Little bits that I need to remember chem

Question 1

What is disproportionation ?

Answer 1

a reaction in which a substance is simultaneously oxidized and reduced, giving two different products.

Question 2

Why do giant covalent bonds have high melting and boiling points?

Answer 2

because their strong covalent bonds must be overcome before they can melt or boil

Question 3

What are the features of a diamond? (3)

Answer 3

• It has a giant, rigid covalent lattice

-All the strong covalent bonds mean that it is a very hard substance with a very high melting point

• there are no charged particles, so it does not conduct electricity

Question 4

What are the features of graphite?

Answer 4

• has a giant covalent structure and a very high melting point
• has layered, hexagonal structure
• layers are held together by weak intermolecular forces so the layers can slide past each other, making graphite soft and slippery
• one electron from each carbon atom is delocalised = allows graphite to conduct heat and electricity

Question 5

Why is graphite soft and slippery?

Answer 5

because the layers are held together by weak intermolecular forces so the layers can slide past each other,

Question 6

What is an element?

Answer 6

An element is a substance made from only one type of atom. Elements cannot be decomposed into simpler substances by chemical means.

Question 7

What is a saturated solution?

Answer 7

A saturated solution is one in which no more solute will dissolve at a given temperature.

Question 8

What is a compound?

Answer 8

A compound is a substance made from different elements bonded together.

Question 9

What is a mixture?

Answer 9

Mixtures (for example, air or tap water) contain more than one element or compound.

Question 10

What are properties of ionic compounds?

Answer 10

Ionic compounds are generally solids at room temperature. They are made of a giant lattice of positive and negative ions. A lattice is a huge, continuous, regular structure.

There is a strong overall electrostatic attraction between all of the positive and negative ions.
This means that ionic compounds have high melting points as it is difficult to overcome the many strong attractions between the positive and negative ions.

do not conduct electricity as solids because the ions cannot move around freely. However, if a compound is melted, it does conduct electricity because the ions can move and carry the charge.

Many ionic compounds dissolve in water and will conduct as a solution because the solvated ions can move to carry the charge.

Question 11

What are the physical properties of group 1

Answer 11

Melting and boiling points – are low for metals and decrease down the group due to an increase in atomic radius = outer electrons less attracted = decrease in metallic strength

Densities – are low for metals and generally increase down the group.

Hardness – they are soft and they become softer down the group. (This is due to decreasing metallic strength

Conductivity – they are good conductors of heat and electricity.

Question 12

What are the chemical properties of group 1 metals

(how reactive they are)

Answer 12

The alkali metals are very reactive. The elements have to be stored in oil to prevent them from reacting with oxygen and water in the air.

When freshly cut and exposed to the air, the shiny metals will quickly react with oxygen and tarnish, forming the metal oxide.

The alkali metals react with non-metals to form ionic compounds.

As Group 1 is descended, the elements become more reactive.

Question 13

Describe group 1 metal reactions with water

Answer 13

When lithium, sodium or potassium are added to cold water, they visibly react.

Lithium, sodium and potassium float on water, moving around on the surface and fizzing.

Hydrogen gas is produced, which burns with a ‘squeaky pop’ sound when ignited.

Potassium reacts so exothermically that the hydrogen produced spontaneously ignites and burns with a lilac flame, characteristic of potassium ions.

A soluble metal hydroxide is also formed, so the resultant solution will be alkaline and have a high pH, which would turn universal indicator blue or purple.

Question 14

Why do group 1 metals become more reactive as you go down the group?

Answer 14

The atomic radii increase as the group is descended.
The outermost electron is an increased distance from the nucleus.
The attraction between the outermost electron and the nucleus decreases as the group is descended.
This is despite there being an increase in nuclear charge

Question 15

What are the physical properties of Group 7 metals

Answer 15

Low melting and boiling points, which increase down the group.

As the halogen molecules get larger down the group, with increasing numbers of electrons within the molecules, the strength of their intermolecular forces increases.

This means that a greater amount of energy is required to break the intermolecular forces and change state. Hence the melting and boiling points increase down Group 17.

Poor conductors of heat and electricity.

Question 16

What are the chemical properties of Group 7 metals?

Answer 16

The reactivity of the halogens decreases as the group is descended.

When the halogens react, their atoms gain an electron. They get less reactive down the group because as the group is descended the atoms get larger, meaning that the incoming electron joins a shell that is at a greater distance from the nucleus. This new electron does not feel as strong a force of attraction to the nucleus despite nuclear charge increasing down the group.

Question 17

Describe the group 7 reactions with alkali metals?

Answer 17

The halogens react vigorously with heated alkali metals to form metal halide salts

Question 18

What are the physical properties of Group 8 metals?

Answer 18

Very low melting and boiling points, which increase down the group.

-Larger “intermolecular” forces that exist between its atoms. The size of the noble gas atoms, and the numbers of electrons present in the atoms, increase down the group, leading to stronger forces between the atoms in the solid or liquid phase. These forces require more energy to be overcome and so the melting/boiling points increase.

The densities of the noble gases increase down the group.

Question 19

Why does more electrons or bigger molecule leads to larger intermolecular forces?

Answer 19

The more electrons you have, and the more distance over which they can move, the bigger the possible temporary dipoles and therefore the bigger the dispersion forces.

Question 20

What are the chemical properties of group 8 (theres only one)

Answer 20

The noble gases have a complete outer shell of electrons, making the atoms very unreactive.

Question 21

What is electrolysis? Describe the principle of it

Answer 21

Electrolysis is the breakdown of an ionic compound using electricity. For electrolysis to occur, the ions need to be mobile. This can be done either by dissolving the ionic compound in water or by melting it. The mixture containing mobile ions is called the electrolyte. A direct current is then applied through the electrolyte using two electrodes.

Positive ions are attracted to the negative electrode (the cathode) and negative ions are attracted to the positive electrode (the anode).

Reduction occurs at the cathode and oxidation occurs at the anode.

Question 22

What happens during the electrolysis of molten binary ionic compounds?

Answer 22

n molten electrolytes, the cation and the anion of the compound are discharged.

Question 23

What are physical processes and name the different types? (8)

Answer 23

Physical processes are used when separating individual elements or compounds from a mixture. All of the techniques rely on there being a difference in a physical property between the substances being separated

• decanting
  -filtration
• fractional distillation
• simple distillation
• funnel
• evaporation and crystallisation
• chromatography
  -centrifugation

Question 24

Describe filtration and when do you use it?

Answer 24

Filtration is used to separate a liquid (or solution) from an insoluble solid. The solid particles are larger and are trapped by the mesh of the filter paper. The smaller liquid particles are able to pass through the filter paper into the collection vessel. This separated liquid is known as the filtrate and the solid is the residue.

Question 25

Describe how to use a separating funnel and when to use it

Answer 25

A separating funnel is used to separate two immiscible liquids. When two immiscible liquids are added to a separating funnel, they form two layers. The upper layer has the lower density. When the tap is opened, the lower layer can be poured out. The narrowing walls of the separating funnel make it easier to close the tap the moment the last drop of the lower layer has passed through.

Question 26

Describe simple distillation and when to use it

Answer 26

is used to separate two substances with differing boiling points. Simple distillation is typically used to separate the solvent from a solution, leaving the solute behind.

The mixture is heated to above the boiling point of the solvent. The solvent becomes a vapour and starts to spread out through the apparatus. As the vapour hits the condenser it cools and condenses as droplets which run down the condenser to the collection vessel. The higher boiling point solute remains in the heated flask. If the solute is stable to heating, it can also be collected once the solvent has been removed.

Question 27

Describe Fractional distillation

Answer 27

Fractional distillation is used to separate miscible liquids (ones soluble in each other) from a mixture. Like simple distillation, fractional distillation requires each liquid to have a different boiling point.

During the distillation, the mixture is heated. When the temperature of the mixture reaches the boiling point of the component with the lowest boiling point, the temperature no longer rises and the first component boils. This lowest boiling point component rises up the fractionating column towards the condenser where it is condensed and collected. The thermometer at the entrance to the condenser monitors the boiling point of the component being distilled.

Question 28

Describe Evaporation and crystallisation and when to use it

Answer 28

used to separate the solvent from a solute and uses the difference in boiling point and/or volatility to separate the mixture.

To separate the solute, the solution is heated gently until crystals just begin to appear. This is the crystallising point. The remaining concentrated solution is then left to evaporate. It’s not sensible to heat to dryness because some solids may decompose if heated too strongly.

Question 29

Describe centrifugation and when to use it

Answer 29

used to separate heterogeneous mixtures based on their differences in particle mass. It can be used to separate mixtures of gases but it is more commonly used to separate solids from liquids or solutions.

If a liquid is mixed with a solid, the solid particles to settle to the bottom of a container as they are more dense than the liquid. When the solid is small or finely divided, random motion and collisions of the particles causes them to settle much more slowly and in some cases they do not settle to the bottom. = this is encouraged by the spinning

(i know everything else from a level bio)

Question 30

Describe Chromatography and when to use it

Answer 30

used to separate mixtures of different solutes, such as dyes in ink, or it can be used to separate mixtures of different liquids.

differences in the relative affinity to the stationary phase of the chromatogram to the mobile phase (the solvent) lead to the separation of the substances.

a small sample of the mixture is spotted on to a piece of chromatography paper. This paper is then placed into a tank or beaker which contains a solvent at the bottom and the lid is replaced. The solvent then rises up the paper by capillary action and through the mixture. The different components each have a different tendency to adsorb to the paper. If the component adsorbs more strongly to the paper (the stationary phase) then it does not travel up as readily.

Question 31

When is decanting used

Answer 31

When there is solid at the bottom of a liquid

Question 32

Why is water always added at the bottom of the leigburg condenser?

Answer 32

to ensure that there is always cold water in the jacket and that condensation occurs all the way along the condenser.

Question 33

What is the formula for the RF value

Answer 33

distance travelled by sample/ distance travelled by solvent

Question 34

What are the important practical features of chromatography that you must remember?

Answer 34

The sample must be placed above the solvent in the tank so that it spreads up with the rising solvent rather than dissolves in the solvent at the bottom.

The position of the sample is marked with a pencil line. Pencil is used because it does not dissolve in most solvents and so does not move. It gives a clear fixed start position for measuring Rf values.

The solvent front should not reach the top of the paper.

A lid is kept on the tank to ensure that the atmosphere in the tank has a saturated solvent vapour. This prevents the solvent evaporating from the paper rather than rising.

Question 35

How do you test for purity in chromatography?

Answer 35

producing one spot ( the substance is using a constant stationary phase and solvent is always the same.)

Question 36

How do you test for purity in distillation

Answer 36

If a liquid starts to boil off at a higher temperature than expected at a particular pressure, this indicates the presence of an impurity.

Question 37

How do you test for purity in evaporation and crystallisation

Answer 37

If a solution is evaporated to dryness, any solid residue is a dissolved impurity.

Question 38

What are the general differences between a pure and an impure compound?

Answer 38

In general, pure substances have definite, sharp melting and boiling points whereas impure substances melt and boil over a range of temperatures.

Question 39

Metal + acid= ?

Metal carbonate + acid =?

metal hydroxide + acid = ?

metal oxide + acid =?

Answer 39

salt + hydrogen

co2 + water + salt

salt + water (same for metal hydroxide and oxide)

Question 40

What is pH?

What happens to the H+ concentration as the pH increases by one unit?

Answer 40

a measure of hydrogen ion concentration in aqueous solution.

decreases by a factor of 10,

Question 41

What is a base?

Answer 41

a substance that can accept H+ ions, or one that has the ability to form OH−(aq) in solution.

Question 42

What are the limitations of bond energies?

Answer 42

Bond energies are average values. This means that values calculated using them are not specific to the molecules used. It is not unusual for the actual (measured) value to have a difference from the calculated value of over 10%.

There is also the limitation that calculating the enthalpy change can only be done for reactions which take place entirely in the gaseous state.

To obtain more accurate values for the enthalpy change of reactions, calorimetry experiments can be used.

Question 43

What are the assumptions made during calorimetry calculations (qmct)

Answer 43

Density of the solution is assumed to be the same as water

the specific heat capacity of solutions is assumed to be the same as that for pure water.

As the water is the major component of the calorimeter and its contents, it can be assumed that only the water has absorbed any heat and that the calorimeter does not absorb any energy.

Question 44

What are the problems faced during calorimetry ?

Answer 44

Incomplete combustion can be a problem
—————–This is especially true when larger molecules are used as the fuel. The ratio of fuel:oxygen is higher for larger molecules and the air is only 21% oxygen. When a fuel does not burn completely, less energy is released.

Heat loss to the surroundings is more likely in this open system
—— closed polystyrene cup prevents, or at least slows, heat loss. In a combustion experiment, heat can be lost before it reaches the calorimeter, and it can also be lost from the calorimeter if not insulated. Heat loss and mass loss from the calorimeter is a more significant problem when the water is allowed to get very hot.

Heat is lost to the calorimeter
The calorimeter in this experiment must be a conductor. Some heat will be absorbed by the calorimeter. This error could be removed by calculating the energy change of the calorimeter as well as the water and adding the values together.

Question 45

The larger the hydrocarbon/ longer the carbon chain length: (4)

Answer 45

• the more viscous it is
• higher its boiling point
• less volatile it is
• less flammable

Question 46

Describe catalytic cracking and why it occurs?

Answer 46

Longer chain hydrocarbons are less useful than shorter chained ones

The longer chain molecules are passed over a heated catalyst and are broken down into shorter chain molecules. There are no particular ways in which the larger molecules are broken down. They are random events producing smaller hydrocarbons, some of which contain carbon-to-carbon double bonds (alkenes).

Question 47

What are the differences between condensation and addition polymerisation

Answer 47

• condesation produces water or HCL whereas additon polymerisation produces no other product
• in an addition polymerisation there is only one type of monomer molecule. However, condensation polymerisation often involves two different types of monomer molecules. Each monomer must have at least two (similar or different) functional groups. This allows it to form linkages at two different positions in the molecule.

Question 48

What are the two main types of condensation polymers?

Answer 48

polyesters and polyamides.

Question 49

What are polyamides?

Draw the condenstion polymerisation equation for polyamides

Answer 49

Polyamides are condensation polymers in which the monomers are joined by amide linkages.

To form an amide linkage the carboxyl group of a carboxylic acid, combines with an amine group, -NH2.

Question 50

Draw an amide linkage

Answer 50

Question 51

What are polyesters?

Draw the condensation polymerisation equation for polyesters

Answer 51

Polyesters are condensation polymers in which the monomers are joined by ester linkages.

To form an ester linkage the carboxyl (COOH) group of a carboxylic acid, combines with a hydroxyl (OH) group of an alcohol

Question 52

Describe the chemical structure of a protein (what chemical groups are they made up of)

Answer 52

Proteins are formed from long chains of amino acids joined by amide linkages (aka peptide bonds). These long chains are then folded into particular shapes to make the protein.

many amino acids = protein which are made up of:
- an amino group (−NH2)
- a carboxyl group (−COOH)
- an organic ‘R-group’ (or ‘side-chain’) that is unique to each amino acid.
- H
- These three groups are bonded to the same (central) carbon atom.

Question 53

Describe what biodegradable polymers are.

Answer 53

Biodegradable polymers break down (degrade) after their intended use to produce such natural products as: CO2, N2, H2O, and so on. The action of microorganisms or enzymes usually brings about this natural breakdown.

Biodegradable polymers often contain ester or amide linkages.

Question 54

Describe what non-biodegradable polymers are.

Answer 54

Non-biodegradable polymers are not broken down after their intended use. Most polymers are of this type and they tend to consist of long chains of carbon and hydrogen atoms. The strong bonding between these atoms makes them resistant to breakdown by microorganisms or enzymes.

Question 55

What is the reactivity series a measure of?

Answer 55

how easily metals lose electrons to form positive ions.

(the easier it can the more reactive it is)

Question 56

Transition metals are the _______ reactive metals

Answer 56

least

Question 57

Why are more reactive metals harder to extract (metals at the top of the reactivity series)

Answer 57

Very reactive metals form stable oxides and other compounds. A lot of energy is needed to reduce them to extract the metal.

Question 58

How are metals below carbon in the reactivity series extracted from ores?

Answer 58

By reducing using carbon or carbon monoxide

Question 59

How are metals more reactive than carbon extracted from ores?

Answer 59

Metals above carbon in the reactivity series cannot be extracted using carbon and therefore must be extracted using electrolysis.

In this process, electricity is used to break down the molten ionic compound into its constituent ions.

The positive metal ions are then attracted to the negative electrode (cathode) where they are discharged by gaining electrons.

Question 60

Why is electrolysis expensive?

Answer 60

because it uses a considerable amount of electrical energy

Question 61

What are examples of cheaper ways of extraction

Answer 61

phytomining (using plants) and bioleaching (using bacteria) have been devised to avoid traditional mining methods involving digging, moving and disposing of large amounts of rock.

Question 62

Why are alloys stronger than pure metals?

Answer 62

the different-sized particles disrupt the structure and prevent the layers from sliding over each other, thereby greatly increasing the strength of the material.

Question 63

Describe why aluminium is useful

Answer 63

• It is soft and malleable.
  -It is corrosion resistant and non-toxic
• Its low density and good electrical conductivity make it useful in conductor cables.
  -When alloyed, aluminium provides high strength and low density

Question 64

Describe why copper is useful

Answer 64

Copper is a good conductor of electricity, so it is ideal for electrical wires.
It’s hard and strong but can be bent.
It is below hydrogen in the reactivity series, so it doesn’t react with water.

Question 65

Why is titanium useful?

Answer 65

Titanium is corrosion resistant, has a low density and is a very strong metal.

Question 66

What’s the deal with transition metals?

Answer 66

usually have more than one oxidation state

transition metals often form coloured compounds.

usually strong with high density, high melting points and are generally unreactive.

Many transition metal particles are similar in size to each other, which makes them particularly suitable for alloying

Question 67

Why are transition metals good catalysts?

Answer 67

• they can form stable ions in different oxidations states

Question 68

What are the main components of air and their percentage in air?

Answer 68

nitrogen 78.1%

oxygen 20.95%

argon 0.9%

carbon dioxide 0.04%

Water vapour and other gases

Question 69

How is fractional distillation used to separate gases in air?

Answer 69

• Air is cooled to −200°C so it becomes liquid
• At this temperature water and carbon dioxide will have solidified – they are removed to prevent them from clogging up the jets used during this process.
• Nitrogen and Oxygen are also liquified at this temperature and are passed into the fractioning column.
• The air is warmed in the fractioning column, and nitrogen boils first, turning into a gas and rising to the top of the fractioning column, condensing there to be collected.
• Oxygen remains liquid whilst nitrogen is boiled off as it has a higher boiling point than nitrogen. It is then released from the bottom of the fractioning column when all the nitrogen has been boiled off.

Question 70

Describe the process of global warming

Answer 70

As the energy from the Sun reaches the Earth, greenhouse gases allow short wavelength radiation, such as ultraviolet and visible light, to pass through, heating the surface of the Earth. As the Earth then cools, it emits longer wavelength radiation, such as infrared radiation.

Greenhouse gases, such as CO2 and CH4, are able to absorb infrared radiation, so some of the energy radiated from the Earth is trapped in the atmosphere and the temperature rises. The higher the proportion of greenhouse gases in the atmosphere, the more energy is absorbed.

Question 71

What human activites has increased the concentration of methane in the atmosphere

Answer 71

cattle farming
rice fields
landfill sites

Question 72

What is CO?
What are common sources of carbon monoxide and how do it harm the environment

Answer 72

Carbon monoxide is a colourless, odourless, poisonous gas.

It binds more strongly to the haemoglobin in the blood than oxygen and greatly reduces the amount of oxygen that the blood can carry around the body.

gas fires used in heating
gas boilers used for heating (water/central heating)
engines in cars and other vehicles

Question 73

What are common sources of carbon dioxide and how does it harm the environment

Answer 73

respiration (by plants and animals)
decay of dead plants or animals
dissolved carbon dioxide escaping from water (mainly sea water)

greenhouse effect, leading to global warming and climate change.

Question 74

What is so2
What are common sources of sulfur dioxide and how does it harm the environment

Answer 74

Sulfur dioxide is a poisonous, colourless, acidic gas with a choking smell.

It reacts with water and oxygen in the atmosphere to produce sulfuric acid, one of the components of ‘acid rain’.

The sulfuric acid in acid rain erodes stonework, increases metal corrosion, increases the leaching of soil (removal of important minerals)

harmful to animal and plant life (especially all forms of marine life).

Sulfur dioxide also causes breathing difficulties and can trigger asthma attacks.

Question 75

What are common sources of oxides of nitrogen and how does it harm the environment

Answer 75

Nitrogen is not very reactive however when the temperatures are very high (e.g. burner units like car engines)

They react with oxygen and water in the atmosphere to generate nitric acid, another component of ‘acid rain’.

They are also toxic gases and can trigger asthma attacks.

Question 76

Why are chlorine and flourine used to produced drinking water?

Answer 76

Chlorine gas is added to water in controlled quantities to sterilise the water as it kills harmful bacteria.

Fluoride ions (for example, in sodium fluoride) may be added to drinking water as fluoride helps protect against tooth decay.