Chemical Reactions

Question 1

How does magnesium react with oxygen?

Answer 1

Rapidly
Releases a great deal of heat and light
Vigorous reaction

Question 2

How does iron react with oxygen?

Answer 2

Slowly, could take weeks or months

Question 3

What happens when metals react with oxygen?

Answer 3

Form a metal oxide
Oxidation reaction takes place, because the metal has gained oxygen
Metal atoms have been oxidised

Question 4

How do you compare the reactivity of magnesium, zinc, iron and copper?

Answer 4

Use a dilute acid because they don’t react with water

Question 5

What determines how rapidly a metal reacts?

Answer 5

When metals react, they lose electrons and form a positive ion.
So the reactivity of a metal depends on its ability to lose an electron and form a positive ion.

Question 6

How are unreactive metals such as gold found?

Answer 6

In the earth as the metal itself.

Question 7

How do you extract a metal from a compound?

Answer 7

Use a displacement reaction.

Most of the time carbon is used because it is extremely cheap.

Question 8

What is oxidation in terms of electrons?

Answer 8

Loss of electrons

Question 9

What is reduction in terms of electrons?

Answer 9

Gain of electrons

Question 10

What do acids produce in aqueous solution?

Answer 10

Hydrogen ion H+

Question 11

What are bases?

Answer 11

Chemicals which can neutralise acids, producing a salt and water.
They are usually metal oxides or metal hydroxides.
Some examples are copper oxide, iron (III) hydroxide and sodium hydroxide.

Question 12

What are bases that are soluble in water?

Answer 12

Alkalis.
This means that copper oxide and iron (III) hydroxide are bases only, because they are insoluble in water.
Sodium hydroxide is soluble in water, so it is both a base and an alkali.

Question 13

What is a neutralisation reaction?

Answer 13

When a base reacts with an acid to neutralise it, producing salt and water.

Question 14

What do alkalis produce in aqueous solution?

Answer 14

Hydroxide ions (OH-)

Question 15

What is the pH of acids?

Answer 15

0-6

Question 16

What is the pH of neutral solutions?

Answer 16

7

Question 17

What is the pH of alkalis?

Answer 17

8-14

Question 18

Difference between a pH probe and universal indicator

Answer 18

pH probe determines it electronically- so you are given a numerical value.
Universal indicator changes colour depending on whether the solution is an acid, alkali or neutral.
Green-neutral
Red- very acidic
Purple-very alkaline

Question 19

Neutralisation reaction between an acid and an alkali.

Answer 19

The acid will proceed hydrogen ions and the alkali will produce hydroxide ions.
The hydrogen ions react with the hydroxide ions to produce water

Question 20

Formula for hydrochloric acid

Answer 20

HCl

Question 21

Formula for sulfuric acid

Answer 21

H2SO4

Question 22

Formula for nitric acid

Answer 22

HNO3

Question 23

Why does magnesium react rapidly with acids?

Answer 23

Higher than magnesium on the reactivity series, so it is a lot more reactive.
Magnesium can easily displace hydrogen from acids.

Question 24

Why does iron react slowly with acids?

Answer 24

Iron is only slightly more reactive than hydrogen

Question 25

What are salts?

Answer 25

They contain a positive ion which comes from the base or alkali. Also contain a negative ion which comes from the acid.

Question 25

What are salts?

Answer 25

They contain a positive ion which comes from the base or alkali. Also contain a negative ion which comes from the acid.

Question 26

Metal carbonates:

Answer 26

sodium carbonate - Na2CO3 calcium carbonate - CaCO3 potassium carbonate - K2CO3

Question 27

Required Practical 1: Making soluble salts using an acid.

Answer 27

Equipment: - beaker - gauze - tripod - bunsen burner - heatproof mat 1. Start with a fixed volume of dilute sulfuric acid. This is our limiting reactant. We don't want any acid remaining in the end because it would contaminate the salt. 2. Gently heat the acid until it's almost boiling. 3. Use a spatula to add small amounts of copper oxide to the acid. 4. Stir the solution using a glass rod. 5. The copper oxide will react and seem to disappear. 6. Continue adding copper oxide if the solution continues to be clear blue. 7. Stop adding copper oxide if some powder remains after stirring. 8. The reaction has stopped because all the acid has reacted. Solution of copper sulphate is now neutral. 1. We must remove the unreacted copper oxide. Use filtration as it is insoluble. 2. Filter funnel and filter paper. Now to make the crystals of copper sulfate: 1. Place the copper sulphate solution and place this in an evaporating basin. 2. Heat this gently over a beaker of boiling water. 3. Do this until half the solution remains. 4. Leave the solution for 24 hours in a cool place so the crystals can form. 5. Scrape the crystals onto a paper towel and pat them dry.

Question 27

Required Practical 1: Making soluble salts using an acid.

Question 28

Why can't you react copper with sulphuric acid?

Answer 28

Copper isn't reactive enough for the reaction to actually take place.

Question 29

Where could the metal ion in the salt come from?

Answer 29

The metal itself. Metal oxide. Metal hydroxide. Metal carbonate.

Question 30

Where does the negative ion in the salt come from?

Answer 30

The acid.

Question 31

Strong acids vs weak acids.

Answer 31

Strong acids fully ionise in aqueous solutions and we know this as the arrow goes in one direction only. Examples are hydrochloric acid, sulfuric acid and nitric acid. Weak acids partially ionise in aqueous solutions. Reversible reactions. Examples are carbonic acid, ethanoic acid and citric acid.

Question 31

Strong acids vs weak acids.

Answer 31

Strong acids fully ionise in aqueous solutions and we know this as the arrow goes in one direction only. Examples are hydrochloric acid, sulfuric acid and nitric acid. Weak acids partially ionise in aqueous solutions. Reversible reactions. Examples are carbonic acid, ethanoic acid and citric acid.

Question 32

What does the pH scale do?

Answer 32

Gives us an idea of the concentration of hydrogen ions produced by an acid. Strong acids have a lower pH than weak acids for a given concentration. As the pH scale decreases by one unit, the concentration of hydrogen ions increases by ten times. This is one order of magnitude. So for example, pH 1 has a 100x greater concentration of hydrogen ions than pH 3. This is two orders of magnitude.

Question 33

Concentrations of acids.

Answer 33

This tells us the amount of acid molecules in a given volume of a solution. A dilute acid will have fewer acid molecules in a given volume than a concentrated acid even if the strength of the acid is the same.

Question 34

Required Practical 2: Carrying out a titration

Answer 34

1. Use a pipette to transfer 25cm^3 of sodium hydroxide solution into a conical flask. 2. Add 5 drops of indicator such as methyl orange to the alkali in the conical flask. 3. Place the conical flask on a white tile so we can see a colour change more clearly. 4. Fill a burette with sulfuric acid. 5. Add acid to the alkali until the solution is neutral. When we see a colour change, we now add acid drop by drop until it is neutral. 6. Swirl the solution so it mixes. 7. The colour change will be from yellow to permanently red. 8. Read the volume of acid added from the burette. Make sure your eye is level with the surface of the liquid as there is a meniscus. Read from the bottom of the meniscus. 9. Repeat the titration several times until we get two readings within 0.1cm^3. 10. Take a mean of these for a final volume.

Question 35

Why can't solid ionic compounds conduct electricity?

Answer 35

The ions are locked in place and are not free to move. They are held in place by strong electrostatic forces of attraction. When an ionic compound is melted or dissolved in water, the forces of attraction are broken and the ions are free to move. These liquids can now conduct electricity. These are called electrolytes.