3.1.2 Amount of substance

Question 1

Avogadro constant

Answer 1

6.02 x 10^23 , number of particles in substance = number of moles x Avogadro constant

Question 2

• using mass of substance, Mr , and amount in moles
• using concentration, volume

Answer 2

• (substance) Moles (mol)= mass(g) / Mr
• (solution) concentration(mol/dm3) = moles(mol) or mass(g) / volume(dm3)

cm3 /1000 =dm3

Question 3

ideal gas equation

Answer 3

PV=nRT where

pressure -

(Pa), volume(m3), n = (mol) moles, R = gas constant (8.31) T = temperature.(K - c+273)

Question 4

calculating theoretical mass

Answer 4

1. balance equation
2. work out Mr of species as grams
3. divide to find one gram of reactant x by mass in question

Question 5

ionic equations

Answer 5

1. write equation (balance)
2. write out charges of all elements and cancel out the same elements - leave water as it is ( ion )
3. new equation with symbol

Question 6

Percentage yield

Answer 6

Actual yield / theoretical yield x 100

• theoretical yield - amount of products formed assuming no products are lost and all reactants react fully

Question 7

Atom economy

Answer 7

How efficient a reaction is -= mr of desired product / sum of mr of all reactants x 100

• importance - high atom economies:
• produce less waste & benefits the environment
• raw materials are used efficiently , more sustainable
• less by products - less time. /money separating product
• companies use reactions towards 100% atom economy