Booklet 3 - Chemical Measurements...

Question 1

What is Relative atomic mass?

Answer 1

The average mass of all isotopes

Question 2

What is relative formula mass?

Answer 2

It is similar to relative atomic mass, however it deals with formulae.

Question 3

What can the formulae be in relative formula mass?

Answer 3

Can be elements or compounds

Question 4

How do we find relative formula masses?

Answer 4

By adding the relative atomic masses together

Question 5

What is the conservation of mass?

Answer 5

• It is when the same atoms are present at the start and end of the reaction, this means mass must have been conserved.
• i.e the total mass of the reactants must equal the total mass of the products.

Question 6

How does using the Ar/Mr values and the conservation of mass help us?

Answer 6

It helps us to predict the masses of reactants and products in reactions.

Question 7

What is Avagadro’s number?

Answer 7

6.02x1023 which is equal to 1 mole

Question 8

What is the symbol unit for moles?

Answer 8

Mol

Question 9

What can measurements of amounts in moles apply to?

Answer 9

Atoms, molecules, ions, electrons, formulae, equations.

Question 10

What is the mathmatical equation for linking moles and mass?

Answer 10

Mass (g) = Mr x moles (n)

Question 11

What can the masses of reactants and products be calculated from?

Answer 11

Balanced symbol equations

Question 12

If you already have the masses of reactants and products what can you do? What is it called?

Answer 12

Use them to find out the ratio of reactants to products. It is called Stroichiometry

Question 13

When a small amount of hydrogen gas is ignites with oxygen in a test tube during the squeaky pop test. What is all of the hydrogen is converted into?

Answer 13

Water vapour

Question 14

What is the oxygen from air involved in the reaction present in? What happens to the hydrogen?

Answer 14

Present in excess, there is more oxygen present than is necessary. The hyrdogen reacts and runs out before the oxygen does.

Question 15

What is the hydrogen said to be?

Answer 15

The limiting reactant, it limits the amount of water vapour produced.

Question 16

When reacting sodium metal in a large water trough, the sodium will completely react bedore the water is even close to being used up. What is the sodium?

Answer 16

The limiting reactant as once it has reacted no futher hydrogen gas is porduced and the fizzing stops.

Question 17

What is common in a chemical reaction involving two reactants?

Answer 17

It is common to use one of the teactabts in excess to ensure that the other reactant, i.e the limiting reactant is used completely

Question 18

What is the concentration of a solution?

Answer 18

The amount of solid material (solute) dissolved in a certain colume of liquid (solvent).

Question 19

What does the concentration become when there is more solute in the liquid?

Answer 19

More concentrated the solution becomes

Question 20

What is concentration measures in?

Answer 20

Grams of substance per cubic decimetre of water (g/dm3)

Question 21

What is the general formula for concentration?

Answer 21

Concentration g/dm3 = mass (g) ➗volume in (dm3)

Question 22

What are the 3 reasons that is may not be possible to obtain the calculated amount of product?

Answer 22

1) . The reaction may not go to completion
2) . Some product may be lost when it is separated from the reaction mixture
3) . Some of the reactants may react in ways different to the expected reaction (side reactions)

Question 23

What is percentage yeild?

Answer 23

The amount of product obtained is known as the yield when compared with the maximim theoretical amount as a percentage.

Question 24

What is the equation for percentage yield?

Answer 24

%yield = mass of product actually made ➗ theoretical mass of product

Question 25

What is atom economy?

Answer 25

Also called atom utilisation it is a measure of the amount of starting materials that end up as useful products.

Question 26

Why is it important to use reactions with a high atom economy?

Answer 26

It is important for sustainable development and for economic reasons as this will lead to less wasteage of atoms.

Question 27

What is the equation for percentage atom economy?

Answer 27

% atom economy = mass of useful product ➗ total mass of reactants. X 100

Question 28

What is the equation for converting g/dm3 to mol/dm3 ?

Answer 28

Moles = mass➗Mr

Question 29

What is the equation for converting from mol/dm3 to g/dm3?

Answer 29

Mass = moles x Mr

Question 30

What is the equation for concentration using the unit of Mol/dm3?

Answer 30

Concentration in mol/dm3 = moles ➗ volume (dm3) (rearranged from moles = concentration (mol/dm3) x volume)

Question 31

What is the volume of 1 mole of any gas at room temperature and preassure?

Answer 31

24dm3

Question 32

What is the equation to work out the volume of any gas?

Answer 32

Volume of any gas = moles (n) x 24

Question 33

What is the equation for concentration in g/dm3 ?

Answer 33

Concentration g/dm3 = mass (g) ➗volume in dm3

Question 34

What is the limiting reactant?

Answer 34

The reactant that us completely used up, it limits the amount if products