What in medicine ? Flashcards
1
Q
What is the general formula for alcohols ?
A
ROH
2
Q
What is the general formula for aldehydes ?
A
RCHO
3
Q
What is the general formula for ketones ?
A
RCOR’
4
Q
What is the general formula for carboxylic acids ?
A
RCOOH
5
Q
What is the general formula for acid anhydrides ?
A
(RCO)2O
6
Q
What is the general formula for esters ?
A
RCOOR’
7
Q
What is the general formula for ethers ?
A
ROR’
8
Q
What is the general formula for ethers ?
A
ROR’
9
Q
Which of the homologous series has the general formula RCOR’ ?
A
Ketones
10
Q
What is the functional group for an alcohol ?
A
-OH
11
Q
What does the primary, secondary and tertiary structure of an alcohol dependent on ?
A
Which arbon atom the -OH group is bonded to
12
Q
How do you oxidise alcohols ?
A
By using the oxidising agent of potassium dichromate (VI)
13
Q
What are primary alcohols oxidised to ?
A
Aldehydes and then to carboxylic acids
14
Q
What are secondary alcohols oxidised to ?
A
Ketones only
15
Q
What are tertiary alcohols oxidised to ?
A
Aren’t oxidised
16
Q
How are primary alcohols oxidised to aldehydes and then to carboxylic acid ?
A
- Gently heating a primary alcohol with potassium dichromate(VI) solution and sulfuric acid in a flask produces an aldehyde.
- Once the aldehyde is formed, there will be lots of oxidising agent around ready to turn it into a carboxylic acid.
- To just get to the aldehyde, you need to remove it from the oxidising agent as soon as possible.
- You can do this using distillation apparatus. The aldehyde evaporates and is distilled off quickly.
- To produce the carboxylic acid, the alcohol has to be vigorously oxidised.
- The alcohol is mixed with excess oxidising agent and heated under reflux.
- Heating under reflux means you can increase the temperature of an organic reaction to boiling point, without losing volatile solvents, reactants or products.
- Any vapourised compounds are cooled so that they condense and drip back into the reaction mixture.
17
Q
How will secondary alcohols oxidise to ketones ?
A
- Refluxing a secondary alcohol with acidified dichromate(VI) will produce a ketone.
- Ketones can’t be oxidised easily, so even prolonged refluxing won’t produce anything more.
18
Q
How are alcohols turned into alkenes ?
A
In a dehydration reaction
19
Q
How can you make ethene ?
A
Eliminating water from ethanol in a dehydration reaction
C2H5OH –> CH2=CH2 + H2O
20
Q
Describe how a dehydration reaction when a alcohol turns into a alkene ?
A
- An alcohol vapour is passed over a hot catalyst of aluminium oxide > the catalyst provides a large surface area for the reaction.
OR - Reflux the alcohol with excess concentrated sulfuric acid at 170oC. The alkene produced is then collected over water.
21
Q
Describe what happens in the method when concentrated sulfuric acid acts as a dehydrated agent in the elimination reaction ?
A
- The hydroxyl group will be bond to the H+ ion from the strong acid. So the alcohol is protonated, giving the oxygen a positive charge.
- The positively charged oxygen will pull electrons away from the neighbouring carbon, and water will fall off, creating an unstable carbocation intermediate.
- The carbocation loses H+ and the alkene of formed.
22
Q
When alcohols react with carboxylic acid, what do they form ?
A
Esters
23
Q
What is esterification ?
A
When you react a carboxylic acid with an alcohol, in the presence of an acid catalyst to form an ester.
24
Q
Alcohols react with carboxylic acids to create esters. But alcohols also react with … to create esters ?
A
Acid anhydrides.
25
What are two ways to create esters ?
Alcohols and carboxylic acids
Alcohols and acid anhydrides.
26
What is formed when you react an alcohol with a carboxylic acid ?
Ester and water
27
What is formed when you react an alcohol with an acid anhydride ?
Ester and carboxylic acid
28
What is a substitution reaction ?
When an alcohol will react with compounds containing halide ions.
29
How do you make 2-chloro-2-methylpropane ?
You need to shake 2-methylpropan-2-ol with hydrochloric acid.
30
What is the difference between a primary alcohol, a secondary alcohol and a tertiary alcohol ?
Primary > one r-group
Secondary > two r-groups
Tertiary > three r-groups
31
What will acidified potassium dichromate(VI) oxidise secondary alcohols to ?
Ketones only
32
Describe two ways that alcohols can be dehydrated ?
- Alcohols vapour can be passed over a hot catalyst of aluminium oxide
OR
- Reflux alcohol with excess concentrated sulfuric acid. The alkene can then be collected over water.
33
Name two functional groups that can be reacted together to form an ester ?
Alcohol and carboxylic acid
Alcohol and acid anhydride
34
Give the reagents and conditions needed to produce a carboxylic acid ?
Using an oxidising agent, Potassium dichromate(VI), this then needs to be heated under reflux.
35
Write the shortened structural formulae for the products of the following reactions.
a) ethanoic acid + ethanol
b) butan-2-ol + hydrogen bromide
c) ethanoic anhydride + methanol
d) ethanol refluxed with concentrated sulfuric acid
a) CH3COOCH2CH3 + H2O
b) CH3CHBrCH2CH3 + H2O
c) CH3COOCH3 + CH3COOH
d) CH2CH2 + H2O
36
What functional groups do phenols have ?
-OH group
37
What is the formula for phenols ?
C6H5OH
38
What is the test for phenols ?
Add phenol to a neutral iron(iII) chloride solution and shake
39
What is the positive colour for the presence of phenol ?
A purple colour
40
Are phenols weak acids or strong acids ?
Weak acids
41
How is a weak acids formed by phenols ?
Phenols dissolve a little bit in water to form a phenoxide ion an a H+ ion. So the solution formed is a weak acid.
42
What is produced when phenols react with alkalis ?
Salt and water
43
Do phenols react with a carbonate solution ?
No, phenols do not react with carbonate solutions.
44
What is a good way to tell the difference between a carboxylic acid and phenol ?
Carboxylic acids react with alkalis and produced CO2 gas.
45
Do phenols react with acid anhydrides to produce esters ?
Yes
46
Will phenols react with acid anhydrides? What will they produce ?
Yes
An ester and an carboxylic acid
47
Will phenols react with carboxylic acids ?
No
48
What is a good way of determining whether a substance is a phenol or an alcohol ?
A phenol will react with an acid anhydride but not a carboxylic acid.
49
How can you test a compound to see if it is a phenol ?
Test using Iron(III) chloride and shake
50
Are phenols acidic, alkaline or neutral ? Explain your answer.
Weak acids, because they react with water to form a phenoxide ion and an H+ ion.
51
A student has solutions of phenol, ethanoic acid and salicylic acid (which has a phenol and a carboxylic acid group). Neutral iron(III) chloride solution and sodium carbonate solution are added, separately to samples of each solution. Complete the table below showing the results of each test.
Neutral iron(iii) chloride solution
Phenol = purple
Ethanoic acid = no colour change
Salicylic acid = purple
Sodium carbonate solution
Phenol = no reaction
Ethanoic acid = gas evolved
Salicylic acid = gas evolved
52
A student has solutions of phenol, ethanoic acid and salicylic acid (which has a phenol and a carboxylic acid group). Neutral iron(III) chloride solution and sodium carbonate solution are added, separately to samples of each solution. Complete the table below showing the results of each test.
Neutral iron(iii) chloride solution
Phenol = purple
Ethanoic acid = no colour change
Salicylic acid = purple
Sodium carbonate solution
Phenol = no reaction
Ethanoic acid = gas evolved
Salicylic acid = gas evolved
53
What does refluxing prevents ?
The loss of any volatile organic substances
54
How do you reflux ?
- Heat the solution in a flask fitted with a vertical liebig condenser - this causes the solution to continuously evaporate and then condenses back into the flask, giving it time to react.
- Heat the solution electronically - heating mantles. This avoids naked flames that might ignite the compounds.
55
How do you distill ?
- Gently heat it in distillation apparatus. The substance will evaporate out of the mixture in order of increasing boiling point.
- When evaporated substance enters the condenser, it is cooled and condenses back to a liquid, which can be collected by placing a flask at the open end of the condenser.
- A thermometer shows the boiling point of the substance that is evaporating at any given time. If you know the boiling point of your pure product, you can use the thermometer to find out when it's evaporating and therefore when to collect it.
- Sometimes a product is formed that will go on to react further if it's left in the reaction mixture. If the product has a lower boiling point than the starting material, the reaction can be carried out in distillation apparatus. The product is distilled from the reaction mixture as soon as it forms, and is collected in a separate container.
56
How are volatile liquid purified ?
By redistillation
57
Describe the process of redistillation ?
- After distillation, the product will probably still contain impurities
- If a product and its impurities have different boiling points, then redistilisation can be used to separate them. You just use the same distillation apparatus as shown above, but this time you heat the impure product, instead of the reaction mixture.
- When the liquid you want boils, place a flask at the open end of the condenser ready to collect your pure product.
- When the thermometer shows the temperature is changing, put another flask at the end of the condenser because a different liquid is about to be delivered.
58
What does separation remove ?
Water soluble impurities from the product
59
Describe the process of separation ?
- If a product is insoluble in water then you can use separation to remove any impurities that do dissolve in water, such as salts or in water soluble organic compounds.
- Once the reaction to form the product is completed, pour the mixture into a separating funnel, and add water.
- Shake the funnel and then allow it to settle. The organic layer is less dense than the aqueous layer so should float on top. Any water soluble impurities will have dissolved in the lower aqueous layer. You can then open the stopper on the separating funnel and run off the aqueous layer. This leaves you with the product in the funnel.
60
How do you remove water from a purified product ?
Drying it.
61
Describe the process of drying a purified product ?
- If you use separation to purify a product, the organic layer will end up containing trace amounts of water, so it has to be dried.
- To do this, add an anhydrous salt such as Magnesium sulfate, or Calcium chloride. The salt is used as a drying agent > it binds to any water present to become hydrated.
- When you first add the salt to the organic layer it will be lumpy. This means you need to add more. You know that all the water has been removed when you swirl the mixture and it looks like a snow globe.
- You can then filter the mixture to remove the solid drying agent.
62
What is filtration used to do ?
To isolate solid organic products
63
Describe the process of filtration ?
- If the reactants in an organic reaction are liquids and the product you are after is a solid, you can isolate the product from the reaction mixture by filtration.
- Pour the reaction mixture, containing the liquid and solid, into a Buchner funnel with filter paper on the bottom.
- Below the funnel there should be a seled side-arm flask attached to a vacuum line. The reduced pressure inside the flask, caused by the vacuum line removing air, will force the liquid through the funnel, leaving the solid product on the filter paper to be collected.
64
Describe the process of recrystallization for the purification of organic solids ?
- Add very hot solvent to the impure solid util it just
dissolves > it's really important not to add too much solvent.
- This should give a saturated solution of the impure product
- Leave the solution to cool down slowly. Crystals of the product form as it cools.
- The impurities stay in solution. They're present in much smaller amounts then the product, so they'd take much longer to crystallise out.
- Remove the crystals by filtration and wash them with ice-cold solvent. The crystals then need to be dried > leaving you with crystals of your product that are much purer than the original solid.
65
Why is the choice of solvent for recrystallisation important ?
- When you recrystallise a product, you must use an appropriate solvent for that particular substance. It will only work if the solid is very soluble in the hot solvent, but nearly insoluble when the solvent is cold.
- If your product isn't soluble enough in the hot solvent you won't be able to dissolve it at all.
- If your product is too soluble in the cold solvent, most of it will stay in the solution even after cooling. When you filter it, you lose most of your product, giving it a very low yield.
66
What is a good way to determine purity ?
Measuring melting point
67
Describe the process of measuring the melting point to determine the purity ?
- You can use melting point apparatus to accurately determine the melting point of an organic solid.
- Pack a small sample of the solid into a glass capillary and place it inside the heating element.
- Increase the temperature until the sample turns from solid to liquid.
- You usually measure the melting range, which is the range of temperatures from where the solid begins to melt to where it has melted completely.
- You can look up the melting point of a substance in data books and compare it to your measurements.
- Impurities in the ample will lower the melting point and increase the melting range.
68
Why might you want to avoid naked flames when performing experiments involving organic compounds ?
They might ignite the compounds
69
Name two ways of purifying organic products.
- Recrystallisation
- Distillisation
70
A student carried out an experiment to make hex-1-ene from hexan-1-ol, using the following procedure:
- Mix 1cm3 hexan-1-ol with concentrated phosphoric acid in reflux apparatus, and reflux for 30 minutes.
- Once the mixture has cooled, pour it into a separating funnel, add 5cm3 water. Stopper the separating funnel, shake it an then allow the layers to separate. Remove the aqueous layer. Dry the organic layer.
a) What is meant by reflux and why is it a technique sometimes used in organic chemistry ?
b) What organic compound is removed in the separating
step ?
c) Explain why step 2) would give pure hex-1-ene.
a) Reflux is continuous boiling/evaporation and condensation. It is done to prevent the loss of volatile liquids while heating.
b) Unreacted hexan-1-ol
c) The unreacted hexan-1-ol is water-soluble, hex-1-ene is insoluble in water. So the hexan-1-ol dissolves in the aqueous layer and is removed when it's run off. Drying the organic layer removes water from the product, giving pure hex-1-ene.
71
A scientists refluxes ethyl ethanoate with dilute sodium hydroxide, and obtains impure solid sodium ethanoate.
a) Describe how she could purify this solid by recrystallisation from an appropriate solvent.
b) What would make a solvent appropriate for this recrystallisation process ?
c) Describe the melting point range of the impure sodium ethanoate compared to the pure product.
a) Dissolve the solid product in a minimal amount of hot solvent. Leave the saturated solution to cool slowly and filter to remove the crystals of pure product. Wash the crystals in cold solvent, and then dry them off.
b) An appropriate solvent is one which sodium ethanoate is very soluble in hot solvent and nearly insoluble in cold solvent.
c) The melting point range of the impure product is lower broader then that of the pure product.
72
How can molecules be separated and identified ?
Using chromatography
73
How can molecules be separated and identified ?
Using chromatography
74
What is chromatography ? and what does it involve.
Chromatography is used in chemistry to separate mixtures of molecules. It involves a mobile phase and a stationary phase.
75
Describe thin layer chromatography ?
- In thin layer chromatography the stationary phase is a thin layer of silica (silicon oxide) or alumina (aluminium oxide) fixed to a glass or metal plate.
- Draw a line in pencil near the bottom of the thin layer chromatography plate and put a small drop of each mixture to be separated on the line.
- Place the plate in the beaker with a small volume of
solvent (this is the mobile phase). The solvent level must be below the baseline.
- Leave the beaker until the solvent has moved almost to the top of the plate. Then remove the plate from the beaker and allow it to dry. Before it's evaporated you should mark how far the solvent travelled up the plate (this line is called the solvent front).
- As it moves up the plate, the solvent will carry the substance in the mixture with it > but some chemicals will be carried faster than others and so travel up the plate. This result is called a chromatogram.
- You can use the positions of the chemicals on the chromatogram to identify what the chemicals are.
76
How are colourless chemicals revealed ?
Using UV light or Iodine
77
How does UV light work to reveal colourless chemicals ?
Many thin layer chromatography plates have a special fluorescent dye added to the silica or alumina layer that glows when UV light shines on it. Where there are spots of chemical on the plate they cover the fluorescent dye and do not glow. You can put the plate under a UV lamp and draw around the dark patches to show where the spots of chemical are.
78
How does iodine vapour work to reveal colourless compounds ?
If you leave the plate in a sealed jar with a couple of iodine crystals, the iodine vapour will act as a locating agent > so it sticks to the chemicals on the plate and they'll show up as purple spots.
79
Can chromatography be used to purify substances ?
Yes
80
Describe how chromatography can be used to purify substances ?
- The thin layer chromatography method separates very small quantities of chemicals > ideal for identifying what makes up a mixture.
- You can also use chromatography to separate large quantities of a mixture in an organic synthesis.
- You need larger-scale equipment though, such as glass column packed with silica or alumina. You then pour your mixture into the column and run solvent through it continually.
- The different chemicals in the mixture move down the column at different rates, so they come out at different times, meaning you get pure chemicals.
81
How do you know how many chemicals are present on a mixture ?
Count the number of spots that form on the plate.
82
How do you find out what chemical each element is ?
Calculate the Rf value
83
What is the formula for Rf ?
Rf = (distance travelled by spot) / (distance travelled by solvent)
84
Do the Rf values differ depending on how big the plate is or how far the solvent travels ?
No, the Rf value is always the same no matter how big the plate is or how far the solvent travels
85
What causes different Rf values ?
- Composition of thin layer chromatography plates
- The solvent
- The temperature change even slightly
86
Is it difficult to keep the conditions of thin layer chromatography identical ?
Yes
87
What are the names of the two phases that are used in all forms of chromatography ?
- Mobile phase
- Stationary phase
88
Give two uses of chromatography ?
- Separating mixtures
- Purify substances
89
Wat is the formula for calculating Rf values ?
Rf = (Distance travelled by spot) / (Distance travelled by solvent)
90
The solvent front on the chromatogram was measured at 8cm from the baseline, and substance 1 travelled 5.6cm. Calculate the Rf value of substance 1.
Rf = (Distance travelled by spot) / (Distance travelled by solvent)
Rf = 5.6 / 8
Rf = 0.7
91
All the substances on the chromatogram above are colourless. Suggest two methods that could have been used to make these colourless chemicals visible
- A fluorescent dye could have been added to the thin layer chromatography plate and then a UV light shone on it to reveal the spots. Or the spots could have been exposed to iodine vapour.
92
What does infrared spectroscopy help to identify ?
Organic molecules
93
Describe the process of infrared spectroscopy ?
- A beam of infrared radiation is passed through a sample of a chemical.
- The Infrared radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy.
- Bonds between different atoms absorb different frequencies of infrared radiation. Bonds in different places in a molecules absorb different frequencies too > so the O-H bond in an alcohol and the O-H bond in a carboxylic acid absorb different frequencies.
94
What does the infrared spectrometer produce ?
A spectrum that shows you what frequencies of radiation the molecules are absorbing. If can also be used to identify the functional groups in a molecule.
95
Can you use an infrared spectrometer to see if a functional group has changed ? Example.
Yes
For example, if you oxidise an alcohol to an aldehyde you'll see the O-H absorption disappear from the spectrum, and a C=O absorption appear. If you then oxidise it further to a carboxylic acid an O-H peak at a slightly lower frequency than before will appear, alongside the C=O peak.
96
What is mass spectrometry used for ?
To help identify compounds
97
How do mass spectrometry help to identify compounds ?
- A mass spectrum is produced by a mass spectrometer. The molecules in the sample are bombarded with electrons, which remove an electron from the molecule to form a molecular ion, M+.
- To find the relative molecular mass of a compound you look at the molecular ion peak. The mass/charge value of the molecular ion peak is the molecular mass.
98
Can a molecular ion be broken into smaller fragments ?
Yes
99
How can molecules be broken down into smaller fragments ?
- The bombarding electrons make some of the molecular ions break up into fragments.
100
How is a fragmentation pattern formed ?
The fragments that are ions show up on the mass spectrum, making up a fragmentation pattern. Fragmentation patterns are actually pretty cool because you can use them to identify molecules even their structure.
101
What is the molecular mass for the fragment CH3+ ?
15
102
What is the molecular mass for the fragment C2H5+ ?
29
103
What is the molecular mass for the fragment CH3CH2CH2+ ?
43
104
What is the molecular mass for the fragment OH+ ?
17
105
How can you combine infrared spectrometer and mess spectrometer to identify a compound ?
- Work out what functional group are in the compound from its infrared spectrum
- Use the mass spectrum to work out the structure of the molecule.
106
Which parts of a molecule absorb infrared energy ?
Covalent bonds
107
Why do most infrared spectra of organic molecules have a strong, sharp peak at around 3000cm^-1 ?
Most molecules have a C-H bond
108
What is meant by molecular ion ?
The molecules in a sample are bombarded with electrons, which remove an electron from the molecule.
109
What is the M peak ?
The relative molecular mass of a compound
110
How do fragments get formed ?
Bombarding electrons make some of the molecular ions break up into fragments.
111
What does sustainable chemistry means ?
Not using up all the earths resources.
112
What are some of the principles of sustainable chemistry ?
- Use renewable resources
- Ensure all the chemicals and processes involved are as safe as possible
- MAke sure that waste is minimised and products are biodegradable or recycled.
113
What are some ideas for renewable resources ?
- Use raw materials where possible.
- Use renewable energy sources. Many chemical processes use energy from fossil fuels which will soon run out. Solar power and bioethanol from plants are a couple of alternatives.
- If it's not possible to use energy from renewable sources then energy usage should be minimised. This saves money, reduces production and helps prolong fossil fuel resources.
114
WHat are some ideas to ensure all the chemicals and processes involved are as safe as possible ?
- Where possible, chemical reactions should be designed to use and produce substances which are non-toxic and not harmful to humans or the environment.
- Substances and chemical processes should be chosen and designed to minimise the risk of accidents such as chemical releases, explosions and fires.
- Where possible, technologies and methods for monitoring and controlling processes which involve hazardous substances should be improved.
115
What are some ideas to ensure all the chemicals and processes involved are as safe as possible ?
- Where possible, chemical reactions should be designed to use and produce substances which are non-toxic and not harmful to humans or the environment.
- Substances and chemical processes should be chosen and designed to minimise the risk of accidents such as chemical releases, explosions and fires.
- Where possible, technologies and methods for monitoring and controlling processes which involve hazardous substances should be improved.
116
What are some ideas to make sure that waste is minimised and products are biodegradable or recyclable ?
- It's better to prevent waste being produced than to clean it up after its been created.
- The atom economy of a reaction should be as high as possible. This means more of the reactants are turned into product, rather than waste.
- Catalysts should be used where possible. This cuts down on the amount of reagents needed for a reaction and reduces waste.
- Unnecessary steps in chemical reactions should be avoided, if possible, to prevent waste.
- Chemical products should be designed to be biodegradable or recyclable.
117
List four ways in which the chemical industry can be made more sustainable ?
- Use more raw materials
- Use renewable energy sources
- Energy usage should be minimised
- Designed to produce substances which are not toxic or harmful to humans
118
Which of the following statements is a principle of green chemistry:
a) Make sure raw materials used are 'fair trade'
b) Store waste safely after it is produced
c) Use catalysts where it is possible
d) Add steps to a chemical reaction if it will reduce energy usage
C
