1. Chemical changes

Question 1

What reactants are needed to produce metal oxides?

Answer 1

metal + oxygen

Question 2

When metals become metal oxides, are metals oxidised or reduced? Explain your answer.

Answer 2

Metals are oxidised
because they gain oxygen.

Question 3

What is reduction and oxidation in terms of oxygen?

Answer 3

Oxidation is the gaining of oxygen
Reduction is the loss of oxygen

Question 4

When metals react with other substances, what kind of ions are produced?

Answer 4

metal ions are positive

Question 5

What is the reactivity of a metal due to?

Answer 5

The reactivity of a metal is due to its tendency to form positive ions

Question 6

How can displacement occur in a reaction with metals?

Answer 6

A more reactive metal can displace a less reactive metal from a compound.

Question 7

Put the metals (and hydrogen and carbon) in order of the reactivity series.

Answer 7

Potassium, sodium, lithium, calcium, magnesium, aluminium, carbon, zinc, iron, nickel, tin, lead, hydrogen, copper, mercury, silver, gold, platinum.

Question 8

When describing reactions of metals with water or acids, what conditions are they limited to?

Answer 8

They occur at room temperature and do not include reactions with steam.

Question 9

Describe the reactions of potassium, sodium, lithium, calcium with water.

Answer 9

Fizz, giving off hydrogen gas, leaving an alkaline solution of metal hydroxide.

They produce lots of hydrgoen bubbles as well as heat.

Potassium burns with a lilac flame when reacting with water.

Question 10

Describe the reactions of magnesium, zinc and iron with water.

Answer 10

Very slow reaction.

Question 11

Describe the reactions of tin and lead with water.

Answer 11

Slight reaction with steam.

Question 11

Describe the reactions of copper, silver and gold with water.

Answer 11

No reaction, even with steam.

Question 12

Describe the reactions of potassium, sodium and lithium with dilute acids.

Answer 12

Explode
EXTREMELY VIOLENT REACTION

Question 13

Describe the reactions of calcium, magnesium, zinc and iron with acids.

Answer 13

Fizz/bubbles, giving off hydrogen gas
Form a salt and hydrogen gas

Question 14

Describe the reaction of copper, silver and gold with acids.

Answer 14

No reaction

Question 15

Describe the reaction of tin and lead with acids.

Answer 15

React slowly with warm acid.

Question 16

Describe the reaction of different metals with oxygen.

Answer 16

Potassium, sodium, lithium react with oxygen very vigorously at room temperature.

calcium, magnesium, aluminium, zinc, iron, nickel and tin, lead, copper and silver react very slowly or when heated.
Calcium and magnesium react will particularly and produce lots of heat and light when heated, or we might see a colour change going from shiny to a dull black colour.

Gold and platinum do not react.

Question 17

What is a displacement reaction?

Answer 17

A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds or in solution.

Question 18

What elements are found as native metals and why?

Answer 18

Gold, silver and platinum because they are so unreactive. Most metals are found as compounds that require chemical reactions to extract the metal.

Question 19

What metals can be extracted from their oxides by carbon?

Answer 19

Metals less reactive than carbon (i.e zinc, iron, tin, lead etc.)

Question 20

What is the equation for reduction by carbon?

Answer 20

metal oxide + carbon –> metal + carbon dioxide

Question 21

What is an ore?

Answer 21

An ore is a rock containing enough mineral to make it economical to extract.

Question 22

What are the most common minerals and what is extracted from them?

Answer 22

Haematite - iron is extracted
bauxite - aluminium is extracted
galena - lead is extracted
rutile - titanium is extracted
chalcopyrite - copper is extracted

Question 23

What is oxidation and reduction in terms of electrons?

Answer 23

Oxidation is the loss of electrons, reduction is the gain of electrons
(oil rig - oxidation is loss, reduction is gain)

Student should be able to:
* write ionic equations for displacement reactions
* identify in a given reaction, symbol equation or half equation
which species are oxidised and which are reduced

Question 24

What is a redox reaction?

Answer 24

A reaction in which both oxidation and reduction takes place. ## Footnote (HT only) Students should be able to: * explain in terms of gain or loss of electrons, that these are redox reactions * identify which species are oxidised and which are reduced in given chemical equations. Knowledge of reactions limited to those of magnesium, zinc and iron with hydrochloric and sulfuric acids

Question 25

What are the products in a reaction of Metal + acid?

Answer 25

Metal + acid --> salt + hydrogen (MASH)

Question 26

What is a salt?

Answer 26

A salt is a compound formed when the hydrogen in an acid is wholly or partially replaced by a metal ion (or ammonium in NH4+)

Question 27

What are the 5 ways of making a salt?

Answer 27

metal + acid --> salt + hydrogen acid + base --> salt + water acid + metal carbonate --> salt + water + carbonate metal hydroxide + acid --> salt + water metal oxide + acid --> salt + water *metal hydroxide and metal oxides are bases

Question 28

What is the chemical formula of the following acids: inorganic/strong acids: sulphuric acid hydrochloric acid Nitric acid Ethanoic acid (weak/organic acid)

Answer 28

H2SO4 HCl HNO3 CH3OOH

Question 29

What is an alkali? What is an example of an alkali?

Answer 29

An alkali is a solution with a pH value of more than 7. Example: soluble metal hydroxides

Question 30

What is a base? What are 2 examples of bases?

Answer 30

The oxide, hydroxide or carbonate of a metal hat will react with an acid, forming a salt as one of the products. (If a base dissolves in water, it is called an alkali. Bases are proton (H= ion) acceptors. Examples: insoluble metal hydroxides and metal oxides

Question 31

Why are reactions between metals and acids often slower?

Answer 31

Most metals are not soluble, which means that they are often slower and may need heating to make them react.

Question 32

How can soluble salts be made?

Answer 32

Soluble salts can be made from acids by reacting them with solid insoluble substances, such as metals, metal oxides, hydroxides or carbonates. The solid is added to the acid until no more reacts and the excess solid is filtered off to produce a solution of the salt. Salt solutions can be crystallised to produce solid salts

Question 33

What is the aim of RP1?

Answer 33

preparation of a pure, dry sample of a soluble salt from an insoluble oxide or carbonate using a Bunsen burner to heat dilute acid and a water bath or electric heater to evaporate the solution.

Question 34

Give the method for RP1.

Answer 34

1. Measure 20cm3 of acid in a measuring cylinder and pour it into a beaker. 2. Heat the acid gently using a Bunsen Burner. 3. Add small amounts of insoluble base in this case copper oxide in excess (until no more reacts thus no more effervescence is produced). 4. Filter using filter paper and funnel the solution to remove the excess copper oxide. 5. Pour the solution into the evaporating basin. 6. Evaporate the solution using a water bath until crystals start to form. 7. Leave the evaporating basin in a cool place for at least 24 hours. 8. Gently pat the crystals dry between two pieces of filter paper.

Question 35

What are the safety precautions when making a sample of a soluble salt?

Answer 35

Wear safety goggles as sulphuric acid is corrosive. ● Make sure hair is tied back. ● When the Bunsen burner is not in use, turn it off or leave it on the orange safety flame. Acid is an irritant. Metal powder is harmful.

Question 36

What is the difference between acids and alkalis in aqueous solutions?

Answer 36

Acids produce hydrogen ions (H+) in aqueous solutions, whereas aqueous solutions of alkalis contain hydroxide ions (OH–).

Question 37

What is the pH scale?

Answer 37

The pH scale, from 0 to 14, is a measure of the acidity or alkalinity of a solution, and can be measured using universal indicator or a pH probe.

Question 38

What is the difference in pH between acidic, neutral and alkali solutions?

Answer 38

A solution with pH 7 is neutral. Aqueous solutions of acids have pH values of less than 7 and aqueous solutions of alkalis have pH values greater than 7.

Question 39

What happens in a neutralisation reaction?

Answer 39

In neutralisation reactions between an acid and an alkali, hydrogen ions react with hydroxide ions to produce water.

Question 40

What is the ionic equation for a neutralisation reaction?

Answer 40

H+ (aq) + OH- (aq) --> H2O (l)

Question 41

What are the types of substances and their relative pH of the following substances: Hydrochloric acid Ethanoic acid Pure water Ammonia Sodium Hydroxide

Answer 41

Hydrochloric acid - pH 1 - strong acid Ethanoic acid - pH 4 - weak acid Pure water - pH7 - neutral solution Ammonia - pH10 - weak alkali Sodium Hydroxide - pH 14 - strong alkali

Question 42

What is the pH of an acid/alkali?

Answer 42

The pH of an acid or alkali is a measure of the concentration of the h+ ions in the solution. The more H+ ions there are in a given volume of solution, the lower the pH.

Question 43

What is the relationship between concentration of H+ ions and pH?

Answer 43

For every decrease of 1 on the pH scale, the H+ ion concentration increases by a factor of 1-. Eg 1.0 x 10-1 pH: 1 1.0 x 10-2 pH:2 etc. etc.

Question 44

What is the equation to find the concentration of a solution?

Answer 44

concentration = mol / volume concentration = amount of solute (g) / volume of solution

Question 45

How do you convert between mol/dm3 and g/dm3?

Answer 45

mol/dm3 x Mr = g/dm3 (tip: g/dm3 is always greater than mol/dm3)

Question 46

Why might an acid/alkali be measured in a pipette or a Burette?

Answer 46

pipette measures a fixed volume (accurately) (but) burette measures variable volume (allow can measure drop by drop)

Question 47

Describe how you would carry out the titration practical.

Answer 47

Aim: pipette measures a fixed volume (accurately) (but) burette measures variable volume allow can measure drop by drop 1. Use the pipette to measure 25cm3 of sodium hydroxide into the conical flask. 2. Place the conical flask on a white tile. 3. Fill the burette with sulphuric acid using a funnel. 4. Record the initial reading of acid in the burette. - Make sure to always take readings from the bottom of the meniscus. 5. Add a 5 drops of indicator in this case phenolphthalein to the conical flask. 6. Slowly open the burette tap while swirling the conical flask. 7. Add acid drop-by-drop near the endpoint. - At this point the colour will start to change slightly. 8. Close the burette when a colour change occurs in phenolphthalein. - The solution turns from pink to colourless. 9. Record the final reading of acid in the burette and calculate the titre. This is the volume of acid used to neutralise the alkali. Repeat until you have concordant results. - These are within 0.1cm3 of each other. 11. Present results in a table and calculate the mean titre discarding any anomalies when calculating the mean. 12. Calculate the number of moles of sodium hydroxide used in the titration. 13. In the balanced equation the ratio between sodium hydroxide and sulphuric acid is 2:1. Therefore to find out the moles of sulphuric acid divide the moles of sodium hydroxide by 2. 14. Use the formula [concentration= moles/volume (mean titre volume)] to work out the concentration of sulphuric acid. Safety precautions Wear safety goggles when working with acids. Tie hair back. Report any broken glassware immediately.

Question 48

What is a strong acid and what are some examples?

Answer 48

A strong acid is completely ionised in aqueous solution (or water). Examples of strong acids are hydrochloric, nitric and sulfuric acids.

Question 49

What is a weak acid and what are some examples?

Answer 49

A weak acid is only partially ionised in aqueous solution (or water). Examples of weak acids are ethanoic, citric and carbonic acids.

Question 50

What is the relationship between the pH of an acid and the strength of the acid?

Answer 50

For a given concentration of aqueous solutions, the stronger an acid, the lower the pH. As the pH decreases by one unit, the hydrogen ion concentration of the solution increases by a factor of 10.

Question 51

What is the difference between a concentrated and dilute acid?

Answer 51

Dilute acid - small amount of acid per unit volume Concentrated acid - big amount of acid per unit volume

Question 52

How can an acid be strong and dilute?

Answer 52

(strong because) completely ionised (in aqueous solution) (dilute because) small amount of acid per unit volume

Question 53

What are electrolytes?

Answer 53

When an ionic compound is melted or dissolved in water, the ions are free to move about within the liquid or solution. These (ionic) liquids and solutions are able to conduct electricity and are called electrolytes.

Question 54

What is electrolysis?

Answer 54

Use of electricity to break components down (decomposition of ionic compounds using electricity)

Question 55

What is an electrode?

Answer 55

Inert rod that conducts electricity - come in pairs, one negative (cathode) and one positive (anode).

Question 56

What is the process of electrolysis?

Answer 56

Passing an electric current through electrolytes causes the ions to move to the electrodes. Positively charged ions move to the negative electrode (the cathode), and negatively charged ions move to the positive electrode (the anode). Ions are discharged at the electrodes producing elements. This process is called electrolysis.

Question 57

Where do metal ions (cations) go and where to non-metal ions (anions) go in electrolysis?

Answer 57

Cations (metal ions) go to the negative electrode (cathode), where they gain electrons. Anions (non-metal ions) go to the positive electrode (anode), where they lose electrons. This is because opposite charges attract (pos ions to neg elec, neg ions to pos elec) At electrons the ions are discharged (gain/lose electrons) so that they have no charge.

Question 58

What happens when you electrolysise a molten ionic compound?

Answer 58

When a simple ionic compound (eg lead bromide) is electrolysed in the molten state using inert electrodes, the metal (lead) is produced at the cathode and the non-metal (bromine) is produced at the anode.

Question 59

When is electrolysis used to extract molten compounds?

Answer 59

Metals can be extracted from molten compounds using electrolysis. Electrolysis is used if the metal is too reactive to be extracted by reduction with carbon or if the metal reacts with carbon. Large amounts of energy are used in the extraction process to melt the compounds and to produce the electrical current.

Question 60

How is aluminium manufactured?

Answer 60

Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite using carbon as the positive electrode (anode).

Question 61

Why is a mixture of aluminium oxide and cryolite used to extract aluminium?

Answer 61

Aluminium oxide melts at over 2000 C. Cryolite is another ionic compound. Aluminium is mixed with cryolite which lowers the melting point of the mixture. Molten mixture cna be electrolysed at 950C, which reduces the cost of heat energy.

Question 62

Why does the positive electrode have to be replaced at regular intervals?

Answer 62

Oxide ions move towards the positive electrode (anode.) As the electrode is made of carbon, carbon dioxide is formed, making the electrode wear away. As the electrode is made of carbon, carbon dioxide is formed making the elecrtrode wear away. The electrodes are made of graphite (carbon).

Question 63

Why is aluminiun expensive?

Answer 63

Large amounts of energy is required, for a long time. High temperature required, otherwise aluminium solidifies and requires more energy to make it molten again.

Question 64

Write down the half equations of molten aluminium extraction.

Answer 64

2O2- - 4e- --> O2 Al3+ + 3e- --> Al C + O2 --> CO2 (anodes react with oxygen, not a half equation but whatever)

Question 65

In the electrolysis of aqueous solutions, what determines which ions are discharged, what order is this in at each electrode? Why does this happen?

Answer 65

The ions discharged when an aqueous solution is electrolysed using inert electrodes depend on the relative reactivity of the elements involved. At the negative electrode (cathode), hydrogen is produced if the metal is more reactive than hydrogen. At the positive electrode (anode), oxygen is produced unless the solution contains halide ions when the halogen is produced. This happens because in the aqueous solution water molecules break down producing hydrogen ions and hydroxide ions that are discharged.

Question 66

Describe the electrolysis practical.

Answer 66

Aim: what happens when aqueous solutions undergo electrolysis. 1.Add about 50cm3 of copper chloride solution to a beaker. 2. Add the lid and insert electrodes through the holes making sure the electrodes don’t touch. 3. Attach crocodile leads to the electrode and connect the rods to the DC terminals of a low voltage power supply. 4. Set the power supply to 4V and switch the power supply on. 5. Using the forceps hold the litmus paper near the positive electrode. 6. After a few minutes turn the power supply off and observe the negative electrode. 7. Record observations at the electrodes. Safety precautions: Safety goggles must be worn. Room should be well ventilated because large quantities of chlorine gas is toxic.

Question 67

What are the types of reactions that happen at each electron and how can this be represented by half equations?

Answer 67

During electrolysis, at the cathode (negative electrode), positively charged ions gain electrons and so the reactions are reductions. At the anode (positive electrode), negatively charged ions lose electrons and so the reactions are oxidations. Reactions at electrodes can be represented by half equations, for example: 2H+ + 2e- → H2 and 4OH- → O2 + 2H2O + 4e or 4OH- – 4e- → O2 + 2H2O