Chemistry- Required Practicals Flashcards
Explain why a spot in chromatograpy didn’t move
[X] is insoluble in the solvent
How to explain that an ink has the most number of different substances in it
[X] gives the most spots
How do calculate Rf value?
distance travelled by the solute/distance travelled by the solvent
Why do the spots of ink need to be placed above the solvent line?
So the solvent will run through the spots
otherwise the spots transfer onto the solvent
How to get more accurate chromatography results?
Longer paper
What is the stationary phase?
[the water]/the paper
In the experiment ink X did not move, how to fix this?
Use a different solvent X can dissolve in
[2]
When you react HCl and sodium thiosulfate the mixture turns cloudy, why?
one of the products is sulfur, a precipitate
How do you measure the sodium thiosulfate reaction time?
Flask placed on top of a black crossed
Measure time until the cross is obscured by precipitate
How to keep a reaction at a constant temp?
Place the container in a water bath
Explain in terms of particles how decreasing the temp affects the reaction rate
fewer successful collisions w/ activation energy
bc decreased temp means particles have lower energy
particles move slower and reaction rate decreases
How could you tell a reaction has finished?
No more effervescence
no further colour change
solid soluble substance remains at bottom of flask and doesn’t dissolve
Describe how you would obtain a solution of copper sulfate from the mixture and how you would obtain pure dry cuso4 crystals from the solution
filter
collect filtrate
heat in evaporating basin on tripod
until crystals start to appear
remove heat, cover w/ filter paper
let cool + crystallise
seperate crystals using a suitable methpd
put crystals on absorbent paper
dry in a warm place
Why does an acid + calcium hydroxide practical have the pH change it does?
solution is acidic
acids have low pH
excess H+ ions
alkali neutralises acid, OH-+H+ -> H2O
amount of H+ ions has reduced
now an excess of OH- ions
Equipment for measuring liquids more accurately
pipette/burette/measuring cylinder
equipment for measuring solids more accurately
mass balance
What colour change would occur if phenolphatheilewefunin was in a mixture that went from 2 to 10?
colourless to pink
Describe how a titration should be carried out (just say “alkali” or “acid”)
Include the final repeat without the indicator
pipette to measure alkali
into conical flask
add few drops of methyl orange
put flask on white tile
fill burette with acid
read liquid level from burette
add acid from burette
add dropwise until end point
until indicator just changes colour
read burette level
repeat until concordant results
mix the same volumes of sulfuric acid and ammonia solution
but leave out indictor
How to explain that the results aren’t concordant
[x] should not be used because burette readings are not read to 2dp
[x] should not be used because the volume is not concordant with the other two
Explain the purification of copper practical
copper atoms form copper ions at anode
copper atoms oxidised/lose electrons
cu->cu2+ + 2e
copper ions pass into solution and are attracted to cathode
cathode increases in size, pinkbrown colour on cathode surface,solid copper deposited on cathode
copper ions form atoms
cu2+ + 2e -> Cu
cus04 is blue
colour remains the same since for every cu ion entering the solution at the anode one is removed at the cathode
before electrolysis is carried out you need to weigh each electrode
what do you do first
electrodes cleaned to remove impurities NAH THIS NEEDS TO BE MORE SPECIFIC
“a precipitate forms, it is yellow/cream” explain why the anion cannot be certain
bromides give cream precipitates
iodides give yellow precipitates
what is the instrument used to do flame emission spectroscopy?
flame photometer
Give the molecule that forms when propanol undergoes dehydration
propene
give the formula of the functional group that is formed when an alcohol is oxidised
COOH
How to improve the alcohol fuel practical
move beaker closer to spirit burner
use metal calorimeter instead of glass
use draft shields
place a lid on beaker
insulate the sides of the beaker
Describe what will happen to the brightness of the light bulb over a long period
of time connected to a fuel cell
Starts bright, becomes dimmer, goes out over time
Describe how the pH of the mixture is determined when a drop of it is placed
on the universal indicator paper.
observe / look at) colour produced on (universal
indicator) paper (1)
* compare to pH {chart / scale}
In the method, universal indicator paper is used to determine the pH.
Explain why litmus paper would not be a suitable indicator to use in
this experiment.
- litmus paper only shows if the solution is {acidic /
alkaline} (1) - does not show how acidic or alkaline the solution is
state the meanings of the terms actual yield and theoretical yield.
amount of product formed in the reaction vs
calculated amount of product formed if all reactant was used to form product with no losses
Before the electrolysis is carried out, the mass of each electrode is determined.
Explain what should be done to the copper electrodes before their masses
are determined.
electrodes cleaned using emery paper
to remove surface oxide/grease/impurities
If the waste product, carbon dioxide, was used to make fizzy drinks, what would happen to the atom economy
co2 no longer waste product
atom economy increases to 100%
