4 - Physical Chemistry Flashcards
1
Q
What is the pH of the strongest acid?
A
pH0 (e.g. a car battery or stomach acid)
2
Q
What is the pH of the strongest alkali?
A
pH14 (e.g. caustic soda)
3
Q
What is the pH of neutral?
A
pH7 (e.g. pure water)
4
Q
What is the universal indicator colour for an acid?
A
Red
5
Q
What is the universal indicator colour for an alkali?
A
Purple
6
Q
What is the universal indicator colour for neutral?
A
Green
7
Q
What colour is litmus paper in acidic solutions?
A
Red
8
Q
What colour is litmus paper in alkaline solutions?
A
Blue
9
Q
What colour is litmus paper in neutral solutions?
A
Purple
10
Q
What colour is phenolphthalein in acidic solutions?
A
Colourless
11
Q
What colour is phenolphthalein in alkaline solutions?
A
Pink
12
Q
What colour is methyl orange in acidic solutions?
A
Red
13
Q
What colour is methyl orange in alkaline solutions?
A
Yellow
14
Q
What is an acid?
A
A source of H+ ions
15
Q
What is an alkali?
A
A source of OH- ions
- Can be used as a soluble base
16
Q
What is a base?
A
A substance that can neutralise an acid
Acid + base –> salt + water
H+ + OH- –> H2O
17
Q
What does an acid + metal oxide make?
A
Acid + metal oxide –> salt + water
18
Q
What does an acid + metal carbonate make?
A
Acid + metal carbonate –> salt + water + carbon dioxide
19
Q
Sodium salts
A
Soluble
20
Q
Potassium salts
A
Soluble
21
Q
Ammonium salts
A
Soluble
22
Q
Nitrates
A
Soluble
23
Q
Most chlorides
A
Soluble
24
Q
Silver chloride
A
Insoluble
25
Most sulphates
Soluble
26
Barium sulphate
Insoluble
27
Calcium sulphate
Insoluble
28
Most carbonates
Insoluble
29
Sodium carbonate
Soluble
30
Potassium carbonate
Soluble
31
Ammonium carbonate
Soluble
32
How can you make soluble salts using acids and insoluble bases?
- Add the metal oxide, carbonate or hydroxide to the acid
- The acid has been neutralised when the excess solid sinks to the bottom of the flask
- Filter out the excess base
- Evaporate water off for pure solid cystals
33
How can you make soluble salts using acids and insoluble bases?
- Add the metal oxide, carbonate or hydroxide to the acid
- The acid has been neutralised when the excess solid sinks to the bottom of the flask
- Filter out the excess base
- Evaporate water off for pure solid crystals
34
How can you make soluble salts using an alkali?
- You have to add just the right amount to neutralise the acid
- Use an indicator to show when it is finished
- The best way is to use titrations
- Repeat without an indicator so the salt isn't contaminated
35
How can you make insoluble salts?
- Precipitation reactions
- Pick two solutions with the ions needed
- mix together
36
What is the equation to work out the moles of a concentration?
moles = concentration x volume
37
When are titrations used?
To find out the exact concentration of how much acid is needed to neutralise a quantity of alkali (or vice versa)
38
Describe how to do a titration
- Using a pipette and pipette filler add some alkali (about 25cm3) to a conical flask with some drops of indicator
- Fill a burette with the acid at eye level
- Using the burette, add the acid to the alkali slowly whilst stirring and go very slowly towards the end point
- The indicator changes colour when all the alkali has been neutralised
- Record the volume of acid to neutralise the alkali
- Repeat
39
What does a pipette do?
Measures only one volume of solution
40
What does a burette do?
Measures different volumes and let you add the solution drop by drop
41
What is an example of a slow rate of reaction?
The rusting of iron
42
What is an example of a moderate rate of reaction?
A metal reacting with an acid to form bubbles
43
What is an example of a fast rate of reaction?
An explosion
44
What factors effect the rate of reaction?
- Temperature
- Concentration (or pressure for gases)
- Catalyst
- Size of particles (or surface area)
45
What is the equation for rate of reaction?
Rate of reaction = amount of reactant used or amount of product formed / time
46
What is the equation for rate of reaction?
Rate of reaction = amount of reactant used or amount of product formed / time
47
How can you measure the rate of reaction with precipitation?
- the product must form a cloudy precipitate
- Observe a marker through the solution and measure how long it takes to disappear
- The quicker it disappears the quicker the reaction
- Use a timer
- Not very accurate as there are different views on when the marker has disappeared
48
How can you measure the rate of reaction with the change in mass?
- On a mass balance
- Time how long it takes for the mass to stop dropping
- When it stops changing the reaction has stopped
- The most accurate method as the mass balance is very accurate
49
How can you measure the rate of reaction with the volume of gas given off?
- Involves a gas syringe
- The more gas given off in a shorter time period the faster the reaction
- Gas syringes are very accurate so very accurate method
50
Describe an experiment for volume of gas
- Hydrochloric acid and marble chips
- Measure the volume of gas with a gas syringe
- Repeat with the marble chips more crunched up
- The more powdered the marble chips are the faster the reaction as there is a larger surface area
51
Describe an experiment for the loss in mass
- Magnesium metal in dilute HCl
- Gives off hydrogen gas
- Use a mass balance to measure the amount of mass lost
- Use a timer
52
Describe an experiment for a cloudy precipitate
- Sodium thiosulphate and HCl produce a cloudy yellow precipitate of sulphur
- Time how long it takes for the cross to disappear
- Can be heated in a water bath to show the effects of temperature increase
53
Describe an experiment for volume of gas through decomposition
- The decomposition of hydrogen peroxide (H2O2)
- Catalyst of manganese(IV) oxide
- Other catalysts can be potato peel or blood
- Oxygen gas is given off which is measure in a gas syringe
- Repeat using stronger catalysts
54
Describe an experiment for volume of gas through decomposition
- The decomposition of hydrogen peroxide (H2O2)
- Catalyst of manganese(IV) oxide
- Other catalysts can be potato peel or blood
- Oxygen gas is given off which is measure in a gas syringe
- Repeat using stronger catalysts
55
How does temperature increase the rate of reaction?
- Particles have more energy
- Move around more
- Collide more frequently and with more force
56
How does the concentration (or pressure) increase the rate of reaction?
- More concentrated means more particles knocking about
- More collisions
- In a gas they are more squashed together so collide more frequently
57
How does a larger surface area increase the rate of reaction?
- Larger surface area means more area to 'work on'
| - More collisions more often
58
How does a catalyst increase the rate of reaction?
- Works by giving the particles an easier pathway to each other
- Lowers the activation energy so the particles have more energy to react
59
What is the activation energy?
The initial energy needed to break bongs
60
What is an exothermic reaction?
- Energy is given out to the surroundings (normally as heat)
- Show by a rise in temperature
- Bond forming is exothermic
- On a graph the products is below the reactants
61
What is an endothermic reaction?
- Energy is taken from the surroundings (normally as heat)
- Shown by a drop in temperature
- Bond breaking is endothermic
- On a graph the products are above the reactants
62
What is the enthalpy change?
The overall energy change in the reaction
- Positive number = endothermic
- Negative number = exothermic
63
What does an energy level diagram look like with a catalyst?
The line will be lower than the line without a catalyst
64
What is the equation for enthalpy change?
Enthalpy change = total energy absorbed in breaking bongs - total energy released in making bonds
65
What is the bond energy?
The total amount of energy in a bond
| - Changes with every compound
66
How can you find enthalpy changes using calorimetry?
- Used for dissolving, displacement or neutralisation reactions
- Mix the reactants in a polystyrene cup
- Reduce heat loss by putting it in a beaker of cotton wool to provide insulation
- To reduce evaporation put a lid on the cup
67
How can you find enthalpy changes using calorimetry?
- Used for dissolving, displacement or neutralisation reactions
- Mix the reactants in a polystyrene cup
- Reduce heat loss by putting it in a beaker of cotton wool to provide insulation
- To reduce evaporation put a lid on the cup
- Take the temperature every 30s until it reaches its peak
68
How can you find enthalpy changes using calorimetry (combustion)?
- Heat 50cm3 of water in a copper container (conductor of heat) and record initial temperature
- Use a screen to act as a draught excluder (and stay away from an open window)
- Weigh the spirit burner and lid
- Stir constantly and check temperature until it reaches 50*C
- Put out the flame and measure finial temperature of water
- Weigh the spirit burner and lid again
- Calculate the enthalpy change
69
How can you calculate the molar enthalpy change?
- Calculate the energy transferred
- Work out how many moles were produced (m = m / Mr)
- Divide the energy produced by the moles
70
How can you calculate the energy transferred?
- Work out the amount of reactant burnt (using measurements taken during the experiment)
- Work out the temperature before and after heating
- 4.2 x amount of reactant x temperature difference
- Answer in joules
71
Give an example of a reversible reaction
- Thermal decomposition of ammonium chloride (NH4Cl)
- White solid breaks into ammonia and hydrogen gases
- Cooling returns it to ammonium chloride
72
What is a dynamic equilibrium?
- When the relative quantities of reactants and products will reach a certain balance and stay there
- The forward and reverse reactions cancel each other out
- Taking place at exactly the same rate
73
How can changing the temperature give you more product? (reversible reactions)
- the endothermic will use up more heat
| - The exothermic reaction will give out more heat
74
How can changing the pressure give you more product? (reversible reactions)?
- If raised it will encourage the reaction with fewer molecules of gas (the endothermic reaction)
- If lowered it will encourage the reaction with more molecules of gas (exothermic)
