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Higher Chemistry > Important things to remember > Flashcards

Important things to remember Flashcards

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1
Q

What elements in the periodic table are monatomic?

A

The noble gases - Helium, Neon, Argon, Krypton, Xenon and Radon

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2
Q

Which elements are covalent molecular?

A

Diatomic elements - Cl, Br, O, H, N, I, F
P4, S8 and fullerenes (eg C60)

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3
Q

What are examples of covalent networks?

A

Boron, Carbon (diamond, graphite) and Silicon

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4
Q

What is a covalent bond?

A

A covalent bond is when atoms are held together by electrostatic forces of attraction between the negatively charged shared pair of electrons and the positively charged nuclei.

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5
Q

What is an ionic bond?

A

An ionic bond is an electrostatic attraction between the positive ions of one element and the negative ions of another element.

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6
Q

What are London Dispersion Forces?

A

LDFs are forces of attraction that can operate between all atoms and molecules. They are formed as a result of electrostatic attraction between temporary and induced dipoles caused by movement of electrons in atoms and molecules.

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7
Q

What are permanent dipole-dipole interactions?

A

Permanent dipole-dipole interactions are additional electrostatic forces of attraction between polar molecules.

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8
Q

What is hydrogen bonding?

A

Hydrogen bonding occurs between hydrogen and O, N or F. These strongly electronegative elements pull the electrons away from the Hydrogen resulting in a positive charge on the Hydrogen atom.

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9
Q

What is unusual about ice?

A

Ice is less dense than water. When water freezes, hydrogen bonds between the molecules hold them away from each other forming an open structure with a lower density than expected.

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10
Q

Where can you find the best oxidising and reducing agents?

A

Reducing agents at the top right corner and Oxidising agents at the bottom left corner

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11
Q

What are some examples of oxidising agents?

A

Hydrogen peroxide (H2O2), permanganate ions (MnO4) and dichromate ions (Cr2O7)

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12
Q

What is an example of a reducing agent?

A

Carbon Monoxide (CO)

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13
Q

Some uses of oxidising agents?

A

They can kill fungi and bacteria and inactivate some viruses. Oxidising agents are ideal for bleaching hair or clothing.

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14
Q

What is the covalent radius?

A

Half the distance between the nuclei of 2 covalently bonded atoms of the same element.

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15
Q

Are bond breaking and bond making endothermic or exothermic?

A

Bond breaking is ENDOTHERMIC
Bond making is EXOTHERMIC

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16
Q

What is ionisation energy?

A

The energy require to remove one mole of electrons from one mole of gaseous atoms

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17
Q

What is electronegativity?

A

A measure of the attraction an atom involved in a bond has for the shared pair of electrons in the bond.

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18
Q

Does an exothermic reaction have a positive or negative enthalpy change?

A

Negative

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19
Q

Does an endothermic reaction have a positive or negative enthalpy change?

A

Positive

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20
Q

What is the formula used to calculate the heat energy released?

A

Eh = cm Δ T

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21
Q

What is the enthalpy of combustion?

A

The enthalpy of combustion of a substance is the enthalpy change when one mole of the substance burns completely in oxygen.

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22
Q

What is Hess’s Law

A

Hess’s Law states that the enthalpy change for a chemical reaction is independent of the path taken to transform the reactants into products.

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23
Q

What is the molar bond enthalpy?

A

The energy required to break one mole of bonds in a diatomic molecule. The mean molar bond enthalpy is the average energy required to break one mole of bonds if it occurs in numerous compounds.

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24
Q

What are the requirements for a reaction to occur?

A
  • Particles must collide with each other
  • Particles must have energy greater than the activation energy
  • They must collide with the correct alignment.
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25
Q

What is relative rate?

A

1/ the time taken for the reaction

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26
Q

How does a higher concentration affect a reaction?

A

There are more reactant particles in a given volume which means that more collisions will take place among them.

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27
Q

How does surface area affect a reaction?

A

If particle size is smaller, there is a large number of particles on the surface of the solid that are able to take part in collisions.

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28
Q

How does increasing temperature affect a reaction?

A

Temperature is a measure of the average kinetic energy of the particles in a substance. Increasing temperature means that the particles have a greater kinetic energy and are more likely to have energy above the activation energy.

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29
Q

How does increasing pressure affect a reaction?

A

Pressure is a measure of how often gas particles collide with the walls of the container. If pressure is increased, there will be more reacting particles in a given volume which means more collisions will take place which increases reaction rate.

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30
Q

What is the activation energy?

A

The minimum energy required by the colliding particles to form an activated complex.

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31
Q

What is an activated complex?

A

An unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction.

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32
Q

What does a catalyst do?

A

It lowers the activation energy which means that more particles have sufficient energy to successfully collide. They increase reaction rate without getting used up.

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33
Q

What are some factors influencing industrial design?

A
  • Availability, sustainability and cost of feedstocks
  • Opportunities for recycling
  • Energy requirements
  • Marketability of by-products
  • Product yield
34
Q

What are some environmental considerations?

A
  • Minimising waste
  • Avoiding the use or production of harmful substances
  • Products that can biodegrade
35
Q

What is the atom economy?

A

The proportion of the total mass of all starting materials converted into the desired product

= mass of desired product / total mass of reactants x 100

36
Q

What is the molar volume?

A

The volume occupied by one mole of any gas at a certain temperature or pressure. It is the same for all gases at the same temperature and pressure.

37
Q

What is equilibrium?

A

When the rate of the forward reaction = the rate of the reverse reaction. The concentrations of the products and reactants remain constant.

38
Q

How does temperature affect the equilibrium?

A

High temperatures favour the endothermic reaction and low temperatures favour the exothermic reaction

39
Q

How does pressure affect the equilibrium?

A

High pressures favour the side with the least moles of gaseous atoms and low pressures favour the side with the most moles of gaseous atoms.

40
Q

How does a catalyst affect the equilibrium?

A

It has no effect on the position of equilibrium but allows equilibrium to be established faster.

41
Q

How are esters formed?

A

Condensation reactions between alcohols and carboxylic acids with the elimination of water.

42
Q

Some uses of esters?

A

In flavourings, medicine, industrial solvents and fragrances

43
Q

What chemicals are used in condensation reactions?

A

Concentrated sulphuric acid acts as a catalyst and sodium hydrogen carbonate neutralises the solution.

44
Q

What is hydrolysis?

A

When a molecule reacts with water to break down into smaller molecules.

45
Q

What are fats and oils and why are they important?

A

Esters consisting of glycerol and 3 long-chain fatty acids. They act as a concentrated source of energy and are essential for the transport and storage of fat-soluble vitamins in the body.

46
Q

What is the difference between fats and oils?

A

Oils have a higher degree of unsaturation than fats. This means that fats can pack together more closely and their intermolecular forces are stronger. Therefore fats have higher melting points than oils.

47
Q

How do you test for unsaturation?

A

By titrating different fats and oils with bromine solution. The one that can decolourise the largest volume of bromine has the highest degree of unsaturation.

48
Q

How can oils be converted into fats

A

By hydrogenation in the presence of a nickel catalyst. This reduces the degree of unsaturation in an oil. It can also be called ‘hardening’.

49
Q

How are soaps made?

A

Fats and oils undergo alkaline hydrolysis using an alkali such as sodium hydroxide.

50
Q

What are soaps?

A

Sodium salts of fatty acids

51
Q

Key structure of soaps and detergents?

A

They have a hydrophobic tail that dissolves in grease and oil and a hydrophilic head which dissolves in water.

52
Q

How is grease removed by soaps?

A

Agitating the grease with soap and hot water causes the balls to break up into ball-like structures. The hydrophobic tails dissolve in the grease whilst the anionic hydrophilic heads remain in the surrounding water on the surfaces of the micelles. These negatively charged micelles repel each other which allows them to be suspended in the water.

53
Q

What is hard water?

A

Water with a high concentration of dissolved metal ions such as Ca and Mg

54
Q

What is the difference between soaps and detergents?

A

Detergents are synthetic and don’t form scum with hard water like soaps do.

55
Q

What is an emulsion?

A

An emulsion contains small droplets of one liquid dispersed in another liquid.

56
Q

What does an emulsifier do?

A

It prevents polar and non-polar liquids from separating into layers.

57
Q

What is the structure of an emulsifier?

A

They consist of glycerol bonded to only one or two fatty acids which leaves free hydroxyl groups. The hydroxyl groups can dissolve in polar substances like water and the fatty acids can dissolve in non-polar substances.

58
Q

How are proteins made?

A

The condensation reaction between lots of amino acids

59
Q

What are the functional groups present in an amino acid?

A

amino group (-NH2) and a carboxyl group (-COOH)

60
Q

What are essential amino acids?

A

Amino acids that must be acquired from our diet because our bodies don’t produce them.

61
Q

What happens when proteins are heated?

A

They denature. When proteins denature in food it can change the texture when cooked.

62
Q

What is the link called between amino acids?

A

Peptide link (-HNCO)

63
Q

How can tertiary alcohols be separated from primary and secondary ones?

A

They can’t be oxidised using hot copper oxide or acidified dichromate solutions

64
Q

What do primary alcohols become when oxidised?

A

Aldehydes

65
Q

What do secondary alcohols become when oxidised?

A

Ketones

66
Q

Can aldehydes be oxidised further and what is a key feature of them?

A

Yes they oxidise to become carboxylic acids and they are tend to be flavour and aroma molecules.

67
Q

How can you differentiate between an aldehyde and a ketone?

A

By using oxidising agents:

Fehling’s solution - changes from blue to a brick red precipitate
Tollins’ reagent - forms a silver mirror from colourless
Acidified dichromate - orange to green

68
Q

What are the colour changes of copper oxide and acidified dichromate?

A

Copper oxide - black to brown solid
Acidified dichromate - orange to green

69
Q

What causes foods to taste unpleasant?

A

Compounds may react with oxygen in the air and undergo oxidation. The oxidation of edible oils can give food a rancid flavour.

70
Q

What is an antioxidant?

A

A molecule that prevents unwanted oxidation reactions occurring as it is easily oxidised in place of the compounds it has been added to protect.

71
Q

What are major components in the smell and flavour of food?

A

Essential oils.

72
Q

What are essentials oils and what can they be used for?

A

They are complex mixtures of volatile, non water-soluble molecules extracted from plants which have a characteristic aroma.

73
Q

Methods used to extract essential oils?

A

Steam distillation and solvent extraction

74
Q

What are terpenes?

A

They are key components in most essential oils. They are built by joining together isoprene units. (C5H8) They can be oxidised in plants to produce terpenoids which are some of the compounds responsible for distinctive aromas of spices.

75
Q

What are the effects of UV light?

A

It can cause sunburn and accelerates the aging of skin because it can provide enough energy to break bonds within molecules.

76
Q

What are free radicals?

A

Atoms or molecules that are highly reactive due to the presence of unpaired electrons.

77
Q

What are the 3 stages of free radical chain reactions?

A

Initiation, propagation and termination

78
Q

What are free radical scavengers?

A

Molecules that react with free radicals to form stable molecules and terminate chain reactions. They are electron donators.

79
Q

How do we protect ourselves from UV?

A

By wearing sunblock

80
Q

What is chromatography?

A

A technique used to separate the components present within a molecule.

81
Q

How does chromatography work with amino acids?

A

Amino acids are colourless so they are dyed with ninhydrin.

Higher Chemistry (1 decks)

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