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Chemistry AS OCR > 2.1 > Flashcards

2.1 Flashcards

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1
Q

The changing atom

What was the first step of understanding the atom?

A
  • The Greek philosoper Democritus developed the first idea of the atom.
  • He suggested you could divide a sample of matter only a certain number of times.
  • Eventually he believed you would end up with a particle that could not be split any further.
  • He called this particle átomos
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2
Q

What was the second stage of understanding the atom?

A

In the 1800s, John Dalton developed his atomic theory.

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3
Q

What was Daltons atomic theory?

A
  • atoms are tiny particles that make up elements
  • atoms cannot be divided
  • all atoms of a given element are the same
  • atoms of one element are different from those of every other element
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4
Q

What else did Dalton do apart from his atomic theory?

A

Dalton used his own symbols to represent atoms of different elements. He also developed the first table of atomic masses.

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5
Q

What discovery came after Dalton?

A
  • 1897 - 1906 (you dont need to know exact dates for the changing atom)
  • Joseph John (J.J.) Thompson descovers electrons.
  • Scientists had recently discovered cathode rays, which were emitted from cathode ray tubes.
  • Thompson discovered that cathode rays were a stream of particles with the following properties.
  1. They had a negative charge
  2. They could be deflected by both a magnet and an electric field.
  3. They had a very, very small mass.
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6
Q

What did J.J Thompson conclude?

A

Cathode rays were, in fact, electrons. Thomson concluded that they must have come from within the atoms of the electrodes themselves. The idea that an atom could not be split any further, proposed by ancient Greeks and by dalton, had ben disproved.

  • Thomson prposed that atoms are made up of negative electrons moving in a sea of positive charge
  • The overall negative charge is the same as the overall positive charge.
  • It is often referred to as the plum pudding model.
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7
Q

When was an advancement made on the plum pudding model?

A

1909-11 - Ernest Rutherford’s gold leaf experiment

In 1909, Rutherford and to of his students, Hans geigner and Ernest Mardsten, carried out an experiment where they directed alpha-particles towrads a sheet of very thin gold foil. They measured any deflection (change in direction) of the particles. Rutherford calculated that a plum-pudding atom would hardly deflect alpha particles at all.

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8
Q

What were the results of Ernest Rutherfords’s gold-leaf experiment?

A
  1. Most of the particles, as expected, were not defelected at all.
  2. However, a small percentage of particles were deflected through large amgles.
  3. A very few particles were actually deflected back towards the scource.
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9
Q

What did Ernest Rutherford propose in 1911 based on their results?

A
  • The positive charge of an atom and most of it’s mass are concentrated in a nucleus, at the centre.
  • Negative electrons oribit this nucleus, just as planets orbit the sun,
  • Most of an atom’s volume would be the space between the tiny nucleus and the orbiting electrons.
  • The overall positive chrage and neagative charges must balance.
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10
Q

What discovery came after the gold-leaf experiment

A

1913 - Niels Bohr’s planetary model and Henry Moseley’s work on atomic numbers

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11
Q

Describe Niels Bohr’s planetary model.

A

In 1913, the Danish physicist Niels Bohr altered Rutherford’s model to allow electrons to follow only certain paths. Otherwise electrons would spiral into the nucleus. This was the planetary atom, inwhich electrons orbited a central nuclear ‘sun’ in shells.

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12
Q

What did Bohr’s model help to explain?

A

Some periodic properties such as;

  • spectral lines in the emission spectra
  • the energy of electrons at different distances from the nucleus.
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13
Q

What did Henry Moseley discover to help our understanding of the atom?

A

In the same year as Bohrs discovery, Henry Moseley discovered a link between X-ray frequencies and an elements atomic (i.e. its order in the periodic table). At the time, moseley couldn’t explian this.

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14
Q

What discovery towards understanding the atomic number happened after Henry Moseley and Niels Bohr’s discovery?

A

1918 - Rutherford discovers the proton

Rutherfords discovery of the proton was able to explain Moseley’s finding that an atom’s atomic number was lined to X-ray frequencies. We now know that the atomic number tells us the number of protons in an element’s atom.

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15
Q

What discovery towards understanding the atomic number happened after rutherford discovers the Proton?

A

In 1923, the french physicist Louis de Brogile suggested that an electron had wave-like propertiesin an atom. He also introduced the idea of atomic orbitals.

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16
Q

What discovery towards understanding the atomic number happened after Louis de Brogile’s suggestion?

A

In 1926, the Austrian physicist called Erwin Schrödinger suggested that an electron had wave-like properties in an atom. He also introduced the idea of atomic orbitals.

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17
Q

What discovery towards understanding the atomic number happened after wave and particle behavior suggestions?

A

1932 - James Chadwick discovers the neutron.

James chadwick - and English physicist - observed a new type of radiation emmitted form some elements. He showed that this new type of radiation was made up of uncharged particles with approximately the same mass as a proton. These uncharged particles become known as neutrons, because they have no charge.

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18
Q

Describe the understanding of the atom in moden day.

A

It is now thought that protons and neutrons themselves are made up of even smaller particles called quarks. Our understanding of the atom is likely to progress with time as science advances futher and further.

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19
Q

What is the order of scientists in discovering the atom?

A
  1. fifth century - Democritus
  2. early 1800’s - Dalton
  3. 1897-1906 - J.J.Thomson
  4. 1909-11 - Ernest Rutherford
  5. 1913 - Niels Bohr
  6. 1913 - Henry Moseley
  7. 1918 - Rutherford
  8. 1923 - Louis de Brogile
  9. 1926 - Erwin Schrödinger
  10. 1932 - James Chadwick
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20
Q

What are ions?

A

Many atoms react by loosing or gaining electrons to form charged particles called ions. Ions are charged because they have unbalanced numbers of protons and electrons, and so the charges no longer cancel each other out.

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21
Q

Does the existence of isotopes effect reactions?

A

Chemical reactions involve electrons, neutrons make no diference to chemical reactivity.

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22
Q

What is relative isotopic mass?

A

is the mass of an atom of an isotope compared with one-twelfth of the mass of an atom of carbon-12. (for an isotope the relative isotopic mass is the same as the mass number. (for an isotope the relative isotopic mass is the same as the mass number)

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23
Q

What is the relative atomic mass?

A

is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12. (most elements contain a mixture of isotopes, chemists combine the contribution from each isotope to arrive at the relative atom mass. )

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24
Q

What is relative molecular mass?

A

The mass of a molecules is measured as the relatrive molecular mass by comparason with carbon-12. You can find the relative molecular mass by adding together the relative atomic masses of each atom making up a molecule.

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25
Q

What is the relative formula mass?

A

Compounds with giant structures do not exist as simple molecules. You can find the relative formula mass by adding togther the relative atomic masses of each atom making up a formula unit.

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26
Q

What equation links amount of substance and the mole?

A

m=MXn

You can have a mole of any chemical species

Molar masses can be applied to any chemical substance.

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27
Q

What is a mass spectrometer used for?

A
  1. to identify an unkown compound
  2. to find the relative abundance of each isotope of an element
  3. determine structual infomation about molecules
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28
Q

How does a mass spectrometer dertermine mass?

A

A mass spectrometer determines the mass of a molecule by measuring it’s mass to charge ratio. it does this by causing the substances to become a positive ion.

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29
Q

How do you calculate relative atomic mass from a mass spectrum of isotopes of an element?

A
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30
Q

How do you calculate relative abundance from a mass spectrum?

A

% mass of isotope = total height of isotope A / height of all isotopes } X 100

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31
Q

What atoms do not normally form ions?

A

Atoms of Be, B, C, and Si do not normally form ions because they require too much energy to transfer the outer shell electrons to form ions.

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32
Q

What are molecular ions?

A

Groups of covantly bonded atoms can also loose or gain electrons to form ions, they are molecular ions. (NH4+)

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33
Q

Can elements form more than one charge?

A

Some elements can form more than one ion, each with a different charge, such as iron (II) for Fe2+ and iron (III) for Fe3+.

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34
Q

What is Advogadros hypothesis?

A

In 1811, Advogadro put forward his hypotheis which stated that under the same conditions of temperature and pressure, a mole of any gas will fill the same volume of space.

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35
Q

What equations do you use to calculate amounts using gas volumes?

A

n = V (in dm3) / 24

n = V (in cm3) / 24,000

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36
Q

The ideal gas equation, gasses are assumed to behave in an ideal way, what is the ideal way?

A
  • they are in continuous motion and do not experience any intermolecular forces
  • they exert pressure when they collide with each other and the walls of the containers
  • all collisions between gas molecules and between gas molecules and the container wealls are elastic - they do not cause kinetic energy to be lost.
  • the kinetic energy of gasses increases with increasing temperature
  • gas miolecules are so small compared to the size of the container they are found in that any differences in sizes os gas molecules can be ignored (they can be imagined as indenticle perfect spheres.
37
Q

What is the ideal gas equation?

A

pV = nRT

  • Where p is pressure
  • V is volume
  • n is the number of moles
  • R is the gas constant, with a value of 8.314 J mol-1 K-1
  • T is temperature
38
Q

What are the units for the ideal gas equation?

A
  • pressure - pascal 1 atm = 101325 Pa
  • volume - cubic metres 1m3 = 1000 dm3
  • temperature - kelvin OoC = 273 K
39
Q

Describe concentration.

A

The concentration of a solution tells you how much solute is dissolved in a given amount of solvent. In a solution with a concentration of 2 moles of solute dissolved in every 1 dm3 of solution.

40
Q

What equation links moles, concentration and volume?

A

n = CXV (in dm3)

n = C X V (in cm3) / 1000

41
Q

How do you make a standard solution?

A

1. Weigh out a solute

  1. Dissolve solute in a beaker - transfer to a volumetric flask washing repreatedly
  2. fill the flask to the graduation line
  3. invert the flask
42
Q

What is the mass concentration of a solute?

A

The mass dissolved in 1 dm3 of solution.

43
Q

What is the equation for percentage yeild?

A

Percentage yeild = actual amount, in mol, of product / theoretical amount, in mol, of product X 100

44
Q

What does atom economy take into account?

A

Atom economy considers not only the desired product, but also all the by-products of a chemical reaction. It describes the efficiency of a reaction in terms of all the atoms involved. A reaction with high atom economyuses atoms with minimal waste.

45
Q

What happens to waste products?

A

By products are often considered as waste and have to be disposed of. This is costly, poses me enviromental problems and wastes resources. By-products may be sold on or used elsewhere in the chemical plant.

46
Q

What is the chemical equation for atom economy?

A

Atom economy = molecular mass of the desired product / sum of molecular masses of all products X 100

47
Q

What reactions have an atom economy of 100%?

A

Addition reactions have an atom economy of 100%.

48
Q

What reactions always have an atom economy of less than 100%?

A

Reactions involving subsistution or elimination have an atom economy of less than 100%.

49
Q

What is the formula of sulphuric acid?

A

H2SO4

50
Q

Hydrochloric acid?

A

HCl

51
Q

Nitric acid?

A

HNO3

52
Q

Ethanoic acid

A

CH3COOH

53
Q

Give one short definition of a an acid

A

A proton donor

H2SO4(l) + H+(aq) HSO4-(aq)

54
Q

What is the difference between stong and weak acids?

A

Strong acids almost fully dissociate whereas weak acids only partially dissociate.

  • Concentrated - a large amount of solute per dm3.
  • Dilute - a small amount of solute per dm3

2 mol dm-3 and 2M mean the same thing, but use 2 mol dm-3.

55
Q

What is a species?

A
  • A species is a type of particle that takes part in a reaction
  • A species could be an atoom, ion, molecule, empiricle formula or electron
56
Q

What is a compound with a giant structure represented by?

A

Its empiricle formula

57
Q

How can you work out moles from mass?

A

n=m/M

58
Q

How can you work out moles from gas volumes?

A

n = V (in dm3) / 24 or n = V(in cm3)/24000

59
Q

Why may a 100% yeild not be achieved?

A
  • The reaction may not go to eqilibrium
  • Side reactions may occur, leading to by-products
  • The reactant may not be pure
  • Some of the reactanats or products may be left behind in the apparatus used in the experiment.
  • Separation and purification may result in the loss of some of the by-products
60
Q

What is a salt?

A

A salt is an ionic compound

  • The positive ion or cation in a salt is usually a metal ion or an ammonium ion, NH4
  • The neagtive ion, or anion, in a salt is derived from an acid
  • The formula of a salt is the same as that of a parent acid except the H+ has been replaced by a parent acid.
61
Q

What salts does sulfuric acid form?

A

H2SO4 forms sulphate salts such as potassium sulfate K2SO4.

62
Q

What salts does hydrochloric acid form?

A

HCl forms sulphate salts for example sodium chloride, NaCl

63
Q

What salts does nitric acid form?

A

HNO3 forms nitrate salts for example calcium nitrate Ca(NO3)2

64
Q

What are acid salts?

A

H2SO4 has two H+ if only one H+ is relaced NaHSO4, sodium hydrogensulphate is created which is an acid salt.

H2SO4 → NaHSO4

NaHSO4 → Na2SO4

Acids with two H+ ions are called diprotic acids.

65
Q

What are the products of acid and carbonate?

A

Acid + carbonate → salt + carbon dioxide + water

66
Q

Give the symbol and ionic equation for an acid + a carbonate.

A

2HCl (aq) + CaCO3 (s) → CaCl2 + H2O + CO2(aq)

2H+ + CaCO3(s) →Cu2+(aq) + H2O(l) + CO2 (g)

67
Q

What are the products of acid + metal oxide?

A

Salt and water

68
Q

What are the symbol equation and ionic equation for acid + a metal oxide?

A

2HCl(aq) + CuO(s) → CaCl2 (aq) + H2O (l) + CO2 (g)

2H+ = CuO → Cu2+ + H2O

69
Q

What are the products of acid + aklali?

A

salt and water

70
Q

What are the symbol and ionic equations for an acid + an alkali?

A

HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)

H+(aq) + OH-(aq) → 2LiCl (s) + H2 (g)

71
Q

What are the products of an acid and a metal?

A

Salt and hydrogen

72
Q

`What is the symbol equation for an acid and a metal?

A

2Li(s) + 2HCl (aq) → 2LiCl(s) + H2 (g)

73
Q

What are ammonium salts?

A

When acids are neutralised by aqueous ammonia, ammonia salts are formed, containing the ammonium ion NH4.

74
Q

What is the symbol equation for the formation of ammonium salts?

A

NH3(aq) + HNO3(aq) → NH4NO3(aq)

75
Q

What is the meaning of hydrated?

A

The crystalline form containing water.

76
Q

What is the meaning of anhydrous?

A

The form containing no water.

77
Q

What is the dot formulae?

A

Empiricle formula of the compund is separated from the water of crystalisation by a dot. The relative number of water molecules is shown after the dot.

78
Q

What is the dot formulae for copper sulfate pentahydrate?

A

5H2O molecules for each formula unit of CuSO4.

CuSO4·5H2O

79
Q

How do you determine the empiricle formula?

A

Once you know how many atoms of each element are present, you can work out which ones are part of water molecules and which ones are part of the main compound.

80
Q

What does the water of crytalisation corrospond to?

A
  • When hydrated salts are heated, the water of crytalisation is driven off by evapouration.
  • The amount of water lost corrosponds to how much water of crystalisation was in the salt sample.
81
Q

How do you calculate empiricle formula of a hydrated salt?

A
  1. First calculate the amount, in mol, of anhydrous MgSO4
  2. Then calculate the amount, in mol, of water
  3. Finally determine the formula of the hydrated salt - work out the molar ratio and divide by the smallest number.
82
Q

What is a titration?

A
  • During volumetric analysis, you measure the volume of one solution that reacts wit a measured volume of a different solution.
  • An acid-base titration is a special type of volumetric analysis in which you react a solution of an acid with a solution of a alkali.
83
Q

Name three indicators and there colours in acid and base.

A
  1. methyl orange - red in acid, yellow in base and orange at its end point.
  2. bromothymol blue - yellow in acid, blue in a base and green at its end point
  3. phenolpthalien - colourless in acid, pink in base and pale pink at its end point
84
Q

How do you calculate an unkown from titration results?

A
  1. The first step is always calculate in mol of the base that reacted n=C X V(in cm3) / 1000
  2. The second step is always to calculate the amount in mol of the acid that was used
  3. Then calculate the concentration in moldm-3 of acid (C= n X 1000(cm3)/V)
  4. The last steps are, to calculate the amount, in mol of HX that was used in the titration
85
Q

What is the oxidation number of an uuncombined element?

A

0, for example C,Na,O2 and P4

86
Q

What are the four types of ionisation energy question?

A
  1. Successive ionisation energy
  2. Down the group
  3. Across the group
  4. Identify the element
87
Q

What do you need to include in successive ionisation energy question?

A

General trend (small)

  • Greater energy required
  • Decreased repulsion
  • Decreased atomic radius

Jumps in energy (large)

  • Less shells
  • less shielding
  • Smaller atomic radius
  • Greater nuclear attraction
  • Greater energy required
    *
88
Q

What do you need to include in an across the period question?

A
  • Atomic number
  • Number of protons
  • Nuclear charge
  • Electrons added to same shell, no change in shielding
89
Q

What do you need to include in a down the group ionisation energy question?

A
  • Greater shells
  • Greater shielding
  • Increasing atomic radius
  • Nuclear attraction decreases
  • Energy required

Chemistry AS OCR (7 decks)

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