Chemical changes

Question 1

What is the ph scale?

Answer 1

measure of how acidic or alkaline a solution is

goes from 0 - 14

Question 2

what does a lower ph of a solution mean?

Answer 2

it is more acidic

Question 3

what does a higher ph of a solution mean?

Answer 3

it is more alkaline

Question 4

What does ph 7 mean?

Answer 4

it is a neutral substance (e.g pure water)

Question 5

What is a indicator?

Answer 5

its a dye that changes colour depending on whether its above or below a certain Ph

Question 6

What is a Ph probe?

Answer 6

used to measure Ph electronically by being attached to a Ph Meter. given in a numerical value

Question 7

What is an acid?

Answer 7

a subtance that forms aqueous substances with a pH of less than 7 . Accids form H+ ions in water.

Question 8

What is a base?

Answer 8

a substance with a pH greater than 7

Question 9

what is an alkali?

Answer 9

a base that dissolved in water to form a soltuion with a pH greater than 7. Alkali forms 0H- ions in water.

Question 10

What is the reaction between acides and bases called?

Answer 10

neutralisation

Acid + base –> salt + water

Question 11

What can neutralistation between acids and alkalis be seen in terms of h+ and OH- ?

Answer 11

H+(aq0 + OH- ( aq ) –> H20 (l)

Question 12

What happens when a acid neutralises a base?

Answer 12

the products are neutral ( pH of 7)

Question 13

What is universal indicator?

Answer 13

used to estimate the pH of a solution because it can turn a variety of colours.

Question 14

What is titration?

Answer 14

a method of analysing the concentration of solutions.allows you to find out exactly how much acid is needed to neutralise a quantity of alkali - or vice versa.

Question 15

What does litmus show?

Answer 15

red in acids , blue in alkalis

Question 16

what does methyl orange show?

Answer 16

yellow in alkalis , red in acids

Question 17

what does phenolpthalein show?

Answer 17

pink in alkalis , colourless in acids.

Question 18

What does a strong acid do in water?

Answer 18

ionises completely , all acid particles dissociate to realease H+ ions.

Question 19

What does a weak acid do in water?

Answer 19

do not fully ionise in solution. Only a small proportion of acid particles dissociate to realse H+ ions

Question 20

What happens if the concentration of H+ ions is higher?

Answer 20

the rate of reaction will be faster, so strong acids will be more reactive than weak acids of the same concentration.

Question 21

What happens for every decrease of 1 on the pH scale?

Answer 21

the concentration of H+ ions increases by a factor of 10

Question 22

Forumla for factor H+ ion concentration changes by

Answer 22

10^-x X is the different in pH

Question 23

what is the difference between strong acid and concentrated acids?

Answer 23

strength tells you what proportion of the acid molecules ionise in water , concentration measures how much acid there is in a certain volume of water.

Question 24

Example of bases.

Answer 24

metal oxides , metal hydroxides , metal carbonates

Question 25

What is the reactivity series?

Answer 25

a list of metals in order of their reactivity towards other substances.

Question 26

How is the reactivity of a meatl determined?

Answer 26

how easily they lose electrons - forming positive ions.

Question 27

the reactity series example

Answer 27

page 55

Question 28

forumla of how metals react with acids

Answer 28

acid + metal –> salt + hydrogen

Question 29

Forumla of how metals react with water

Answer 29

Metal + water —> Metal Hydroxide + Hydrogen

Question 30

What is a reaction that seperates a metal from its oxide called?

Answer 30

Reduction reaction

Question 31

What is oxidation?

Answer 31

Gain of oxygen
e.g magnesium is oxidised to make magnesium oxide
2Mg + 02 –> 2MgO

Question 32

What is reduction?

Answer 32

Loss of oxygen
e.g copper is reduced to copper
2CuO + C —> 2Cu + CO2

Question 33

About the reactivity series ( Reduction)

Answer 33

Metals higher than carbon have to be extracted using electrolysis
Metal below carbon can be extracted by reduction using carbon

Question 34

What does OIL RIG mean? ( electron wise)

Answer 34

Oxidation Is Loss, Reduction is gain

Question 35

What is displacement?

Answer 35

involves one metal kicking another one out of a compound.

A more reactive metal will displace a less reactive metal from its compound.

Question 36

Example of displacement.

Answer 36

Fe + CuSO4—> FeSO4 + Cu
iron + copper sulfate —> iron sulfate + copper

the iron loses 2 electrons to become a 2+ ion- its oxidised
the copper ion gains these 2 elecrtons become a copper atom - its reduced.

Question 37

What does electrolysis mean?

Answer 37

splitting up with electricity

Question 38

What happens during electrolysis?

Answer 38

an electric current is passed through an electrolyte. The ions move towards the elctrodes , where they react, and the compound decompeses .The positive ions wil move towards the cathode ( negative electrode) and gain electrons(they are reduced).The negative ions in the electrolyte will move towards the anode (positive electrode) and lose electrons .(they are oxidised)
they form the uncharged element and are discharged from the electrolyte.

Question 39

What is an electrolyte?

Answer 39

a liquid or solution that can conduct electricity.

Question 40

What is an electrode?

Answer 40

a solid that conducts electricity and is submerged in the electrolyte.

Question 41

Why can’t ionic solids be electrolysed?

Answer 41

they are in fixed positions and can’t be moved.

Question 42

How can metals be extracted from their ores using electrolysis?

Answer 42

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