Quantitative Chemsitry Flashcards
How do you calculate the percentage mad of an element in a compound
Percentage mass of an element in a compound=
Ar x number of atom of that element
—————————————————
Mr of the compound
x 100
What is the mole
The name given to an amount of a substance
What does mole of the substance contain
Just amount of the substance that contains an Avogadros number of particles
Why is the avogadros constant used
The mass of the number of atoms or molecules of any substance is exactly the same number of grams as the relative atomic mass or relative formula mass of the element or compound
Give an example of the moles
Carbon has a Ar of of 12
So one mole of carbon weights 12g
How do you calculate Mr
the sum of the relative atomic masses of the atoms in the numbers shown in the formula
Properties of chemical reactions with mass
Mass is conserved
No atoms are destroyed no atoms are created
What is the first explaination for mass changing in reactions
If mass increases it’s probs because of one of reactants is a gas found in the air and all other products are solid,liquids or aqueous
Before reaction if gas floating around in the air , but not contained in reaction vessel so u can’t account for mass
When gas reactions to form part of product,it becomes contained inside reaction vessel ,so total mass of stuff inside reaction vessel increases
What’s the second explaination for mass changing on reactions
if mass decreases probs bc one or more of products are gasses and all the reactants are solids liquids or aqueous
Before reaction all reactants are contained in reaction vessel
If vessel isn’t enclosed then any gasses can escape from reaction vessel as they’re formed
They’re no longer contained in reaction vessel so you can’t account for their mass, so total mass of stuff inside reaction vessel decreases
How do you balance equations using reacting masses
Divide the mass of each substances by relative formula mass to find the number of moles
Divide number of each substance by the smallest number of moles in reaction
If any numbers aren’t whole numbers, multiply all the numbers by same amount that they become while numbers
Write a balanced symbol equation
How do you calculate the concentration
Concentration =mass of solute
———————
Volume of solvent
Properties of concentration and definition
The amount of substance in a certain volume
The more solute there is in a given volume the more concentrated the solution
Facts about reactions getting used in a reaction
The reaction stops when all of one of the reactants is used up, any other reactants are in excess(usually added in excess to make sure other reactant is used up
The reactant that’s used up in a reaction is called the limiting reactant
The amount of product formed is directly proportional to the amount of limiting reactant, this is due to if adding more reactant there will be more reactant particles to take part in reaction
How can you calculate the Mass of product formed in a reaction using the mass of the limiting reagent
Write out the balanced equation
Work out relative formuka mass of reactant and prouuct you want
Find out how many moles there are in the substance you know the mass of
Used balance equation to work out how many moles they’ll be in the other substance
Use number of moles to calculate the mass
