Quantative Chemistry Flashcards
How do you find relative formula mass?
Look at atomic mass on the periodic table
How do you find mass of an element in a compound?
Ar X no. of atoms of that element
———————————————— X100
Mr of the compound
What is Avogadro’s number?
6.02X 10*23
How much mass does one mole of carbon have if it has a relative atomic mass of 12?
12g
How do you work out the no. of moles?
mass in g/ Mr
When will mass increase?
Gas is a reactant
Before the reaction it is floating in the air therefore it is not contained
When a gas reacts it becomes part of the reaction vessel
When will mass decrease?
Gas is a product
If the vessel isn’t enclosed then the gas can escape
How do you balance equations using reacting masses?
Divide each mass by its Mr to get no. of moles
Divide no. of moles by the smallest no. of moles
Then write a balanced symbol equation
What is the reactant that is used up called?
Limiting reactant
What is the amount of limiting reactant directly proportional too?
Amount of product formed
How much does one mole of gas occupy at room temperature?
24dm*3
How do you find volume of a gas?
Mass of gas
————————- X 24
Volume of solvent
How do you find concentration in g/dm*3?
mass of solute/ volume of solvent
How do you find concentration in mol/dm*3?
no. of moles of solute/ volume of solvent
How do you convert from mol/dm3 to g/dm3?
mass= moles X Mr
How do you convert from g/dm3 to mol/dm3?
moles= mass/Mr
How do you find atom economy?
Mr of desired product
——————————– X100
Mr of all reactants
What does 100% atom economy mean?
All reactants have been turned into the desired product
If the atom economy what does that mean the process is?
“Greener”
How do you find percentage yield?
mass of product made
———————————————- X100
max theoretical mass of product
Why are yields always less than 100%?
As some products or reactants always get lost
What are the reasons for product or reactant always being lost?
Reactants will all not react to make a product
There may be a side reaction
You lose some product when you separate it from the reaction mixture
Why in a reversible reaction will there never be 100% yield?
Because products can turn back into reactants
Why does side reactions cause not 100% yield?
May react with gases in the air or impurities to form extra products
How do you lose some product when you separate?
If you filter a liquid you remove some solid particles
Lose bits of the liquid that remains with the solid on the filter paper
