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core practical's Flashcards

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1
Q

give examples of irritants in a experiment and how you can reduce their risk

A

weak acids ands alkali
wear goggles

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2
Q

give examples of irritants in a experiment and how you can reduce their risk

A

strong acids and alkalis
wear goggles

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3
Q

how can you reduce risk around flammable substances

A

keep away from naked flame/use water bath or heating mantle

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4
Q

how can you reduce risk around toxic substances

A

wear gloves, avoid skin contact, wash hands after use

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5
Q

how can you reduce risk when using highly oxidizing substances

A

keep away from flammable/easily oxidized materials

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6
Q

what are potential errors when using a gas syringe

A

gas escaping before bung is inserted
gas may be soluble so a true reading will not be given
dependent on temp and pressure so these must be kept constant

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7
Q

when is heating in a crucible used

A

measuring mass lost in thermal composition
measuring mass gain when reacting magnesium in oxygen

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8
Q

why should the lid on the crucible be left on

A

improves accuracy as it prevents loss of solid from the crucible but should be loose to allow gas to escape

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9
Q

describe the process of making a solution

A

weigh the mass of solid in the test tube then transfer to a beaker
weigh the empty test tube
calculate the mass of solid
add 100cm^3 of distilled water and use glass rod to help dissolve
the solution may need to be heated gently to help it dissolve
pour solution into 250cm^3 graduated flask via a funnel
rinse the beaker and funnel and add washings to the flask
make up to the mark with distilled water
invert flask several times to ensure uniform solution

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10
Q

where should the graduated flask be filled to

A

the bottom of the meniscus should be on the line

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11
Q

why can graduated flasks not be heated

A

the heat would cause the flak to expand and then the volume would be inaccurate

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12
Q

what is the chemical equation for the reaction between ethanoic acid and calcium carbonate

A

2CH3COOH + CaCO3 -> (CH3COOH)2Ca + H2O + CO2

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13
Q

why is it more accurate to find the mass of a solid by weighing the weight the mass of solid in the test tube then transfer to a beaker then weighing the empty test tube after

A

as some of the solid may be lost when it is transferred to the test tube therefor it is important to re-weigh to ensure accurate results are obtained

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14
Q

how could you reduce gas lost from a reaction involving a gas syringe

A

having one person add the calcium carbonate and the other ready to put the bung in the test tube reduces the time for the gas to escape

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15
Q

how can you ensure an accurate mass is obtained on a balance

A

balance should be 2-3dp
weigh in a test tube
transfer to reaction vessel
re-weigh empty test tube
subtract the mass of the empty test tube from the first mass reading

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16
Q

why is a volumetric pipette better than a measuring cylinder

A

it has a smaller uncertainty

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17
Q

why should a pipette be rinsed with sodium hydroxide solution after washing with water (core prac 2)

A

to ensure there are no impurities left in the pipette that may disrupt the reaction

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18
Q

core prac 2 titration of sulfamic acid (in burette) and sulfuric acid (in flask) why is there no need for the conical flask to be dried in between titrations

A

the sulfamic acid will neutralize the sodium hydroxide therefor any left over residue will be neutral and have no effect on the reaction

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19
Q

what is the colour change of phenylalanine

A

colourless in acid <-> pink in alkali

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20
Q

what is the colour change of methyl orange

A

red in acid <-> yellow in alkali

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21
Q

what is the general method for carrying out a titration

A
  • rinse equipment
  • pipette 25cm^3 into conical flask
  • fill burette with acid and ensure jet space is filled
  • add a few drops of indicator to conical flask
  • place a white tile under the conical flask to ensure colour change can be seen
  • add acid slowly whilst swirling the misture going drop by drop near the end point
  • note the burette reading at the start and end of the titration
  • repeat titration until you get 2 concordant results
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22
Q

what does titrated solution A with solution B

A

A should be in the conical flask
B should be in the burette

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23
Q

why is a conical flask used over a beaker for titrations

A

easier to swirl the mixture without spilling the solution

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24
Q

describe how a pipette should be used

A

rinse with substance to go in it
fill till the bottom of the meniscus is on the graduation line
touch the surface of the solution with the pipette to ensure correct amount is added

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25
Q

why is it important to rinse equipment with the substance being added before carrying out a titration

A

any residual water may react with previous substances and and lower their concentration so a larger titer will be recorded

26
Q

why should the funnel not be left in the top of the burette

A

small drops of liquid may fall from the funnel during the titration giving a lower titer volume

27
Q

why must the jet space be filled before commencing a titration

A

remove air bubbles to ensure accurate titer calculating as if it is not filled the titer volume would be larger than expected

28
Q

how should titer results be recorded

A

always to 2dp ending in 0.00 or 0.05

29
Q

why should indicators be added in very small volumes

A

in high volumes they can effect the titration results as they are often weak acids/alkalis

30
Q

what does 2 concorant results mean for titrations

A

2 readings within 0.1 of each other

31
Q

why is it important to do repeat titrations

A

allows anomalous results to be spotted and discounted

32
Q

what is the equation for the titration of acetic acid with sodium hydroxide

A

CH3CO2H + NaOH -> CH3CO2
-Na+ + H2O

33
Q

what is the equation for the titration of sulfuric acid with sodium hydroxide

A

H2SO4 + 2NaOH -> Na2SO4 +2H2O

34
Q

what is the equation for the titration of hydrochloric acid and sodium hydroxide

A

HCl + NaOH -> NaCl +H2O

35
Q

what is the equation for the titration of sodium bicarbonate with hydrochloric acid

A

NaHCO3 + HCl -> NaCl + CO2 + H2O

36
Q

what is the equation for the titration of sodium carbonate with hydrochloric acid

A

Na2CO3 + 2HCl -> 2NaCl + CO2 + H2O

37
Q

how can you reduce percentage uncertainty in titrations

A

replacing measuring cylinder with pipettes or burettes which have lower apparatus uncertainty
increase the volume of the substance in the conical flak or lower the concentration of the substance in the burette

38
Q

how can you reduce uncertainty when weighing substances

A

use a more accurate balance
weigh a larger mass
weighing sample in test tube before and after then calculating the difference

39
Q

why does the pink colour of the phenylalanine fade after the end point for the titration of hydrochloric acid with sodium hydroxide

A

excess sodium hydroxide reacts with carbon dioxide in the air forming sodium carbonate and water

40
Q

whats the equation for the reaction of sodium hydroxide with carbon dioxide

A

NaOH + CO2 -> Na2CO3 + H2O

41
Q

why is it better to have a titer around 25cm^3 rather than 10cm^3

A

the larger the volume the smaller the percentage error

42
Q

what type of a reaction is hydrolysis of halogenoalkanes

A

nucleophilic substitution

43
Q

how do you measure the rate of hydrolysis in halogenoalkanes (core prac 4)

A

in separate test tubes place the different halogenoalkanes and add ethanol
place the halogenoalkane-ethanol solutions and the silver nitrate solution in a water bath so that is it all the same temperature then add the silver nitrate to the halogenoalkane-ethanol solution and measure the time taken for the precipitate to form

44
Q

what trend is shown for the reactivity of halogenoalkanes (hydrolysis reaction core prac 4)

A

as you go down group 7 halogenoalkanes the time taken for a precipitate to form increases so rate of reaction decreases
as branching increases in time taken for the precipitate to form decreases so rate of reaction increases

45
Q

what precipitate forms inthe hydrolysis of 1-iodobutane with silver nitrate solution

A

silver iodide

46
Q

why is ethanol used for the hydrolysis of halogenoalkanes

A

to ensure the halogenoalkanes dissolve so that they can react with the water molecules as they are insoluble in water

47
Q

why is water able to act as a nucleophile

A

it has a lone pairs of electrons from the oxygen

48
Q

why is water used as a nucleophile for the hydrolysis of halogenoalkanes with silver nitrate solution instead of hydroxide ions

A

because hydroxide ions would form silver hydroxide instantly

49
Q

what must be added if hydrolysis of halogenoalkanes is done with NaOH and not water (before silver nitrate is added)

A

HNO3 must be added to neutralize NaOH

50
Q

what is the formula form silver nitrate

A

AgNO3

51
Q

what are the reagents and conditions for the partial oxidation of primary alcohols and what will be observed

A

potassium dichromate(VI) and dilute sulfuric acid
warm gently and distill out the aldehyde as it forms
orange -> green

52
Q

what is distillation

A

a separation technique used to separate an organic product from its reacting mixture, need to collect the distillate of the approximate boiling point range of the desired liquid

53
Q

what is the equation for the oxidation of ethanol to ethanal

A

CH3CH2OH + [O] -> CH3CHO + H2O

54
Q

how do you heat under reflux

A

substance is boiled in round-bottomed flask fitted with a vertical condenser and as it evaporates it is cooled by the water in the liebig condenser and so condenses back to a liquid and drops back into the flask to be heated again

55
Q

why is heating under reflux used

A

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

56
Q

why are anti-bumping granules used when heating under reflux

A

to allow smooth boiling and prevent bubbles forming and splashing hot liquid up the sides of the flask

57
Q

what is the equation for the oxidation of ethanol to ethanoic acid

A

CH3CH2OH + 2[O] -> CH3COOH + H2O

58
Q

summarise the experiment for the chlorination of 2-methylpropan-2-ol

A

add conc HCl
put rubber bung on and swirl
open bung to release pressure
add anhydrous CaCl2 and shake
distill the two layers in a separating funnel
top layer - organic product
lower layer - aqueous layer

59
Q

2-methylpropan-2-ol has a bp of 82 and is soluble in water whereas 2-chloro-2-methylpropane has a bp of 51 and is insoluble in water
explain these differences

A

2-methylpropan-2-ol can form hydrogen bonds therefor is soluble
it has stronger intermolecular hydrogen bonds which require more energy to overcome
2-chloro-2-methylpropane cannot form hydrogen bonds therefor is not soluble
only forms intermolecular london forces and dipole-dipole interactions which require less energy to overcome

60
Q
A
61
Q
A

Chemistry (46 decks)

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