Unit 3b - Titration, Energy And Chemcial Tests Flashcards
1
Q
What is “a mole”?
A
It is simply the name given to a certain number
2
Q
When can you use moles as a unit of measurement?
A
When you’re talking about an amount of a substance
3
Q
What is the experiment you do to find out how much alkali is needed to neutralise an acid?
A
Titration
4
Q
What is concentration?
A
A measure of how crowded things are
5
Q
What can the concentration of a solution be measured in? (2)
A
Moles per dm3 (I.e moles per litre) this means that 1 mole of stuff in 1 dm3 of solution has a concentration of 1mol/dm3
Grams per dm3 so 56 grass of stuff dissolved in 1 dm3 of solution has a concentration of 56 grass per dm3
6
Q
If you increase the amount of solute you dissolve in a given volume what happens to the concentration?
A
It increases because the more crowded the solute molecules are the more concentrated the solution is.
7
Q
What is 1dm3 equivalent to?
A
1 litre and 1000cm3
8
Q
What does a titration allow you to find out exactly?
A
How much acid is needed to neutralise a quantity of alkali (or vice versa)
9
Q
Explain the stages of a titration
A
- Put some alkali in a flask along with some indicator - phenolphthalein or methyl orange
- Add the acid a bit at a time to the alkali using a burette giving the flask a regular swirl. (Go especially slowly when you think the alkalis almost neutralised)
- The indicator changes colour when all the alkali has been neutralised
- Record the results down and best to repeat a couple of times
- Calculate a mean
10
Q
Why don’t you use universal indicator while carrying out a titration?
A
Because it changes colour gradually and we want a definite colour change
11
Q
What are the indicators most commonly used in a titration?
A
Phenolphthalein and methyl orange
12
Q
What colour will phenolphthalein go during a titration?
A
As it is added to an alkali it will be pink but in an acid it will be colourless
13
Q
What colour will methyl orange be in a titration?
A
It is yellow in alkalis but red in acids
14
Q
What is the equation to do a titration calculation when it’s in moles per dm3?
A
C V C V
1 1 2 2
-------- = --------
N N
1 2
C= concentration v= volume N=mole ratio
15
Q
The way to find the concentration in trams per dm3
A
- Work out the relative formula mass for the acid (adding up all the atomic masses)
- Figure out the concentration in moles using the equation
- Convert the concentration in moles into concentration in grams (Mass in grams = moles x relative formula mass)
16
Q
Whenever chemical reactions occur what changes?
A
Energy meaning when chemicals get together it either heats up or cools down
17
Q
How can you measure the amount of energy released by a chemical reaction in solution?
A
By taking the temperature of the reagents (making sure they are the same) mixing them in a polystyrene cup and measuring the temperature of the solution at the end.
18
Q
What is the biggest problem with energy measurements?
A
The amount of energy lost to the surrounding
19
Q
How can you reduce energy lost to the surroundings?
A
Putting insulation around the experiment e.g cotton wool and putting s lid on a cup to reduce energy lost by for example evaporation
20
Q
What does the method of taking a temperature, mixing in a polystyrene cup and measuring the temperature after work for testing? (2)
A
Reactions of solids with water e.g dissolving ammonia nitrate in water and neutralisation reactions
21
Q
Example of how the polystyrene method would be used using hydrochloric acid and sodium hydroxide
A
- Place 25cm3 of dilute hydrochloric acid in a polystyrene cup and record the temperature
- Put 25cm3 of dilute sodium hydroxide in a measuring cylinder and record the temperature
- As Long as they’re at the same temperature add the alkali to the acid and stir
- Take the temperature of the mixture every 30 seconds and record the highest temperature is reaches
(This method can also be used when energy is being absorbed - there will be a fall in temperature)
22
Q
What are the two types of reactions?
A
Exothermic and endothermic
23
Q
What is an exothermic reaction and an example?
A
Is one which gives out energy to the surroundings, usually in the form of heat and usually shown by a rise in temperature for example fuel burning or neutralisation reactions
24
Q
What is an endothermic reaction and an example?
A
Is one which takes in energy from the surroundings, usually in the form of heat and is usually shown by a fall in temperature for example photosynthesis
25
What will energy always do in relation to bonds?
Energy must always be supplied to break bonds and energy is always released when bonds form
26
What happens during a chemical reaction?
Old bonds are broken and new bonds are formed
27
Why is bond breaking endothermic?
Because energy must always be supplied to break existing bonds
28
What kind of process is breaking existing bonds?
Endothermic
29
Which is forming new bonds exothermic?
Because energy is released when new bonds are formed
30
Why kind of process is forming new bonds?
Exothermic
31
A diagram to show bond breaking - exothermic
```
Energy
Supplied
⚫️🔴 ---> ⚫️ + 🔴
Strong Bond
bond Broken
```
32
A diagram to show bond forming - exothermic
```
Energy
Supplied
⚫+️🔴 ---> ⚫️ 🔴 + energy released
Strong
bond formed
```
33
What happens to the energy needed in an endothermic reaction?
The energy required to break old bonds is greater than the energy released when new bonds form
34
What happens to the energy needed in an exothermic reaction?
The energy released in bond formation is greater than the energy used in breaking old bonds
35
How do cooling packs work?
They use an endothermic reaction to draw heat from an injury the pack contains two different compartmented with different chemicals in and when you use it you snap the partition and the chemicals mix and react taking in heat
36
What does burning fuels release?
Energy
37
How do you calculate how much fuel energy is released?
Using Calorimetry
38
How can you measure the amount of energy released when a fuel is burnt?
Burn the fuel and use the flame to heat up some water this is called calorimetry
39
What does a calorimetry usually use?
A glass or metal container
40
Why are calorimetrys usually made of copper?
Because copper conducts heat well
41
Explain the steps of a calorimetry
1. Put 50g of water in the copper can and record its temperature
2. Weigh the spirit burner and lid
3. Put the spirit burner underneath the can and light the wick. Heat the water, stirring constantly, until the temperature reaches about 50*c
4. Put out the flame using the burner lid and measure the final temperature of the water
5. Weigh the spirit burner and lid again
42
What is the equation for figuring out the energy per gram of, for example, methylated spirit in a calorimetry
```
Q=mc🔺T
Q = energy transferred (in J)
M = mass of water (in g)
C= specific heat capacity of water (=4.2)
🔺T= temperature change (in *C)
```
(You must also know how much fuel was released to heat up the water and then divide your answer to the equation by whatever the difference of mass of fuel is and times by 100 to find how much energy is released per gram)
43
Where is energy wasted in a calorimetry?
In heating the can, air etc
44
What are two ways we use the energy from fuels for?
To generate electricity and to power cars
45
What are the downsides to the fuel? (4)
1. Harmful effects on the environment e.g burning fossil fuels releases carbon dioxide, a greenhouse gas which causes global warming and other types of climate change.
2. It's expensive to slow down the effects and developing alternate energy sources like tidal power costs money
3. Crude oil is running out and we use a lot of fuel from crude oil e.g petrol and diesel and as if runs out the prices increase. That means everything transported by Lorry etc gets more expensive too
4. The price of crude oil has a big economic effect
46
What can energy be measured in?
Calories , joules (1 calorie = 4.2 joules)
47
What are the two ways you can use hydrogen as a fuel?
By burning it in a combustion engine or by using it in a fuel cell
48
When hydrogen and oxygen react what do they produce?
Water and energy
49
What is the reaction between hydrogen and oxygen?
Exothermic meaning it releases energy
50
What can hydrogen gas be burnt in as a fuel in the combustion engines of vehicles?
Oxygen
51
What is the word equation for reacting hydrogen and oxygen?
Hydrogen + oxygen ---> water
52
What is the pros of using hydrogen in a combustion engine?
It combines with oxygen in the air to form just water so it's very clean
53
What are the cons of using hydrogen as a fuel in a combustion engine?
You need a special, expensive engine. Although hydrogen can be made from water you still need to use energy from another source to make it. It's also hard to store safely as it's very explosive.
54
What is a fuel cell?
An electrical cell that's supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity
55
What does a fuel cell use to produce electrical energy?
Fuel and oxygen
56
What kind of fuel cell can hydrogen be used in?
A hydrogen-oxygen fuel cell
57
When were fuel cells developed and why?
In the 1960s as part of the space programme to proved electrical power on spacecraft because they were more practical than solar cells and safer than nuclear power
58
How does a fuel cell differ from a battery?
It doesn't run down or need recharging from the mains because it'll produce energy in the form of electricity and heat as long as the fuel is supplied
59
What is the car industry developing fuel cells for?
To replace conventional petrol/ Diesel engines
60
What conventional pollutants do the fuel cell vehicles not produce?
No greenhouse gases, nitrogen oxides, sulfur dioxide or carbon monoxide
61
What are the by products of a fuel cell?
Water and heat
62
What kind of cities would, by using a fuel cell vehicle, be a big advantage?
In cities where air pollution from traffic is a big problem
63
How can fuel cells help?
Helps countries be less dependant on crude oils
64
Why are fuel cells not likely to be the end of either conventional power stations or dependency on fossil fuels? (3)
1. Hydrogen is a gas so it takes up a lot of space to store than liquid fuels like petrol
2. It's very explosive so it's difficult to safely store
3. The hydrogen fuel is made from hydrocarbons (from fossil fuels) or electrolysis of water which requires energy and the energy needs to be generated somehow - usually by fossil fuels
65
What does forensic science involve a lot of?
Chemical tests
66
If it has a positive and negative part what kind of compound is it?
Ionic
67
What do flame tests identify?
Metal ions
68
How do you test for various metal ions?
By putting your substance in a flame and seeing what colour the flame goes
69
What colour in a flame test would lithium (Li+) give?
Crimson flame
70
What colour in a fame test would sodium (Na+) give)
A orange flame
71
What colour in a flame test would potassium (K+) give?
Lilac
72
What colour in a flame test would calcium (Ca2+) give?
Red
73
What colour in a flame test would barium (Ba2+) give?
A green flame
74
Method to flame test a compound in a lab
Clean the wire loop by dipping it into hydrochloric acid and rinsing with distilled water.Dip a clean wire loop into a sample of the compound and put the wire loop in the bleak blue part of the Bunsen flame.
75
What kind of ion do metals always form?
Positive
76
When added to NaOH what do some metal ions form?
A coloured precipitate
77
Why do many metal hydroxides precipitate out of a solution when formed?
Because they are insoluble
78
Explain the sodium hydroxide test
If the flame test doesn't work, add a few drops of sodium hydroxide solution to a solution of the mystery compound in hopes of forming an insoluble hydroxide and if you get a coloured insoluble hydroxide you can tell which metal it is
79
What is the colour of precipitate in a sodium hydroxide test for calcium (Ca2+)
White
80
What is the colour of precipitate in a sodium hydroxide test for copper (II) (Cu2+)
Blue
81
What is the colour of precipitate in a sodium hydroxide test for Iron (II) (Fe2+)
Green
82
What is the colour of precipitate in a sodium hydroxide test for Iron (III) (Fe3+)
Brown
83
What is the colour of precipitate in a sodium hydroxide test for magnesium (Mg2+)
White
84
What is the colour of precipitate in a sodium hydroxide test for aluminium (Al3+)
White at first but it rediscovers in excess NaOH to form a colourless solution
85
What is the ionic reaction for calcium in a sodium hydroxide test
Ca2+ + 2OH- ---> Ca(OH)
| 2
86
What is the ionic reaction to copper (II) in a sodium hydroxide test?
Cu2+ + 2OH- ---> Cu(OH)
| 2
87
What is the ionic reaction to iron (II) in a sodium hydroxide test?
Fe2+ + 2OH- ---> Fe(OH)
| 2
88
What is the ionic reaction to iron (III) in a sodium hydroxide test?
Fe3+ + 3OH- ---> Fe(OH)
| 3
89
What is the ionic reaction to aluminium in a sodium hydroxide test
Al3+ + 3OH- ---> Al(OH)
3
Then
Al(OH) + OH ---> Al(OH) -
3 4
90
What is the ionic reaction to magnesium in a sodium hydroxide test
Mg2+ + 2OH- ---> Mg(OH)
| 2
91
How can you test if a gas contains carbon dioxide?
Bubble it through limewater if it's carbon dioxide the limewater turns cloudy
92
How can you test for carbonate ions (CO 2-)
| 3
Because carbonates react with dilute acids to forM Carbon Dioxide and you Bubble this through limewater and if it turns cloudy then the gas is carbondixoide but if it doesn't then it's not
93
How do you test for halide ions like chloride (Cl-) , bromide (Br-) or iodide (I-) ?
Add dilute nitric acid (HNO. ) followed by silver nitrate
3
Solution (AgNO. )
3
94
What colour precipitate does chloride give in the test for halide ions?
White of silver chloride
95
What colour precipitate does bromide give in the test for halides?
Cream precipitate of silver bromide
96
What colour precipitate does iodide give in the test for halide ions?
A yellow precipitate of silver iodide
97
What is the equation for chlorides reaction in the test for halide ions?
Ag+ + Cl- ---> AgCl
98
What is the equation for bromides reaction in the test for halide ions?
Ag+ +Br- ---> AgBr
99
What is the equation for iodides reaction in the test for halide ions?
Ag+ +I- ---> Agl
100
What is the test for sulfate ions (SO 2-)
| 4
Add dilute HCl followed by barium chloride solution, BaCl
| 2
101
In the sulfate test what does a white precipitate of barium sulfate mean?
The original compound was a sulfate
102
The equation for the sulfate test
Ba2+ + SO 2- ---> BaSO
| 4. 4
103
What do energy level diagrams show?
If a reaction is exothermic or endothermic
104
In exothermic reactions what is 🔺H?
-ve (meaning it goes down)
105
What does🔺H represent?
The energy change
106
In an exothermic energy level diagram what does it look like?
The product (this thing that is made) is at a lower energy level than the reactant (the thing that we started with) showing a decrease of the curve on the graph
107
What does the different in height on an exothermic energy level diagram (from where the reaction starts ignoring the initial increase of energy to where the product is) represent?
The energy given out in the reaction (per mole)
108
What does the initial rise of the line in exothermic energy level diagrams represent?
The energy needed to break old bonds - the activation energy
109
On an exothermic energy level diagram what represents the activation energy?
The initial rise of the line from the reactants until it drops back down to where the reactants energy first started
110
What on a exothermic energy level diagram redo resents the energy given out?
The heigh from the reactants energy to the products
111
In endothermic reactions what is 🔺H?
+ve (meaning it needs more energy to create the product)
112
What does an endothermic energy level diagram look like?
The reactants are at a lower energy than the products showing the graph increasing as a higher energy is needed to create product than the reactants
113
What does the difference in height represent in an endothermic energy level diagram?
The energy taken in during the reaction (per mole)
114
What does the activation energy represent?
The minimum energy needed by reacting particles to break their bonds
115
If a catalyst is used what happens to the activation energy?
It is lowered
116
What does a catalyst provide?
A different pathway for a reaction that has a lower activation energy (so the reaction happens more easily and quickly)
117
On an energy level diagram when a catalyst is added where is that represented?
From the reactants energy the initial curve but Its the lower curve up until the reactants energy again
118
With a catalyst what happens to the overall energy change (🔺H)shown on an energy level diagram?
It remains the same
119
How do you calculate bond energy?
Firstly, you spit up the equation for example if you had H
2
On one side of the equation That would mean you have H-H and you should be given the bond energy for that. Then you should add up all the bond energy on one side. Do the same on the other side and look at the difference. If it's a bigger number on the product side it's an exothermic reaction and the answer should be the change from reactant to product but with a minus sign. But if it's a smaller number on the product side then the reaction is endothermic and it should be the change without a minus sign.
120
Do the bond energy calculations for H + Cl ---> 2HCL
2 2
When H-H=436kl/mol Cl-Cl=242kj/mol H-Cl=431kj/mol
1. H-H + Cl-Cl--->2H-Cl
2. H-H + Cl-Cl = 436+242= 678kj
3. Cl-H = 431
4. 431 x 2 = 862kj
5. 862 - 678 = 184 kj/mol
6. The answer is 🔺H = -184kj/mol because the reaction is exothermic
