Chemical changes

Question 1

Acids

Answer 1

Acids release hydrogen ions when dissolved in water
Ph is less than 7
Turn blue litmus paper red

Question 2

When acids react with metals

Answer 2

Acid + Metal = Salt + Hydrogen gas

Question 3

When acids react with metal oxides/hydroxides

Answer 3

Acid + base = salt + water

Question 4

When acids react with metal carbonates

Answer 4

Acid + carbonate = salt + water + carbon dioxide

Question 5

Examples of acids

Answer 5

Hydrochloric acid
Sulfuric acid
Nitric acid

Question 6

Bases

Answer 6

Bases are substances that neutralize acids to form salt and water
Bases that dissolve in water are called alkalis and release hydroxide ions

Question 7

Bases properties

Answer 7

Feel slippery
Turn red litmus paper blue
Ph is greater than 7

Question 8

Examples of bases

Answer 8

Sodium hydroxide
Calcium hydroxide
Ammonia

Question 9

Neutralization key reaction

Answer 9

Hydrogen ions + Hydroxide ions = water

Question 10

The Ph scale

Answer 10

Ranges from 0-14
If lower than 7 it is an acid
If 7 it is neutral
If greater than 7 it is an alkaline

Question 11

Strong acids

Answer 11

strong acids completely ionize in water, meaning they fully dissociate into hydrogen ions and their corresponding negative ions

Question 12

Examples of strong acids

Answer 12

Hydrochloric acid
Sulfuric acid
Nitric acid

Question 13

Ph of strong acids

Answer 13

Strong acids usually have a low Ph, (roughly 0-1) as they produce a high concentration of hydrogen ions

Question 14

Weak acids

Answer 14

weak acids partially ionize in water, meaning only a small proportion of their molecules dissociate to release hydrogen ions

Question 15

Examples of weak acids

Answer 15

Ethanoic acid
Citric acid
Carbonic acid

Question 16

Ph of a weak acid

Answer 16

Weak acids have a higher Ph (about 4-6) because they produce fewer hydrogen ions

Question 17

Reaction rates of acids

Answer 17

Strong acid reaction rates are faster with metals/carbonates
weak acid reaction rates are slower with metals/carbonates

Question 18

Conductivity of acids

Answer 18

strong acids higher conductivity
weak acids lower conductivity

Question 19

Strong bases

Answer 19

fully ionize in water to release lots of hydroxide ions

Question 20

Weak bases

Answer 20

partially ionize in water producing fewer hydroxide ions

Question 21

Electrolysis

Answer 21

A chemical process that uses electricity to break down an ionic compound into its element. It occurs in electrolytic cells which contain a liquid or molten electrolyte that conducts electricity

Question 22

Electrolyte

Answer 22

The liquid or molten substance that conducts electricity
It must contain free ions which allow electric current to flow
Examples: molten lead bromine, aqueous solution sodium chloride

Question 23

Electrodes

Answer 23

Cathode (negative electrode): attracts positive ions where reduction occurs
Anode(positive electrode): attracts negative ions where oxidation occurs

Question 24

Reduction

Answer 24

gain of electrons and the loss of oxygen

Question 25

Oxidation

Answer 25

loss of electrons and the gain of oxygen

Question 26

How does electrolysis work

Answer 26

1. Ions in the electrolyte move to the electrodes 2. At the electrodes ions are discharged to form neutral atoms or molecules 3. The products of electrolysis depend on: -nature of electrolyte (molten or aqueous) -Reactivity of ions

Question 27

Electrolysis of aqueous solution (cathode)

Answer 27

Cathode: -if the metal is less reactive than hydrogen the metal is discharged -if the metal is more reactive than hydrogen then hydrogen gas is produced

Question 28

Electrolysis of aqueous solution (anode)

Answer 28

Anode: -if halide ions are present (group 0) they are discharged first - if no halides are present oxygen gas is produced from the hydroxide ions

Question 29

Electrolysis of sodium chloride solution

Answer 29

Products: -hydrogen gas at the cathode -Chlorine gas at the anode -sodium hydroxide remains in solution

Question 30

Electrolysis of aluminium oxide

Answer 30

aluminium is extracted from bauxite ore using electrolysis. Cryolite is added to lower the melting point - at the cathode aluminium metal is produced -at the anode oxygen gas is produced which reacts with the carbon electrodes to form carbon dioxide

Question 31

the reactivity series

Answer 31

-Potassium K -Sodium Na -Lithium Li -Calcium Ca -Magnesium Mg -Carbon C -Zinc Zn -Iron Fe -Hydrogen H -Copper Cu

Question 32

Separating metals from metal oxides

Answer 32

1. metals less reactive than carbon: -extracted by reduction with carbon -eg iron is extracted from iron oxide in blast furnace 2.metals more reactive than carbon: -extracted by electrolysis or molten ores -eg aluminium is extracted from aluminium oxide using electrolysis

Question 33

Native metals

Answer 33

metals like gold are found unreacted and require no extraction

Question 34

Phytomining

Answer 34

Uses plants to absorb metal compounds from the soil

Question 35

Phytomining method

Answer 35

1.plants are grown on metal rich soil and absorb the metal into their tissues 2. plants are harvested, dried, and burned 3. the metal is extracted from the ash using electrolysis or displacement -eg copper can be extracted using phytomining

Question 36

Advantages of phytomining

Answer 36

-environmentally friendly -useful for extracting metals from low grade ores

Question 37

Disadvantages of phytomining

Answer 37

-slower process -produces smaller amounts of metal compared to traditional methods

Question 38

Bioleaching

Answer 38

uses bacteria to extract metals from ores by breaking down the ore and producing a solution containing the metal ions

Question 39

Bioleaching method

Answer 39

1.bacteria feed on the ore, releasing metal ions into the solution 2.the metal ions are extracted from the leachate through electrolysis or displacement -eg copper is extracted from copper sulfide ores

Question 40

advantages of bioleaching

Answer 40

- environmentally friendly -low energy requirement -minimal waste

Question 41

disadvantages of bioleaching

Answer 41

-slow process -toxic by products -low yield