Chemistry- Required Practicals

Question 1

Explain why a spot in chromatograpy didn’t move

Answer 1

[X] is insoluble in the solvent

Question 2

How to explain that an ink has the most number of different substances in it

Answer 2

[X] gives the most spots

Question 3

How do calculate Rf value?

Answer 3

distance travelled by the solute/distance travelled by the solvent

Question 4

Why do the spots of ink need to be placed above the solvent line?

Answer 4

So the solvent will run through the spots
otherwise the spots transfer onto the solvent

Question 5

How to get more accurate chromatography results?

Answer 5

Longer paper

Question 6

What is the stationary phase?

Answer 6

[the water]/the paper

Question 7

In the experiment ink X did not move, how to fix this?

Answer 7

Use a different solvent X can dissolve in

Question 8

[2]
When you react HCl and sodium thiosulfate the mixture turns cloudy, why?

Answer 8

one of the products is sulfur, a precipitate

Question 9

How do you measure the sodium thiosulfate reaction time?

Answer 9

Flask placed on top of a black crossed
Measure time until the cross is obscured by precipitate

Question 10

How to keep a reaction at a constant temp?

Answer 10

Place the container in a water bath

Question 11

Explain in terms of particles how decreasing the temp affects the reaction rate

Answer 11

fewer successful collisions w/ activation energy
bc decreased temp means particles have lower energy
particles move slower and reaction rate decreases

Question 12

How could you tell a reaction has finished?

Answer 12

No more effervescence
no further colour change
solid soluble substance remains at bottom of flask and doesn’t dissolve

Question 13

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

Answer 13

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

Question 14

Why does an acid + calcium hydroxide practical have the pH change it does?

Answer 14

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

Question 15

Equipment for measuring liquids more accurately

Answer 15

pipette/burette/measuring cylinder

Question 16

equipment for measuring solids more accurately

Answer 16

mass balance

Question 17

What colour change would occur if phenolphatheilewefunin was in a mixture that went from 2 to 10?

Answer 17

colourless to pink

Question 18

Describe how a titration should be carried out (just say “alkali” or “acid”)
Include the final repeat without the indicator

Answer 18

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

Question 19

How to explain that the results aren’t concordant

Answer 19

[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

Question 20

Explain the purification of copper practical

Answer 20

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

Question 21

before electrolysis is carried out you need to weigh each electrode
what do you do first

Answer 21

electrodes cleaned to remove impurities NAH THIS NEEDS TO BE MORE SPECIFIC

Question 22

“a precipitate forms, it is yellow/cream” explain why the anion cannot be certain

Answer 22

bromides give cream precipitates
iodides give yellow precipitates

Question 23

what is the instrument used to do flame emission spectroscopy?

Answer 23

flame photometer

Question 24

Give the molecule that forms when propanol undergoes dehydration

Answer 24

propene

Question 25

give the formula of the functional group that is formed when an alcohol is oxidised

Answer 25

COOH

Question 26

How to improve the alcohol fuel practical

Answer 26

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

Question 27

Describe what will happen to the brightness of the light bulb over a long period
of time connected to a fuel cell

Answer 27

Starts bright, becomes dimmer, goes out over time

Question 28

Describe how the pH of the mixture is determined when a drop of it is placed
on the universal indicator paper.

Answer 28

observe / look at) colour produced on (universal
indicator) paper (1)
* compare to pH {chart / scale}

Question 29

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.

Answer 29

• litmus paper only shows if the solution is {acidic /
  alkaline} (1)
• does not show how acidic or alkaline the solution is

Question 30

state the meanings of the terms actual yield and theoretical yield.

Answer 30

amount of product formed in the reaction vs
calculated amount of product formed if all reactant was used to form product with no losses

Question 31

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.

Answer 31

electrodes cleaned using emery paper
to remove surface oxide/grease/impurities

Question 32

If the waste product, carbon dioxide, was used to make fizzy drinks, what would happen to the atom economy

Answer 32

co2 no longer waste product
atom economy increases to 100%