Experimental techniques (chem) Flashcards
Why can copper(II)sulfate crystals not be obtained by evaporation to dryness?
White powder of anhydrous copper(II)sulfate will be obtained instead of blue crystals of hydrated copper(II)sulfate.
What is a hydrated salt?
A hydrated salt is a salt that contains water of crystallisation.
What happens when hydrated salts are gently heated?
Hydrated salts lose their water of crystallization to form anhydrous salt.
What is the effect of a larger difference in boiling points of liquids in a fractionating column?
The larger difference in boiling points of liquids allows for more complete separation.
What role do glass beads or glass folds play in a fractionating column?
They provide a large surface area for condensation of vapour.
How can good separation of liquids be achieved in a fractionating column?
By using a long fractionating column.
What happens to the melting point when a substance is impure?
The melting point is lowered.
Why is a water bath preferred over direct heating for ethanol?
Ethanol is flammable.
What is the purpose of the side arm in a boiling tube?
It allows vapour to escape to prevent pressure from building up inside the tube.
What happens to the boiling point when a substance is impure?
The boiling point is raised.
Why would a thermometer show 100℃ when placed over boiling impure water?
It measures the temperature of steam; only pure water evaporates while impurities stay.
How can purity of a substance be tested in paper chromatography?
A pure substance always gives a single spot, while an impure substance shows more than one.
what are the processes that occur in the fractionating column
evaporation and condensation
state the physical quantity, smallest division (if any) and accuracy of digital stopwatch
time; - ; +- 0.01s
state the physical quantity, smallest division (if any) and accuracy of laboratory thermometer
temperature; 1 degree celcius; +-0.5 degrees
state the physical quantity, smallest division (if any) and accuracy of electronic balance
mass; - ; +-0.01g
state the physical quantity, smallest division (if any) and accuracy of marked/graduated beaker
approximate volume of liquid or solution; - ; -
state the physical quantity, smallest division (if any) and accuracy of measuring cylinder
accurate volume of liquid or solution; 1 cm^3; +-0.5cm^3
state the physical quantity, smallest division (if any) and accuracy of of pipette
very accurate volume of liquid or solution; - ; -
cnn measure odd volumes e.g. 21.0cm^3, 25.5cm^3
state the physical quantity, smallest division (if any) and accuracy of burette
very accurate volume; 0.1cm^3; +-0.05cm^3
very accurate variable volumes between 0.00cm^3 to 50.00cm^3
state the physical quantity, smallest division (if any) and accuracy of volumetric flask
very accurate volume; - ; -
for larger volumes
state the physical quantity, smallest division (if any) and accuracy of marked/graduated gas syringe
volume of gas; - ; -
up to 100cm^3
state the solubility of ammonia in water and its density compared to air
extremely soluble; less dense
state the solubility of carbon dioxide in water and its density compared to air
slightly soluble; denser
