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(A-level) Chemistry > Module 2.1 > Flashcards

Module 2.1 Flashcards

1
Q

What is relative atomic mass

A

The average mass of 1 atom of an element relative to 1/12th the mass of a carbon 12 atom

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2
Q

How do you calculate relative atomic mass

A

(sum of the mass × abundance of each isotope) ÷ total abundance

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3
Q

How can you check if your calculated Ar is accurate

A

You can check your calculated value to the accurate periodic table value ( which is compared to 1/12th a carbon atom)

If your calculation is an average of the isotopes you calculated with it could be accurate

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4
Q

What is relative molecular mass

A

The average mass of one molecule relative to 1/12th the mass of a carbon-12 atom

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5
Q

How do you calculate mR (relative molecular mass)

A

-Count the number of atoms in the element
-Multiple the ar of each element by the number of times it is present in the molecule

  • add all the calculated values together
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6
Q

How do you calculate moles (using mr)

A

Moles = mass / mr

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7
Q

What is Avogadros constant

A

A constant to show the number of particles in 1 mol

6.02×10²³

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8
Q

How do you calculate the number of particles in a molecule

A

Particles = moles × avogadros constant ( 6.022×10²³)

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9
Q

How do you calculate the number of atoms in a molecule

A

First find the number of particles in the molecule

Then multiply by the number of atoms in the molecule

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10
Q

How to calculate the number of protons / electrons in a set mass of a molecule

A

First find the number of particles in the molecule. (Moles × avogadros constant)

Then multiply by the number of atoms, to find the number of atoms

Finally multiply by the atomic number

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11
Q

Calculating the number of protons in a molecule example

How many protons in 6.0g of nitrogen gas

A

N² = 14×2 = 28

Moles = 6/28

Particles in molecule = 6/28 × 6.022×10²³

Particles in atom = 2 × 1.290428571×10²³

Number of protons = 2.580857143×10²³ × 7. (7 is the atomic number/
= 1.8066×10²⁴

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12
Q

What is concentration

A

The number of particles in a given volume

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13
Q

What are the two main units of concentration

A

Mol/dm³

g/dm³

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14
Q

Formula for moles using concentration

A

Moles = concentration × volume

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15
Q

How do you convert cm³ to dm³

A

Divide the cm³ by 1000

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16
Q

What is the relative charge and relative mass of an electron

A

Charge = -1
Mass = 1/1836 th the mass of a proton

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17
Q

What is the relative charge and relative mass of a proton

A

Charge = +1

Mass = 1

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18
Q

What is the relative charge and relative mass of a neutron

A

Charge = 0

Mass = 1

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19
Q

What is the actual charge on a proton / electron

A

± 1.60217733×10–¹⁹ C

(±1.6×10-¹⁹)

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20
Q

What the overall charge of an atom

A

0 (it is neutral)

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21
Q

Where is the majority of an atoms mass

A

In the nucleus ( where protons + neutrons are located)

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22
Q

What is the atomic number

A

Number of protons and electrons

It is always smaller than mass number

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23
Q

What is the mass number

A

The total mass in an atom (protons + neutrons)

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24
Q

What is an isotope

A

An element with a different number of neutrons

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25
Q

What are cations

A

Positive ions which have fewer electrons that protons

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26
Q

What are anions

A

Negative ions with more electrons than protons

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27
Q

How is the mass of carbon 12 defined

A

It is defined as exactly 12 atomic mass units

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28
Q

What is measured in the relative atomic mass of an element

A

The isotopic mass of each isotope and the abundance of each isotope

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29
Q

what is the calculation for concentration

A

c = n/v

(n = moles or grams , v = volume in dm3)

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30
Q

What is water of crystallisation

A

Water molecules (often seen as crystals) surrounding a metal compound or salt

It means these molecules are hydrated

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31
Q

How do you calculate percentage purity

A

(pure mr / impure mr) x 100

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32
Q

How do you find moles of water, from knowing the percentage of water in a hydrated substance

e.g k2CO3 . xH2O
it is 11.5% water

A

k2CO3 = 138.2 mr

100 - 11.5 = 88.5% potassium carbonate

H20 = 18

88.5 / 139.2 = 0.640376
11.5 / 18 = 0.63889

0.640376 / 0.63889 = 1.002326
= 1
so there is 1 mol of water

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33
Q

How do you find moles of water, from knowing the percentage of water in a hydrated substance

A

Find the percentage mass of each substance

Find the mr of each substance

Divide the percentage mass by the mr to find the moles

Divide the moles by each other to find the molar ratio

34
Q

What is atom economy

A

A measure of how efficiently atoms are used up in a chemical reaction

35
Q

how do you calculate atom economy

A

(mr of desired product / mr of reactants) x 100

36
Q

How do you calculate the mol of a gas at room temperature and pressure

A

mol = volume / 24dm3
n = v/24

the volume and gas constant (24dm3) have to be in the same unit s

37
Q

What is the ideal gas pressure equation

A

pV = nRT

p is pressure (in Pa)
v is volume (m³)
n is the number of moles
R is the gas constant - 8.314 J
/mol / k
T is the temperature (K = c° + 273k)

38
Q

when is the ideal gas equation used

A

When gases are in the ‘ideal’ state.

  • in continuous motion
  • Do not experience any intermolecular forces
    -Exert pressure when they collide
    -Kinetic energy increases with temp
    -The sizes are ignored
39
Q

What is a standard solution

A

A solution of a known concentration

(in mol/dm3)

40
Q

How do you make a standard solution

A

Weigh the mass by difference in a beaker (subtract the mass of the weighing boat from the mass of the weighing boat + substance)

-Fully dissolve the solute in a solvent using a stirring rod to mix

-Transfer the solution to a volumetric flask using a funnel

  • rinse the stirring rod and funnel into the volumetric flask using a beaker
  • Fill the volumetric flask to 250cm³ with the solvent
  • ensure the bottom of the meniscus is at 250cm³
  • Invert the flask several times to mix
41
Q

What is a species (in an equation)

A

The ion, element or compound that takes part in the reaction

42
Q

What is a simple molecule

A

A compound that holds a few atoms together by covalent bonds.

It cant conduct electricity

43
Q

What is a giant structure

A

Where many atoms or ions bond together in a repeating pattern.

e.g Giant covalent structure or ionic compounds

44
Q

Why are giant compounds written using empirical formula

A

As the number of atoms / ions in the structure depends on the size of the crystalline structure

45
Q

What is percentage yield

A

A percentage that shows how much of the product is produced in comparison to its theoretical yield

46
Q

How do you calculate percentage yield

A

(actual yield / theoretical yield) x 100

47
Q

Why is percentage yield not always 100%

A

The reaction may not go to completion (could be in equilibrium)

Side reactions could occur - making byproducts

The reactants might not be pure

48
Q

Why do we use process with higher atom economy

A

A higher atom economy means that less waste will be produced (as the amount of byproducts is lower)

49
Q

What was Ernest Rutherford’s experiment + results

A

They fired alpha particles at a thin sheet of gold foil

Most particles were not deflected
A small percentage were deflected at small angles + some where deflected directly back to the source

This proved the positive charge of an atom (and most of its mass) are concentrated in a central nucleus
Negative electrons orbit the nucleus

50
Q

What was Daltons atomic theory

A

Atoms are tiny particles that make up elements
Atoms cant be divided
All atoms of a given element are the same
Atoms of one element are different to atoms of another element

51
Q

What did he discover / what was J J Tomosons model

A

He found that cathode rays were a stream of particles with:
A negative charge
A very small mass
They could be deflected by magnetic and electric fields

He proposed that atoms were made up of a ‘sea’ of electrons moving in a positive charge
(The plum pudding model)

52
Q

What did Niels Bohr do

A

He altered Rutherford’s model and placed electrons in fixed shells
This prevented them from spiraling into the nucleus

53
Q

What is the value of the gas constant in pv = nRt

A

R = 8.314 J /mol / k

54
Q

What is the difference between isotopes of the same atom

A

They have a different number of neutrons

Therefore they have a different mass number

55
Q

What is mass spectrometry

A

A mass spectrometer is a piece of apparatus which can:

  • Identify an unknown compound
  • Find the relative abundance of each isotope of an element
  • Determine structural information about molecules
56
Q

How does a mass spectrometer work

A

It determines the mass of a molecule / isotope by measuring the mass to charge ratio of ions

It makes substances positive ions which are then separated based on their mass and charge

57
Q

How do you determine relative atomic mass from a mass spectrometer

A

(sum of (percentage abundance × mass : charge) ÷ 100

(The same equation as usual for RAM)

58
Q

What are molecular ions

A

Molecules that are covalently bonded and lose / gain electrons to be ions

E g OH-

59
Q

How do you calculate the moles of a gas at room temperature and pressure

A

Use the equation

Moles = volume ÷ 24dm³

n= v/24

60
Q

What is an acid

A

An acid is a proton (H+) donator
They have a pH of less than 7

All acids contain hydrogen

61
Q

What is a base

A

A proton (H+) acceptor
They are used to neutralise acids

E.g
Metal oxides
Metal hydroxides
Metal carbonates
Metal hydrogen carbonates

62
Q

What is an alkali

A

An alkali is any substance that when dissolved gives a pH greater than 7
They release OH- ions in water

(Any base that is soluble in water is an alkali)

63
Q

What are amphoteric substances

A

Substances that behave as both an acid and bases - they can accept and donate protons

64
Q

How are salts formed

A

Neutralisation of an acid with a base

65
Q

How are titrations carried out

A
  • using a volumetric pipette add a measured volume of one solution into a conical flask
  • add a suitable indicator

-place the other solution in a burette

  • add the solution in the burette into the conical flask until the reaction has been completed (when the indicator changes colour)
  • Repeat more accurately (by droppping the pipette liquid in at a slower place) until you get 3 or more concordant titres

Before using the burette rinse it (using what you will place into the burette) to prevent any reactions from occuring

66
Q

What are the colour changes in phenolphthalein

A

Acid + neutral = colourless
Base = pink

67
Q

What is an oxidation number

A

The number of electrons an atom uses to bind to another atom

68
Q

What are the key rules for oxidation numbers

A

An element in its natural state has an oxidation number of 0

Oxygen has -2 UNLESS IN PEROXIDES

Hydrogen is +1 except in metal hydrides where it becomes -1

In simple ions the oxidation number is the charge of an ion

Combined fluorine is always -1 (e.g CaF2 Ca = 2+ F2 = -2 so F= -1 (except in its natural state)

69
Q

What is a redox reaction

A

A reaction with both oxidation and reduction

70
Q

What is oxidation

A

The loss of electrons

71
Q

What is reduction

A

The gain of electrons

72
Q

What is an oxidising agent

A

The species which gains (accepts) electrons

73
Q

What is a reducing agent

A

The species which loses (donates) electrons

74
Q

What is a half equation

A

An equation showing how the oxidation state of an atom / molecular ion changes

75
Q

How do you write a half equation

A

Balance the equation on each side
Then write the electron difference on the side that is more positive

E.g O2 +4e- → 2O 2-

E.g Li →Li+ + e-

76
Q

How do you balance half equations when oxygen is involved (acidic conditions)

A

Balance the equation

Add H+ to the more negative side and H2O to the positive

Balance the equation

Put the electron difference on the more positive side

77
Q

How do you combine two half equation reactions to create 1 equation

A

Multiply the half equations to have the same number of electrons

The electrons then cancel out

78
Q

How do you create a half equation in cold alkaline conditions

A

First (if oxygen is present)
Balance the equation
Add H+ to the negative side and H2O to the positive
Add the electron difference

Then add OH- to both sides
Balance this with the H+ ions
Add the OH- and H+ on one side to make water
Simplify the water on both sides (one should cancel out)

79
Q

What is Disproportionation

A

When an atom is both oxidised and reduced in a reaction

80
Q

What are the stages to follow in complex mole calculations (calculations where a solution is dissolved, made into a standard solution and titred)

A

Draw out the equations transfers

1) Find the moles in the beaker that has been titred against

2) Divide the moles by the volume in the burette, and multiply by the volume in the volumetric beaker (typically 250)

3) apply the molar ratio

This gives you the moles of the dissolved solution

81
Q

How do you calculate percentage uncertainty

A

(uncertainty × trials) ÷ (absolute value) × 100

The absolute value for titrations is (final - initial)
The uncertainty is the error on the readings

(A-level) Chemistry (7 decks)

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