Principles Of Chemistry

Question 1

What are the three states of matter?

Answer 1

• solid
• liquid
• gas

Question 2

What three things determine how strong the forces of attraction are between particles of a material?

Answer 2

• the material
• the temperature
• the pressure

Question 3

Describe the arrangements, movement and energy of the particles in a solid

Answer 3

• in solids, there are strong forces of attraction between particles, holding close together in fixed positions to form a very regular lattice arrangement
• particles don’t move from their positions, so all solids keep a definite shape and volume and don’t flow
• particles vibrate about their positions. They vibrate more when it becomes hot and expands

Question 4

Describe the arrangements movement and energy of the particles in liquids

Answer 4

• in liquids, there is a weak force of attraction between particles.
• they are randomly arranged and free to move past each other but they tend to stick closely together
• they have a definite volume but don’t keep a definite shape; will flow to fill the bottom of container
• particles are constantly moving with random motion. The hotter it gets, the faster they move, causing them to expand slightly

Question 5

Describe the arrangements movement and energy of the particles in gases

Answer 5

• in gases, the force of attraction between the particles is very weak
• they’re free to move and are far apart. Particles travel in straight lines
• gases don’t keep a definite shape or volume and will always fill an container
• particles move constantly with random motion. The hotter the gas gets, the faster they move.
• they either expand when heated or their pressure increases

Question 6

What are the names for the interconversions of solids, liquids and gases?

Answer 6

• solid to liquid = melting (energy is supplied)
• solid to gas = subliming (energy is supplied)
• liquid to gas = evaporating (energy is supplied)
• liquid to solid = freezing (energy is given out)
• gas to liquid = condensing (energy is given out)

Question 7

What happens when substances change from one state to another?

Answer 7

• when a solid is heated, its particles gain more energy
• this makes the particles vibrate more, which weakens the forces that hold the solid together. this makes the solid expand
• at a certain temperature, the particles have enough energy to break free from their positions. This is called melting and the solid turns into a liquid
• when a liquid is heated, the particles gain even more energy
• this energy makes the particles move faster, weakening and breaking the bonds holding the liquid together.
• at a certain temperature, the particles have enough energy to break their bonds. This is evaporating and the liquid turns into a gas.

Question 8

What is diffusion?

Answer 8

• the gradual movement of particles from places where there are lots of them to places where there are fewer.

Question 9

What does potassium manganate (VII) and water show?

Answer 9

• diffusion
• if you take a beaker of water and place some potassium manganate at the bottom, the purple slowly spreads out to fill the beaker
• the particles are diffusing out
• random motion of particles causes the purple colour to eventually be evenly spread out through the water
• adding more water would dilute it, as particles spread further apart

Question 10

What does ammonia (NH3) and hydrogen chloride (HCl) show?

Answer 10

• diffusion speeds of gases
• a white ring of ammonium chloride will form in the glass tube
• the NH3 gas diffuses from one end of the tube and the HCl gas diffuses from the other. When they meet they react to form ammonium chloride
• It forms nearest the end of the tube where hydrochloric acid was
• the particles of ammonia are smaller and lighter than the particles of hydrochloric acid, so they diffuse through the air more quickly

Question 11

What does bromine gas and air show?

Answer 11

• bromine gas is a brown, strongly smelling gas
• fill half a gas jar full of bromine gas, and the other half full of air, separated with a gas plate
• when you remove the glass plate, the bromine gas will slowly diffuse through the air
• random motion of the particles means that the bromine will eventually diffuse right through the air

Question 12

What are all substances made up of?

Answer 12

• atoms

Question 13

What is the nucleus?

Answer 13

• the middles of the atom
• it contains protons and neutrons
• it has a positive charge because of the protons
• almost the whole mass of the atom is concentrated in the nucleus
• size wise it is tints compared to the rest of the atom

Question 14

What are electrons?

Answer 14

• they move around the nucleus in energy levels called shells
• they’re negatively charged
• they’re tiny, but cover a lot of space
• the size of their orbits determines how big the atom is
• they have virtually no mass

Question 15

What are the relative masses and relative charges of protons, neutrons and electrons?

Answer 15

• Relative Mass:
  • Proton = 1
  • Neutron = 1
  • Electron = 1/2000
• Relative Charge:
  • Proton = +1
  • Neutron = 0
  • Electron = -1
• therefore, protons are heavy and positively charged, neutrons are heavy and neutral and electrons are light and negatively charged

Question 16

What is the charge on electrons relative the the charge in protons?

Answer 16

• the same size as the charge in protons but opposite

- this means the number of electrons always equals the number of protons in a neutral atom

Question 17

What happens if some electrons are added or removed?

Answer 17

• the atom becomes charged and is then an ion

Question 18

What is the atomic number?

Answer 18

• it tells you how many protons there are

Question 19

What do atoms of the same element have the same number of?

Answer 19

• protons

Question 20

How do you deduce the number of neutrons?

Answer 20

• subtract atomic number from mass number

Question 21

What are molecules?

Answer 21

• groups of atoms
• atoms can join together to form molecules
• some molecules are made from just one element, others more than one
• molecules are held together by covalent bonds

Question 22

What are elements?

Answer 22

• elements consist of one type of atom only

Question 23

What are compounds?

Answer 23

• a compound is a substance that is made of two or more different elements which are chemically joined/bonded together
• such as carbon dioxide is a compound
• it is very difficult to separate the two original elements again

Question 24

What are mixtures?

Answer 24

• unlike a compound, there’s no chemical bond between the different parts of a mixture
• they can be separated out by physical methods
• air is a mixture
• crude oil is a mixture of different length hydrocarbon molecules

Question 25

What is filtration?

Answer 25

• filtration can be used if your product is an insoluble solid that needs to be separated from a liquid reaction mixture
• it can be used in purification as well. Solid impurities in the reaction mixture can be separated out using filtration
• filter paper folded in a cone shape

Question 26

What is crystallisation?

Answer 26

• used to separate a soluble solid from a solution
• pour the solution into an evaporating dish
• slowly heat the solution. Some of the solvent will evaporate and the solution will be more concentrated
• stop heating when crystals form
• remove the dish from heat and leave in a warm place for the solvent to slowly evaporate
• dry the product in a drying oven or a desiccator

Question 27

How do you separate rock salt?

Answer 27

• it’s a mixture of salt and sand
• you need filtration and crystallisation
• grind up the rock salt
• dissolve in a beaker and stir
• filter through filter paper in a funnel
• evaporate in an evaporating dish to let it crystallise

Question 28

What is chromatography?

Answer 28

• separates mixtures

- departed dyes

Question 29

How do you do paper chromatography?

Answer 29

• draw a line near the bottom of a sheet of filter paper with a pencil
• add spots of different dyes to the line at regular intervals
• loosely roll the sheet up and put it in a beaker of solvent e.g. water
• put a lid to stop solvent evaporating
• the solvent seeks up the paper, carrying dyes with it
• each different dye will move up the paper at a different rate
• a chromatogram is made

Question 30

How does chromatography separate mixtures?

Answer 30

• different dyes move up the paper at different rates

- the higher it travels up, the more soluble the dye is

Question 31

What is the Rf value?

Answer 31

Rf value = a/b = distance travelled by the ‘spot’ / distance travel by the solvent

• use the centre of spot
• draw a solvent line

Question 32

What is distillation used to separate?

Answer 32

• mixture that contain liquids

Question 33

Describe simple distillation

Answer 33

• used to separate out a liquid from a solution
• heat the solution in a side-arm flask. the part of the solution that has the lowest boiling point will evaporate
• the vapour is then cooled, condenses in the condenser and is collected
• the rest of the solution is left behind the flask
• however, can only be used with things that have very different boiling points

Question 34

Describe fractional distillation

Answer 34

• used to separate a mixture of liquids
• put your mixture in a flask and out a fractionating column (filled with glass rods) on top. then heat it
• the different liquids all have different boiling points, so they will evaporate at different temperatures
• the liquids with the lowest boiling point evaporates first. when the temperature on the thermometer matches the boiling point of this liquid, it will reach the top of the column
• liquids with higher boiling points might also start to evaporate. but the column is cooler towards the top, so they will only get part of the way up before confessing and running back down
• when the first liquid has been collected, you raise the temperature until the next one reaches the top

Question 35

What are the vertical columns in a period table called?

Answer 35

• groups

Question 36

What do electrons always occupy?

Answer 36

• shells (also called energy levels)

Question 37

What energy levels/shells are always filled first, closest to the nucleus?

Answer 37

• the lowest energy levels

Question 38

Why would an atom react?

Answer 38

• when the atom is not full

Question 39

What are isotopes?

Answer 39

• different atomic forms of the same element, which have the same number of portions, but different numbers of neutrons

Question 40

What is relative atomic mass?

Answer 40

• the relative atomic mass of an element is the weighted average mass of the isotopes of the element. It is measured on a scale on which a carbon-12 atom has a mass of exactly 12 units