Quantitative chemistry Flashcards
What is concentration measured in?
Measured in Molarity (M), Molality (m), or Percentage (%)
what is relative formula mass, Mr?
if you have a compound, the relative formula mass is the total of all the relative atomic masses of all the atoms
how to calculate the percentage mass of an element in a compound?
(Ar X number of atoms of that element) / Mr of the compound X 100
What is the Avogadro constant?
6.02 X 10^23
What is “the mole”?
The mole is the name given to an amount of a substance
why do we use Avogadro constant?
the mass of that number of atoms or molecules of any substance is exactly the same number of grams as the relative atomic mass (Ar) or relative formula mass (Mr) of the element or compound
How do you calculate the number of moles?
mass in g / Mr
What is the conservation of mass?
During a chemical reaction, no atoms are destroyed and no atoms are created. This means there are the same number and types of atoms on each side of a reaction equation
why might the mass in a reaction increase?
One of the reactants is a gas that is found in air and all the products are solids, liquids or aqueous
why might the mass in a reaction decrease?
One of the products is a gas and all the reactants are solids, liquids or aqueous
How to balance equations using reacting masses?
1) divide the mass of each substance by its relative formula mass to find the number of moles
2) divide the number of moles of each substance by the smallest number of moles in the reaction
3) if any of the numbers are not all whole numbers, multiply all numbers by the same amount so they are all whole numbers
4) write the balanced symbol equation for the reaction by putting these numbers in front of the chemical formulas
What is a limiting reactant?
The reactant that runs out first, causing a reaction to stop. All other reactants will be in excess.
How to find the mass of a product formed in a reaction, using the mass of the limiting reactant and the balanced reaction equation?
1) write out the balanced equation
2) work out the relative formula masses (Mr) of the reactant and product you want
3) use the balanced equation to work out how many moles there’ll be of the other substance
5) use the number of moles to calculate the mass
How to calculate the volume of gas?
mass of gas / Mr of gas X 24
What is concentration?
the amount of a substance in a certain volume of a solution is called its concentration
how to calculate concentration in g/dm^3?
concentration = mass of solute / volume of solvent
how to calculate concentration in mol/dm^3?
concentration = number of moles of solute / volume of solvent
what does the atom economy tell you?
how much of the mass of the reactants was wasted when manufacturing a chemical and how much ends up as useful products
how to calculate atom economy?
relative formula mass of desired products / relative formula mass of all reactants X 100
What does the percentage yield tell you?
The overall success of an experiment. It compares what you think you should get (theoretical) to what you get (actual)
how to calculate percentage yield?
mass of product actually made / maximum theoretical mass of product X 100
What will a yield always be?
It will always be less than 100%
why might you not get 100% yield?
1) not all reactants reacted to make the product
2) there might be side reactions
3) you lose some product when separating it from the reaction mixture
