Amount of Substance

Question 1

What does the formula unit show?

Answer 1

The ratio of each type of atom in an ionically bonded lattice

Question 2

What is the mass of the formula unit called and what’s its symbol?

Answer 2

The relative formula mass

Symbol: Mf but sometimes Mr is still used

Question 3

How do you work out relative formula mass?

Answer 3

Average mass of one formula unit of an element of compound/ 1/12 the mass of one atom of carbon-12

Question 4

How many particles does a mole contain? And what is this number called?

Answer 4

6.023 x 10▪23 particles. The avagadro constant.

Question 5

What is the mass of a mole of atoms of an element in grams?

Answer 5

The relative atomic mass in grams

Question 6

What was amedeo avagadros hypothesis?

Answer 6

That at the same temperature and pressure equal volumes of different gases contain the same number of particles

Question 7

How do you work out How many atoms are there in 0.200 mol helium gas?

Answer 7

You times it by the avagadro constant

Question 8

What is the formula for Mr mole lives under the hill?

Answer 8

Mass= Mr x mol

Question 9

How do you get the number of moles from the number of atoms or molecules?

Answer 9

You divide by the avagadro constant

Question 10

What are the assumed properties of an ideal gas?

Answer 10

• It is made up of identical particles in continuous random motion
• the particles can be thought of as point like with position but with zero volume
• the particles do not react when they collide
• collisions between particles are perfectly elastic- the total kinetic energy if the particles after the collision is the same as before
• the particles have no intermolecular forces

Question 11

Which gases behave most like ideal gases?

Answer 11

Hydrogen, nitrogen, oxygen and the noble gases

Question 12

What is Boyle’s law in words and formula

Answer 12

At constant temperature T, the volume V of a fixed mass of gas is inversely proportional to the pressure P applied to it

P x V =constant

Question 13

What happens to gases as the temperature is increased?

Answer 13

The gases expand because their molecules move faster and are further apart so their density decreases and vice versa if the temperature decreases.

Question 14

What is Jacques Charles law?

Answer 14

At constant pressure the volume of a fixed mass of gas is proportional to its temperature

V= constant x T

Question 15

What happens at absolute zero temperature (-273.15 ° c)

Answer 15

Gases reach zero volume

Question 16

How do you convert °c to Kelvin?

Answer 16

Add 273

Question 17

What is the ideal gas equation?

Answer 17

pV= nRT

P= pressure of the gas in Pascals (pa)
V= volume of the gas in m3
n= number of moles of the gaseous particles 
R = molar gas constant (8.31 J K-1 mol -1)
T = temperature in Kelvin (K)

Question 18

What is the empirical formula?

Answer 18

The simplest whole number ratio of atoms of each element that are in a compound

Question 19

What is the molecular formula?

Answer 19

The actual number of atoms of each element used to make a molecule of formula unit

Question 20

How do you work out the empirical formula?

Answer 20

Convert the masses of each element to moles to get the ratio of each element and then divide by the smallest number.

Question 21

What is a chemical equation?

Answer 21

A shorthand way of writing a chemical reaction. It uses chemical formulae for the reactants and products. Formulae use letter symbols to represent the elements and numbers to show how many atoms or each element are involved

Question 22

What are the different state symbols and what do they mean?

Answer 22

(S) solid
(l) liquid
(g) gas
(Aq) aqueous

Question 23

What does it mean to balance an equation?

Answer 23

Make sure that there are the same amount of each element on both sides of the reaction

Question 24

What is the calculation for percentage yield and what is it used to Express?

Answer 24

It is used to Express how close the actual yield is to the theoretical yield

Percentage yield = actual yield/ theoretical yield x100

Question 25

What is the calculation for percentage atom economy and what is it used for?

Answer 25

It is a way to compare the maximum mass of a product that can be obtained with the mass of the reactants

Percentage atom economy = molecular mass of desired product/ sum of molecular masses for all reactants x 100

Question 26

What benefits will chemical processes with high atom economies have?

Answer 26

They will have economic, ethical and environmental benefits for industry and the society it serves

Question 27

What is the use of an ionic equation?

Answer 27

They provide a shorthand way to show the essential chemistry involving the ions in a reaction

Question 28

How do you work out an ionic equation?

Answer 28

1) write out the full equation
2) write the equations as ions and cancel the ions that appear on both sides

Remember that covalently bonded molecules dont form ions

Question 29

What are the ions that appear of both sides of an equation known as?

Answer 29

Spectator ions

Question 30

What are common solvents?

Answer 30

Water and ethanol

Question 31

What is concentration measured in?

Answer 31

Mol dm-3 and g dm-3

Question 32

What is the calculation for concentration?

Answer 32

Concentration (mol dm-3) = moles of solute/ volume of solution (dm3)

C = n/v

Question 33

What practical do chemists do to determine unknown concentrations?

Answer 33

A titration

Question 34

How do you make a volumetric solution?

Answer 34

1) a known number of moles in a solute must be dissolved in demonised water and the solution made up to a known volume
2) weigh a weighing boat and measure the required mass of compound into it. The number of moles can be calculated from the mass and the relative molecular or formula mass of the compound.
3) the compound needs to be transferred quantitavely (all transferred) which is done by putting a small funnel in the neck of a volumetric flask. The compound is tipped in and any remaining in the container is washed in using a wash bottle containing demonised water
4) start to fl thrlask adding demonised water and swirling the contents to make sure the compound dissolves. Do this until the solution is about 1 cm below the flasks graduation mark. Deionised water is then added drop by drop until the bottom of the meniscus is just level with the graduation mark.

Question 35

How do you carry out an acid base titration?

Answer 35

1) pour some of the solution to be analysed into a beaker
2) use a clean dry pipette with a safety filler to draw the solution to just above the graduation line. Make sure the pipette is below the solution at all times.
3) controlling the release with the safety filler the solution is drained out until the bottom of the meniscus is level with the graduation line on the pipette.
4) the filler is then removed and the solution is emptied into the conical flask.
5) the brunette is then clamped. Before use the burete rinsed a few times with the volumetric solution
6) the volumetric solution is poured in through a funnel and then the volume is recorded.
7) the volumetric solution is added from a burette in tests and as the end point gets closer the colour takes longer to change.
8) the titration is then added drop by drop when it is close to the end titration. The burette reading is recorded when there is a colour change..
9) you should start by doing a rough titration and repeat until 3 concordant results are obtained