Module 2 - Acids and Redox

Question 1

formula for sulphuric acid

Answer 1

H2SO4

Question 2

formula for nitric acid

Answer 2

HNO3

Question 3

formula for ethanoic acid

Answer 3

CH3COOH

Question 4

formula for sodium carbonate

Answer 4

Na2CO3

Question 5

formula for sodium hydroxide

Answer 5

NaOH

Question 6

formula for potassium hydroxide

Answer 6

KOH

Question 7

formula for phosphoric acid

Answer 7

H3PO4

Question 8

define a hydrogen ion

Answer 8

has no electrons in its outer shell so it is also known as a proton

Question 9

define an acid

Answer 9

in water an acid releases hydrogen ions (H+) into solution (proton donor)

Question 10

define a strong acid

Answer 10

releases all of its hydrogen ions in solution and completely disassociates/ ionises

Question 11

define a weak acid

Answer 11

only releases a small number of its hydrogen ions in solution and partially disassociates/ ionises

Question 12

define a base

Answer 12

a compound that neutralises an acid, by accepting a hydrogen ion, to form a salt (proton acceptor)

Question 13

what are bases generally

Answer 13

metal oxides
ammonia

Question 14

describe what a base does

Answer 14

donates 2 electrons to the hydrogen ion to form a dative covalent bond
bases can either have a lone pair or a negative charge

Question 15

define an alkali

Answer 15

a type of soluble base that releases hydroxide ions

Question 16

what are alkalis typically

Answer 16

hydroxides

Question 17

how is ammonia classified as an alkali

Answer 17

it takes a proton from water to form ammonium and hydroxide

Question 18

define a salt

Answer 18

the product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions

Question 19

product for metal + acid

Answer 19

salt + hydrogen

Question 20

product for metal oxide + acid

Answer 20

salt + water

Question 21

product for metal hydroxide + acid

Answer 21

salt + water

Question 22

product for metal carbonate + acid

Answer 22

salt + carbon dioxide + water

Question 23

product for ammonia + acid

Answer 23

ammonium salt

Question 24

what do neutralisation reactions form

Answer 24

salts

Question 25

observations in carbonate reactions

Answer 25

-there will be effervescence due to the CO2 gas evolved
-the solid carbonate will dissolve

Question 26

describe the method for making a standard solution

Answer 26

1. weigh out the mass of the solid using weigh by difference, to 2 decimal places
2. place the solid into a beaker
3. add 100cm3 of distilled water to the beaker
4. stir the solution to dissolve the solid
5. transfer the solution to a 250cm3 volumetric flask
6. rinse the equipment into the volumetric flask
7. make up the solution to the 250cm3 line with distilled water using a pipette, with the bottom of the meniscus on the line
8. put on the lid and invert several times to mix

Question 27

what is used to calculate the mean titre

Answer 27

• only concordant results

Question 28

describe concordant results

Answer 28

-2 or 3 values within 0.10cm3
-so results are accurate and repeatable
-the titration technique is consistent

Question 29

rules for recording titrations

Answer 29

-results should be clearly recorded in a table
-result should be recorded in full (i.e. both initial and final
readings)
-record titre volumes to 2dp (0.05 cm3)

Question 30

describe the method for titrations

Answer 30

1.rinse all glassware with distilled water and the solution that will be used
2.measure 25cm3 of standard solution with a pipette and filler and put in the conical flask
3.add 3-4 drops of indicator
4. place on a white tile to see the colour change better
5. using a funnel, fill the burette with acid to the zero mark with the bottom of the meniscus on this line
6. complete rough titration looking for the endpoint while swirling the conical flask
7. repeat the experiment adding the acid drop by drop to reach the endpoint
8. rinse the conical flask between titrations with distilled water
9. record out titres into a table
10. calculate the mean titre using concordant results

Question 31

safety precautions of a titration

Answer 31

-acids and alkalis are corrosive
(at low concentrations acids are irritants)
-wear eye protection and gloves
-if spilled immediately wash affected parts after spillage
-if substance is unknown treat it as potentially toxic and wear gloves

Question 32

why must the jet space in the burette be filled with acid

Answer 32

-if the jet space is not filled properly prior to commencing the titration it will lead to errors if it then fills during the
titration
-leading to a larger than expected titre reading

Question 33

why must a conical flask be used in a titration

Answer 33

-it is easier to swirl the mixture in a conical flask than a beaker without spilling the contents

Question 34

why must only a few drops of indicator be used in a titration

Answer 34

-they are generally weak acid
-if too much is added the result will be affected

Question 35

why can distilled water be used to wash the flask during a titration

Answer 35

-so all the acid on the side is washed into the reaction mixture to react with the alkali
-does not react with reagents or change the number of moles of acid added

Question 36

steps for titration calculation

Answer 36

-moles
-ratio
-question

Question 37

levels of precision of different equipment

Answer 37

-different equipment can measure to different levels of precision

Question 38

uncertainty in measurements

Answer 38

-there is uncertainty when you make a measurement
-the uncertainty is half the smallest possible unit you can make

Question 39

equation for percentage uncertainty

Answer 39

uncertainty of equipment/ size of measurement
x100

Question 40

how to calculate maximum percentage uncertainty in a final result

Answer 40

-add all the individual equipment uncertainties together

Question 41

what needs to be taken into account when calculating uncertainty

Answer 41

-how many times you read off a piece of equipment to get an answer

Question 42

how do you decrease apparatus uncertainties

Answer 42

-increase the size of the measurement made

Question 43

what is a volumetric flask

Answer 43

-a type of laboratory flask calibrated to contain a precise volume at a particular temperature

Question 44

what are volumetric flasks used for

Answer 44

-precise dilution and preparation of standard solution

Question 45

equation for calculating new concentration

Answer 45

original volume/ new volume
x original concentration

Question 46

what is an oxidation number/state

Answer 46

-a measure of the number of electrons that an atom uses to bond with an atom of another element
-oxidation numbers are derived from a set of rules

Question 47

rules for oxidation numbers

Answer 47

1- the oxidation number of a neutral element is zero
2-the oxidation number of a monatomic ion is the same as the charge on the ion
3-the sum of all oxidation numbers in a neutral compound is zero
4-the sum of all oxidation numbers in a polyatomic ion is equal to the charge on the ion
5-in compounds the elements of group 1 are +1, group 2 are +2, group 3 are +3
6-the oxidation number/state of hydrogen in a compound is usually +1
-if the hydrogen is part of a binary metal hydride (compound of hydrogen and some metals), then the oxidation state of hydrogen is -1
7-fluorine always has an oxidation number of -1 in compounds
8-the oxidation number of oxygen is usually -2
-if the oxygen is in a peroxide it has an oxidation number of -1
-if the oxygen is bonded to fluorine the number is +1
9-in transition metals the oxidation number can vary
10-chlorine, bromine and iodine usually have oxidation numbers of -1 except when in a compound with oxygen