Topic 5 - Separate Chemistry Flashcards
1
Q
What is a yield?
A
The amount of product you get from a chemical reaction
2
Q
What do you mesure the yield in?
A
Grams/moles
3
Q
What is an actual yield?
A
The amount we actually get produced in a chemical reaction.
4
Q
What is a theoretical yield?
A
The amount of product you’d expect to get
5
Q
What are the 3 main reasons that an actual yield is different to the theoretical yield?
A
- Reactants might not all react
- There could be side reactions
- ## We may loose some of the products.
6
Q
What does it mean when the reactants dont all react?
A
Some of the mixture will be reactants.
This could be if the reaction is slow or if the reaction is reversibe.
7
Q
What does it mean when a chemical reaction has side reactions?
A
Reactants react to produce a different side product than the one we were expecting. E.g reacting with the air.
8
Q
How may some products be lost in a chemical reaction?
A
Gases may diffuse
Filtering may not capture all of the liquid or solid
9
Q
Why do we calculate the percentage yield?
A
To tell us what percentage of the theoretical yield we actually got.
10
Q
What is the equation for percentage yield?
A
Actual yield / Theoretical yield x 100
11
Q
What is atom economy?
A
A measure of how many reactant atoms form a desired product.
12
Q
How do you calculate atom economy?
A
Mr of desired products/ Mr of all reactants
13
Q
What are the 3 factors considered when creating the indsutrial Haber process?
A
- Cost of extracting and refining raw materials
- Energy costs ( High temp and pressure )
- Have to be able to control conditions to maximise yield but also react at an acceptable rate
14
Q
How do catalysts affect equilibrium
A
They do not move equilibrium, however increase rate of reaction wich then in turn icreases the rate that the equilibrium is reached
15
Q
Where are transition metals located?
A
in the middle of the periodic table
As they are located around eachother, in similar groups, they have the same/similar properties
16
Q
What are some everyday examples of transition metals?
A
Copper
Iron
Zinc
Gold
Silver
Platinum
17
Q
What properties do transiton metals have on a general level?
A
All the typical properties of metals
- Relatively hard, strong
- They’re shiny and malleable
- Conduct heat and electricity well
- High melting points ( one exclusion )
- High densitys
18
Q
Which transition metal doesn’t have a high melting point?
A
Mercury, which is liquid at room temp
19
Q
Compare the densitys of alkalai metals and transition metals
A
Transition metals are denser
e.g. At room temp, Potassium has a density of 0.9g cm-3, while copper has a density of 9.0g cm-3, and iron is 7.9g cm-3
20
Q
How do the properties of transition metals make them useful?
A
Gold in jewlery - shiny and malleable
Gold in some electrical components - Great electrical conductor and really corrosion resistant
Copper for pipes - malleable and corrosion resistant
Copper in wiring - good electrical conductor
They also make good catalysts
21
Q
Transition metals
What is a catalyst
A
A catalyst speeds up the rate of reaction without being changed or used up itself
22
Q
What are some examples of how transition metals make good catalysts?
A
Iron is the catalyst in the haber process for making ammonia
Vanadium pentoxide (V2O5) is the catalyst for making sulfuric acid in the contact process
23
Q
What is a common physical property of transition compounds?
A
The compounds of transition metals are very colorful
- What color they are depends on the transition metal ion they contain
24
Q
What color are compounds with Fe²⁺?
A
Light green
25
what color are compounds with Fe³⁺
Orange/brown
26
What color are compounds with Cu²⁺?
blue
27
Why are pure metals malleable?
Because they have a regular arrangement of identical atoms. The layers of ions can slide over eachother
| This means alloys are used for certain jobs instead
28
How are alloys made?
By adding another element to a metal - another metal or a non-metal
As we understand the properties of metals, alloys can be designed for specific uses
29
Why are alloys stronger than pure metal?
Different elements have different sized atoms. This upsets the aligned layers of pure metal, making it more difficult for them to slide over one another, making alloys stronger
30
Use carbon and iron as an example for making alloys and their strength
When carbon is added to iron, the smaller carbon atoms will upset the layers of pure iron atoms, making it more difficult for them to slide over one another, making the alloy stronger
31
Why are alloys created?
**Sometimes pure metal dont have the properties needed**
For example, alloys of iron called steels are often used instead of pure iron - with other metals added to make steels
32
What are alloys of iron called?
Steels
| this is made of steel and carbon
33
Why is steel more useful than iron?
Steel is harder than iron. Its also stronger than iron, as long as the percentage of Carbon does not get greater than 1%
Iron will rust (corrode) fairly quickly, but steel is much less likely to rust - a small amount of Carbon makes a big difference
34
What are some things made out of steel?
Girders, Bridges, Engine parts, Cutlery, Washing machines, Pans, Ships, tools, Cars
35
What is bronze made out of and what are it's uses?
**Bronze = Copper + Tin**
Bronze is harder than copper
**Uses**: Medals, decorative ornaments and statues
36
What is brass made out of and what are it's uses?
**Brass = Copper + Zinc**
Brass is more malleable than bronze and is used in situations where lower friction is required, e.g. Water taps and door fittings
37
What are gold alloys used for?
**To make Jewllery**
- Pure gold is very soft and malleable
-> Metals like Zinc, Copper and silver are used to strengthen the gold
38
How does gold carats work?
**Pure gold = 24 carat**
So the alloy 18 carat gold would be 75% pure gold
39
What are aluminum alloys often used for?
**To make Aircrafts**
Aluminium has a low density - important in aircraft manufacture. But pure aluminium is not strong enough for making aeroplanes, so its alloyed with small amounts of other metals to increase its strength
40
What is magnalium made of and used for?
**Magnalium = Aluminium + Magnesium**
When made with small amounts of magnesium (about 5%), magnalium is stronger, lighter, and corrodes less easily than pure aluminium
-> Used to make parts for cars/Aeroplanes
Magnalium with a higher magnesium content, (about 50%), is used in fireworks, as its reactive and burns brightly, like magnesium but more stable
41
What reaction is the Corrosion of metals
**A redox reaction**
The metal loses electrons, so its oxidised.
Simealtaneously, oxygen gains electrons when it reacts with metal
42
When can metals corrode, and what do they form?
Metals can corrode in the prescence of Oxygen and water to form their metal oxides
43
what is Oxidation?
Oxidation is loss of electrons, gain of oxygen or loss of hydrogen
44
what is reduction?
Reduction is gain of electrons, loss of oxygen or gain or hydrogen
45
What is rusting?
The corrosion of iron
46
When can rusting happen?
When the iron is in contact with oxygen (from the air) and water
47
What is an experiment used to show that iron can only rust with the prescence of water and oxygen?
- Iron nail in boiling tube with just water - no rust
- > Boiling water beforehand removes Oxygen and oil can be used to stop Air from getting in
- Iron nail in a boiling tube with just air - no rust
- > Calcium chloride can be used to absorb any water from the air
Iron nail in a boling tube with both - RUST
48
How do you prevent rusting
**Coating the iron with a barrier**
1) Painting
2) Oiling or Greasing
3) Sacraficial protection - Galvanising
4) Electroplating
49
What is ideal to prevent rusting on large/small structures?
Painting - this is also visually appealing as it can be nice and colorful
50
When is oiling or greasing used to prevent rust?
When Moving parts are involved e.g. bike chains
51
# Preventing rust
What is sacrificial protection?
Placing a more reactive material with the iron - The water and oxygen react with this "sacrficial" Metal instead of reacting with the object you're protecting
52
What is an example of sacrificial protection?
**Galvanising**
Where a coat of Zinc is put onto an iron substance to prevent rusting
The Zinc acts as a sacrificial protection - its more reactive than iron, so it'll lose electrons and corrode in preferance to iron. It aslo acts as a barrier
53
What things are often galvanised?
Steel buckets and corrugated iron roofing
54
What is electroplating?
coating the surface of a material with another material using electrolysis
The Cathode is the object you're going to electroplate, the anode is the bar of metal you're using for the plating (e.g. Silver)
Your electrolyte is a solution containing the metal ions of the metal you're using for the plating
55
What are some common uses of electroplating?
**Household objects** e.g. Cutlery and cooking utensils - to stop them corroding
-> The metals used for protection are unreactive and dont corrode easily
**Jewlery/Decorative items** - Often electroplated with metals like gold and silver.
Improves appearance - shiny / attractive
56
What is an example of electroplating?
**Electroplating silver onto a brass cup**
Cathode: Brass cup
Anode: Silver
Electrolyte: Silver nitrate solution
The silver ions from the electrolyte move towards the cathode and the metal gets deposited on the brass cup
-> The anode keeps a consistant supply of silver ions
57
What are the half equations for the electroplating of silver onto a brass cup?
**Cathode:**
Ag⁺ + e⁻ = Ag
**Anode**
Ag -> Ag⁺ + e⁻
58
What do titrations allow you to do?
Find out exactly how much acid is needed to neutralise a given quantity of alkali ( or vice versa )
59
What is the Method for titration?
1) Using a pipette, mesure out a set volume of alkali into a flask. Add a few drops of an indicator into a flask.
2) Fill a burette with a standard solution (known concentration) of acid
3) Use the burette to add acid into the alkali a bit at a time. Swirl the flask regularly - go slowly when you think the acid's almost neutralised
4) The indicator changes color when all the alkali has been neutralised
5) Record the titre (volume of acid used to neutralise the alkali)
6) Repeat this process a few times, making sure you have concordant results - take a mean
60
What indicators are commonly used in titrations?
Phenolphthalein
Methyl Orange
61
Why is universal indicator not used in titrations?
It shows a gradual color change - we want a single color
62
How should you fill the burette in titrations?
With it below eye level
-> Prevent acid splashes
-> Read from meniscus
63
What is a burette?
the long thing that drips acid into an alkali solution in titrations
64
How do you find out when the alkalai will be almost neutralised
Do a rough titrations
65
What can you put a flask on during titration to make the color change easier to see?
a white tile
66
What color does phenolphthalein change?
**Neutral/acid**: Colorless
**Alkali:** Pink
67
What color does methyl orange turn?
**Alkali**: Yellow
**Acids:** Red
68
What is the titre?
The volume of acid used to neutralise the alkali
69
What equation relates moles, concentration and volume
mol = conc (mol/dm3) x Vol ( dm3)
70
What can concentration be mesured in for titrations
Moles per dm3
| or it can be g/dm3
71
How to change cm into dm
/1000
72
What is percentage yield?
Actual yield / Theoretical yeild
Times 100
73
How is a high atom economy better for profits and the environment?
Low atom economy = Fast use of resources = Unsustainable = Unprofitable
-> Lots of waste products - need to think of disposal
Often more than one way to make a product, so use the most effecient way
74
What other things (apart from atom economy) have to be considered industrially?
1) the percentage yield - Higher the better
2) Rate of reaction - need to be sensibly fast
3) If its reversible, to keep yield of products high you may need to alter equlibrium position by changing reaction conditions (expensive)
75
What things should be considered when designing an industrial process?
1) Cost of extracting and refining raw materials - if its economically viable
-> If raw materials are too expensive to produce, it may not be profitable to make a product
2) Energy costs
3) Important to be able to control the conditions ( Temp, pressure, catalyst) to maximise your yield, but keep your reaction running at an acceptable rate
76
How are energy costs important to consider when designing an industrial process?
Energy costs (associated with reaching and maintaining conditions needed for the reaction e.g. temp / pressure) also affect whether a reaction is profitable.
Generally, High temps and pressures cost more to maintain, so low temperatures and pressures are used when possible
77
What does the haber process produce?
ammonia
78
what is the reaction for the haber process?
N2(g) + 3H2(g) ⇌ 2NH3(g) (+heat)
79
What are the conditions for the haber process?
**Pressure (high):** 200atm
**Temperature**: 450*c
Iron Catalyst
80
Why are the pressures high for the haber process
| 200 atm
High pressures favour the forward reaction ( less moles on right)
So pressure is set as high as possible to give the best yield, without making the plant too expensive to build (e.g too expensive would be about 1000atm)
| So, the operating pressure is 200atm
81
Why is the temp 450* for the haber process?
The forward reaction = exothermic, so yield of ammonia would be greater at lower temperatures
BUT lower temp = Lower RofR
So in industry, the temp is kept high to inrease RofR
| 450* is a compromise between max yield and speed of reaction
82
What affects how quickly equlibrium is reached?
Temperature, pressure and concentration
Increased RofR = faster rate at which equlibrium is reached
Equilibrium is always reached at higher temps, pressures and concentration -> Remember this could decrease depending on reaction
Catalysts
83
Do catalysts affect the position of equilibrium?
NO - it does not favour any side of equilibrium
But it does increase the rate at which equilibrium is reached
84
What are the 3 main ingredients in fertilisers?
Nitrogen, phosphorus, potassium
-> Plants absorb these from soil
85
What happens if plants dont get enough nutrients, how do fertilisers help this?
Their growth and life processes are affected
- Fertilisers supply these elements if they're missing from the soil, or provide more of them
- This increases crop yield, as the crops can grow faster and bigger
86
What are the advantages of ammonia fertilisers compared to traditional fertilisers (manure)?
- You can control the compositions of chemicals in them, as well as how much is made.
- Ammonia fertilisers are also soluble, so all the chemicals can dissolve into the soil to reach the plants
87
What does the diagram for the haber process look like?
Hydrogen and nitrogen gas are sent into a condenser in a 3:1 ratio, this reacts to form liquid ammonia
88
what can ammonia, water and oxygen react in a series to form?
nitric acid
89
What can you get by mixing ammonia with acids?
Ammonium salts
90
# Fertilisers
What is an example of ammonium salts?
Ammonia + Nitric acid -> ammonium nitrate
2NH3(aq) + HNO3(aq) -> NH4NO3(aq)
91
how is ammonium sulfate produced?
ammonia + dilute sulfuric acid
92
How can most fertilisers be made?
Titration
-> Acid (nitric, sulfuric, phosphoric) and alkali (ammonia or potassium hydroxide) to get the fertiliser salt.
93
How is ammonium sulfate(aq) made?
1) set up titration apparatus, add methyl orange indicator to the ammonia - it'll turn yellow
2) Slowly add the dilute sulfuric acid from the burette into the ammonia, untill the yellow color just turns to red. Gently swirl the flask as you add the acid, especially when you get close to the acid
3) When the color just changes to red, it means all the ammonia had been neutralised and you've got ammonia sulfate solution
4) To get pure ammonia sulfate (without indicator), note the volume of sulfiric acid needed then repeat the titration without the indicator.
94
How would you obtain solid ammonium sulfate from titrated aqueous ammonium sulfate?
Gently evaporate the solution (using a steam bath) untill only a little bit is left. Leave it to crystallise then filter out the crystals and leave them to dry
95
Why isnt titration used to make ammonium sulfate industrially?
Its impractical to use burettes and steam baths for large quantitys, and using crystalisation to get solid ammonium sulfate is too slow
96
How is ammonium sulfate made industrially?
1) Ammonia and sulfuric acid needs to be made from their raw materials
2) Ammonia from the haber process and sulfuric acid from the contact process
One industrial method uses a large chamber filled with ammonia gas. Sulfuric acid is sprayed into the reaction chamber, where it reacts with ammonia to produce ammonia sulfate powder
97
What is the molar volume?
the volume occupied by one mole of gas
98
What are the units for molar volume?
dm3/mol
99
What equation links, molar volume, volume and moles
Volume/moles = molar volume
100
What is avagadro's law of gas?
Under the same conditions, the same number of moles of different gases occupy the same volume
101
What does one mole of gas always occupy?
One mole of gas always occupies **24dm3** ( **= 24 000 cm3**) at room temperature and pressure
| (RTP = 20* and atm = 1
102
what is a cell?
A store of internal energy that can be transferred as an electric current in a circuit
102
what do fuel cells do?
use fuel and oxygen to produce electricity
103
What do chemical cells do?
Produce a voltage across the cell untill one of the reactants have been used up
104
What is a fuel cell?
a type of chemical cell that's supplied with fuel and oxygen and uses energy from the reaction between them to produce electrical energy efficiently
| e.g. a hydrogen-oxygen fuel cell
105
How does a hydrogen-oxygen fuel cell work?
Hydrogen as fuel, the reaction between H2 and O2 releases energy, which in turn can produce a voltage.
It doesnt produce any pollutants, only water
106
What is the equation for a Hydrogen - Oxygen fuel cell?
Hydrogen + Oxygen -> Water
2H2 + O2 -> H2O
107
What are the advantages of Hydrogen-oxygen fuel cells?
1) **Much more efficient** than power stations or batteries at producing electricity. If using the heat produced as well, their efficiency can be greater than 80%
2) Electricity is **generated directly from the reaction** (no turbines, generators ect.)
3) Less stages = **Reduces opportunity for energy to be lost as heat**
4) **No energy lost to friction** ( unlike fossil fuel power stations)
5) No major pollutants
108
What would be the benefit of Fuel cell vehicles?
They dont produce any contentional pollutants
-> (No greenhouse gases, no nitrogen oxides, no sulfur dioxide, no carbon monoxide)
Only by-products are water and heat
This would be a major advantage in cities, where pollution from traffic is a major problem
109
What could fuel cell power replace?
1) Smelly petrol and diesel cars, lorries and buses
2) Batteries - which are incredibly polluting to dispose of because they're usually made of highly toxic metal compounds
110
Why will fuel cells NOT end our reliance on conventional power stations or our dependance on fossil fuels?
1) Hydrogen is a gas so it takes up more space to store than liquid fuels like petrol
2) Its very explosive so is hard to store safely
3) The hydrogen fuel is often made either from hydrocarbons ( fossil fuels) or by electrolysis of water, which uses electricity ( the electricity provided usually comes from fossil fuels)
