topic 5 Flashcards
mole
amount of substance in grams that has the same number of particles as there are atoms in 12 grams of carbon-12
relative atomic mass
average mass of one atom compared to one twelfth of the mass of one atom of carbon-12
molar mass
mass in grams of 1 mole of a substance and is given the unit g/mol
amount formula
mass / molar mass
gas volume
amount x 24
concentration
amount / volume
cm^3 to dm^3
divide by 1000
cm^3 to m^3
divide by 1,000,000
dm^3 to m^3
divide by 1000
% mass
mass of chemical / total mass of compund x100
Avogadro’s constant
6.02 x 10^23
no. of particles
amount of substance x Avogadro’s constant
density
mass / volume
empirical formula
simplest ratio of atoms of each element in the compound
method for finding empirical formula
- divide each mass by the atomic mass of the element
- divide by the smallest one of the number
- may need to multiply to get a whole number
molecular formula
actual number of atoms of each element in the compound
making a solution
diluting a solution
new diluted concentration
original conc x
original vol/new diluted vol
cAvA = cBvB
ideal gas equation
pV = nRT
p - pressure - Pa
V - volume - m^3
T - temperature - K
n - moles
using a gas syringe
reacting volumes of gas
equal volumes of any gases measured under the same conditions of temperature and pressure contain equal numbers of molecules
molar volume
volume occupied by 1 mole of any gas
titration procedure
- rinse equipment
- pipette 25cm^3 of alkali into conical flask
- touch surface of alkali with pipette
- add acid solution from burette
- make sure the jet space is filled with acid
- add a few drops of indicator
- observe colour change for the indicator used
- use a white tile underneath the flask to help observe the colour change
- add acid to alkali while swirling mixture and add acid drop-wise at end point
- note burette reading before and after addition of acid
- repeats titration until at least 2 concordant results are obtained
safety precautions
- acids and alkalis are corrosive (at low concentration acids are irritant)
- wear eye protection and gloves
colour change phenolphthalein
pink to colourless
end point - no colour
colour change methyl orange
yellow to red
end point - orange
measurements
values taken as the difference between the judgements of two values
readings
values found from a single judgement when using a piece of equipment
% uncertainty
uncertainty /
measurement made on apparatus x 100
% yield
actual / theorotical x 100
percentage atom economy
mass of useful products / mass of all reactants x 100
how is salt formed
when the H+ ion of an acid is replaced by a metal ion or an ammonium ion
metal displacement reactions
more reactive metals will displace less reactive metals from their compounds
halogen displacement reactions
a halogen that is a strong oxidising agent will displace a halogen that has a lower oxidising power from one of its compounds
precipitation reactions
insoluble salts can be made by mixing appropriate solutions of ions so that a precipitate is formed
hazard
a substance or procedure that has the potential to do harm
e.g. of hazards
toxic
flammable
harmful
irritant
corrosive
oxidising
carcinogenic
risk
probability or chance that harm will result from the use of a hazardous substance or a procedure
minimising risk - irritant
dilute acids and alkalis
wear goggles
minimising risk - corrosive
stronger acids and alkalis - wear goggles
minimising risk - flammable
keep away from naked flames
minimising risk - toxic
wear gloves
avoid contact with skin
wash hands after use
minimising risk - oxidising
keep away from flammable materials
safety dealing with excess acid
Sodium hydrogen carbonate (NaHCO3) and calcium carbonate (CaCO3) are good for neutralizing excess acid if acid spills because they are not corrosive and will not cause a hazard if used in excess. They have no toxicity
