Section 4: Physical Chemistry

Question 1

What is an indicator?

Answer 1

A chemical that changes colour in the presence of an acid or alkali.

Question 2

What colours do indicators turn in acids?

Answer 2

Litmus - red
Universal - red
Methyl Orange - red
Phenolphthalein - colourless

Question 3

What colours do indicators turn in alkalis?

Answer 3

Litmus - blue
Universal - blue
Methyl Orange - yellow
Phenolphthalein - pink

Question 4

What is the pH scale, and how does it classify alkaline and acidic substances?

Answer 4

A scale from 0-14 which measures the acidity of a substance by the concentration of hydrogen ions. A low number (0-6) shows an acid, 7 is neutral, and a high number (8-14) is alkaline.

Question 5

What is the connection between universal indicator and the pH scale?

Answer 5

Universal indicator shows in gradient how acidic or alkaline the solution is. It will turn darker blue for stronger alkalis, green for neutral substances and orange-red for acids.

Question 6

What are acids?

Answer 6

Acids are substances which dissociate hydrogen ions when dissolved in water.

Question 7

What are alkalis?

Answer 7

A base which that can dissolve in water and release hydroxide ions.

Question 8

What are the products of a neutralisation reaction if the base is a metal?

Answer 8

salt and hydrogen

Question 9

What are the products of a neutralisation reaction if the base is a metal oxide?

Answer 9

salt and water

Question 10

What are the products of a neutralisation reaction if the base is a metal hydroxide?

Answer 10

salt and water

Question 11

What are the products of a neutralisation reaction if the base is a metal carbonate?

Answer 11

salt, water and carbon dioxide

Question 12

What are the general rules for predicting the solubility of salts in water? (List the types of soluble salts)

Answer 12

All nitrates, all chlorides except silver and lead, all sulphates except barium, lead and calcium, sodium and potassium carbonate, and all sodium, potassium and ammonium salts

Question 13

What are the general rules for predicting the solubility of salts in water? (List the types of insoluble salts)

Answer 13

silver chloride, lead chloride, barium sulphate, lead sulphate, calcium sulphate and all carbonates except potassium and sodium

Question 14

How do you prepare soluble salts from acids with a soluble base?

Answer 14

1) Add acid via burette to alkali and indicator until neutral
2) Measure volume of acid added; throw away solution as it contains the indicator
3) Add same volume of acid to same amount of alkali without indicator
4) Evaporate until crystals begin to form, and leave the solution to cool

Question 15

How do you prepare soluble salts from acids with an insoluble base?

Answer 15

1) Gently warm the acid
2) React/add base in excess. Test with pH paper to ensure reaction is complete.
3) Filter and evaporate until crystals begin to form
4) Leave solution to cool

Question 16

How do you prepare insoluble salts?

Answer 16

1) Make two solutions of SOLUBLE salts, each one containing an ion of the salt to be made
2) Add the solutions
3) Filter off precipitate which is the insoluble salt
4) Wash the residue with distilled water to remove any of the other salt solutions
5) Dry with filter paper or on warm gauze

Question 17

How do you carry out acid-alkali titrations?

Answer 17

1) Clean out the burette with distilled water, and then the acid, so there is no contamination.
2) Using a pipette, put alkali of a known volume into a conical flask. Add an indicator, so that it is clear that the end point has been reached.
3) Fill the burette with acid. Neutralise the alkali by adding exactly the amount of acid needed to change the colour of the indicator.
4) Repeat the experiment.

Question 18

What is an exothermic reaction?

Answer 18

A chemical reaction in which heat energy is given out

Question 19

What is an endothermic reaction?

Answer 19

A chemical reaction in which heat energy is taken in

Question 20

Describe a simple calorimetry experiment.

Answer 20

Measure the temperature at the beginning of the experiment, measure the temperature at the end. How ever much heat has gone up or down is the calorimetry of the reaction.

Question 21

How do you calculate molar enthalpy change from heat energy change?

Answer 21

molar enthalpy change = change in temperature . mass of water . 4.2 / number of moles

Question 22

How is delta H used to represent the enthalpy change for exothermic and endothermic reactions?

Answer 22

delta H is negative for exothermic reactions (they LOSE heat) , and positive for endothermic reactions (they GAIN heat)

Question 23

How do you represent an exothermic reaction on a simple energy level diagram?

Answer 23

The products are on a lower level than the reactants.

Question 24

How do you represent an endothermic reaction on a simple energy level diagram?

Answer 24

The products are on a higher level than the reactants.

Question 25

Is the breaking of bonds exothermic or endothermic?

Answer 25

endothermic

Question 26

Is the making of bonds exothermic or endothermic?

Answer 26

exothermic

Question 27

How do you use average bond energies to calculate the enthalpy change during a chemical reaction?

Answer 27

To work out the enthalpy change you do:
the sum of bond energies in the reactants - the sum of bond energies in the products
Use the equation for the reaction to do this

Question 28

Describe a simple experiment investigating the effects of surface area on the rate of reaction

Answer 28

Put a set mass of magnesium in hydrochloric acid
Time the reaction
Change the from of magnesium keeping the mass the same (powder, wire, strips)
The more surface area (the smaller the pieces of magnesium) the faster the reaction

Question 29

Describe a simple experiment investigating the effects of concentration on the rate of reaction

Answer 29

Put a set mass of marble chips into dilute hydrochloric acid
Time the reaction
Change the ratio of water to hydrochloric acid
The more concentrated the hydrochloric acid (the lower the ratio of water) the faster the reaction

Question 30

Describe a simple experiment investigating the effects of temperature on the rate of reaction

Answer 30

Put a set mass of magnesium powder into a set mass of hydrochloric acid
time the reaction
Carry out this reaction at different temperatures
The higher the temperature the faster the rate of reaction

Question 31

Describe a simple experiment investigating the effects of a catalyst on the rate of reaction

Answer 31

If you have hydrogen peroxide it will not decompose
If you put it with manganese dioxide it will decompose into water and oxygen
The manganese dioxide will be unaltered by the reaction
The more of the catalyst the faster the reaction

Question 32

What are the effects of changes in surface area, concentration, pressure, temperature and the use of a catalyst on the rate of reaction?

Answer 32

Higher temperature, more surface area, higher concentration, higher pressure and use of a catalyst all make a reaction faster.

Question 33

What is activation energy? How is it represented on a reaction profile?

Answer 33

The minimum energy required for a chemical reaction to take place. It is shown by a rise in energy before a drop on a reaction profile.

Question 34

What does collision theory say?

Answer 34

Particles must collide with enough energy and in the right orientation to react. A higher frequency of collisions will therefore increase the number of successful collisions.

Question 35

Explain the effect of surface area on the rate of a reaction using particle collision theory.

Answer 35

Particles collide more frequently if there is more surface area, as there are more points contact between the reactants. Faster rate of reaction.

Question 36

Explain the effect of concentration/pressure on the rate of a reaction using particle collision theory.

Answer 36

There is more chance of particles colliding at a higher concentration/pressure, so they react more often. Faster rate of reaction.

Question 37

Explain the effect of temperature on the rate of a reaction using particle collision theory.

Answer 37

Particles move about more and will collide more frequently the higher the temperature; they will react more often. Increases the rate of reaction.

Question 38

How does a catalyst speed up a reaction?

Answer 38

Catalysts provide an alternative pathway with a lower activation energy for the reaction to take place.

Question 39

What are reversible reactions?

Answer 39

A reaction where the reactants can react to form products and the products can react to form the original reactants.

Question 40

What symbol shows that a reaction is reversible?

Answer 40

⇌

Question 41

Describe the reversible reaction of the dehydration of hydrated copper sulfate.

Answer 41

If you add water to copper sulphate you can make hydrated copper sulphate.
If you remove the water from hydrated copper sulphate you can make copper sulphate.

Question 42

Describe the effect of heat on ammonium chloride.

Answer 42

When heated, ammonium chloride splits into to hydrogen chloride and ammonia.
Hydrogen chloride and ammonia can be reacted to make ammonium chloride.

Question 43

What is dynamic equilibrium?

Answer 43

Dynamic equilibrium happens in a closed system, when a forward and backward reaction are happening at the same time, and at the same rate. The concentration of the products and reactants remains constant, though not equal because both reactions are happening at the same rate.

Question 44

What are the effects of changing the pressure in reversible reactions?

Answer 44

If you increase the pressure, the system will oppose the change. The reaction with the products that have the least moles will occur more frequently, so equilibrium will shift. The yield of the products on this reaction will increase.

Question 45

What are the effects of changing the temperature in reversible reactions?

Answer 45

If you increase the temperature, the system will oppose the change. The forward/backward reaction will occur more frequently because it is endothermic. Equilibrium will shift.