mass?

Answer 1

n = m/Mr
Mol = mass in grams/ molar mass in       g mol-1

Question 2

Purpose of Avogadro’s constant

Answer 2

Number of atoms needed to have 12g of carbon-12

Huge number

Question 3

What is unit for molar mass

Answer 3

G mol-1

Question 4

Ionic equation method?

Difference between net and complete equation?

Answer 4

Balance equation, write correct formula/charge of each charge and how much there are, write aq after each ion, bring down s,l,g compounds unchanged.

Complete is everything same method as above
Net has repeated ions (spectator ions) removed

Question 5

How do you get number of molecules of a compound?

Answer 5

Multiply avogadros constant with number of moles

Question 6

Difference between molecular formula and empirical formula

Answer 6

Molecular shows number and type of atoms of each element in one molecule

Empirical is simplest whole number ratio of each element in compound

Question 7

How do you workout empirical formula from data

Answer 7

Divide all mass by their Mr, divide smallest number to get ratios and then adjust to get whole numbers

Question 8

What does volume of gas depend on

Answer 8

Temp and pressure

Question 9

Pressure at room temp

Answer 9

101000 Pa

Question 10

What is room temp

Answer 10

20 degrees c

Or 293 K

Question 11

Convert from kelvin to degrees c

Answer 11

Minus 273

Question 12

Molar volume of gas at RTP

Answer 12

24 dm3 mol-1

Or 24000 cm3 mol-1

Question 13

How will a higher temp affect volume of gas

Answer 13

More kinetic energy so move further apart increasing volume of gas.

Question 14

How will a higher pressure affect volume of gas

Answer 14

The forces of container push molecules closer together decreasing volume

Question 15

Formula for volumes of gases not at RTP

Units

Answer 15

pV= nRT

Pressure in Pa
Volume in m3
N is number of moles in mol
R is gas constant 8.314
T is temp in kelvins K

Question 16

M3 to dm3 to cm3

Answer 16

1m3
Is 1,000 dm3
Is 1,000,000 cm3

Question 17

MgO exp

Why do you meed to raise the crucible

Answer 17

Needs oxygen from air to react with Mg

Question 18

MgO exp

Purpose of breaking up MgO whilst hearing

Answer 18

To ensure all Mg reacts as theres increased surface area

Question 19

MgO exp

Why does the formula show less oxygen than is present in pure MgO

Answer 19

Not all Mg reacts

Possible that Mg reacts with nitrogen from air too

Question 20

MgO exp

Why does Mg reacts with O rather than N from air

Answer 20

O2 has double bond
N has triple bond

O requires less energy to break so it is easier

Question 21

Concentration formula in g dm-3

Concentration in mol dm-3

Answer 21

Mass of solute in g divided by volume of solution in dm3

Replace mass of solute by number of moles

Question 22

What is a hydrated salt?

Why is water trapped in salt?

Answer 22

During salt crystallisation from an aqueous solution some molecules of water is trapped within the solid lattice.

Water is a polar molecule

Question 23

What is the water trapped in a hydrated salt called

Answer 23

Water of crystallisation

Question 24

How do you remove the water in a hydrous salt ?

What is new substance called?

Answer 24

Heat the salt means water is removed from structure

An anhydrous salt

Question 25

What is atom economy
Definition
Not formula

Answer 25

Way of measuring how much of your reagents makes useful products

Question 26

Atom economy formula

Answer 26

Mr of useful product divided by total Mr of all products

Multiplied by 100 to get percentage

Question 27

Percentage yield formula

Answer 27

Percent yield= actual yield divided by theoretical yield multiplied by 100

Question 28

2 ways of lowering percentage uncertainty

Answer 28

Increase accuracy of measuring equipment

Increase overall mass of reagents used

Question 29

Percentage uncertainty
Measurement has uncertainty of +/- 0.5
Reading of 15.7

Answer 29

0.5 / 15.7 * 100