CL 3- amount of substance

Question 1

relative molecular mass

definition

Answer 1

the average mass of a molecule compared to 1/12th of the mass of 1 atom of carbon-12

Question 2

water of crystallisation

definition and calculation

Answer 2

the water contained within an ionic lattice
WOC= mass of water/mass of hydrated salt x 100

Question 3

anhydrous

definition

Answer 3

salt crystals that don’t contain water of crystallisation

Question 4

hydrous

definition

Answer 4

salt crystals that contain water of crystallisation

Question 5

percentage yield

definition & calculation

Answer 5

a measure of how much product was made during a chemical reaction compared to how much should have been made
yield= actual yield/theoretical yield x 100

Question 6

examples that reduce yield

Answer 6

• filtering, heating and evaporating; lost product when transferring reactants
• if reaction is incomplete

Question 7

atom economy

definition and calculation

Answer 7

a measure of how many atoms of the reactants are used in the useful products
atom economy= mr of desired products / mr of total products x 100

Question 8

importance of high atom economy

don’t need all reasons

Answer 8

• minimise the waste of non-renewable reactants
• reduce pollution from waste products
• minimise energy use so high costs
• reduce the use of water used for cooling reactants

Question 9

salt

definition

Answer 9

an ionic compound where H⁺ in an acid is replaced with metal or ammonium ion