Core Practicals Flashcards
What is an example of an Irritant and what precautions should you take?
Dilute acids and alkalis - wear goggles
What is an example of corrosives and what precautions should you take?
Stronger acids and alkalis - wear goggles
What precautions should you take with flammable items
Keep away from naked flames
What should you do with toxic items
Wear gloves - avoid skin contact - wash hands after use
What should you do with oxidising agents
Keep away from flammable / easily oxidised materials
They don’t make a substance combust but they promote the combustion
What are some potential errors in using a gas syringe
Gas can escape before bung is inserted
Some gasses are soluble in water so the true amount of gas is not measured
When drawing a diagram for gas volumes in CP1 what are some important points
Make sure gas syringe some measurement marking on the barrel to show measurements can be made
No gaps between beaker and bung so mo gas can escape
What does the volume of a gas depend on and therefore what extra readings should you take
The pressure and the temperature - therefore take reading of both of these
How can moles of gas be calculated in CP1
What are the units
PV=nRT
P = Pa
V = m^3 (1000 dm^3 = 1 m^3)
n = moles
R = 8.31 J mol^-1 K^-1
T=K (0 = 273K)
How else can the volume of gas be measured other than a syringe
Can be measured with a tube into a measuring cylinder that is turned upside down in water.
What is the method for CP1 measuring the molar volume of a gas
Detailed method
1. Measure 30 cm3 of 1 mol dm⁻3 ethanoic acid and transfer
to a conical flask.
2. Attach conical flask to gas syringe or use collection over
water method
3. Measure the mass of a weighing bottle with approximately
0.05 g of calcium carbonate
4. Add the calcium carbonate to the conical flask- quickly
resealing the bung so no gas escapes
5. Measure the final total volume of gas
6. Reweigh the empty weighing bottle test tube from step 3
7. Repeat the experiment several more times, increasing the
mass of calcium carbonate by about 0.05 g each time.
What reaction can we use the heating of a crucible
Mneasureing mass loss in various thermal decompositions
Mass gain when reacting magnesium in oxygen
What graph would you plot in CP1 Measuring the molar volume of a gas
Volume of CO2 in Cm^3 against Mass of CaCO3 in g
What affect does the lid on the crucible pay
It improves the accuracy of the eperiment as it prevents loss of solid
It still allows loss of gas as you should have a loose fitting
What is the method of crystallisation of calcium sulphate crystals
Weigh an empty clean dry crucible and lid .
•Add 2g of hydrated calcium sulphate to the crucible and weigh
again
•Heat strongly with a Bunsen for a couple of minutes
•Allow to cool
•Weigh the crucible and contents again
•Heat crucible again and reweigh until you reach a constant mass (
do this to ensure reaction is complete).
What is the equation for removal of water from calcium sulphate
CaSO4.xH2O(s) → CaSO4(s) + xH2O(g)
Forms calcium sulphate crystals if remove the water
What are the ranges of masses that shouldn’t be used
And why
Small amounts such as 0.100 g due to large percentage uncertainties in weighing
Large amounts such as 50 g as the decomposition is unlikely to be fully completed
How do you make a solution in a 250 volumetric flask
Put known mass in a beaker
Add 100cm^3 of distilled water to the beaker and make sure all dissolved (might need to heat it up)
Pour into volumetric flask with funnel
Rinse beaker and funnel multiple times to make sure all substance in volumetric flask
Make up to mark last few drops use dropping pipette
Invert flask several times to make sure uniform
What is the genral method to carry out a simple acid-base titration
rinse equipment (burette with acid, pipette with alkali, conical flask with distilled water)
•pipette 25 cm3 of alkali into conical flask
•touch surface of alkali with pipette ( to ensure correct amount is added)
•adds acid solution from burette
•make sure the jet space in the burette is filled with acid
•add a few drops of indicator and refer to colour change at end point
•use a white tile underneath the flask to help observe the colour change
•add acid to alkali whilst swirling the mixture and add acid drop wise at end point
Why are titrations done
To find out the concentration of one substance by reacting it with another substance of known concentration
Where is the substance without the known concentration put
How is it measured
In the conical flask
Volumetric pipette
Why is a conical flask used in preference to a beaker for titrations
It is easier to swirl the mixture without spilling the contents
How do you properly use a burette
Rinse it out with substance the is getting put into it (makes sure no residual water in the burette)
Don’t leave funnel in the burette as small drops of liquid might fall from the funnel into the burette
Make sure no air bubbles are in the jet space
Make sure to read the bottom of the meniscus
Always given to 2.dp and to the closest 0.05
Why should you only add a few drops of indicators in A-B titrations
They are usually a weak acid and therefore could affect the titration result
How can you wash the side of the conical flask in the middle of a titration if some substance in on the walls
Use distilled water as won’t affect the titration reading
How close doe concordant results need to be
Within 0.10cm^3
How to calculate % uncertainty for measurments made on apperatus
% uncertainty = ± uncertainty
Measurement made on apparatus X 100
