Practical Skills

Question 1

What is a standard solution?

Answer 1

A solution of known concentration

Question 2

Why are acid-base indicators used?

Answer 2

To detect when a reaction reaches completion/ becomes neutral, usually by the presence of a color change

Question 3

What are concordant results?

Answer 3

Titres that are within 0.1 cm3 of each other

Question 4

risk in glassware hazards

Answer 4

may break and cut you

Question 5

risk in chemical hazards

Answer 5

may be flammable,

may be toxic,

and may be an irritant or corrosive, causing irritation to skin, eyes, lungs.

Question 6

For a Hess’s cycle the sum of the clockwise enthalpy changes … the sum of the anticlockwise enthalpy changes

Answer 6

equals

Question 7

how can you reduce the uncertainty in the mass measurement?

Answer 7

use a balance with a greater resolution,

use a larger mass

Question 8

percentage uncertainty

Answer 8

100 x absolute uncertainty/ calculated value

Question 9

why may an experimental value for enthalpy change be different from the theoretical value?

Answer 9

heat loss to surroundings,

incomplete combustion,

non-standard conditions,

evaporation of alcohol/ water.

Question 10

how do you prevent heat loss to surroundings/ apparatus?

Answer 10

insulate the beaker by placing it in a polystyrene cup with a lid,

avoid large temperature differences between surroundings and calorimeter

use a bomb calorimeter

Question 11

other than preventing heat loss, how can the accuracy of this experiment be improved?

Answer 11

read the thermometer at eye level to avoid parallax errors,

stir the solution so the temperature is evenly distributed,

use a digital thermometer for more accurate and faster readings,

use greater concentrations and masses, leading to a greater temperature change and thus smaller uncertainty.

Question 12

what is accuracy?

Answer 12

the more accurate the data, the closer it is to the actual value.

Question 13

how can the rate of reaction be measured?

Answer 13

initial rates method – i.e. the iodine clock reaction,

a continuous monitoring method – i.e. measuring the volume of gas released in a reaction over time

Question 14

BaCl2
initial
after 10 drops of NaOH
excess NaOH

Answer 14

colorless solution
colorless solution
colorless solution

Question 15

CaBr2
initial
after 10 drops of NaOH
excess NaOH

Answer 15

colorless solution
slight white ppt
slight white ppt

Question 16

MgCl2
initial
after 10 drops of NaOH
excess NaOH

Answer 16

colorless solution
slight white ppt
white ppt

Question 17

SrCl2
initial
after 10 drops of NaOH
excess NaOH

Answer 17

colorless solution
slight white ppt
slight white ppt

Question 18

BaCl2
initial
after 10 drops of H2SO4
excess H2SO4

Answer 18

colorless solution
white ppt
white ppt

Question 19

CaBr2
initial
after 10 drops of H2SO4
excess H2SO4

Answer 19

colorless solution
slight white ppt
slight white ppt

Question 20

MgCl2
initial
after 10 drops of H2SO4
excess H2SO4

Answer 20

colorless solution
slight white ppt
colorless solution

Question 21

SrCl2
initial
after 10 drops of H2SO4
excess H2SO4

Answer 21

colorless solution
white ppt
white ppt

Question 22

carbonate ions + HCl, in delivery tube with open end, added into Ca(OH)2. If Ca(OH)2 goes cloudy, meaning carbonate ions were present in the other test tube.

Answer 22

bubububutterfly

Question 23

Add HCl and BaCl2 to the suspended sulfate solution. If sulfate ions are present, a white ppt of BaSO4 will form.

Answer 23

flowers and grass and berries and nectar

Question 24

what is the order of testing ions? (carbonate, halide and sulfate). explain.

Answer 24

carbonate -> sulfate -> halide
this prevents false positive results occurring i.e. unexpected insoluble precipitates such as Ag2SO4, Ag2CO3 and BaCO3 could form.

Question 25

methyl orange

Answer 25

red=acid | yellow= base

Question 26

phenolphthalein

Answer 26

colorless=acid | pink=base

Question 27

why are anti-bumping granules used in distillation?

Answer 27

to allow smooth boiling -- preventing bubbles caused by vapor to cause upwards splashing in the flask

Question 28

testing for an alcohol

Answer 28

add (1cm3?) of sample to a test tube, and add a small piece of Na. presence of alcohol is indicated by effervescence and a white crystalline solid is left. if a phenolphthalein indicator was added, in a positive result the colorless solution will turn pink, due to basic salt formed.

Question 29

testing for carboxylic acid

Answer 29

add na2co3 to the sample. if a carboxylic acid is present, co2 will be given off.

Question 30

https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/organic-tests-flashcards/ slide 13, mls

Answer 30

ceeh ikik

Question 31

rate of reaction

Answer 31

the change in concentration of reactants or products over time

Question 32

what is an initial rates method if want2 ngertiin example: https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/measuring-rate-of-reaction-flashcards/ slide 9

Answer 32

the method involves measuring the initial rate of reaction for multiple different concentrations to observe how rate of reaction varies.

Question 33

https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/measuring-rate-of-reaction-flashcards/ initial rates method example what is the issue with this experiment?

Answer 33

Some low I- concentrations may take too long to react, delayed stopwatch reactions, concentrations may not be exact due to measuring apparatus

Question 34

what is a continuous monitoring method https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/measuring-rate-of-reaction-flashcards/ slide 15

Answer 34

this involves measuring the change in concentration of a reactant or product over time (or measuring the volume of gas released) as reaction progresses

Question 35

https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/measuring-rate-of-reaction-flashcards/ slide 15 issues?

Answer 35

some gas may escape before the bung is added, the Mg strips may be of different mass, surface area, etc. which will affect the rate of reaction.

Question 36

https://www.physicsandmathstutor.com/chemistry-revision/a-level-aqa/practical-skills/measuring-rate-of-reaction-flashcards/ slide 15 how do u prevent gas escaping?

Answer 36

place the solid reactant upright inside a sample tube in the conical flask, tipping the tube over by moving the conical flask around to start the reaction

Question 37

why does a pH probe need to be calibrated

Answer 37

so that the pH values for each pH reading are accurate

Question 38

what are the main steps in producing a pure organic solid?

Answer 38

1. synthesis of the compound (usually using reflux, distillation, etc.) 2. filtration (usually vacuum filtration) 3. purification (recrystallization)

Question 39

why is heating under reflux used?

Answer 39

allows heating for a long period of time, prevents the flask from boiling dry, prevents volatile reactants/ products escaping, ensures even heating.

Question 40

how do you use laboratory equipment to filter under reduced pressure?

Answer 40

using a buchner funnel and a buchner flask, connected by rubber tubing to the vacuum source. the funnel contains a layer of filter paper, pour the substance onto the filter paper and the liquid will be sucked through via vacuum filtration into the flask, the solid will remain on the paper

Question 41

how do you purify a solid product?

Answer 41

by recrystallisation. 1. add minimum amount of warm solvent to the impure sample until it has dissolved 2. allow to cool, crystals should form 3. when no more form you can filter under reduced pressure to obtain a dry crystalline solid.

Question 42

organic layer

Answer 42

liquids less dense than water

Question 43

how do you purify a liquid organic product?

Answer 43

1. you can use a separating funnel to isolate the organic layer from the aqueous layer 2. add anhydrous MgSO4 to the organic product to get rid of all water 3. you can then purify the liquid by distillation, which separates the substances by boiling point

Question 44

what can be reacted with transition metals for a precipitation reaction to occur?

Answer 44

aqueous NaOH, | NH3.

Question 45

what are the uses of thin layer or paper chromatography?

Answer 45

to separate a liquids mixture into its constituent components for analysis. This allows identification by the calculation and comparison of Rf values.

Question 46

Rf value

Answer 46

distance travelled by component: distance travelled by solvent

Question 47

why must any lines drawn on the tlc plate be in pencil?

Answer 47

because if drawn in ink, this will dissolve in the solvent and run up the plate with the other components, contaminating the plate.

Question 48

why should the solvent be below the pencil line?

Answer 48

if above the pencil line, the solvent will dissolve all samples and they will not run up the plate

Question 49

in tlc, paper chromatography, what happens if your sample is too concentrated?

Answer 49

the spots overlap

Question 50

in tlc, paper chromatography, what happens if you use less solvent and have a high baseline?

Answer 50

you will get large spots

Question 51

how do you view the spots on a tlc plate?

Answer 51

some spots may be visible, others may only be visible under UV light. sometimes the plate is sprayed with a chemical/ locating agent to show invisible spots.

Question 52

universal indicator

Answer 52

shades of yellow orange red = acid | shades of blue green = base

Question 53

percentage error

Answer 53

margin of error/ actual or mean measurement x 100%