Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

AQA A Level Chemistry > Practicals > Flashcards

Practicals Flashcards

1
Q

Potential errors in using a gas syringe

A
  • gas escapes before bung inserted
  • syringe sticks
  • some gases (CO2 and SO2) are soluble in water so true amount not measured
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Why is the burette rinsed in titration?

A

because the acid or alkali may be diluted by residual water in it or may react with substances left from before

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Why is only water used to rinse conical flasks between titrations?

A

because it doesn’t add any extra moles of reagents

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is considered concordant titre results?

A

those within 0.10 cm3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Sensitivity uncertainty of balance

A

+/- 0.001g

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Sensitivity uncertainty of volumetric flask

A

+/- 0.1 cm3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Sensitivity uncertainty of 25cm3 pipette

A

+/- 0.1 cm3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Sensitivity uncertainty of burette

A

+/- 0.15 cm3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Equation for percentage uncertainty

A

+/- (uncertainty/ measurement made) x 100

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How to reduce uncertainties in titration- apparatus

A
  • replace measuring cylinders for pipettes or burettes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How to reduce uncertainty in burette reading

A

Make the titre a larger volume by increasing the vol and conc of a substance in the conical flask or decreasing the conc of the substance in the burette

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Reducing uncertainties in measuring mass

A

use a balance that measures to more dp or use a larger mass of a solid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

In a calorimetry experiment, what is an issue if the reaction is slow?

A

the exact temp rise is difficult to obtain as cooling is occurring simultaneously

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What do we do to counteract this?

A

take readings at regular intervals and extrapolate the temp curve/line back to the time the reactants were added together

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Errors in the calorimetry method

A

-energy transfer to surroundings
-assumes all solutions have same specific heat cap/density of H2O
-neglecting specific heat cap of the calorimeter
-reaction may be incomplete/slow
-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

General method to calculate the enthalpy change of reaction

A

1- use q=mcAT
2- work out moles of reactants used
3- divide q by the no of moles of reactant not in excess to get AH
4- add sign and unit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How to measure reaction rate in sodium thiosulfate and HCl experiment

A

1/time

the time is the time taken for the cross to disappear

18
Q

Why does the cross disappear in sodium thiosulfate and HCl experiment?

A

due to cloudiness of sulfur

19
Q

InK= constant -Ea/RT

k is proportional to rate. What adjustments can we make?

A

Replace InK for In(rate_

20
Q

What is magnesium hydroxide classed as in water? How does it appear?

A

insoluble- a white ppt, slightly alkaline (pH 9) due to very slight dissolving
Mg2+ (aq) + 2OH-(aq) –> Mg(OH)2
(s).

21
Q

What is calcium hydroxide classed as in water? How does it appear?

A

partially soluble- white ppt, more alkaline (pH 11) than magnesium

22
Q

What is the test for group 2 ions?

A

add dilute sodium hydroxide

23
Q

Test for ammonia gas

A

turns red litmus paper blue

24
Q

Test for sulfate ion

A

-BaCl2 solution acidified with HCl used as the reagent
-Added to sample
-When added to a solution with sulfate ions, a white ppt of Barium sulfate forms
Ba2+ (aq) + SO4
2-(aq) –> BaSO4
(s)

25
Q

Why is HCl needed for test for sulfate ions?

A

to react with carbonate impurities often found in salts which would form a white barium carbonate ppt

26
Q

Why is H2SO4 not use in the test for sulfate ions?

A

it contains sulfate ions- false positive

27
Q

Test for halide ions with silver nitrate

A
  • test solution is made acidic with nitric acid (react with carbonates to avoid formation of Ag2CO3 ppt)
  • then silver nitrate added dropwise
28
Q

Test for halide ions with silver nitrate- results

A

-Fluorides produce no precipitate
-Chlorides produce a white precipitate
Ag+
(aq) + Cl- (aq) –> AgCl(s)
-Bromides produce a cream precipitate
Ag+
(aq) + Br- (aq) –> AgBr(s)
-Iodides produce a pale yellow precipitate
Ag+
(aq) + I- (aq) –> AgI(

29
Q

Test for carbonate ions

A
  • add any dilute acid- effervescence

- bubble gas through limewater to test for CO2 (limewater turns cloudy)

30
Q

Why does the reducing power of halides increase going down the group? What reaction is used to test this?

A

The ions get bigger so it is easier to give away outer electrons as the pull from the nucleus gets weaker.
-Reaction with conc sulfuric acid

31
Q

Fluoride and Chloride with conc sulfuric acid

A

Not strong enough reducing agents to reduce the S in H2SO4 so redox
reactions occur. Only acid-base reactions occur. (H2SO4 is an acid)

32
Q

Fluoride and conc H2SO4- equ and obs

A

NaF(s) + H2SO4
(l) –>NaHSO4
(s) + HF(g)
Observations: White steamy fumes of HF are evolved

33
Q

Chloride and conc H2SO4- equ and obs

A

NaCl(s) + H2SO4
(l) –> NaHSO4
(s) + HCl(g)
Observations: White steamy fumes of HCl are evolved.

34
Q

Bromide and conc. H2SO4- equ and obs

A 
NaBr(s) + H2SO4
(l) --> NaHSO4
(s) + HBr(g)
Observations: White steamy fumes of
HBr are evolved.
35
Q

Partial oxidation of primary alcohols- product, reagent, conditions and observations

A

P= aldehyde
R= potassium dichromate solution and dilute sulfuric acid
C= limited amount of dichromate, warm gently and distil out the aldehyde
O= : the orange
dichromate ion (Cr2O7
2-) reduces
to the green Cr3+

36
Q

Full oxidation of primary alcohols- product, reagent, conditions and observations

A

P= carboxylic acid
R=potassium/sodium dichromate solution and sulfuric acid
C= excess of dichromate, heat under reflux
O= orange
dichromate ion (Cr2O7
2-) reduces
to the green Cr3+

37
Q

Why are anti-bumping granules used?

A

to prevent vigorous, uneven boiling by making small bubbles to form instead of large ones

38
Q

How is tollen’s reagent made?

A

mixing aqueous ammonia and silver nitrate

39
Q

On a conc vs time graph, how can you calculate the initial rate?

A

take the gradient at time= 0

40
Q

Recrystallisation: causes of loss of yield

A
  • crystals lost when filtering or washing
  • some product stays in solution after recrystallisation
  • other side reactions occurring

AQA A Level Chemistry (14 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions