Amount of Substance (2.1.3) (B) Flashcards
What is the limiting reagent
The product that is not fully used up
What is in excess
The product that is fully used up
What are the steps to ‘reacting masses’
Step 1: Write a balanced equation
Step 2: Work out the moles of the substance that you have been given the mass of
Step 3: Using the ratio from the balanced equation work out the moles of substance in question
Step 4: Work out the mass of substance in question
When the question involves masses and gases at RTP what now?
Step 1: Write a balanced equation
Step 2: Work out the moles of the substance that you have been given the mass of
Step 3: Using the mole ration work out the number of moles of gas produced
Step 4: rearrange the RTP gas equation to find the volume
When the question involves masses and gases but NOT at RTP what now?
Step 1: Write a balanced equation
Step 2: Work out the moles of the substance that you have been given the mass of
Step 3: Using the mole ration work out the number of moles of gas produced
Step 4: rearrange the ideal gas equation to find the volume
In questions of reacting masses with limiting reagents what are the steps
Step 1: Write a balanced equation
Step 2: Work out the moles of products, then figure which one is in excess and which is the limiting reagent
Step 3: Use the moles of the limiting reagent and the ratio from the balanced equation to figure out the moles of substance in question
Step 4: Work out the mass of substance in question
what is the formula for percentage atom economy
(Mr of desired product / Mr of all products ) x 100
What is the environmental and economic reasons why reactions with high atom economies are preferable to reactions with low atom economies
Environmental: better for the environment as there is less waste
Economic: costs less due to less waste made, waste costs money to dispose
If there is only one product what us the % atom economy
100%
What are the reasons why percentage yield is normally less than 100%
- incomplete reaction
- side reactions
- loss of product during washing or recrystallisation
- loss of product transferring from one piece of equipment to another
What is the rearranged formula to find actual yield
% yield x theoretical yield / 100
What is the formula to find % yield
% yield = ( mass of specified product collected / theoretical maximum mass of product ) x 100
What is the rearranged formula to find theoretical yield
actual yield x 100 / % yield
How to do a % yield question
Step 1: Work out the moles of the reactant
Step 2: Using the mole ratio from the balanced chemical equation work out the theoretical moles of substance in question that SHOULD have been produced
Step 3: Using theoretical moles of substance in question, calculate the theoretical maximum mass of that substance
Step 4: Work out the % yield
What is important to note about the big numbers when doing % yield calculations
Only use the big numbers for the mole ratios
