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
