topic 3 recap Q. chemical calculations Flashcards
what is the conservation of mass?
atoms are not created or destroyed so total mass before = total mass after
when a metal forms a metal oxide, why does the mass increase?
atoms from gaseous oxygen have been added from the air?
what is relative formula mass?
the sum of the relative atomic masses of each atom in a substance
when an acid reacts with a metal why does the mass decrease?
a gas is produced and escapes into the air?
what are the 4 state symbols?
(s) solid
(l) liquid
(g) gas
(aq) dissolved in water
if the amount of solute in a solution is increased what happens to the concentration?
increases
what is a mole?
mass of a substance that contains 6.02 x 1023 paricles
how can you tell when a symbol equation is balanced?
the number of atoms of each element is the same on both sides.
which formula is used to calculate the number of moles from mass and Mr?
moles = mass/Mr
give the value for avagadros constant
6.02 x 10 23
what is the unit for concentration?
g/dm3 or mol/dm3
which formula is used to calculate the mass of a substance from number of moles and Mr?
mass= moles x Mr
if the volume of water in a solution increased what happens to the concentration?
decreases
what is a limiting reactant?
the reactant that is completely used up in a chemical reaction
which formula is used to calculate volume from concentration and mass?
volume (dm3) = mass (g) / concentration (g/dm3)
which formula is used to calculate concentration from mass and volume?
concentration (g/dm3) = mass (g) / volume(dm3)
how can you convert a volume reading in cm3 to dm3?
divide by 1000
which formula is used to calculate mass from concentration in g/dm3 and volume?
mass (g) = concentration (g/dm3) x volume (dm3)
What is the yield of a reaction?
mass of product obtained from the reaction
What is the theoretical yield of a reaction?
maximum mass of the product that could have been produced
Why is the actual yield always less than the theoretical yield?
- reaction may be reversible
- some of the product can be lost on separation
- unexpected side reactions between reactants
What is the percentage yield?
actual yield as a proportion of theoretical yield
How is percentage yield calculated?
actual yield divided by theoretical yield x 100
Why is a high atom economy desirable?
results in less waste/is more sustainable
What is atom economy?
measure of how many atoms of the reactants end up as useful products
How is percentage atom economy calculated?
(Mr of useful product/Mr of all products) × 100
How can concentration in mol/dm3 be calculated?
concentration (mol/dm3) = moles (mol) / volume (dm3)
What is a titration?
method used to calculate the concentration of an unknown solution
What is the end-point?
the point at which the reaction is complete (when the indicator changes colour) and no substance is in excess
How should solution be added from the burette close to the end point?
drop by drop, swirling in between
Why is a white tile used in titration?
to see the colour change better
What is a titre?
volume of solution added from the burette
What are concordant titres?
titres within 0.1 cm3 of each other
What volume does one mole of any gas occupy at room temperature and pressure?
24 dm3 or 24 000 cm3
