topic 4 - chemical changes

Question 1

how to measure the pH

Answer 1

• indicator - changes colour
• pH probe attatched to a pH meter

Question 2

acids

Answer 2

• pH less than 7
• form H+ ions in water

Question 3

base

Answer 3

• pH greater than 7
• alkali is a base that dissolves in water
• alkalis form OH- ions in water

Question 4

neutralisation reaction equation

Answer 4

acid + base –> salt and water

Question 5

apparatus to titration

Answer 5

• pipette - volume of solution
• burette - drop by drop
• concile flask

Question 6

what colour will titration go

Answer 6

• phenolphthalein is pink in alkali
• colourless in acid

Question 7

how to increase accuracy of titration

Answer 7

• do a rough titration first so that when you know roughly where it will change colour then you can do much smaller and closer intervals
• remove anomalous results
• repeat multiple times

Question 8

strong acids

Answer 8

• ionise completely in water
• all particles dissociate to release H+ ions

Question 9

weak acids

Answer 9

• don’t fully ionise
• small amounts dissociate and release H+ ions
• equilibrium lies to the left

Question 10

the science behind what the pH is a measure of

Answer 10

the concentration of H+ ions in a solution

Question 11

what is the strength of an acid

Answer 11

what proportion of the acid molecules ionise in water

Question 12

what is the concentration of an acid

Answer 12

how much acid there is in a certain volume of water
- the larger amount of acid - the more concentrated

Question 13

equation for neutralisation reaction of metal oxides and metal hydroxides

Answer 13

acid + metal oxide —> salt + water
acid + metal hydroxide —> salt + water

Question 14

equation for the reaction of metal carbonates

Answer 14

acid + metal carbonate —> salt + water + carbon dioxide

Question 15

reactivity series

Answer 15

Potassium
Sodium
Lithium
Calcium
Magnesium
Carbon
Zinc
Iron
Hydrogen
Copper

Question 16

how are metals ordered in the reactivity series

Answer 16

how easily they can loose electrons to form positive ions

Question 17

which metals react with water and equation

Answer 17

potassium, sodium, lithium, calcium
metal + water —> metal hydroxide + hydrogen

Question 18

what happens when metals react with acids

Answer 18

create a salt and produce hydrogen gas

Question 19

whats oxidation and reduction

Answer 19

oxidation: gain of oxygen - loss of electrons
reduction: loss of oxygen - gain of electrons

Question 20

which metals can be extracted from carbon and which from electrolysis

Answer 20

• higher than carbon = electrolysis - ££££££
• below carbon = by reduction using carbon

Question 21

whats a redox reaction

Answer 21

oxidation and reduction happening at the same time

Question 22

definition of a displacement reaction

Answer 22

a more reactive metal displacing a less reactive metal from its compound

Question 23

basics of electrolysis

Answer 23

• electrcial current passed through electrolyte and their ions move toards the electrodws where they react and the compound decomposes

Question 24

anode and cathode in ELECTROLYSIS

Answer 24

POSITIVE ANODE (loss electrons and get oxidised)
NEGATIVE CATHODE (gain electrons and be reduced)

Question 25

why CANT an ionic solid be used in electrolysis

Answer 25

- bc the ions are fixed and cant move - solution - molten ionic compound bc ions can move freely and conducts electricity

Question 26

how is aluminion extracted during electrolysis - molten

Answer 26

aluminion has to be extracted from its ore bauxite by electrolysis 1. aluminion oxide mixed with cryolite to lower melting point - molten mixture - conduct electricity 2. positive Al3+ go to negative cathode and gain 3 electrons and sink to bottom of tank 3. negative O2- ions go to positive anode and lose 2 electrons which then combine to form O2 molecules

Question 27

word and chemical equation for electrolysis of aluminion

Answer 27

aluminion oxide ---> aluminion + oxygen

Question 28

electrolysis of aqueous solutions - what happens at the cathode and anode

Answer 28

- CATHODE - if H+ ions and metal ions are present then HYDROGEN GAS will form if more reactive than hydrogen. if less reactive than hydrogen a solid layer of pure metal will be produced instead - ANODE - if OH- and halide ions are present then chlorine/bromine/iodine will be formed. if no halide ions are present then the OH- ions are discharged and oxygen will form- bubbles

Question 29

what ions are there in water

Answer 29

H+ and OH-

Question 30

half equation for electrolysis at cathode - aluminion

Answer 30

Al3+ + 3e- ---> Al

Question 31

half equation for electrolysis at anode - oxygen

Answer 31

2O2- ---> O2 + 4e-