c5 - chemical changes

Question 1

where are most metals found and what has happened to them?

Answer 1

• most found as compounds in rocks
• many have been oxidised (had oxygen added to them)

Question 2

how do we extract metals?

Answer 2

reduction - remove oxygen

Question 3

define an ore

Answer 3

rocks that contain enough of a metal or a metal compound to make it economically worthwhile to extract the metal

Question 4

define the reactivity series

Answer 4

list of metals in order of their reactivity, most reactive metals at top and least reactive metals at the bottom

Question 5

what can the most reactive metals do?

Answer 5

form positive ions most easily

Question 6

how does the group 1 react with water?

Answer 6

react vigorously giving off hydrogen gas and leaving alkaline hydroxide solutions e.g potassium + water -> potassium hydroxide + hydrogen

Question 7

how does magnesium metal react with cold water?

Answer 7

• very slowly
• less reactive metals such as copper do not react at all with water

Question 8

what is produced when metals react with water or dilute acid?

Answer 8

hydrogen gas

Question 9

what is produced when metals such as magnesium react with acids?

Answer 9

a salt and hydrogen gas

Question 10

how can we judge the relative reactivity of magnesium zinc and iron?

Answer 10

by the rate at which metal gives off hydrogen gas

Question 11

learn main reactions with water and dilute acids

Answer 11

also skipped page 5.2

Question 12

define oxidation (electrons)

Answer 12

loss of electrons

Question 13

define reduction (electrons)

Answer 13

gain of electrons

Question 14

what factors contribute to whether it is worth extracting a particular metal?

Answer 14

• how easy it is to extract it from its ore
• how much metal the ore contains
• changing demand for the metal

Question 15

what form is gold and some other metals found in?

Answer 15

• unreactive
• found as metal
• can be separated from rocks by physical methods

Question 16

how are other metals extracted?

Answer 16

by chemical reactions

Question 17

how can you extract metals less reactive than carbon?

Answer 17

heating with carbon
- reduction reaction because carbon removes the oxygen from the oxide to produce the metal

Question 18

give an example of displacement using carbon

Answer 18

lead oxide + carbon - heat -> lead + carbon dioxide

Question 19

how are metals more reactive than carbon extracted?

Answer 19

electrolysis of the molten metal compound

Question 20

what metals will acids react with?

Answer 20

metals that are above hydrogen in the reactivity series

Question 21

what does an acid + metal produce?

Answer 21

a salt + hydrogen

Question 22

what are salts produced from hydrochloric acid?

Answer 22

chlorides

Question 23

what are salts produced from sulfuric acid acid?

Answer 23

sulfates

Question 24

what are salts produced from nitric acid?

Answer 24

nitrates

Question 25

define a redox reaction

Answer 25

a reaction in which both oxidation and reduction occur

Question 26

what ions do salts contain?

Answer 26

positive metal ions (or ammonium ions) and a negative ion from an acid

Question 27

how do you work out the formula of salts?

Answer 27

1) get the formula of the ions
2) figure out what needs to happen to balance these chargesto be neutral - salts are neutral

Question 28

what happens when an acid reacts with a base?

Answer 28

a neutralisation reaction takes place, a salt and water is produced

Question 29

what does an acid + base produce?

Answer 29

a salt + water

Question 30

why do you add excess of the base when making a salt?

Answer 30

to ensure all the acid has reacted

Question 31

how are soluble salts made?

Answer 31

by reacting an acid and an alkali

Question 32

what does an acid + an alkali produce?

Answer 32

salt + water

Question 33

what do you use to show reaction between an acid + alkali is complete?

Answer 33

use indicator or a pH meter

Question 34

how can the solid salt be obtained from the solution?

Answer 34

crystallisation

Question 35

how else are soluble salts made?

Answer 35

reacting an acid and a carbonate

Question 36

what does an acid + carbonate produce?

Answer 36

a salt + water + carbon dioxide

Question 37

what does calcium carbonate + hydrochloric acid produce?

Answer 37

calcium chloride + water + carbon dioxide

Question 38

what is powdered limestone used for?

Answer 38

to raise pH of acidic soils or lakes affected by acid rain, making use of the reaction between calcium carbonate and acid

Question 39

what is the pH of pure water?

Answer 39

7, neutral

Question 40

define acids

Answer 40

substances that produce hydrogen ions when they are added to water

Question 41

define an aqueous solution

Answer 41

when you dissolve a substance in water

Question 42

define bases

Answer 42

• react with acids and neutralise them
• metal oxides and metal hydroxides are bases

Question 43

define alkalis

Answer 43

• bases that dissolve in water to make alkaline solutions
• they are soluble hydroxides and produce hydroxide ions

Question 44

what happens in aqueous solutions?

Answer 44

hydrochloric acid ionises completely to hydrogen ions and chloride ions

Question 45

define strong acids

Answer 45

those which ionise completely in aqueous solutions

Question 46

what happens when ethanoic acid dissolves in water?

Answer 46

does not ionise completely, some of the ethanoic acid molecules remain as molecules in the solution

Question 47

what conditions are equilibrium reached in aqueous solutions?

Answer 47

when both whole molecules and their ions are present in the solution

Question 48

define weak acids

Answer 48

those which do not ionise completely in aqueous solutions

Question 49

how do strong and weak acids act in aq solutions of equal concentration?

Answer 49

weak acids have a higher pH and react more slowly than strong acids

Question 50

what happens when hydrochloric acid ions increase by a factor of 10?

Answer 50

pH value decreases by one unit