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Chemistry > Unit 3b - Titration, Energy And Chemcial Tests > Flashcards

Unit 3b - Titration, Energy And Chemcial Tests Flashcards

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1
Q

What is “a mole”?

A

It is simply the name given to a certain number

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2
Q

When can you use moles as a unit of measurement?

A

When you’re talking about an amount of a substance

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3
Q

What is the experiment you do to find out how much alkali is needed to neutralise an acid?

A

Titration

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4
Q

What is concentration?

A

A measure of how crowded things are

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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

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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.

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7
Q

What is 1dm3 equivalent to?

A

1 litre and 1000cm3

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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)

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9
Q

Explain the stages of a titration

A
  1. Put some alkali in a flask along with some indicator - phenolphthalein or methyl orange
  2. 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)
  3. The indicator changes colour when all the alkali has been neutralised
  4. Record the results down and best to repeat a couple of times
  5. Calculate a mean
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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

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11
Q

What are the indicators most commonly used in a titration?

A

Phenolphthalein and methyl orange

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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

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13
Q

What colour will methyl orange be in a titration?

A

It is yellow in alkalis but red in acids

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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

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15
Q

The way to find the concentration in trams per dm3

A
  1. Work out the relative formula mass for the acid (adding up all the atomic masses)
  2. Figure out the concentration in moles using the equation
  3. Convert the concentration in moles into concentration in grams (Mass in grams = moles x relative formula mass)
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16
Q

Whenever chemical reactions occur what changes?

A

Energy meaning when chemicals get together it either heats up or cools down

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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.

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18
Q

What is the biggest problem with energy measurements?

A

The amount of energy lost to the surrounding

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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

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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

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21
Q

Example of how the polystyrene method would be used using hydrochloric acid and sodium hydroxide

A
  1. Place 25cm3 of dilute hydrochloric acid in a polystyrene cup and record the temperature
  2. Put 25cm3 of dilute sodium hydroxide in a measuring cylinder and record the temperature
  3. As Long as they’re at the same temperature add the alkali to the acid and stir
  4. 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)
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22
Q

What are the two types of reactions?

A

Exothermic and endothermic

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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

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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

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25
Q

What will energy always do in relation to bonds?

A

Energy must always be supplied to break bonds and energy is always released when bonds form

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26
Q

What happens during a chemical reaction?

A

Old bonds are broken and new bonds are formed

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27
Q

Why is bond breaking endothermic?

A

Because energy must always be supplied to break existing bonds

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28
Q

What kind of process is breaking existing bonds?

A

Endothermic

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29
Q

Which is forming new bonds exothermic?

A

Because energy is released when new bonds are formed

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30
Q

Why kind of process is forming new bonds?

A

Exothermic

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31
Q

A diagram to show bond breaking - exothermic

A 
Energy 
      Supplied 
⚫️🔴 ---> ⚫️ + 🔴
Strong       Bond 
bond           Broken
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32
Q

A diagram to show bond forming - exothermic

A 
Energy 
      Supplied 
⚫+️🔴 ---> ⚫️ 🔴     + energy released 
                     Strong        
                      bond formed
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33
Q

What happens to the energy needed in an endothermic reaction?

A

The energy required to break old bonds is greater than the energy released when new bonds form

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34
Q

What happens to the energy needed in an exothermic reaction?

A

The energy released in bond formation is greater than the energy used in breaking old bonds

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35
Q

How do cooling packs work?

A

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

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36
Q

What does burning fuels release?

A

Energy

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37
Q

How do you calculate how much fuel energy is released?

A

Using Calorimetry

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38
Q

How can you measure the amount of energy released when a fuel is burnt?

A

Burn the fuel and use the flame to heat up some water this is called calorimetry

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39
Q

What does a calorimetry usually use?

A

A glass or metal container

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40
Q

Why are calorimetrys usually made of copper?

A

Because copper conducts heat well

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41
Q

Explain the steps of a calorimetry

A
  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
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42
Q

What is the equation for figuring out the energy per gram of, for example, methylated spirit in a calorimetry

A 
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)

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43
Q

Where is energy wasted in a calorimetry?

A

In heating the can, air etc

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44
Q

What are two ways we use the energy from fuels for?

A

To generate electricity and to power cars

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45
Q

What are the downsides to the fuel? (4)

A
  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
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46
Q

What can energy be measured in?

A

Calories , joules (1 calorie = 4.2 joules)

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47
Q

What are the two ways you can use hydrogen as a fuel?

A

By burning it in a combustion engine or by using it in a fuel cell

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48
Q

When hydrogen and oxygen react what do they produce?

A

Water and energy

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49
Q

What is the reaction between hydrogen and oxygen?

A

Exothermic meaning it releases energy

50
Q

What can hydrogen gas be burnt in as a fuel in the combustion engines of vehicles?

A

Oxygen

51
Q

What is the word equation for reacting hydrogen and oxygen?

A

Hydrogen + oxygen —> water

52
Q

What is the pros of using hydrogen in a combustion engine?

A

It combines with oxygen in the air to form just water so it’s very clean

53
Q

What are the cons of using hydrogen as a fuel in a combustion engine?

A

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
Q

What is a fuel cell?

A

An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity

55
Q

What does a fuel cell use to produce electrical energy?

A

Fuel and oxygen

56
Q

What kind of fuel cell can hydrogen be used in?

A

A hydrogen-oxygen fuel cell

57
Q

When were fuel cells developed and why?

A

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
Q

How does a fuel cell differ from a battery?

A

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
Q

What is the car industry developing fuel cells for?

A

To replace conventional petrol/ Diesel engines

60
Q

What conventional pollutants do the fuel cell vehicles not produce?

A

No greenhouse gases, nitrogen oxides, sulfur dioxide or carbon monoxide

61
Q

What are the by products of a fuel cell?

A

Water and heat

62
Q

What kind of cities would, by using a fuel cell vehicle, be a big advantage?

A

In cities where air pollution from traffic is a big problem

63
Q

How can fuel cells help?

A

Helps countries be less dependant on crude oils

64
Q

Why are fuel cells not likely to be the end of either conventional power stations or dependency on fossil fuels? (3)

A
  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
Q

What does forensic science involve a lot of?

A

Chemical tests

66
Q

If it has a positive and negative part what kind of compound is it?

A

Ionic

67
Q

What do flame tests identify?

A

Metal ions

68
Q

How do you test for various metal ions?

A

By putting your substance in a flame and seeing what colour the flame goes

69
Q

What colour in a flame test would lithium (Li+) give?

A

Crimson flame

70
Q

What colour in a fame test would sodium (Na+) give)

A

A orange flame

71
Q

What colour in a flame test would potassium (K+) give?

A

Lilac

72
Q

What colour in a flame test would calcium (Ca2+) give?

A

Red

73
Q

What colour in a flame test would barium (Ba2+) give?

A

A green flame

74
Q

Method to flame test a compound in a lab

A

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
Q

What kind of ion do metals always form?

A

Positive

76
Q

When added to NaOH what do some metal ions form?

A

A coloured precipitate

77
Q

Why do many metal hydroxides precipitate out of a solution when formed?

A

Because they are insoluble

78
Q

Explain the sodium hydroxide test

A

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
Q

What is the colour of precipitate in a sodium hydroxide test for calcium (Ca2+)

A

White

80
Q

What is the colour of precipitate in a sodium hydroxide test for copper (II) (Cu2+)

A

Blue

81
Q

What is the colour of precipitate in a sodium hydroxide test for Iron (II) (Fe2+)

A

Green

82
Q

What is the colour of precipitate in a sodium hydroxide test for Iron (III) (Fe3+)

A

Brown

83
Q

What is the colour of precipitate in a sodium hydroxide test for magnesium (Mg2+)

A

White

84
Q

What is the colour of precipitate in a sodium hydroxide test for aluminium (Al3+)

A

White at first but it rediscovers in excess NaOH to form a colourless solution

85
Q

What is the ionic reaction for calcium in a sodium hydroxide test

A

Ca2+ + 2OH- —> Ca(OH)

2

86
Q

What is the ionic reaction to copper (II) in a sodium hydroxide test?

A

Cu2+ + 2OH- —> Cu(OH)

2

87
Q

What is the ionic reaction to iron (II) in a sodium hydroxide test?

A

Fe2+ + 2OH- —> Fe(OH)

2

88
Q

What is the ionic reaction to iron (III) in a sodium hydroxide test?

A

Fe3+ + 3OH- —> Fe(OH)

3

89
Q

What is the ionic reaction to aluminium in a sodium hydroxide test

A

Al3+ + 3OH- —> Al(OH)
3
Then
Al(OH) + OH —> Al(OH) -
3 4

90
Q

What is the ionic reaction to magnesium in a sodium hydroxide test

A

Mg2+ + 2OH- —> Mg(OH)

2

91
Q

How can you test if a gas contains carbon dioxide?

A

Bubble it through limewater if it’s carbon dioxide the limewater turns cloudy

92
Q

How can you test for carbonate ions (CO 2-)

3

A

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
Q

How do you test for halide ions like chloride (Cl-) , bromide (Br-) or iodide (I-) ?

A

Add dilute nitric acid (HNO. ) followed by silver nitrate
3
Solution (AgNO. )
3

94
Q

What colour precipitate does chloride give in the test for halide ions?

A

White of silver chloride

95
Q

What colour precipitate does bromide give in the test for halides?

A

Cream precipitate of silver bromide

96
Q

What colour precipitate does iodide give in the test for halide ions?

A

A yellow precipitate of silver iodide

97
Q

What is the equation for chlorides reaction in the test for halide ions?

A

Ag+ + Cl- —> AgCl

98
Q

What is the equation for bromides reaction in the test for halide ions?

A

Ag+ +Br- —> AgBr

99
Q

What is the equation for iodides reaction in the test for halide ions?

A

Ag+ +I- —> Agl

100
Q

What is the test for sulfate ions (SO 2-)

4

A

Add dilute HCl followed by barium chloride solution, BaCl

2

101
Q

In the sulfate test what does a white precipitate of barium sulfate mean?

A

The original compound was a sulfate

102
Q

The equation for the sulfate test

A

Ba2+ + SO 2- —> BaSO

4. 4

103
Q

What do energy level diagrams show?

A

If a reaction is exothermic or endothermic

104
Q

In exothermic reactions what is 🔺H?

A

-ve (meaning it goes down)

105
Q

What does🔺H represent?

A

The energy change

106
Q

In an exothermic energy level diagram what does it look like?

A

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
Q

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?

A

The energy given out in the reaction (per mole)

108
Q

What does the initial rise of the line in exothermic energy level diagrams represent?

A

The energy needed to break old bonds - the activation energy

109
Q

On an exothermic energy level diagram what represents the activation energy?

A

The initial rise of the line from the reactants until it drops back down to where the reactants energy first started

110
Q

What on a exothermic energy level diagram redo resents the energy given out?

A

The heigh from the reactants energy to the products

111
Q

In endothermic reactions what is 🔺H?

A

+ve (meaning it needs more energy to create the product)

112
Q

What does an endothermic energy level diagram look like?

A

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
Q

What does the difference in height represent in an endothermic energy level diagram?

A

The energy taken in during the reaction (per mole)

114
Q

What does the activation energy represent?

A

The minimum energy needed by reacting particles to break their bonds

115
Q

If a catalyst is used what happens to the activation energy?

A

It is lowered

116
Q

What does a catalyst provide?

A

A different pathway for a reaction that has a lower activation energy (so the reaction happens more easily and quickly)

117
Q

On an energy level diagram when a catalyst is added where is that represented?

A

From the reactants energy the initial curve but Its the lower curve up until the reactants energy again

118
Q

With a catalyst what happens to the overall energy change (🔺H)shown on an energy level diagram?

A

It remains the same

119
Q

How do you calculate bond energy?

A

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
Q

Do the bond energy calculations for H + Cl —> 2HCL
2 2
When H-H=436kl/mol Cl-Cl=242kj/mol H-Cl=431kj/mol

A
  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

Chemistry (6 decks)

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