EXPERIMENTS Flashcards
List the 5 hazards
Irritant Corrosive Flammable Toxic Oxidising
Outline the precautions for the hazards
Irritant/corrosive
Wear goggles
Flammable
Keep away from naked flame
Toxic
Wear gloves and wash hands after use
Oxidising
Keep away from flammable/easily oxidised materials
When is heating in a crucible used
For measuring mass loss in thermal decomposition
And mass gain when magnesium reacts with oxygen
Outline the heating in a crucible method
Weigh empty clean dry crucible and lid
Add 2g of hydrated calcium sulphate to the crucible and reweigh
Heat strongly with Bunsen
Allow to cool
Weigh the crucible again
Repeat until the mass remains constant
Why should large masses of hydrated calcium sulphate (eg 50g) not be used for heating in a crucible
The decomposition is more likely to be incomplete
Why must the crucible be dry
Wet would cause mass loss to be too large
as water would be lost when heating
Why should small amounts of hydrated calcium sulphate (eg 0.1g) not be used in heating of a crucible
Experiment errors in weighing
Are too high
Outline the steps in calculating water of crystallisation
Mass of H2O (initial mass-final mass)
Moles of sulphate (final mass/mr)
Moles of water (calculated mass/18)
Mole ratio (divide everything by the smallest mole value)
When is a gas syringe used
Measuring the volume of a gas
Eg working out moles of gas or reaction rates
Outline how a gas syringe is set up
Closed conical flask
With open piping inserted into flask (solution)
Open syringe with plunger
Measurement markers on the syringe barrel
No gaps so gas can’t escape
What are the potential errors when using a gas syringe
Gas escapes before the bung is inserted
Syringe sticks/gets stuck
Gas is soluble in water
So true amount isn’t measured (eg CO2, SO2)
Outline how the gas equation is used to calculate an Mr
Convert all measurements into correct units (eg C into K)
n= PV/RT
Mr = m/n
Outline how a solution is made
Weigh by difference the sample
Add 100cm3 of distilled water to a beaker and stir with glass rod
Decant into a 250cm3 volumetric flask using a funnel
Rinse beaker and decant in washings
Pipette in distilled water batik the bottom of meniscus is on the graduation mark
Invert the flask several times
Outline the safety precautions for titration
Acids and alkalis are corrosive
(Acids are irritant at low concentration)
Wear eye protection and gloves
Wash spillages immediately
Treat unknown substances as toxic
Outline the titration method
Rinse all equipment with distilled water
Pipette 25cm3 of alkali into conical flask. Touch pipette to the surface.
Add acid solution from the Burette
(Ensuring the jet space is filled with acid)
Add indicator (phenolphthalein for alkali to acid pink to colourless) (Methyl orange for alkaline to acid yellow to red ;HCl))
Use white tile to observe. Swirl the mixture whilst adding acid drop wise
Note reading when change occurs and before adding acid
Repeat until concordance results are obtained
Outline the potential errors in titration
Jet space not filled properly (larger reading)
Beaker instead of conical flask (liquid lost when swirling)
Large amounts of indicator (acidic)
Why does distilled water in the conical flask not affect the results
Doesn’t react with reagents
doesn’t change the number of moles
Outline how the average titre is calculated
Only use two concordance results
Never use the rough
Record in a full table (initial and final readings)
Record trite to 2dp
What are the 5 common titration equations
CH3CO2H + NaOH > CH3CO2-Na+ + H2O
H2SO4 + 2NaOH > NaSO2 + 2H2O
HCl + NaOH > NaCl + H2O
NaHCO3 + HCl > NaCl + CO2 + H2O
Na2CO3 + 2HCl > 2NaCl + CO2 + H2O
Define readings
The values found from a single judgement
when using a piece of equipment
Define measurements
The values taken as
the difference between the two judgements of values
Outline the uncertainty of reading and measurement
Reading -
At least +- 0.5 of the smallest scale
Measurements -
At least +- 1.0 of the smallest scale reading
Outline how apparatus uncertainty is calculated
% uncertainty = uncertainty/measurement x 100
How can apparatus uncertainties be decreased
Decreases the sensitivity:
Greater resolution apparatus
Increase size of measurement
How can you reduce uncertainty in a titration
Pipette/Burette instead of measuring cylinder
(Lower app uncertainty)
Make the titre a larger volume:
Increase volume and concentration in conical flask
Decreasing the concentration in the Burette
How can you reduce uncertainty in measuring mass
More accurate balance
Larger mass (solid)
Weigh by difference
