core practical's

Question 1

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

Answer 1

weak acids ands alkali
wear goggles

Question 2

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

Answer 2

strong acids and alkalis
wear goggles

Question 3

how can you reduce risk around flammable substances

Answer 3

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

Question 4

how can you reduce risk around toxic substances

Answer 4

wear gloves, avoid skin contact, wash hands after use

Question 5

how can you reduce risk when using highly oxidizing substances

Answer 5

keep away from flammable/easily oxidized materials

Question 6

what are potential errors when using a gas syringe

Answer 6

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

Question 7

when is heating in a crucible used

Answer 7

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

Question 8

why should the lid on the crucible be left on

Answer 8

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

Question 9

describe the process of making a solution

Answer 9

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

Question 10

where should the graduated flask be filled to

Answer 10

the bottom of the meniscus should be on the line

Question 11

why can graduated flasks not be heated

Answer 11

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

Question 12

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

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

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

Question 16

why is a volumetric pipette better than a measuring cylinder

Answer 16

it has a smaller uncertainty

Question 17

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

Answer 17

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

Question 18

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

Answer 18

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

Question 19

what is the colour change of phenylalanine

Answer 19

colourless in acid <-> pink in alkali

Question 20

what is the colour change of methyl orange

Answer 20

red in acid <-> yellow in alkali

Question 21

what is the general method for carrying out a titration

Answer 21

• 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

Question 22

what does titrated solution A with solution B

Answer 22

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

Question 23

why is a conical flask used over a beaker for titrations

Answer 23

easier to swirl the mixture without spilling the solution

Question 24

describe how a pipette should be used

Answer 24

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

Question 25

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

Answer 25

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

Question 26

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

Answer 26

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

Question 27

why must the jet space be filled before commencing a titration

Answer 27

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

Question 28

how should titer results be recorded

Answer 28

always to 2dp ending in 0.00 or 0.05

Question 29

why should indicators be added in very small volumes

Answer 29

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

Question 30

what does 2 concorant results mean for titrations

Answer 30

2 readings within 0.1 of each other

Question 31

why is it important to do repeat titrations

Answer 31

allows anomalous results to be spotted and discounted

Question 32

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

Answer 32

CH3CO2H + NaOH -> CH3CO2 -Na+ + H2O

Question 33

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

Answer 33

H2SO4 + 2NaOH -> Na2SO4 +2H2O

Question 34

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

Answer 34

HCl + NaOH -> NaCl +H2O

Question 35

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

Answer 35

NaHCO3 + HCl -> NaCl + CO2 + H2O

Question 36

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

Answer 36

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

Question 37

how can you reduce percentage uncertainty in titrations

Answer 37

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

Question 38

how can you reduce uncertainty when weighing substances

Answer 38

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

Question 39

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

Answer 39

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

Question 40

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

Answer 40

NaOH + CO2 -> Na2CO3 + H2O

Question 41

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

Answer 41

the larger the volume the smaller the percentage error

Question 42

what type of a reaction is hydrolysis of halogenoalkanes

Answer 42

nucleophilic substitution

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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

Answer 45

silver iodide

Question 46

why is ethanol used for the hydrolysis of halogenoalkanes

Answer 46

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

Question 47

why is water able to act as a nucleophile

Answer 47

it has a lone pairs of electrons from the oxygen

Question 48

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

Answer 48

because hydroxide ions would form silver hydroxide instantly

Question 49

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

Answer 49

HNO3 must be added to neutralize NaOH

Question 50

what is the formula form silver nitrate

Answer 50

AgNO3

Question 51

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

Answer 51

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

Question 52

what is distillation

Answer 52

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

Question 53

what is the equation for the oxidation of ethanol to ethanal

Answer 53

CH3CH2OH + [O] -> CH3CHO + H2O

Question 54

how do you heat under reflux

Answer 54

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

Question 55

why is heating under reflux used

Answer 55

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

Question 56

why are anti-bumping granules used when heating under reflux

Answer 56

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

Question 57

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

Answer 57

CH3CH2OH + 2[O] -> CH3COOH + H2O

Question 58

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

Answer 58

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

Question 59

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

Answer 59

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