C5-Chemical Changes

Question 1

How is the reactivity of metals decided

Answer 1

• When metals react they lose electrons and form positive ions
• The reactivity of a metal is decided by how easy or hard it is for that metal to lose electrons

Question 2

How are unreactive metals extracted

Answer 2

Unreactive metals are extracted in their native state in the ground

Question 3

How are more reactive metals extracted found in the ground

Answer 3

More reactive metals are found in the ground as metal oxides as they have reacted with oxygen in the ground

Question 4

How are these more reactive metals extracted

Answer 4

These more reactive metals are extracted by a more reactive element dispacing it from its compound

This is usually carbon as other elements are more expensive so not used. If the metal is more reactive than carbon it is extracted by electrolysis

Question 5

What is an example of a reaction for the extraction of a more reactive metal

Answer 5

Iron oxide + carbon —> carbon dioxide + iron

The iron is reduced
F2+ + 2e- = Fe
Carbon has been oxidised
C+ 2e-=C2+

Question 6

What is oxidation in terms of electrons

Answer 6

Oxidation is loss of electrons

E.g if an atom turns into an ion

Question 7

What is reduction in terms of electrons

Answer 7

Reduction is gain of electrons

For example if an ion turns into an atom

Question 8

What do all acids contain

Answer 8

All acids contain hydrogen

Question 9

How do metals react with acid

Answer 9

Metals higher than hydrogen in the reactivity series displace hydrogen when they react with an acid to form a salt of their metal

Question 10

What is the equation for the reaction of acids and metals

Answer 10

Metal + acid —-> salt + hydrogen

Question 11

What type of salt does hydrochloric acid form

Answer 11

Hydrochloric acid forms salts ending in chloride

Question 12

What type of salt does sulphuric acid form

Answer 12

Sulphuric acid forms acids ending in sulphate

Question 13

How is the speed of the reactions with the metals decided

Answer 13

The further away a metal is on the reactivity series from hydrogen , the more fast it reacts

Question 14

What types of ions do acids produce in an aqueous solution

Answer 14

Acids produce hydrogen ions in aqueous solutions

Question 15

What are bases

Answer 15

Bases are chemicals that can neutralise an acid to produce a salt and water

Question 16

What are soluble bases called

Answer 16

Soluble bases are called alkali’s

Question 17

What is the PH scale and how can it be measured

Answer 17

The PH scale is a scale that tells the acidity or alkalinity of acids

It can be measured using universal indicator or a PH probe

Alkalis have a PH of 8-14

Neutral solutions have a PH of 7

Acids have a PH of 0-7

Question 18

What is the equation for a neutralisation reaction

Answer 18

H+ + OH- = H20

The OH is produced by the alkali and the hydrogen is produced by the acid.

The solution produced has a Ph of 7 and is neutral

Question 19

What happens to a strong acid in an aqueous solution

Answer 19

A strong acid in an aqueous solution fully ionises and the reaction is not reversible

-Strong acids have a lower PH than weaker acids

Question 20

What happens to weaker acids in aqueous solutions

Answer 20

Weaker acids only partially ionise in aqueous solutions and the reaction is reversible

Question 21

What happens to the hydrogen ions in a solution as the PH decreases

Answer 21

For every PH decrease the amount of hydrogen ions increases 10 times

-Strong acids will have lower PH’s as the atoms are fully ionised so their are more hydrogen ions

Question 22

How does the concentration of an acid affect the PH

Answer 22

The concentration of an acid tells us the amount of acid in a given volume of solution. A dilute acid will have less molecules of acid for a given volume of solution than a comcentrated acid .

(You can have a dilute strong acid that is not concentrated)

PH will decrease with increasing concentration

Question 23

What happens when a base or alkali reacts with an acid

Answer 23

When a base or alkali reacts with an acid it produces a salt and water

Question 24

What sort of ions does the salt from this reaction contain

Answer 24

The salt from this reaction contains positive ions from the base and negative ions from the acid

Hydrochloric acid —-> chlorides
Nitric acid —-> nitrates
Sulfuric acid —-> sulphates

Question 25

What happens when metal carbonates react with acids

Answer 25

When metal carbonates react with acid they produce a salt , water and carbon dioxide Metal carbonate + acid ---> salt + water + carbon dioxide

Question 26

What colours do indicators turn depending on what type of solution is being tested

Answer 26

If an acid is present the indicator will turn red If an alkali is present the indicator will turn towards purple

Question 27

Describe the steps in a titration reaction

Answer 27

- Use a pipette to transfer 25cm3 of sodium hydroxide solution into a conical flask( make sure to let all of the solution drain out of the pipette) - Add 5 drops of indicator to the solution to the alkali in the conical flask - Place the conical flask on a white tile so you can see the colour change more clearly - Fill a burette with an acid and add it to the alkali until the solution is neutral. When you start to see a colour change add the acid to the solution drop by drop until the solution is neutral - Record the final volume of acid in the burette and use the initial volume to work out the amount of acid used in the neutralisation - Repeat the experiment until you get two readings within 0.1cm3 of each other

Question 28

Describe the steps in Making a soluble salt

Answer 28

Start with a fixed volume of dilute sulfuric acid. This is the limiting reactant Gently heat the acid until almost boiling Use a spatula to add small amounts of copper oxide to the acid The copper oxide will react and seem to disappear (solution will be blue as that is colour of copper sulphate ) Stop adding copper oxide when the copper oxide powder stays after stirring . At this point the reaction has stopped Use filtration to filter out the excess copper oxide Place the solution in an evaporating basin and heat gently over boiling water until roughly half the solution remains Leave the copper sulphate for 24 hours in a cool place so copper sulphate crystals can form Scrape the crystals onto a paper towel and leave them to dry

Question 29

How can you measure the reactivity of metals

Answer 29

- Add all the metals to acid - Measure the temperature change of the reaction between the acid and the metal over a set period - The greater the temperature change the more reactive the metal Keep the same mass and surface area of metal