C3 Quantitative chemistry Flashcards
What is the law of conservation of mass?
No atoms are gained or lost in a reaction so the mass stays they same
How is relative formula mass calculated?
By adding together the relative atomic masses of all the atoms in the formula
Why does the mass appear to go up or down in an experiment?
If a gas is produced and released into the air the mass will go down, if a gas is a reactant and joins the product the mass
If the range of a set of results is large what does that tell you about the uncertainty of the results?
It is also large
What is a mole?
It is 6.02x10^23
What is the mass of 1 mole?
It depends on the substance, 1 mole of water weighs 18g. 1 moles of carbon dioxide weighs 44g
What is the molar mass of a chemical?
It is the mass of 1 mole of that chemical. It is also the relative atomic mass of that chemical.
What does a balanced equation tell you?
It shows you the ratio of number of moles reacted or used up in a reaction
What does the term limiting reactant mean?
The reactant that is used up first and causes the reaction to stop
What does the term in excess mean?
The reactant that isn’t fully reacted so is left over when the reaction stops
What is the equation for finding moles if you know the mass?
Moles = mass ÷ Mr
What are the units of concentration?
mol/dm3 or g/dm3
What is the equation to find moles if you know the concentration?
Moles = concentration (in mol/dm3) x volume (in dm3)
How can you change a volume from cm3 to dm3
divide by 1000
What volume does 1 mole of a gas occupy at room temperature and pressue?
24dm3
If 1 mole of a gas occupies 50dm3 at a certain temperature, how much would 2.5 moles of a different gas occupy?
50 x 2.5 = 125dm3
What is percentage yield a measure of?
The amount of product lost during a reaction
Why might a yield be less than 100%
The reaction may be reversible, some of the product may be lost when it is separated or some of the reactants may react in different ways
How is percentage yield calculated?
(Actual mass (or moles) ÷ theoretical mass (or moles)) x 100
What is atom economy a measure of?
The amount of reactants that aren’t turned into useful products
Why is high atom economy important?
It makes a reaction more sustainable and more economical
How is atom ecomony calculated?
(Mr of the useful product ÷ Mr of the total products) x 100
What is the atom economy of a reaction with only 1 product?
100% as all the atoms are in the useful product
