OCR 21st century chemisty

What tells you that a formula is a compound?

More than one capital letter e.g. H20

What tells you that a formula is a molecule?

More than one of the same atom chemically joined (One capital letter + number) e.g. O2

What tells you that a formula is an atom?

Just one capital letter and no numbers e.g. Fe, Mg, I and C

How can the properties of different states of matter be explained

The particle model

What is conserved during changes of state in chemical reactions

Matter

Name 2 simple techniques for separating mixtures

Filltration and distillation

What are chemical reactions

rearrangements of atoms

How are chemical reactions represented

Formula and equations

What speeds up chemical reactions

catalysts

What takes place during changes of state

energy changes take place

How have plants changed the atmosphere

Plants changed the atmosphere because they use up more CO2 in photosynthesis than they produce in respiration. They also produce more oxygen than they respire so they put more oxygen into the atmosphere which means that other organisms can live and grow.

What evidence about the development of our atmosphere can ancient iron oxide-containing rocks give scientists?

An iron oxide rock cannot form if there is no oxygen, so scientists know that oxygen must have been present on Earth at the time when these iron oxide containing rocks were formed. The date of the earliest iron oxide rock tells scientists the earliest time that oxygen was produced on Earth.

What evidence about the development of our atmosphere can ancient rocks containing iron sulfide (iron pyrites) give scientists?

The presence of iron sulfide in the rock tells scientists that no oxygen was available when it was formed.

Why is Butane harder to turn into gas then propane?

Propane molecules have lower boiling points than Butane molecules. Therefore the force of attraction between Butane molecules is stronger. They are harder to split up/ break down the molecule into gas.

How can you predict the state (Solid, liquid, gas) of a substance?

The substance will be a gas above its boiling point (mark the boiling point on the thermometer) The Substance will be a liquid between the Melting point and the Boiling point. And it will be a solid below the melting point.

Why do substances have different boiling points?

Mention: Forces of attraction; Kinetic energy; liquid-gas when a liquid is heated.

Particles within a substance have a force of attraction between them that varies from substance to substance. The strength of the force of attraction between particles depends on the atoms and molecules that make up the substance. When a liquid is heated the particles, move faster because they have more kinetic energy. Eventually they have enough energy to overcome the attractive forces between particles and can move apart. The substance is then in a gas state

Name the two types of reaction (heat)?

Exothermic and Endothermic

What does the carbon cycle describe?

how carbon is recycled in nature

What elements make up the atmosphere?

78% Nitrogen, 21% Oxygen, 0.9% Argon and 0.03% Carbon Dioxide

How is carbon dioxide produced? What impact does it have?

Carbon dioxide is produced by human activity and has an impact on climate change.

Define potable water

Water that humans can safely drink

Where is surface water collected?

Rivers, lakes streams, ponds and reservoirs

How can groundwater be obtained?

Digging wells, boring into deep underground aquifers (underground layers of water bearing rock). This water is already high quality because it has been filtered naturally through layers of sand and rock. It still needs to be disinfected to kill any harmful organisms.

Define desalination

Removing salt from sea water

Define distillation

A method of separating a mixture of two or more substances with different boiling points

How can you reduce air pollution?

Taking the bus/ walking, Less combustion, Renewable energy sources, solar power, plant more trees, compost, recycle, improve efficiency of engines.

Engineers are continually working on improving the efficiency of engines. What would a more efficient engine mean for the environment?

A more efficient car engine means that a car will burn less fuel to travel the same distance therefore reducing pollutants - also good for car owners as they will have to buy less fuel.

What does a catalytic converter do?

A catalytic converter changes harmful pollutants into less harmful substances. All new cars have catalytic converters fitted into their exhaust systems (They remove nitrogen oxides from exhaust gases).

Define exothermic

An exothermic process transfers energy to its surroundings, making them warmer. (releases heat)

Define endothermic

An endothermic process uses energy from its surroundings, making them cooler. (absorbs heat)

How can you keep track of changes in energy during a chemical reaction?

Energy level diagrams

Describe/ explain an energy diagram

An energy diagram is constructed like a graph, with energy plotted on the vertical axis and the process of the reaction on the horizontal axis. The energy of the reactants is therefore plotted on the left and the energy of the products on the right. Therefore are usually labelled using the left-hand-side and right-hand-side of the balanced equation for the reaction.

How are power stations fueled?

Coal or natural gas

Which fuels are mainly made up of hydrocarbon molecules?

Natural gas, Petrol, Diesel and fuel oil

What happens when the fuels react with Oxygen/ air?

Carbon dioxide and water vapour are formed. These gases also enter the atmosphere.

What is produced if coal or natural gas combust with insufficent O2 (incomplete combustion) ?

Carbon monoxide (CO) and particles of unburnt carbon called particulates.

What else is produced if the fuel contains sulfur impurities?

Sulfur dioxide (SO2) will be released

What do the high temps inside the furnace cause the nitrogen in the air to do?

React to produce nitrogen monoxide (NO). This is an example of a combustion reaction

What is produced when nitrogen monoxide is oxidised further?

Nitrogen oxide (NO2). This is an oxidation reaction. Together notrogen monoxide and and nitrogen oxide are referred to as nitrogen oxides (Nox)

what devices are there in the UK that measure air pollution?

There are automatic instruments around the country that collect air samples, and measure and record the concentration of a range of pollutants. The media summarise the data in reports that may give the day's overall air quality on a number scale or describe it as low, medium or high quality.

Give two reasons why you may get different results if you measure the concentration of nitrogen dioxide in a sample of air several times.

1) You may use the equipment differently

2) There may be differences in the equipment itself

Define 'mean value'

A type of average found by adding up a set of measurements and then dividing by the number of measurements.

Define accuracy

How close a quantitive result is to its true value.

When do scientists believe that oxygen levels rose dramatically - how long ago?

2.3 billion years ago

How was Oxygen first produced?

Photosynthesising bacteria - these bacteria used energy from sunlight to convert CO2 from air into oxygen. This reaction also uses water and produces glucose.

What was this early oxygen thought to have done before it could enter the atmosphere?

Reacted with other substances

What other factors resulted in the release of larger quantities of Oxygen?

developing plants

What process explains the decrease in CO2 levels?

The Carbon cycle

Suggest other factors that decreased CO2 levels?

CO2 removed when it dissolved into oceans. Photosynthesis uses CO2 + water to produce O2 and glucose so an increase in plant life substantially lowers CO2 levels in the atmosphere. When some of these plants died they formed fossil fuels, locking carbon into the ground. CO2 is also locked into the ground by the formation of sedimentary rock, such as limestone.

What is an Exothermic reaction?

An Exothermic reaction gives out energy to the surroundings

What is an endothermic reaction?

An Endothermic reaction absorbs energy/ takes in energy from its surroundings

What is activation energy?

energy needed to start a reaction

What happens during a neutralisation reaction?

An acid and an alkali react to from a salt and water. Most neutralisation reactions are exothermic.

What occurs during a displacement reaction?

A more reactive element displaces a less reactive element in a compound. These reactions generally result in a release of energy - they tend to be exothermic reactions.

What two elements does the atmosphere mainly consist of?

Nitrogen and Oxygen

What percentage of the Earth's atmosphere is Nitrogen?

78%

What percentage of the Earth's atmosphere is Oxygen?

21%

What percentage of the Earth's atmosphere is Argon?

0.9%

What percentage of the Earth's atmosphere is Carbon Dioxide?

0.037% / 0.04%

What other gases can be found in the Earth's atmosphere?

Water vapour and other noble gases in addition to Argon. Methane, Helium.

State two things that happen during a chemical reaction.

Atoms are rearranged. Bonds between atoms break and the atoms change places. The atoms from the reactants rearrange themselves to form different chemicals.

State the forces of attraction for the three states.

Solids = Strong forces of attraction between particles. Liquids = Weaker, Gases= almost none

Describe the arrangement of the three states

Solids = close/ fixed structure. Liquids = randomy arranged/ generally close together. Gas = Free to move/ far apart.

Describe the movement of the three states

solid= vibration, Liquid= constant random movement. Gas = constant random movement

Describe the four changes of state

Solid -> liquid = melting; liquid -> solid = freezing; Liquid ->Gas = Boiling; gas -> = condensing

What state is a substance if its Melting point is above the temperature?

solid

What state is a substance if its boiling point is below the temperature?

Gas (if the temp is between the two points)

What is produced in incomplete combustion?

Carbon monoxide and particulate Carbon is produced when incomplete combustion occurs.

Why is carbon dioxide useful?

Carbon dioxide is useful because it needs to be present for photosynthesis to occur.

What dissolves in water to create Nitric acid?

Nitrogen oxide. (this is corrosive)

Why are carbon Particulates bad?

When it lands it clings to buildings and causes respiratory problems. Particulate carbon is also called soot.

How is Nitrogen oxide made?

Nitrogen oxide is made up when Nitrogen and Oxygen react in the exhausts of cars

Do particles in solids move?

No they vibrate

Do particles in gases have the least amount of energy?

No they have the most energy, particles in solids have the least.

Are gases always single particles that move around on their own?

Not always they sometimes move compounded together

Which state has more energy: Liquids or Solids?

Liquids

Are liquid particles arranged in a set pattern?

no

Do gases move around by a process called osmosis

No (diffusion)

Explain the four steps of waste water treatment

1) Screening: This removes large solids

2)Settlement: Solid material settles to the bottom of large tanks.

3) Aeration and biological treatment: Bacteria break down remaining organic matter. Aeration provides oxygen for the bacteria.

4) Final settlement: Any remaining fine patterns are allowed to settle to the bottom of the tank. A final filtration stage can make water even cleaner.

Explain the four steps in the treatment of surface water

1) Screening: This removes large solids like leaves and plastics.

2) Clarification: Water is left in large tanks which allows solid matter to settle to the bottom. Chemicals may be added to encourage solid particles to clump together making it easier for them to sink making the water cleaner.

3) Filtration: Any very small particles remaining suspended into the water are left behind in the filter as the water passes through.

4) Disinfection: Chlorine is added to kill any microorganisms in the water. This is called chlorination.

What does the formula of a molecule show?

The number of atoms

What does a molecular formula look like? What does it show?

CH4 (methane) and it shows the number and type of atoms in a molecule

What does a displayed formula look like and what does it show?

It shows the atoms and the covalent bonds in a molecule.

What is the chemical formula for:

Water; Ammonia; Carbon Dioxide; Hydrogen; Chlorine and Oxygen

Water: H2O; Ammonia NH3; Carbon Dioxide; CO2; Hydrogen: H2; Chlorine: Cl2; Oxygen: O2

What do ionic compounds form?

Giant ionic lattices

What does the formula of an ionic compound tell you?

The ratio of the elements in the compound

What is the written ratio for NaCl?

One Chloride atom for every Sodium atom: 1:1

What is the written ratio for MgCl2?

Two chloride atoms to every one Magnesium atom 2:1

What do chemical equations show?

chemical changes

Suggest what a word equation looks like

Methane + Oxygen -> Carbon dioxide + Water

Suggest what a symbol equation looks like

2Mg + O2 -> 2MgO Shows the symbols or formulas of the reactants and products