Section 4 - Physical Chemistry

Question 1

What colour is phenolphalein in acid and alkali?

Answer 1

Acid - colourless

Alkali - bright pink

Question 2

What colour is methyl orange in acid and alkali?

Answer 2

Acid - bright red

Alkali - bright orange or yellow

Question 3

What contains hydrogen ions?

Answer 3

Acids

Question 4

What is a base?

Answer 4

A substance that can neutralises an acid.

Question 5

Acid and base =

Answer 5

Salt and water

Question 6

Acid and metal oxide =

Answer 6

Salt and water

Question 7

Acid and metal carbonate =

Answer 7

Salt and water and carbon dioxide

Question 8

What salts are soluble?

Answer 8

Sodium
Potassium 
Ammonium
Nitrates 
Most chlorides, sulfates

Question 9

Which chlorides and sulfates are insoluble?

Answer 9

Silver chloride

Barium sulfates and calcium sulfates

Question 10

What colour does red litmus paper go in acidic and alkaline solutions?

Answer 10

Acid - no change (red)

Alkali - blue

Question 11

How do you make soluble salts using acids and insoluble bases?

Answer 11

Add insoluble base (metal carbonate, oxide or hydroxide) to the acid
Base will dissolve in the acid and then excess will sink to bottom
Filter out the excess to get a salt solution
Evaporate water to get crystals of the salt

Question 12

How do you make soluble salts using an alkali?

Answer 12

Alkalis are soluble bases so can’t be filtered
So have to add exactly right amount of alkali to neutralise acid
Use an indicator to show when reactions finished
Best way: doing a titration
Repeat without indicator

Question 13

How do you make insoluble salts?

Answer 13

Precipitation reaction

Just mix two solutions that contain the ions you need

Question 14

Explain how to do a titration?

Answer 14

Use a puppeteer and filler to add alkali to a flask wit indicator
Fill a burette with the acid below eye level
Using the burette add the acid a bit at a time
When the indicator changes colour the alkali has been neutralised

Question 15

What is the equation for concentration?

Answer 15

Concentration = number of moles / volume

Question 16

What does the rate of reaction depend on?

Answer 16

Temperature
Concentration
Catalyst
Size of particles

Question 17

What is the equation for enthalpy change using bond energies?

Answer 17

Total energy absorbed to break bonds - total energy release in making bonds

Question 18

How do you work out the molar enthalpy change?

Answer 18

1. Calculate the amount of energy transferred
2. Find out how many moles of fuel produced this heat
3. Work out the heat produced by one mole

Question 19

What colour does blue litmus paper go in acidic and alkaline solutions?

Answer 19

Acid: pink or red
Alkaline: no change (blue)

Question 20

What does universal indicator do?

Answer 20

Gives you an approximate pH value of a solution.

Question 21

Acid are sources of ….. ions and Alkalis are sources of ….. ions.

Answer 21

Acids- hydrogen, H+

Alkalis- hydroxide, OH-

Question 22

What is the difference between hydrogen chloride gas and hydrochloric acid?

Answer 22

Hydrogen chloride is a gas and hydrochloric acid is formed when hydrogen chloride gas is dissolved in water.

Question 23

When is hydrogen chloride acidic and why?

Answer 23

In water but not in methyl benzene as when it is dissolved in water it dissociates (splits up) and forms H+ ions making the solution acidic. Hydrogen doesn’t dissociate in methyl benzene.

Question 24

What is the equation linking the number of moles (n), concentration (c), and volume (v)?

Answer 24

Number of moles = concentration x volume

Question 25

What are the four methods for soluble salts?

Answer 25

1. Metal + acid ➡️ salt + hydrogen
2. Alkalis + acid ➡️ salt + water
3. Base + acid ➡️ salt + water
4. Metal carbonate + acid ➡️ salt + water + carbon dioxide

Question 26

Which salts are soluble?

Answer 26

Salts with nitrates or group 1 elements are soluble.

Question 27

Describe an energy level diagram that is exothermic and an energy level diagram that is endothermic.

Answer 27

EXOTHERMIC REACTION:

• reactants line (first) higher than products line (second)
• 🔺H (difference between two lines) is positive
• energy on x axis
• progress of reactants on y axis.
• Ea = between reactants line and top of curve.

ENDOTHERMIC REACTION:

• reactants line (first) lower than products line (second)
• 🔺H (difference between two lines) is negative
• energy on x axis
• progress of reactants on y axis.
• Ea = between reactants line and top of curve.

Question 28

What is an alkali?

Answer 28

Alkalis are soluble bases, and sources of hydroxide ions.

Question 29

In exothermic reactions…..

In endothermic reactions…..

Answer 29

Heat energy is given off

Heat energy is taken in

Question 30

How do you calculate enthalpy changes from calorimetry experiments?

Answer 30

Using dissolving, displacement, and neutralisation reactions
OR
Using combustion.

Question 31

What is the equation for Heat energy change?

Answer 31

Q = mass x temp change x 4.2

Question 32

What happens to the equilibrium position in reversible reactions if you increase the temperature and increase the pressure?

Answer 32

Increased temperature: endothermic reaction will increase, uses up more heat

Increased pressure: produces less volume

Question 33

What happens to the equilibrium position in reversible reactions if you decrease the temperature and decrease the pressure?

Answer 33

Decreased temp: exothermic reaction will increase, gives out more heat.

Decreased pressure: produces more volume.