Chemistry Unit 3

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  • Created by: Lottie_C
  • Created on: 13-04-16 11:15
Flame tests
used to identify presence of a metal ion in a compound, metal ions change colour of flame when heated in it, different ions give different colours
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Flame test results
lithium is crimson, sodium is yellow, potassium is lilac, calcium is red, barium is green
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Flame test method
dip clean flame test loop in sample solution, hold loop at edge of bunsen burner, observe colour change, clean in acid and rinse with water before repeating
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Precipitates
some reactions form a precipitate, an insoluble solid formed from a few drops of sodium hydroxide added to metal compound solution, colour and properties used to identify metal ions
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White precipitates
calcium, magnesium, aluminium, identify aluminium by adding excess sodium hydroxide as precipitate dissolves
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Carbonates
metal carbonates contain carbonates, presence of this tested by reacting with dilute acids to produce carbon dioxide and water, then collecting gas and bubble it through limewater to see if cloudy
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Halide Ions
halogens include chlorine, bromine and iodine, test for them by adding few drops of nitric acid then few drops of silver nitrate solution and see colour of precipitate, chloride is white, bromide is cream and iodide is yellow
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Sulfate Ions
add few drops of hydrochloric acid, add barium chloride, presence of white precipitate means sulphate ions presence
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transition metals
transition metals react with sodium hydroxide to form precipitate, copper 11 turns blue, iron 11 turns green, iron 111 turns brown
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titration
experiment to determine volumes of acid and alkali needed to produce a neutral solution
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titration method
pipette used to measure alkali, emptied into conical flask, indicator added, colour change, acid placed in burette, run into conical flask whilst swirled, colour change shows correct amount added to neutralise alkali
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indicator
usually phenolphalein which changes from pink in alkali to colourless in acid
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titration results
used to calculate concentration of unknown acid or alkali
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calculating concentrations
convert volumes to dm (cubed) by dividing by 1000, determine number of moles of solution with known concentration (concentration * volume), work out number of moles of unknown solution, calculate concentration of unknown
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Mendeleev
1869, arranged known elements in order of atomic mass, elements with similar chemical properties in same groups
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problems with early periodic table
incomplete, some elements in wrong group, Mendeleev left gaps for elements not discovered
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Modern periodic table
when electrons/protons/neutrons discovered (20th century), table arranged in order of atomic number, elements put in groups, arrangement of elements in terms of electronic structures
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Alkali metals
low density, react with non-metals to form ionic compounds (metal ion has +1 charge, white solids) dissolve in water to form colourless solution, react with water and release hydrogen, form hydroxides, dissolve in water to give alkaline solutions
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Group 7
react with metals to form ionic compounds where halide ion has -1 charge, further down less reactive, higher melting/boiling point
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Group 1
further down an element is, the more reactive it is and it has a lower melting/boiling point
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Transition metals (compared with group 1)
usually higher melting point/densities, stronger/harder, less reactive, do not react vigorously with water/oxygen, have ions with different charges, many form coloured compounds, useful as catalysts
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Displacement
more reactive halogen can displace less reactive halogen from aqueous solution of its salt
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Trends in reactivity
explained by higher energy level of outer electrons, the more easily electrons are lost/less easily electrons are gained
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Hard water
contains dissolved compounds calcium and magnesium, dissolved when water came into contact with rocks
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Problems with hard water
won't easily form a lather with soap (unless you use more soap), forms scale, forms limescale on pipes/boilers/kettles which is a thermal insulator so appliance will take longer to heat, causes scum on surface of tea
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Benefits of hard water
calcium compounds food for development/maintenance of bones/teeth, help to reduce heart disease
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Costs of hard water
increase as more soap needed, when temporary hard ester heated it can produce scale that reduces efficiency
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Permanent hard water
remains hard when boiled
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Temporary hard water
softened by boiling, contains hydrogen carbonate ions that decompose when heated to form carbonate ions which react with calcium and magnesium ions to form precipitates
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Making hard water soft by removing dissolved calcium and magnesium ions (method 1)
adding sodium carbonate which reacts with calcium and magnesium to form precipitate of calcium carbonate/magnesium carbonate
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Making hard water soft by removing dissolved calcium and magnesium ions (method 2)
commercial water softeners such as ion exchange columns with hydrogen/sodium ions which replace calcium/magnesium ions when hard water passes through column
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Drinking water
correct quality essential for life, drinking water should have low levels of dissolved salts and microbes
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Producing correct quality water
choosing an appropriate source, passing water through filter beds to remove any solids, sterilising with chlorine
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water filters
some contain carbon/silver/ion exchange resins which can remove some dissolved substances from tap water to improve taste and quality
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Pure water
produced by distillation which needs large amounts of energy so high costs
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Chlorine
added to drinking water to reduce microbes
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Fluoride
added to improve dental health
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how could you reduce heat loss in calorimetry?
screen to act as draught excluder, a lid
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measuring energy
relative amounts of energy released when substances burn can be measured by calorimetry, used to compare amount of energy released by fuel and foods
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amount of energy released/absorbed
can be calculated by measuring temperature change of solution in insulated container, used for reactions of solid with water of for neutralisation reactions
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energy level diagrams
used to show relative energies of reactants and products, activation energy, overall energy change of reaction
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What happens during chemical reactions?
energy must be supplied to break bonds. energy is released when bonds are formed
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Exothermic reaction
energy released from forming new bonds is greater than the energy needed to break existing bonds
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Endothermic reaction
energy needed to break existing bonds is great than energy released from forming new bonds
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Catalysts
allow chemical reaction to have lower activation energy
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Reversible reaction
products of reactions can react to produce original reactants
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Hydrogen
burned as fuel in combustion engines, also used in fuel cells that produce electricity to power vehicles
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Raw materials needed for haber process
nitrogen obtained from air, hydrogen obtained form natural gas/other sources
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Haber process
purified gases passed over iron catalyst (450 degrees, 200 atmospheres), some react to form ammonia, reversible so ammonia breaks down into hydrogen/nitrogen, when it cools ammonia liquefies and is removed, remaining hydrogen/nitrogen recycled
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reversible reactions
if occurs in closed system, equilibrium reached when reactions occur at same rate in each direction
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equilibrium
relative amounts of reacting substances depend on conditions of reaction
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raising temperature
yield from endothermic reaction increases and yield from exothermic reaction decreases
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lowering temperature
yield from endothermic reaction decreases and yield from exothermic reaction increases
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Gaseous reactions
increase in pressure will favour reaction that produces least number of molecules, shown by symbol equation
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Optimum conditions
the factors together with reaction rates help determine best conditions for industrial processes
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Alcohols
functional group -OH, methanol, ethanol, propanol first 3
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Methanol, ethanol, propanol
dissolve in water to form neutral solution, react with sodium to produce hydrogen, burn in air, used as fuels and solvents
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Ethanol
oxidised to ethanoic acid by chemical oxidising agents or microbial action, main acid in vinegar (aqueous solution), main alcohol in alcoholic drinks
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Carboxylic acids
functional group -COOH, methanoic/propanoic/ethanoic acid
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properties of carboxylic acids
dissolve in water to form acidic solutions, react with carbonates to produce carbon dioxide, react with alcohols with acid catalyst to form esters, don't ionise completely when dissolved in water and so are weak acids
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Aqueous solutions
weak acids have higher PH than strong acids with same concentration
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Esters
functional group -COO-, ethyl ethanoate produced from ethanol and ethnic acid, volatile, distinctive smells, used as flavourings/perfumes
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Other cards in this set

Card 2

Front

Flame test results

Back

lithium is crimson, sodium is yellow, potassium is lilac, calcium is red, barium is green

Card 3

Front

Flame test method

Back

Preview of the front of card 3

Card 4

Front

Precipitates

Back

Preview of the front of card 4

Card 5

Front

White precipitates

Back

Preview of the front of card 5
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