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Aqa a level chemistry > Topic 2: Quantitative chemistry (physical chem) > Flashcards

Topic 2: Quantitative chemistry (physical chem) Flashcards

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1
Q

Define solubility

A

the property of a solid, liquid or gaseous chemical substance called solute to dissolve in a solid, liquid or gas solvent

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2
Q

what is the state symbol of an element if it is soluble in water

A

aqueous (aq)

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3
Q

what are the aqueous substances
(SNACKS)

A

-All common Na+, K+, NH4+ salts

-All nitrates

-Most chlorides except for silver and lead

-Most sulfates except for lead, barium and calcium

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4
Q

what substances are insoluble (solids)

A

-Most carbonates

-Most hydroxides

-most oxides

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5
Q

what happens to hydroxides and sulphates down group 2

A

-Hydroxides are more soluble and sulphates are less soluble down group 1 and 2

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6
Q

what equation links base + acid

A

base + acid –> water + salt

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7
Q

what does MASH stand for

A

metal + acid –> salt + hydrogen

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8
Q

What does CAWCS stand for

A

metal carbonate + acid –> water + carbon dioxide + salt

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9
Q

when does a metal carbonate form

A

when a carbonate ion reacts with a metal cation

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10
Q

what is a metal carbonate described as

A

a base

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11
Q

what is the formula for hydrochloric acid

A

HCL

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12
Q

what is the formula for sulfuric acid

A

H2SO4

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13
Q

what is the formula for nitric acid

A

HNO3

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14
Q

what is a decomposition reaction

A

AB –> A + B
heat is required
if C and O is present CO2 is formed in products

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15
Q

what are the 4 observations in reactions

A

-if solid is in reactants but not in products then the solid dissapears/dissolves

-If a gas is produced bubbling/effervescence occurs

-If an alkali is formed litmus paper will turn blue

-If an acid is formed the litmus paper will turn red

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16
Q

what is the amount of a substance measured in

A

moles

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17
Q

define molar mass

A

the mass of 1 mol of a chemical

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18
Q

what does 1 mol equal

A

12g of carbon

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19
Q

how do you calculate mol

A

mass / mr

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20
Q

how do you calculate the number of atoms/molecules

A

mol x avogadros constant

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21
Q

define mole

A

the total number of atoms present in the molar mass of the substance

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22
Q

calculate the amount in mole of water with 9.36 x 10^24 of atoms

A

9.36 x 10^24 / 6.022 x 10^23

Answer / 3 as there is 3 moles

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23
Q

How many atoms are there in a mole of neon

A

1 x 6.022 x 10^23

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24
Q

Calculate the number of chloride ions in 1 mol of MgCl2

A

Total = 3 moles (1 mole of Mg / 2 mole of Cl

Chloride ion = 2 x 6.022 x 10^23

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25
Q

define empirical formula

A

the simplest whole number ratio of atoms of each element in a compound

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26
Q

define molecular formula

A

the actual number of atoms of each element in a compound

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27
Q

how do you calculate empirical formula

A

1) Find the mr of each element (mass number)

2) Do mass of the element told in question divided by mr

3) Divide the amounts by the smallest amount to find ratio

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28
Q

how do you calculate molecular formula

A

1) calculate mr of empirical formula e.g C3H7 = 43

2) Divide the mass given in the question by mr of empirical formula e.g 86 / 43 =2

3) Multiply the atoms by the number e.g C6H14 is the molecular formula

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29
Q

what does 24dm3 equal

A

1 mol

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30
Q

how do you convert mg to g

A

divide by 1000

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31
Q

calculate the mass of a single atom of this isotope of sodium

A

23 / 6.022 x 10^23

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32
Q

what is the mass of 1mol of oxygen

A

16.0g

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33
Q

what equation links moles, concentration and volume

A

mol = concentration x volume

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34
Q

what is the mass of 1 atom of carbon

A

12 / 6.022 x 10^23 = 1.99 x 10^23

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35
Q

Define combustion

A

a chemical reaction where a fuel is burnt in oxygen

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36
Q

what is the equation for complete combustion

A

hydrocarbon + oxygen –> Water + carbon dioxide

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37
Q

what is combustion analysis

A

calculating the empirical formula of a hydrocarbon by using the masses of the combustion products

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38
Q

how do you calculate combustion analysis

A

1) Calculate moles of carbon dioxide then moles of carbon from that

2) Calculate moles of water and then moles of hydrogen from that

3)Work out masses of carbon and hydrogen to calculate mass of oxygen

4) Calculate moles of oxygen

5) Calculate empirical formula of the compound

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39
Q

Give the formula of the hydroxide of the element in group 2 from Mg to Ba that is least soluble in water

A

Mg(OH)2

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40
Q

which compound has the same empirical formula and molecular formula

A

propane

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41
Q

how do you calculate the amount of protons in 6.0g of nitrogen gas

A

6.0 / 14
(Ans x 6.022 x 10^23) x 7

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42
Q

how do you calculate ionic equations

A

1) rewrite solid, liquid, gases how they are
2) split ionic aq substances into their components
3) eliminate spectator ions

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43
Q

How do you calculate the volume of molecules

A

1) find moles through mass/mr
2) mol x 6.022 x 10^23
3) ans x volume

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44
Q

How do you find the maximum mass of Na2CO3 from 800g from 2NaCl

A

1) find moles of other compounds
2) find moles of Na2CO3
3) moles x mr of Na2CO3

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45
Q

true or false - when calculating empirical formula of compounds they are molecules not atoms

A

false –> only atoms e.g Na2 will be calculated as Na

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46
Q

How do you calculate the number of water molecules

A

1) calculate change in mass
2) calculate final mass
3) calculate moles
4) calculate ratio

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47
Q

what type of reaction is thermal decomposition

A

endothermic

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48
Q

how would you calculate the mole of y when moles of X is present

A

Moles X = Moles Y x (coefficient of x / coefficient of y)

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49
Q

how do you calculate moles

A

number of particles / avogadro’s constant

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50
Q

what is an ideal gas

A

a gas that has zero interactions with other particles and occupies zero space

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51
Q

what is the equation for ideal gas

A

pV = nRT
P = pressure (pascals)

V = volume (m3)

N = moles

R = gas constant (8.31 J/mol/K)

T = temperature (Kelvin)

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52
Q

how do you convert KPa to Pa

A

multiply by 10^3

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53
Q

how do you convert from Cm^3 to M^3

A

divide by 10^6

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54
Q

how do you convert from Dm^3 to m^3

A

divide by 10^3

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55
Q

how do you convert from degrees Celsius to kelvin

A

Add 273

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56
Q

if two moles of CaCO3 decompresses how many moles of CO2 are produced

A

2 moles

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57
Q

how do you calculate the molar mass of gases from ideal gas law

A

1) n = pV / RT
2) mr = mass / moles

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58
Q

how do you calculate percentage uncertainty

A

(uncertainty / mass added) x 100

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59
Q

how can gas be collected

A

-Gas can be collected and measured using either an inverted measuring cylinder or a gas syringe is used to measure the volume of gases produced. (gas syringe is more accurate)

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60
Q

what is 1 mole equivalent to

A

avogadro’s constant

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61
Q

what is avogadro’s law

A

equal volumes of gases under the same conditions of pressure and temperature contain the same number of molecules

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62
Q

what is molar volume

A

the volume occupied by one mole of gas at a specific temperature and pressure

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63
Q

what equation involves volume 24dm^3 and moles

A

volume = moles x 24dm^3

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64
Q

how do you do calculations involving mass

A

1) Moles = Volume / 24dm^3

2) mr = mass / moles

3) identify the gas from the mr (can be diatomic)

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65
Q

define molar mass

A

the mass in grams of 1 mol of substance

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66
Q

what is the volume to volume ratio the same as

A

mole to mole ratio

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67
Q

how do you find volume from an equation

A

1) calculate moles of Mg

2) look at mole to mole ratio

3) find moles of H2

4) moles x 24 = volume

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68
Q

volume of gas equation –>

A

V1 / N1 = V2 / N2

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69
Q

how do you calculate volumes from equations

A

1) state mole of mole ratio

2)find out how much we have of each molecule

3) calculate total volume of gas produced

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70
Q

how do you work out gas volumes

A

1) work out volume of reactant 2 that would react with the given volume of reactant 1

2) determine which reactant is in excess and which fully reacts

3) use the equation to work out the reacting volumes of the other reactants

4) work out the volumes of excess reactant and the volumes of product produced (add together to get total volume)

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71
Q

what mass of iron can be produced from 20Kg of iron oxide

A

1) find mole to mole ratio
2) Find mr of each compound
3) calculate moles from mass of iron oxide
4) multiply moles by mole to mole ratio
2) mr x moles = mass of Fe

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72
Q

do you use the reactant that is in excess or limiting to calculate moles on products

A

limiting

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73
Q

state a reason for the difference in experimental value and calculated value

A

solution was not heated to a constant mass

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74
Q

define mr (molecular mass)

A

the average mass of one molecule

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75
Q

State why the student should use sodium hydroxide solution rather than
water for the final rinse of the burette

A

water would dilute the NaOH

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76
Q

what is the mr of nitrogen gas (halogen)

A

28 (diatomic element so 14 x 2)

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77
Q

What is the final volume of gas remaining at RTP when 10cm3 of methane is completely burned in 30cm3 of oxygen?

A

CH4 (g) + 2O2 (g) —> CO2 + 2H2O (g)

1:2 –> 10:30

1 = 10

2 = 20 (oxygen is in excess) –> 10cm3 excess

CO2 = 10cm3

2H2O = 20cm3

Total final volume –> 10 + 20 + 10 (excess) = 40cm3

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78
Q

what is conservation of mass

A

For any system that is closed to all transfers of matter and energy, the mass of the system must remain constant of time as the systems of mass cannot change

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79
Q

why would there be excess reactants in a reaction

A

-If there are no losses during a chemical reaction, the starting reactants are converted to the required products.

-Not all reactants will be converted to the required products because most of the time in industry, some reactants are added in excess to ensure the most valuable reactant is converted to as must product as possible.

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80
Q

how can you calculate the moles from limiting reactant and mole:mole ratio

A

mr of limiting x (coefficent / coefficent of limiting)

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81
Q

justify why a smaller target titre would not be appropriate

A

smaller titre will increase the percentage uncertainty

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82
Q

state the reason for inverting the flask several times

A

so the solution is homogeneous

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83
Q

state one advantage of using a conical flask rather than a beaker for a titration

A

less chance of splashing

84
Q

define yield

A

the amount of product formed

85
Q

what are the steps to calculating theoretical yield

A

0) Balance the equation

1) Find mol to mol ratio

2) Find moles of compound where mass is given

3) Find moles of desired product using mol to mol ratio

4) Find the mass of desired product

86
Q

if all of one compound decomposes what will be the yield of the desired product

A

100%

87
Q

what are some reasons for less product

A

-reactants may not be totally pure

-some of the product may be lost during transfer of chemicals from one container to another (during separation or purification)

-there may be side reactions to form other products

-some of the reactants may not react because the reaction is too slow

88
Q

what assumption is made when calculating theoretical yield

A

no losses are made and all of the reactants have reacted

89
Q

if copper oxide was impure what would happen to the yield of copper sulfate

A

decrease –> side reactions

90
Q

how do you calculate percentage yield

A

actual yield / theoretical x 100

91
Q

define desired product

A

the amount of product that is useful and required

92
Q

what is atom economy

A

a measure of the amount of starting materials that end up as useful products

93
Q

how do you calculate atom economy

A

(Mr of desired products / total mr of all the products ) x 100

94
Q

what polymer has the highest atom economy

A

alkenes

95
Q

what equipment is used in titrations

A

burette, pipette filler, pipette, conical flask

96
Q

what are the steps to carrying out a titration

A

Carrying out a titration:

1) rinse the pipette with the solution going into the conical flask

2) Pipette a known volume of this solution into a conical flask

3) Rinse the burette into the solution it will contain and run the tap (fill the jet of the burette

4) Read the initial volume at the base of the meniscus

5) Add a few drops of phenopthalein to the conical flask

6) place conical flask on a white tile under the burette

7) Titrate rapidly then dropwise near the end point (colour change from colourless to pink) and record the final volume. Repeat until concordant titres

97
Q

what is a neutralisation reaction

A

base + acid –> salt + water
-pH of reaction is neutralised when water is formed

98
Q

what do coloured indicators do

A

detect the end point of acid base reactions

99
Q

what are the best indicators to use for titrations

A

-Methyl orange or phenolphthalein are the best indicators to use for titration as they give sharp colour changes at the end point

100
Q

what is the purpose of a titration

A

the analyst finds the volume of the sample solution that reacts with the certain volume of a reference solution that has an accurately known concentration. If we know the volume and concentration of one solution and the volume of another we can determine the concentration of an unknown acid or alkali. It works by gradually adding a base of known concentration to an unknown acid solution or vice versa until the solution is neutralised.

101
Q

what is the pH range for an alkali

A

8-14

102
Q

what is the pH range for an acid

A

0-6

103
Q

standard solutions

A

-to accurately complete a titration a solution of known volume and concentration is needed as well as a solution of known volume but unknown concentration

-A standard solution is a solution with a known concentration

-concentration is the mass of solute dissolved in a given volume of solvent

104
Q

what are the steps to making a standard solution

A

1) weigh the substance of solid on the weighing boat then weigh the weighing boat

2) Subtract mass of solid + boat – boat to get mass by difference

3) Dissolve solid in known volume of deionised/distilled water and stir using stirring rod

4) Transfer this to a volumetric flask and rinse washings from the breaker

5) Fill volumetric flask to the graduation line

6) invert volumetric flask

105
Q

why is distilled water used instead of tap water

A

distilled water is purified so wont affect concentration

106
Q

what is the colour change of methyl orange from acid to alkali

A

red to yellow

107
Q

what is the colour change of methyl red from acid to alkali

A

yellow to red

108
Q

what is the colour change of Bromothymol blue from acid to alkali

A

yellow to blue

109
Q

what is the colour change of Phenolphthalein from acid to alkali

A

colourless to pink

110
Q

how do you calculate titre volume

A

start volume - end volume

111
Q

how do you get from mol/dm3 to g/dm3

A

x mr

112
Q

what is the measure of uncertainty in a titration

A

+-0.05

113
Q

is the known or unknown concentration in the conical flask

A

unknown

114
Q

what is the curved upper surface of a liquid in a burette called

A

mensicus

114
Q

what is it called the moment the indicator changes colour

A

end point of an acid base reaction

115
Q

what is the minimum volume of a solution needed to reach the end point called

A

titre

116
Q

what is the name of titres that are close in agreement (+-0.2)

A

concordant

117
Q

true or false - when calculating volumes used we only use concordant titres to increase the accuracy of calculations

A

true

118
Q

how do you calculate concentration

A

moles / volume

119
Q

what is the procedure of dilution

A

-The procedure for dilution is to take a measured volume of a more concentrated solution with a pipette and run it into a graduated flask. The flask is then filled to the mark with pure water.

120
Q

why is it important for there to be no impurities in pharmaceutical industry

A

as impurities could be dangerous and lead to dangerous side effects. In addition impurities could cause side reactions of unwanted products

121
Q

what is the equation for percentage purity

A

(Mass of pure product / mass of impure product) x 100

or

(mass of useful product / total mass of products) x 100

122
Q

how to calculate percentage purity

A

1) Calculate moles of substance you know volume and concentration of

2) Use mole to mole ratio

3) calculate mass (moles x mr)

4) calculate percentage purity

123
Q

crystalisation of water

A

-When a substance crystalises it means it forms a solid crystal structure

-Water molecules are trapped within the crystal structure when a substance crystalises. This is known as the water of crystalisation.

-Crystals have very regular lattice structures

124
Q

define hydrated

A

Hydrated –> a salt that has water incorporated into its crystal structure

125
Q

define anhydrous

A

Anhydrous –> a salt that does not have water present in its crystalline structure

126
Q

what is the notation for a hydrated salt

A

CuSO4 . 5H2O (copper pentahydrate)

127
Q

calculations involving hydrated salts

A

-Calcium chloride is commonly encountered as a hydrated solid with formula CaCl2 . XH2O

-If we heat the salt, the water will evaporate off leaving the anhydrous salt behind

-To determine X the hydrated sample is weighed, heated strongly to drive off the water then reweighed. This reaction can provide us with information about the molar ratios of each compound.

128
Q

steps to calculating hydrated salts

A

1) calculate mass of the water (initial-final)

2) calculate moles of water using mass

3) calculate moles of anhydrous salt

4) Work out mole to mole ratio to find X

129
Q

how can you determine X by a titration

A

-We can also determine X by using titrations because many bases exist as hydrated crystalline solids

-Titrating with a standard acid solution allows us to work out the moles of a base and by difference of water

1) Use titre to calculate moles of acid

2) use equation to work out moles of the base

3) Use original mass to work out mr of hydrated base

4) use mr of anhydrous base to work out moles of water

130
Q

how do you calculate percentage by mass

A

(mass / total mass) x 100

131
Q

what is the issue with too much indicator

A

may affect the end point reaction so smaller volume should be used (2 drops)

132
Q

why is a pipette better than a measuring cylinder for titrations

A

measuring cylinder has greater percentage uncertainty

133
Q

what effect will rinsing have on the titre

A

titre value would increase as solution would be more dilute

134
Q

Calculating X from titre

A

1) calculate moles of acid

2) calculate moles of base using mole to mole ratio

3) Moles of base x Original/new volume

4) Mass / moles = mr of base

5) Mr of acid – mr of base

6) mr / mr of water

135
Q

define accuracy

A

-A measure of the closeness of agreement between an individual result and an accepted value or literature value

136
Q

define precision

A

-The closeness of agreement between independent measurements obtained under the same conditions

137
Q

define reliability

A

repeating the same method over and over again will produce the same results

138
Q

what is equipment accuracy

A

Apparatus either holds an accurate measure e.g volumetric flask or delivers an accurate volume e.g pipette

139
Q

what is equipment precision

A

-Pieces of equipment differ in terms of their precision. The precision of equipment is best represented by the number of decimal places that we can read it to

-more decimal place = more precise

-The value between divisions indicated the precision, the smaller the divisions, the more precise a piece of equipment is

140
Q

how do you calculate the total number of moles of gas present in the mixture

A

1) Mole to mole ratio
2) Divide ratio by mass given in question
3) Add up all numbers

141
Q

what is uncertainty

A

An estimate attached to a measurement which characterizes the range of values within which a true value is said to lie

142
Q

how to calculate uncertainity

A

-To calculate uncertainty you take the increment of the measurement and divide by two

e.g if a piece of equipment has an increment of 0.01 you divide it by 2 = 0.005

143
Q

how do you calculate percentage uncertainity

A

-uncertainty / value of measurement x 100

144
Q

what are the exceptions for uncertainty

A

-Burette and balance

-You need to multiply the uncertainty by 2

-Uncertainty x 2 / value of measurement x 100

145
Q

how do you reduce percentage uncertainity

A

-Decrease the uncertainty of the equipment by using equipment with more decimal places

-Increase the size of the measurement that is being made

146
Q

what effect would rinsing have on the titre value

A

titre value would increase because the solution would be more dilute

147
Q

what is a back titration

A

adding unknown concentration into known concentration that is in excess

148
Q

importance of percentage yield

A

efficient conversion of reactants to products

149
Q

importance of percentage atom economy

A

minimising the amount of by-products

150
Q

titration

A

1) mean titre (volume)
2) amount of base
3) amount of acid
4) mass of acid
5) mass of product
6) percentage change

1) volume of acid
2) moles of acid
3) moles of base in new sample
4) moles of base in original using new
5) mass of base

151
Q

dilution calculations

A

1) moles of known conc
2) mol to mol to find unknown
3) moles of original using volume (original/new)
4) moles / volume taken to be diluted

152
Q

what is the mean titre

A

the volume of acid/base

153
Q

suggest why washing does not give an incorrect result

A

water does not react with the alkali

154
Q

the conc of ethanoic acid calulcated was lower than the actual value. Why?

A

rinsing the burette with distilled water before filling w acid

155
Q

lower volume =

A

greater mr recorded

156
Q

suggest one reason why calcium hydroxide is not used in the titration of a solution of an acid

A

dilution of acid needed or calcium hydroxide may react with CO2 in the air

157
Q

in this experiment the mass of solid remaining in the crubicle was greater than expected. Why

A

incomplete reaction/decomposition

158
Q

explain why this rinsing can improve the accuracy of the end point

A

returns reagent on side of the flask back into the mixture

159
Q

explain why the addition of water during rinsing does not give an incorrect result

A

water is not a reagent

160
Q

suggest why a leak of NO2 gas from the ostwald process will cause atmospheric pollution

A

NO2 contributes to acid rain

161
Q

give one reason why excess air is used in the ostwald process

A

ensures complete combustion

162
Q

suggest one other source of error in using the burette to carry out a titration

A

air bubble in the jet

163
Q

relative atomic vs relative molecular mass

A

atomic = average mass of an atom

molecular = average mass of a molecule

164
Q

density

A

mass / volume

165
Q

number of molecules/atoms

A

mol x avogadro’s constant

166
Q

finding X

A

1) find mass of water
2) calculate moles of salt and water
3) Mol to mol ratio for x

167
Q

mol dm3 –> g dm3

A

x mr

168
Q

calculating dilutions

A

new dilution = old dilution concentration x old/new volume

169
Q

reduce uncertainity in titrations

A

-use pipette instead of measuring cylinder
-increase concentration of substances

170
Q

reduce uncertainity in measuring mass

A

-balance with more decimal places
-calculate mass by difference

171
Q

which suggestion decreases the percentage uncertainity in the mean titre

A

use a more dilute solution of sodium hydroxide in the burette

172
Q

which molecule can accept an electron pair during the foormation of a coordinate bond

A

AlCl3

173
Q

what is the purpose of increasing the concentration of solutions

A

increase titre value so percentage uncertainity would reduce

174
Q

using mean titre to find mr

A

1) calculate mean titre
2) concentration x mean titre = moles
3) mass / moles = mr

175
Q

calculate mass

A

mr / (avogadros x 1000)

176
Q

identify the white precipitate and calculate the percentage mass of MgCl2 in the power

A

1) identify what precipitate is formed
2) find moles of BaSO4
3) find mass of BaCl2
4) (mass of powder - mass of BaCl2) / mass of powder

177
Q

suggest a reason for the difference between calculated value and experimental value

A

solution was not heated to a constant mass

178
Q

unknown concentration =

A

mol:mol value / initial volume

179
Q

true or false -> always balance the equation before doing any calculation

A

true

180
Q

finding X of a hydrated salt

A

X(18) / X(18) + CuCl2

181
Q

total area in a titre

A

0.05 x 3 = 0.15

182
Q

percentage uncertainity from gradient

A

(best gradient - worst gradient) / best gradient

183
Q

percentage increase and decrease

A

increase (new - old) / old

decrease (old - new) / old

184
Q

adding titre uncertainties

A

change in a + change in b for both volumes and the uncertainity

185
Q

line of best fit

A
  • are the data likely to be following an underlying equation (for example, a relationship governed
    by a physical law)? This will help decide if the line should be straight or curved
  • are there any anomalous results?
  • are there uncertainties in the measurements? The line of best fit should fall within error bars, if
    drawn.
    There is no definitive way of determining where a line of best fit should be drawn. A good rule of
    thumb is to make sure that there are as many points on one side of the line as the other. Often the
    line should pass through, or very close to, the majority of plotted points. Graphing programs can
    sometimes help, but tend to use algorithms that make assumptions about the data that may not be
    appropriate.
    Lines of best fit should be continuous and drawn as a thin pencil that does not obscure the points
    below and does not add uncertainty to the measurement of gradient of the line.
    Not all lines of best fit go through the origin. Students should ask themselves whether a 0 in the
    independent variable is likely to produce a 0 in the dependent variable. This can provide an extra
    and more certain point through which a line must pass. A line of best fit that is expected to pass
    through (0,0), but does not, would imply some systematic error in the experiment. This would be a
    good source of discussion in an evaluation.
186
Q

gradient

A

equation of straight line = y=mx+c

m = gradient
c = y-intercept
y = DV
x = IV

187
Q

to find x in hydrated salts

A

divide moles by the smallest number of moles

188
Q

errors using gas syringe

A

*gas escapes before bung inserted
*syringe sticks
* some gases like carbon dioxide or sulphur dioxide are
soluble in water so the true amount of gas is not
measured.

189
Q

air bubble in jet

A

incorrect readings

190
Q

no rinsing

A

. If it is not rinsed out the acid or alkali added may be
diluted by residual water in the burette or may react with
substances left from a previous titration. This would lead to
the concentration of the substance being lowered and a larger
titre being delivered.

191
Q

why is a conical flask better than a beaker

A

A conical flask is used in preference to a beaker because
it is easier to swirl the mixture in a conical flask without
spilling the contents.

192
Q

distilled water in titrations

A

Distilled water can be added to the conical flask during a titration to wash the
sides of the flask so that all the acid on the side is washed into the reaction
mixture to react with the alkali.
It does not affect the titration reading as water does not react with the reagents
or change the number of moles of acid added.

193
Q

manganate redox reaction (purple to colourless)

A

MnO4-(aq) + 8H+ (aq) + 5Fe2(aq) –> Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)

dilute sulphuric acid is used

194
Q

if 10cm portions are titrated from 100cm3 total multiply answer of moles by 10

A

same for 25cm3 in 250cm3 total
multiply by 10

195
Q

percentage by mass

A

calculated mass / given total mass

196
Q

mol to mol ratio for metal ions

A

1:1

197
Q

enthalphy change from experimental data

A
  1. Using q= m x cp x T calculate energy change for quantities used
  2. Work out the moles of the reactants used
  3. Divide q by the number of moles of the reactant not in excess to give H
  4. Add a sign and unit (divide by a thousand to convert Jmol-1
    to kJmol-1
198
Q

q=mct for neutralisation

A

mass = vol of acid + vol of base

199
Q

Strontium and barium salts will not form a hydroxide precipitate on addition of
sodium hydroxide due to their high solubility. The solutions will be highly alkaline

A

also draw the filter paper when drawing a filtration diagram

200
Q

time of flight calculations

A

distance = t x square root 2Ke/ m

time = d x square root m / 2Ke

201
Q

state why it is good practice to rinse the pipette in this way

A

so titration can be done with a known concentration of NaOH

202
Q

2 lone pairs on oxygen molecule

A
203
Q

Shape of ClF4-

A

square planar

204
Q

shape of POCl3

A

tetrahedral

Aqa a level chemistry (19 decks)

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