What are bulk chemicals?
Chemicals that are made on a very large scale.
1 of 183
What are some examples of bulk chemicals?
Ammonia, sulfuric acid, sodium hydroxide and phosphoric acid.
2 of 183
What are fine chemicals?
Chemicals that are made on a smaller scale than bulk chemicals.
3 of 183
What are some examples of fine chemicals?
Drugs, food additives, pesticides and fragrances.
4 of 183
What are the basic raw materials in the chemical industry?
Crude oil, air, water, vegetable material and rocks and minerals(e.g metal ores, salt, limestone and gypsum)
5 of 183
What are feedstocks?
A chemical, or mixture of chemicals, fed into a process in the chemical industry.
6 of 183
What does a reactor for chemical synthesis usually contain and what does it do?
A catalyst to speed up the reaction.
7 of 183
What are five stages in the production of useful chemicals?
1. The preparation of feedstocks. 2. Synthesis. 3. Separation of products. 4. Handling of by-products and wastes. 5. The monitoring of purity.
8 of 183
What leaves the reactor after chemical synthesis takes place?
A mixture of the desired product, by-products and waste.
9 of 183
What happens to the different chemicals in synthesis after separation?
Samples of the product are analysed to monitor the purity. By-products and waste are either fed back into production processes, sold on for other uses or disposed of carefully.
10 of 183
What do chemical plants need a lot of and why?
Energy. Some chemical reactions take place at high temperatures so energy is needed for heating. Electrical power is also needed for pumps to move reactants and products around the plant.
11 of 183
What are the five main types of products the chemical industry produces?
Basic inorganics including fertilisers, petrochemicals and polymers, dyes paints and pigments, pharmaceuticals, and speciality chemicals.
12 of 183
What do petrochemical plants do?
They use hydrocarbons from crude oil to make a great variety of products including polymers.
13 of 183
What are speciality chemicals ued for?
They are used to make other products, they include food flavourings and the liquid-crystal chemicals in flat-screen displays.
14 of 183
What do research chemists do?
They carry out investigations to find the best methods for making new products.
15 of 183
What do people in the technical team do?
They monitor the data collected from computer sensors, to make sure everything is working correctly.
16 of 183
What do analytical chemists do?
They test the purity of samples to make sure they are up o standard.
17 of 183
What has recent legislation done to change the chemical industry?
New laws encourage companies to reduce the formation of pollutants through changes in production methods, and using raw materials that are cost effective and renewable.
18 of 183
What does green chemistry have the potential to do?
To bring about both social and economic benefits. It benefits the society by helping people avoid the dangers of hazardous chemicals and can benefit industry by increasing efficiency and cutting costs.
19 of 183
What is one of the aims of green chemistry?
To use renewable raw materials rather than petrochemicals to make the industry more sustainable.
20 of 183
What are the advantages of using plants as feedstocks?
As plants can be grown year after year they are a renewable resource. The production of products using plant can need less energy than alternative ones that use crude oil. This reduces greenhouse gases and saves crude oil.
21 of 183
What are the disadvantages of using plants as feedstocks?
Growing plants for chemicals takes up land that could be used to grow food. Energy is needed to make fertilisers and for harvesting crops.
22 of 183
What is percentage yield?
A measure of the efficiency of a chemical synthesis. It compares the quantity of product with the amount predicted by the balanced chemical equation.
23 of 183
What is the formula for percentage yield?
Percentage yield=((actual yield)/(theoretical yield)) x 100
24 of 183
To find the theoretical yield you use the reacting masses. How are the reacting masses calcualted?
1. Write down the balanced symbol equation. 2. Work out the relative formula mass of each reactant and product. 3. Convert to reacting masses by adding the units. 4. Scale the quantities to amounts actually used in the synthesis.
25 of 183
What is the formula for atom economy?
Atom economy = ((mass of atoms in the product)/(mass of atoms in the reactants)) x100%
26 of 183
What would happen in an ideal chemical reaction in terms of atoms?
All the atoms in the reactants would end up in the products, and no atoms would be wasted.
27 of 183
What is the problem with using atom economy?
It does not take yield into account and does not allow for the fact that many real world processed use a deliberate excess of reactants.
28 of 183
What is another aim of green chemistry?
TO replace reactants that are highly toxic with alternative chemicals that are not a threat to human health or the environment. This is to protect the health of people working in the industry and also people who live near the industrial plants.
29 of 183
How is energy used in the chemical industry?
To raise the temperature of reactants so a reaction begins or continues. To heat mixtures of liquids to separate and purify products by distillation, To dry product material. To process waste.
30 of 183
What is the usual source of energy?
Burning natural gases or other fossil fuels. Often the energy from burning is used to produce super-heated steam,which can then e used for heating around the chemical plant.
31 of 183
What is the most direct way of reducing the use of energy?
It is to prevent losses of steam from leaking valves on steam pips by installing efficient insulation on reaction vessels or pipes.
32 of 183
If reactions are very exothermic what can the energy be used for?
The reactions can provide the energy to raise steam and generate electricity. The energy is transferred using a heat exchanger.
33 of 183
What is an example of a very exothermic reaction and what is the energy used for?
The first step in the manufacture of sulfuric acid is to burn sulfur. A sulfuric acid plant has no fuel bills and can raise enough steam to generate electric power to contribute significantly to the income of the operation.
34 of 183
Why has the development of efficient catalysts made a significant contribution to chemical production becoming more energy efficient?
Suitable catalysts can speed up the reaction that gives the desired products, without speeding up other reactions that give unwanted by-products. This reduces wasre, and reaction work at lower temperature, saving energy.
35 of 183
What is one way in which energy demand is reduced in processes?
To use biocatalysts (enzymes). Enzymes operate within a limited temperature range, above which they are denatured and no longer work. They also have a limited pH range. This limits the conditions that can be used for enzyme-catalysed processes.
36 of 183
How can waste be cut down on?
To develop processes with higher atom economies, to increase recycling at every possible stage of the life cycle of the chemical product and to find uses for by-products that were previously dumped as waste.
37 of 183
What does the sustainability of a product depend on?
Whether or not the feedstock is renewable, the atom economy, the nature and amount of by-products or wastes and what happens to them, the energy inputs/outputs, the environmental impact, the health and safety risks and the social & economic benefits.
38 of 183
When is recycling at its best and what sort of recycling is this?
Closed-loop recycling. This is when the waste material that is collected can be used to manufacture the same product with no loss in quality.
39 of 183
What is another method of recycling that is not as good as closed-loop recycling?
Open-loop recycling. This is when waste from one product is recovered and used in the manufacture of another, lower quality product.
40 of 183
What is sustainable development?
Sustainable development is about meeting the needs of the present without compromising the ability of future generations to meet their needs.
41 of 183
What is green chemistry about?
Green chemistry is bout the long-term sustainability of the planet and the short-term impacts of the chemical industry on our health and the environment,
42 of 183
What is organic chemistry?
The study of carbon compounds. This includes all of the natural carbon compounds from living things and synthetic carbon compounds.
43 of 183
What sort of bonding is involved in organic chemistry?
44 of 183
How many covalent bonds can carbon, hydrogen and oxygen form?
Carbon-4. hydrogen-1, oxygen-2.
45 of 183
What are alkanes?
Alkanes are hydrocarbons found in crude oil. All the C-C bonds in alkanes are single bonds.
46 of 183
What are the names and molecular formulas of some alkanes?
Methane CH4, Ethane C2H6, Propane C3H8, Butane C4H10, Pentane C5H12 and Hexane C6H14
47 of 183
What are properties of alkanes?
The alkanes are oily and do not dissolve in water or mix with it. At room temperature, alkanes with up to four carbon atoms are gases, 4-17 carbon atoms are liquids, and those with more than 17 are solids.
48 of 183
Describe alkanes burning.
All alkanes burn. The hydrocarbons burn in air, forming carbon dioxide and water. If there is limited air, the products may include soot and carbon monoxide.
49 of 183
Do alkanes react with aqueous acids and alkalis?
No. This is because the C-C and C-H bonds in the molecules are difficult to break and are therefore unreactive.
50 of 183
What does saturated mean?
In the molecules of a saturated compound, all of the bonds are single bonds, for example alkanes.
51 of 183
What are alkenes?
Alkenes are hydrocarbons that contain a C-C double bond.
52 of 183
What are the names and molecular formulas of some alkenes?
Ethene C2H4, Propene C3H6 amd Butene C4H8
53 of 183
What does unsaturated mean?
There are double bonds in the molecules of unsaturated compounds.
54 of 183
Why are alkenes more reactive than alkanes?
It is due to the presence of the double bond.
55 of 183
How can we test for unsaturated bonds?
Alkenes react with bromine water and decolourise it.
56 of 183
Do alkenes react with water.
57 of 183
What are the different uses of ethanol?
It is in alcoholic beverages, used in cosmetic lotions and perfumes and as a fuel.
58 of 183
What are the different uses of methanol?
It is needed to manufacture products such as adhesives, foams, solvents and windscreen washer fluid.
59 of 183
What are the molecular formulas for methanol, ethanol and propanol?
CH3OH, C2H5OH and C3H7OH
60 of 183
What are the the properties of methanol and ethanol and why is this?
They are liquid at room temperature. The attractive forces between molecules of alcohols are stronger than they are in alkanes. The presence of an -OH group gives the molecules this tendency to cling together like water.
61 of 183
What are the differences between alcohols and water?
The boiling point of ethanol is lower than water because the attractions betwen the hydrocarbon parts are very weak. Ethanol mixes in water because of the -OH group. Longer hyrocaron chains do not mix with water because of the oiliness.
62 of 183
What is a functional group and what is this in the alcohols?
The -OH group. It is a reactive group of atoms in an organic molecule.
63 of 183
What do alcohols produce when they burn?
Carbon dioxide and water.
64 of 183
Describe the reaction between sodium and ethanol.
The products are sodium ethoxide and hydrogen. The formula is 2C2H5OH + 2Na = 2C2H5O-Na+ + H2. Sodium ethoxide is an ionic compound and a solid at room temperature
65 of 183
What are the three different ways of producing ethanol?
Fermentation, biotechnology and chemical synthesis.
66 of 183
What are the uses of ethanol produced by the traditional method of fermentation?
It is mainly used as a fuel, with smaller amounts used in alcoholic beverages and the chemical industry.
67 of 183
What are common feedstocks for ethonal produced by fermentation?
Sugar cane, sugar beet, corn, rice and maize.
68 of 183
What are the problems associated with the growing of feedstocks for fermentation?
Large areas of land are needed to grow the crops, and only some parts of the plants can be fermented. However, the plants that cannot be fermented are used to make animal feeds and corn oil.
69 of 183
What has recent developments meant for fermentation?
It means that more plant material can be fermented, and agricultural waste, paper mill sludge, and even household rubbish can be used for fermentation.
70 of 183
How are cellulose polyemers from feedstocks made into simple sugars such as glucose?
Cellulose polymers are heated with acid to break them down.
71 of 183
What is the reaction for the fermentation of glucose?
Glucose= ethanol + carbon dioxide, C6H12O6 = 2C2H5OH + 2CO2
72 of 183
What are the optimum conditions for the fermentation reaction to take place and why?
The reaction is catalysed by enzymes found in yeast. The optimum temperature is between 25-37oC because below this the rate of reaction is too slow and above this the enzymes are denatured. pH also affects the reaction.
73 of 183
Why is the concentration of ethanol produced by fermentation limited to between 14 and 15% ethanol?
This is because if the ethanol concentration rises higher than 5%, it becomes toxic to the yeast, which is killed, and the fermentation stops.
74 of 183
How is it possible to obtain ethanol solutions with a concentration of above 15%?
The mixture is distilled. Distillation is a technique for separating a mixture of liquids by their boiling points. By heating the mixture to a temperature above 78.5oC and below 100oC the ethanol turns into vapour, it it then condensed and collected.
75 of 183
What are the main stages of producing bioethanol that require ethanol?
Producing fertilises for the plants to grow, transporting the feedstock to the factory, processing the feedstock and transporting the ethanol to its point of use.
76 of 183
What feedstocks can be used to produce ethanol using biotechnology?
A wide range of biomass waste can be used, including forestry and wood waste, rice hulls and corn stalks.
77 of 183
How is ethanol produced using biotechnology?
Genetically modified E. coli bacteria are used to convert all plant sugars into ethanol. The bacteria would normally produce ethanoic or lactic acis, but modification means ethanol is produced instead.
78 of 183
What are the optimum temperatures for ethanol to be produced using biotechnology?
The optimum conditions lie within the temperature range 25-37oC and the pH range 6-7.
79 of 183
What is the main feedstock for producing synthetic ethanol?
Ethene which is produced by the cracking of ethane from natural gas. It is also produced by the cracking of naphtha from crude oil.
80 of 183
What is the catalyst used in producing synthetic ethanol and what are the conditions used in the reactor?
A phosphoric acid catalyst is used and the temperature is 300oC with 60-70 x atmospheric pressure.
81 of 183
What is the molecular formula for the reaction of ethene and steam to produce ethanol?
C2H4 + H2O = C2H5OH
82 of 183
What is the atom economy for the reaction and explain why this isn't accurate?
100%, but some side reactions do occur, producing by-products such as polythene. Unwanted molecules are recycled. The overall yield for the reaction is 95%.
83 of 183
What is the functional group of carboxylic acids?
84 of 183
What are some of the names and molecular formulas for carboxylic acids?
Methanoic acid HCOOH, Ethanoic acid CH3COOH, Proponoic acid C2H5COOH and Butanoic acid C3H7COOH
85 of 183
How is vinegar formed?
The oxidation of ethanol produces ethanoic acid. Oxidation coverts beer to malt vinegar, cider to cider vinegar and wine to wine vinegar.
86 of 183
What do some of the carboxylic acids with more carbon atoms have?
Unpleasant smells. The horrible odours of rancid butter, vomit and sweaty socks are caused by carboxylic acids.
87 of 183
Why are carboxylic acids week acids?
Carboxylic acids ionise to produce hydrogen ions when dissolved in water to a lesser extent than the strong acids. Only a small proportion of the molecules ionise so not all of the hydrogens are released as ions into the solution.
88 of 183
What does acid+metal or soluble hydroxide or metal give you?
salt + hydrogen or salt +water or salt + water carbon dioxide.
89 of 183
What causes the taste and smell of bananas, stawberries and pinapples?
90 of 183
What are esters used in?
Many sweet-smelling compounds in perfumes and food flavourings are esters. Some drugs use esters, they are used to make nail-varnish remover and the plasticisers used to make polymers such as PVC soft and flexible are also esters.
91 of 183
What are the reactants used to produce esters and give an example?
An alcohol can react with a carboxylic acid to make esters. For example ethanoic acid + methanol = methyl ethanoate + water
92 of 183
What are the different stages of producing an ester?
1. Heating under reflux. 2. Distillation. 3. Purification by treatment with reagents in a tap funnel. 4. Drying. 5. Distillation
93 of 183
What is an example of a molecule with more than one ester link?
Fats and oils.
94 of 183
Why are fats and oils and important energy store?
Fats and oils release more energy when oxidised than carbohydrates and are therefore and important energy store for plants and animals.
95 of 183
What is the alcohol in fats and oils?
Glycerol which is also called propan-1,2,3-triol. It is a compound with three -OH groups.
96 of 183
What are carboxylic acids in fats and oils often called?
Fatty acids.These are compounds with a long hydrocarbon chain attached to a carboxylic acid group.
97 of 183
What is the difference between fats and oils?
Stearic acid is usually in animal fats it is saturated. These molecules are straight. Whereas oleic acid, which is found in vegetable oils is unsaturated. These molecules are not straight.
98 of 183
How does the difference in structure of fats ans oils explain their different states?
As saturated fats have a regular shape they pack together easily and are sold at room temperature. However, it is more difficult to pact together unsaturated fats and are so liquid at room temperature.
99 of 183
What happens to an ester in water?
It splits up into an alcohol and an acid. This type of change is called hydrolysis,
100 of 183
What does exothermic mean?
An exothermic process gives out energy to its surroundings.
101 of 183
What are some examples of exothermic reactions?
Burning, respiration and neutralisation.
102 of 183
What does and energy-level diagram look like for an exothermic reaction?
The energy of the products is less than the energy of the reactants because energy is lost to the surroundings.
103 of 183
What does endothermic mean?
An endothermic process takes in energy from its surroundings.
104 of 183
What are some example of endothermic reactions?
Electrolysis, photosynthesis and thermal decomposition.
105 of 183
What does and energy-level diagram look like for an endothermic reaction?
The energy of the products is greater than the energy of the reactants because energy is taken in from the surroundings.
106 of 183
What decides whether a reaction is exothermic or endothermic?
It is the difference between the energy taken in to break bonds and the energy given out as new bonds form.
107 of 183
What is the formula for overall energy change?
Overall energy change=energy needed to break bonds - energy given out as new bonds are formed.
108 of 183
Using the formula how do we know if a reaction is exothermic or endothermic?
If the overall energy change is negative then the reaction is exothermic and if the overall energy change is positive then the reaction is endothermic.
109 of 183
What does activation energy mean?
The minimum energy needed in a collision between molecules if they are to react. The activation energy is the height of the energy barrier between reactants and products in a chemical change.
110 of 183
Why does using a catalyst speed up the rate of reaction?
It provides an alternative route for a chemical reaction with a lower activation energy.
111 of 183
What is an irreversible change and give an example?
A chemical change that can only go in one direction such as burning methane in air.
112 of 183
What is a reversible change and give an example?
A chemical change that can go both backwards and forwards depending on the conditions, such as melting and solidifying.
113 of 183
What does equilibrium mean?
A state of balance in a reversible reaction when neither the forward nor the backward reaction is complete. The reaction appears to have stopped. At equilibrium reactants and products are present and their concentrations are not changing.
114 of 183
What are some example of equilibrium?
A solution of litmus in water at pH7 is purple because it contains a mixture of the red and te blue forms of the indicator. Also at 0oC melting ice and water are at equilibrium. The two states of water coexist.
115 of 183
What are two important features of the equilibrium processes?
At equilibrium the concentration of reactants and products do not change. An equilibrium state can be approached from either the 'reactant side' of the 'product side' of a reaction.
116 of 183
What does dynamic equilibrium mean?
Chemical equilibria are dynamic. At equilibrium the forward and backward reactions are still continuing but at equal rates so that there is no overall change.
117 of 183
What are the different uses of ammonia (NH3)?
Fertilisers, explosives and textiles.
118 of 183
What is nitrogen fixation?
The conversion of nitrogen gas into compounds either industrially or by natural means.
119 of 183
Why is nitrogen important for living things?
It is used in making amino acids.
120 of 183
What is the Haber process?
The basis of the Haber process is a reversible reaction between nitrogen and hydrogen gas producing ammonia.
121 of 183
What are the feedstocks in the Haber process?
Air, natural gas and steam. Air for the nitrogen and natural gas and steam react to produce hydrogen.
122 of 183
What are the conditions like in the reactor for the Haber process?
The reactant gases a compressed to about 200 times atmospheric pressure, heated to about 450oC and passed over an iron catalyst.
123 of 183
What is the atom economy of the Haber process?
100% because there are no by-products.
124 of 183
What is the yield in the Haber process?
It is about 15%, but the reaction yield is increased by recycling the unreacted nitrogen and hydrogen gas.
125 of 183
What happens if the temperature changes in the Haber process?
If the temperature increases the is less ammonia and more nitrogen and hydrogen in the equilibrium mixture. This is because the equilibrium changes in a way that takes in energy because this tends to lower temperature.
126 of 183
What is Le Chateller's principle?
It states that 'When the conditions change, an equilibrium mixture of chemicals responds in a way that tends to counteract the change'
127 of 183
What happens if the pressure changes in the Haber process?
If the pressure increases then there is more ammonia and less nitrogen and hydrogen.
128 of 183
Why does the reaction in the Haber never reach equilibrium?
The gases are only in contact with the catalyst for a short time.
129 of 183
Why isn't a higher pressure an lower temperature used in the Haber process?
High-pressure plants are expensive to build and run, they can also be hazardous. If the temperature is too low then the reaction becomes to slow to be economic.
130 of 183
What enzyme fixes nitrogen in organisms at normal temperatures and pressure?
Nitrogenase acts as a catalyst. It contains clusters of iron, molybdenum and sulfur.
131 of 183
What are the best known nitrogen fixing plants?
The root nodules of legumes such as peas, beans and clovers.
132 of 183
What is the effect of industrial nitrogen fixation?
It has significantly increased the amount of fixed nitrogen. High levels of nitrates in rivers and lakes can cause the rapid growth of algae, which can damage ecosystems. Nitrates can also get into drinking water and be harmful to human health.
133 of 183
Why is the production of ammonia a relatively clean process?
The only emissions are carbon dioxide and oxides of nitrogen. In a modern plant both of these gases can be recovered or reduced to very low levels.
134 of 183
If fossil fuel sources of methane run low what alternative ways of producing hydrogen could be used?
The electrolysis of water could become a major source of hydrogen. This feedstock would depend on a cheap and renewable electricity source.
135 of 183
Why is the search for new catalysts an important area of current research and development?
The higher the catalytic activity of a catalyst, the more efficient it it at synthesising ammonia.
136 of 183
What would be possible if chemists produce catalysts that mimic natural enzymes?
It may be possible to produce ammonia at room temperature and pressure. This, of course, would lead to even lower energy use during the production.
137 of 183
What does qualitative mean?
Qualitative analysis is any method of identifying the chemicals in a sample.
138 of 183
What does quantitative mean?
Quantitative analysis is any method of determining the amount of a chemical in a sample.
139 of 183
What is a sample?
A small portion collected from a larger bulk of material for laboratory analysis.
140 of 183
What are the stages in an analysis?
Taking a sample, Measuring out laboratory specimens for analysis, dissolving the sample, measuring a property of the sample in solution, calculating a value from the measurements and estimating the reliability of the results.
141 of 183
What is a replicate sample?
Two or more samples taken from the same material. Replicate samples should be as similar as possible and analysed by the same procedure to help judge the precision of the analysis.
142 of 183
What is a representative sample?
A sample of a material that is as nearly identical as possible in its chemical composition to that of the larger bulk of material sampled.
143 of 183
What do scientists have to decide when sampling?
How many samples, and how many of each, must be collected to ensure they are representative, how many times an analysis should be repeated on a sample to ensure results are reliable, where when, and how to collect the samples of the material, storage
144 of 183
What can chromatography be used for?
To separate and identify the chemicals in a mixture, to check purity of a chemical and to purify small samples of a chemical.
145 of 183
What is meant by the term mobile phase?
The solvent that carries chemicals from a sample through s chromatographic column or sheet.
146 of 183
What is meant by the term stationary phase?
The medium through which the mobile passes in chromatography.
147 of 183
What determines the speed at which the chemical moves?
It depends on whether the chemical is more attracted to the mobile phase or the stationary phase. If it is more attracted to the mobile phase then it will move faster whereas if it is more attracted to the stationary phase it will move more slowly.
148 of 183
What is there for each chemical in the mixture in chromatography?
There is a dynamic equilibrium as the molecules distribute themselves between the stationary phase and the mobile phase.
149 of 183
What are the three types of chromatography?
Paper, thin-layer and gas chromatography.
150 of 183
What are paper and thin-layer chromatography used for?
They are used to separate and identify substances in mixtures.
151 of 183
What are the stationary phases in paper and TLC?
In paper chromatography it is the paper. in TLC it is an absorbant solid supported on a glass or stiff plastic sheet.
152 of 183
What are the mobile phases in paper and TLC?
In both it is a solvent, this could be a substance such as water or ethanol.
153 of 183
What does aqueous mean?
An aqueous solution is a solution in which water is the solvent.
154 of 183
What does non-aqueous mean?
A solution in which a liquid other than water is the solvent.
155 of 183
What are reference materials?
Known chemicals used in analysis for comparison with unknown chemicals.
156 of 183
What is the solvent front?
The furthest position reached by the solvent during paper of thin-layer chromatography.
157 of 183
How can colourless substances be located?
Either develop the chromatogram by spaying it with a locating agent that reacts with the substances to from coloured compounds, or use an UV lamp with TLC plates that contain fluorescers, so that the spots appear violet in UV light.
158 of 183
Why is calculating the retardation factor useful in paper or thin-layer chromatography?
It can help identify chemicals, this is because it does not change provided that the same conditions are used for each chemical.
159 of 183
What is the formula for retardation factor?
Rf = (distance moved by chemical)/(distance moved by solvent) = y/x
160 of 183
What is gas chromatography used for?
It is used to sepaate complex mixtures.
161 of 183
Why is gas chromatography preferred to paper or TLC?
It is more sensitive, which means it can detect small quantities of compounds. It not only identifies which chemicals are in a mixture but can also measure how much of each is present.
162 of 183
What is the mobile phase used in gas chromatography?
It is a gas such as helium. This is the carrier gas.
163 of 183
What is the stationary phase used in gas chromatography?
It is a thin film of a liquid on the surface of a powdered solid. It is packed into a sealed tube which is the column.
164 of 183
Where is the column in gas chromatography?
It is inside an oven, which controls the temperature of the column.
165 of 183
Why is it possible to analyse solids in gas chromatography?
Solids can be injected in solution and then turned to a vapour at the temperature of the column.
166 of 183
Describe the procedure for separating a mixture by gas chromatography.
Once the column is the right temperature the carrier gas is turned on. The sample is injected into the column. The chemicals in the sample turn to gases and mix with the carrier gas. The chemicals emerge from the column and pass in to the detector.
167 of 183
What does a chromatogram look like for gas chormatography?
It consists of a series of peaks, one for each compound in the mixture.
168 of 183
What is the retention time?
It is the time it takes for a component in a mixture to pass through the stationary phase.
169 of 183
What does the height of the peak on a chromatogram mean?
It enables the scientist to say how much there is of a compound.
170 of 183
What is a titration?
An analytical technique used to find the exact volumes of solutions that react with each other,
171 of 183
What are the main pieces of equipment does an acid based titation use?
A pipette, a burette and a conical flask.
172 of 183
What is the formula for concentration?
concentration (g/dm3) = mass (g) / volume (cm3)
173 of 183
What are the stages of measuring a standard solution?
Accurately weigh solute. Dissolve solute in a small amount of solvent. Transfer solution to a graduated flask. Rinse all solution into flask with more solvent. Add solvent drop by drop to make up volume to the mark on flask. Stopper and shake flask.
174 of 183
When calculating concentration what is it necessary to measure?
That concentration is measured in g/dm3 and that 1 litre = 1 dm3 =1000 cm3
175 of 183
How can uncertainty be measured?
It can be written as, for example 99.1 +/- 0.2%. This means that the mean was 99.1% and the scientists are confident the true value lies between 98.9% and 99.3%
176 of 183
What are the two general source of measurement uncertainty?
Systematic error and random error.
177 of 183
What does systematic error mean?
It means that the sane measurement repeated several times gives values that are consistently higher or lower than the true value.
178 of 183
What does random error mean?
It means that the same measurement repeated several times gives different values
179 of 183
What is meant by accuracy?
Accuracy describes how close a result is to the true or 'actual' value.
180 of 183
What is meant by precision?
Precision is a measure of the spread of measured values. A big spread indicates a greater uncertainty than a small spread.
181 of 183
What does valid mean?
Valid means that the techniques and procedures used were suitable for what was being analysed or tested.
182 of 183
What does justifiable mean?
Justifiable means that conclusions reached are backed by sound, reliable sources.
183 of 183
Other cards in this set
What are some examples of bulk chemicals?
Ammonia, sulfuric acid, sodium hydroxide and phosphoric acid.
What are fine chemicals?
What are some examples of fine chemicals?
What are the basic raw materials in the chemical industry?