Principles of Chemistry

Question 1

define solution

Answer 1

mixture formed from a solvent & solute where the solute is present as individual particles

Question 2

define solute

Answer 2

the substance/solid that has been dissolved in a solvent to make a solution

Question 3

define solvent

Answer 3

the liquid that makes up most of the volume of a solution (the solute is dissolved into the solvent)

Question 4

define soluble & insoluble

Answer 4

the substance dissolves into the solvent to form a solution

the substance does not dissolve into the solvent to form a solution

Question 5

define saturated solution

Answer 5

a solution where no more solute can be dissolved into the solvent at that specific temperature

Question 6

define solubility

Answer 6

the mass of a solute that will dissolve in a specific mass of solvent

Question 7

describe a method to investigate the solubility of a solid in water at a specific temperature

Answer 7

1. measure 100cm3 water (with measuring cylinder) & pour into beaker - it has mass 100g
2. put the beaker in a warm water bath to heat the water to a desired temperature & keep the temperature constant (measure with thermometer)
3. measure 100g of solute (with a mass balance) and put into another beaker
4. add one spatula of the solute to the water & stir using a glass rod
5. continue to add spatulas of solute & stir until no more solute dissolves
6. subtract the final mass of the solute left in the beaker from the original 100g to calculate the mass of the solute that dissolved
7. repeat 3 times at that temperature & repeat at different temperatures of water e.g. 20C, 30C, 40C, 50C, 60C, 70C

Question 8

what is the formula that links moles, volume & concentration?

Answer 8

mol = vol x conc

Question 9

what is the formula that links moles & volume for a gas?

Answer 9

mol = vol(dm3) / 24

Question 10

describe the bonding in a metal

Answer 10

giant 3d lattice of positive metal ions surrounded by a sea of delocalised electrons

Question 11

why do metals conduct electricity?

Answer 11

delocalised electrons are free to move through the structure, carrying charge

Question 12

why are metals malleable?

Answer 12

layers of positive metal ions can slide over each other

Question 13

why do metals have high melting points?

Answer 13

a lot of thermal energy is needed to overcome strong electrostatic forces of attraction between positive metal ions and negative delocalised electrons

Question 14

why do covalent compounds not conduct electricity?

Answer 14

they do not contain free moving ions or delocalised electrons that can carry charge

Question 15

why can ionic compounds only conduct electricity when molten or in aqueous solution?

Answer 15

in solids, ions are held in fixed positions so cannot move, carrying charge

when molten or aqueous, ions are free to move carrying charge

Question 16

what is a cation & an anion?

Answer 16

cation - positive ion
anion - negative ion

Question 17

what is current & in wire & solution?

Answer 17

flow of electrons or ions
wire: flow of electrons
solution: flow of ions

Question 18

why can graphite conduct electricity?

Answer 18

it has free-moving delocalised electrons between the layers of carbon atoms as each carbon atom forms 3 covalent bonds (1 electron per C atom can move)

Question 19

what is an electrolyte?

Answer 19

a substance that conducts electricity when dissolved in water or molten

Question 20

describe a method to tell if a substance is an electrolyte or non-electrolyte

Answer 20

1. set up a circuit containing a battery, bulb & inert graphite electrodes dipping in the liquid
2. turn circuit on
3. if substance is an electrolyte, it conducts electricity so the bulb lights

Question 21

describe a method to investigate the electrolysis of aqueous solutions

Answer 21

1. set up a circuit with a power supply, crocodile clips, wire & inert electrodes
2. half fill a beaker with the liquid & place electrodes into the beaker so they do not touch each other
3. turn on power pack to 3V & leave for 2 mins
4. record observations during the experiment

Question 22

what happens to cations & anions during electrolysis?

Answer 22

cations gain electrons to form elements
anions lose electrons to form elements

Question 23

what happens to molten salts during electrolysis?

Answer 23

cations:
positive metal ions are attracted to the negative electrode (cathode) because opposite charges attract
cations gain electrons so are reduced to form metal elements

anions:
negative non-metal ions are attracted to the positive electrode (anode) because opposite charges attract
anions lose electrons so are oxidised to form non-metal elements

Question 24

what happens to aqueous solutions during electrolysis?

Answer 24

positive metal ions & H+ ions are attracted to the negative electrode
the less reactive (b/w metal & H) is reduced to form an element

negative non-metal ions & OH- ions are attracted to the positive electrode
if a group 7 ion is present then it is oxidised to form the group 7 element but if no g7 present, oxygen is produced

Question 25

why do positive graphite electrodes need to be replaced at regular intervals?

Answer 25

carbon in graphite reacts with oxygen to form CO2
so replacing electrodes prevents them from disappearing