Chemistry 3a Flashcards
In the past, what were the obvious ways to categorise elements?
Physical/chemiscal properties and their relative atomic mass
Why did they categories them this way?
They didn’t know about atomic structure or protons/electrons so they didn’t have atomic numbers
When did they discover these things and arrange the elements in order of atomic numbers?
20th century
What was the first good effort of making a periodic table?
Newlands’ Law of octaves in 1864
What did Newlines discover?
That every eight element had similar properties so he listed the known elements in rows of seven
What was wrong with this organisation?
The pattern broke on third row with transition metals because he left no gaps
Why was his work criticised?
His groups contained elements that didn’t have similar properties (carbon and titanium), He mixed up metals and non-metals (oxygen and iron) and he didn’t leave any gaps for elements that hadn’t been discovered yet
What was the other person to try and make te periodic table?
Dmitri Mendeleev in 1869
What did Mendeleev do?
He put the elements in order of atomic mass like Newlines, but he also left gaps to keep similar propertied elements in the same vertical columns (groups)
Why were the gaps that he left very useful?
They predicted the properties of undiscovered elements, which then fit the pattern (convincing evidence for other scientists)
Why did he have to leave big gaps in the first two rows?
The transition metals
When were protons, neutrons and electrons discovered?
Late 19th century and the periodic table, matched what they discovered so scientists then accepted it as a very important and useful summary of the structure of an atom
What is the modern periodic table based on?
Electronic structure
How can you predict an elements chemical properties?
Using the electron arrangement
What do the shells in an atom correspond to?
To an energy level
Apart from the transition metals, what are similarities between elements in the same group?
They have the same number of electrons in their highest occupied energy level (outer shell)
What is an example of this?
Group 6 all have 6 electrons in their outer shell
What does the positive charge of the nucleus do?
Attracts electrons and holds them in place, the further from the nucleus the electron is, the less the attraction
What also makes attraction of the nucleus less?
When there are a lot of inner electrons as they get in away of the nucleus charge, reducing the attraction
What is this effect known as?
Shielding
What does the combination of increased distance and increased shielding mean?
That an electron in a higher energy level is more easily lost because theres less attraction from the nucleus holding it in place. Thats why group 1 metals get more reactive as you down the group
What does increased distance shielding also mean?
That a higher energy level is less likely to gain an electron as theres less attraction from the nucleus pulling electrons into the atom. Thats why group 7 elements get less reactive going down the group
What elements are group 1?
The alkali metals
What happens as you go down group 1?
The alkali metals become more reactive because the outer electron is more easily lost, because its further from the nucleus, and also the metals as you go down have lower melting and boiling points
Whats a similarity between group 1 alkali metals?
They have low density (the first three even have less density than water)
What are the main group 1 elements?
Lithium, sodium, potassium and also rubidium and caesium
How many electrons do the alkali metals have in their outer shell?
One electron
What do the alkali metals form ionic compounds with?
Non-metals
How do alkali metals form ionic compounds?
They’re keen to lose the one electron to make a 1+ ion, so they ALWAYS form ionic bonds and produce white compounds that dissolve in water to form colourless solutions
What is produced when group 1 metals react with water?
They produce hydrogen gas
What happens when lithium, sodium or potassium are put into water?
They react very vigorously and float/move around the surface whilst fizzing a lot, they produce hydrogen, potassium gets hot enough to ignite it, a lighted splint will indicate hydrogen by producing a pop sound.
What do they form?
Hydroxides that dissolve in water to give alkaline solutions
What is an example of this?
2NA(s) + 2H2O(l) -> 2K)H(aq) + H2(g)
As you go down group 7, the halogens have what properties?
They become less reactive because its harder to gain an extra electron as the other shells further from the nucleus. They have a higher melting point and a higher boiling point
What are the halogens?
Non metals with coloured vapours
What is fluorine?
A very reactive, poisonous yellow gas
What is chlorine?
A fairly reactive, poisonous dense green gas
What is bromine?
A dense, poisonous red-brown volatile liquid
What is iodine?
A dark grey crystalline solid or a purple vapour
How do the halogens form ionic bonds with metals?
The halogens form 1- ions called halides when they bond with metals
What is an example of this?
Na+CL- or Fe3+Br-3
What happens with more reactive halogens?
They will displace less reactive ones
How does this happen?
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
What is an example of this?
chlorine can displace bromine and iodine from an aqueous solution of its salt (a bromide of iodide). Bromine will also displace iodine because of the trend in reactivity.
What are transition elements?
Transition elements or transition metals are typical metals and have properties that you would expect of a ‘proper’ metal
What are the properties of transition elements?
Good conductors of heat/electricity, dense, strong, shiny, much less reactive than group 1 metals(don’t react as vigorously with water or oxygen for example), also much denser, stronger and harder than the group 1 metals and have much higher melting points
How many ions do transition metals have?
They usually have more than one ion e.g. Fe2+, Fe3+
What do the different ions usually form?
Different coloured compounds, Fe2+ ions usually give green compounds whereas Fe3+ ions usually form red/brown compounds e.g. rust
Why are the compounds colourful?
Due to the transition metal ion they contain e.g. potassium chromate(VI) is yellow. Potassium manganate(VII) is purple. Copper(II)sulphate is blue.
What do the colours in gemstones and pottery glazes depend on?
The transition metals
What do transition metals and their compounds make?
Good catalysts
What are examples of this?
Iron is the catalyst used in the Haber process for making ammonia. Manganese(IV) oxide is a good catalyst for the decomposition of hydrogen peroxide. And Nickel is useful for turning oils into fats for making margarine
What does soft water produce with soap?
You get a lather
What happens with hard water and soap?
You get a scum
Why does this happen with hard water?
The dissolved calcium ions and magnesium ions in the water react to make the scum which is insoluble. To get a decent lather you need to use more soap-costing more money
What happens when hard water is heated?
It forms furring or scale (mostly calcium carbonate) on the insides of pipes, boilers and kettles. Badly scaled pipes and boilers reduce efficiency of heating systems, and may need to be replaced and scale can even eventually block pipes
What does it mean by ‘scale can be a slight thermal insulator’?
A kettle with scale on the heating element takes longer to boil than a clean non scaled kettle-it becomes less efficient
How can hard water form?
Rain falling on some types of rocks e.g. limestone, chalk and gypsum, can dissolve compounds like magnesium sulphate which is soluble, and calcium sulphate which is only a bit soluble
What are the two types of water hardness?
Temporary and permanent
What is temporary hardness caused by?
The hydrogen carbonate ion, HCO-3 in Ca(HCO3)2
What is permanent hardness caused by?
Dissolved calcium sulphate (among other things as well)
How is temporary hardness removed?
By boiling, when heated, the calcium hydrogen carbonate decomposes to form calcium carbonate which is insoluble. This solid is the ‘limescale’ in kettles
What is the word formula for this?
Calcium hydrogencarbonate = calcium carbonate + water + carbon dioxide
What is the symbol formula for this?
Ca(HCO3)2(aq) = CaCo3(s) + H2O(l) + CO2(g)
How can both types of hardness be softened?
By adding washing soda (sodium carbonate Na2CO3) to it. The added carbonate ions react with the Ca2+ and Mg2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The ions are no longer dissolved in water so they cant keep it as hard water
What is the formula for this?
Ca2+(aq) + CO3 2-(aq) = CaCO3(s)
How can both types of water hardness be removed?
By running water through ‘ion exchange columns’ which are sold in shops. The columns have lots of sodium ions (or hydrogen ions) and ‘exchange’ them for calcium or magnesium ions in the water that runs through them
What is the formula for this?
Na2Resin(s) + Ca2(aq) = CaResin(s) +2NA+(aq)
What can you use to compare the hardness of water samples?
Titration
What is the method for titration?
Fill burette with soap solution, use burette to add 1cm2 of soap to the water, shake and then repeat until a lasting lather is formed. Record how much soap was needed to create a lasting lather. Repeat Then boil fresh samples of each type of water for 10 minutes and repeat
What would the results show?
Distilled water contains little to no hardness only minimum amount of soap needed. Imported water has more hardness than local water, more soap was needed, Local water has temporary hardness and removed by boiling
What can microbes in water cause?
Diseases such as cholera and dysentery
Where does most of our drinking water come from?
Reservoirs. Water flows into reservoirs from rivers and groundwater-water companies choose to build reservoirs where theres a good supply of clean water. Government agencies keep a close eye on pollution in reservoirs, rivers and groundwater
What is the process of the water treatment plan for water from reservoirs?
The water passes through a mesh screen to remove big bits like twigs, chemicals are added to make solids and microbes stick together and fall to the bottom. The water is filtered through gravel beds to remove all the solids. Water is chlorinated to kill off any harmful microbes left
What do people do that aren’t satisfied by the water treatment plan?
They buy filters that contain carbon or silver to remove substances from their rap water. Carbon in the filters removes the chlorine taste and silver is supposed to kill bugs. Some people in hard water areas buy water softeners which contain ion exchange resins
How can totally pure water with nothing dissolved in it be produced?
By distillation. Boiling water to make steam and condensing the steam. This process is too expensive to produce tap water. Lots of energy would be needed to boil all the water we use. Distilled water is used in chemistry labs
Why is fluoride added to drinking water?
It helps to reduce tooth decay
Why is chlorine added to drinking water?
It helps to prevent disease
What is the disadvantage of adding chlorine to water?
Some studies show it links to an increase in cancers, it can react with other natural substances in water to produce toxic by-products which some people think could cause cancer
What is the disadvantage of adding fluoride to water?
In high doses it can cause cancer and bone problems in humans. Some believe it shouldn’t be added to drinking water. Also a concern about whether its right to mass medicate, people can choose where to use a fluoride toothpaste, but not if its in the water they drink
Why do the chemical levels added to water need to be carefully monitored?
Because in some areas the water may already contain a lot of e.g. fluoride, so adding more would be harmful
What is the definition of a reversible reaction?
A reversible reaction is one where the products of the reaction can themselves react to produce the right original reactants (the reaction can go both ways)
What happens if a reversible reaction takes place in a closed system?
A state of equilibrium will always be reached
What does equilibrium mean?
The amounts of reactants and products will reach a certain balance and stay there
What does a closed system mean?
That none of the reactants or products can escape
What happens in a reaction when it reaches an equilibrium?
The overall effort is zero, even though the reaction is still happening in both directions, because the forward and reverse reactions cancel each other out ( same rate of reaction in both directions)
What does the position of equilibrium mean?
The relative amount of reactants and products
In a reversible reaction, what does the position of equilibrium depend strongly on?
The temperature and pressure surrounding the reaction
What happens if you deliberately alter the temperature and pressure?
You can move the position of equilibrium to give more product and less reactants
What are all reactions in one direction and the other?
Endothermic and exothermic
What happens if you raise the temperature in a reaction?
The endothermic reaction will increase to use up the extra heat
What happens if you reduce the temperature in a reaction?
The exothermic reaction will increase to give out more heat
What happens if you raise the pressure of a reaction?
It will encourage the reaction which produces less volume
What happens if you lower the pressure of a reaction?
It will encourage the reaction which produces more volume
What does adding a catalyst do to the equilibrium position?
Nothing, it does change it as it increases both reactions by an equal amount so it just reaches the equilibrium quicker but you have the same amount of product as you would without a catalyst
What is needed to make ammonia?
Nitrogen and hydrogen
What is the symbol equation for making ammonia?
N2(g) + 3H(g) ↔ 2NH3(g) (+heat)
Where is the nitrogen obtained from?
The air which is 78% nitrogen
Where is the hydrogen obtained from?
Natural gas or other sources like crude oil
How does the reaction to make ammonia reach an equilibrium?
The reaction is reversible and happens in both directions so the ammonia breaks down again into nitrogen and hydrogen
What are the industrial conditions for making ammonia?
200 atmosphere pressure, 450ºC and an iron catalyst
What would a higher pressure do?
Favour the forward reaction since there are four molecules of gas on the left for every two on the right
Why is the pressure set to be as high as possible?
To give the best % yield, without making the plant too expensive to build
What is the forward reaction?
Its exothermic so increasing the temperature will move the equilibrium the wrong way-away from the ammonia and towards N2 and H2 so the yield of ammonia would be greater at lower temperatures
What is the problem with reducing the temperature to get a higher yield of ammonia?
Lower temperature means lower rate of reaction so the temperature is increased anyway to make a faster rate of reaction
What is the compromise made and why?
450ºC is a compromise between maximum yield and speed of reaction, its better to wait 20 seconds for a 10% yield than waiting 60 seconds for a 20% yield
What stare is the ammonia formed as?
A gas but as it cools in the condenser it liquefies and is removed
What happens to the unused hydrogen (H2) and nitrogen (N2)?
They’re recycled so nothing is wasted
What does the iron catalyst do?
Makes the reaction go faster which gets it to the equilibrium proportions more quickly but doesn’t affect the position of equilibrium i.e. the % yield. Also keeps costs down
What would happen if there wasn’t a catalyst?
The temperature would have to be increased to make it happen quicker but this would reduce the % yield
What do alcohols end in?
-ol
What fictional group do alcohols have?
-oh
What is the general formula of an alcohol?
CnH2n+1OH
What would the formula be like for an alcohol with 2 carbons?
C2H5OH
What are the first three in the homologous series?
Methanol, Ethanol and Propanol
What is the formula for methanol?
CN3OH
What is the formula for ethanol?
C2H5OH
What is the formula for propanol?
C3H7OH
What is a homologous series?
A group of chemicals that react in a similar way because they have the same functional group (in alcohols its the -oh group)
What are the properties of alcohols?
They are flammable and burn in air to produce carbon dioxide and water, the first three all dissolve completely in water to form neutral solutions, they also react with sodium to give hydrogen and alkoxides (e.g. ethanol gives sodium ethoxide and H2)
What is the main alcohol in alcoholic drinks?
Ethanol because its not as toxic as methanol which causes blindness if drunk, but it still damages the liver and brain
How are methanol, ethanol and propanol useful solvents?
They can dissolve most compounds that water dissolves, but they can also dissolve substances that water can’t dissolve e.g. hydrocarbons, oils and fats
What is ethanol a solvent for?
Perfumes and aftershave lotions. It can mix with both the oils (which give the scent) and the water (which builds it up)
What is methylated spirit (or meths) ?
Ethanol with chemicals e.g. methanol added to it. Its used to clean paint brushes, fuels etc. Its poisonous to drink so a purply-blue dye is also added to stop people accidentally drinking it
How is ethanol used as a fuel?
In spirit burners, it burns fairly cleanly and doesn’t smell. It can also be mixed with petrol and used as fuel for cars. Since pure ethanol is clean burning, the more ethanol there us, the less pollution produced
What do countries such as brazil do?
They have little or no oil deposits but plenty of land and sun so they grow loads of sugar cane which they ferment to form ethanol. Also the sugar cane is a renewable resource
What functional group do carboxylic acids have?
COOH
What do the names of carboxylic acids end in?
Anoic acid, they start with the normal meth/eth/prop
What are the first three carboxylic acids?
Methanoic acid, ethanol can acid and propanoic acid
What is the molecular formula for methanoic acid?
HCOOH
What is the molecular formula for ethanoic acid?
CH3COOH
What is the molecular formula for propanoic acid?
C2H5COOH
What do carboxylic acids produce when they react with carbonates?
Carbon dioxide
What do the salts formed in these reactions end in?
Anoate eg methanoic acid will for a methanoate and ethanoic acid makes an ethanoate etc
What is the word formula for making sodium ethanoate?
Ethanoic acid + sodium carbonate > carbon dioxide + sodium ethanoate
What does carboxylic acid dissolve in water to produce?
Acidic solutions
How do carboxylic acids produce acidic solutions?
When they dissolve they ionise and release H+ ions which are responsible for making the solution acidic.
Why do carboxylic acids only form weak solutions?
Because they don’t ionise completely (not many H+ ions are released). This means that the solutions have a higher ph so are less acidic than aqueous solutions of strong acids with the same concentration
How can ethanoic acid and ethanoic be made?
Oxidising ethanol. Microbes like yeast cause the ethanol to ferment. Ethanol can also be oxidised using oxidising agents
What is the word formula for making ethanoic acid?
Ethanol + oxygen > ethanoic acid + water
Why does wine go off if it’s left open?
The ethanol in it is oxidised
What can ethanoic acid then make when dissolved in water?
Vinegar which is used for flavouring and preserving foods
Where is citric acid (a carboxylic acid) present?
In oranges and lemons and is manufactured in large quantities to make fizzy drinks and is also used to get rid of scale
What are carboxylic acids with longer chains of carbon atoms used to make?
Soaps and detergents in industry, also they are used in the preparation of esters
Why isn’t ethanoic acid usually chosen as a solvent?
Because it makes the solution acidic, however it is a very good solvent for many organic molecules
What functional group do esters have?
COO
What are esters formed from?
An alcohol and a carboxylic acid
What else is usually used in the production of esters?
An acid catalyst eg concentrated sulphuric acid
What is the word formula for esters?
Alcohol + carboxylic acid > ester + water
Why do esters end in oate?
The alcohol forms the first part and the acid forms the second part
What is the symbol formula for making esters?
CH3COOH + C2H5OH > CH3COOC2H5 + H2O
Why are many esters ideal for perfumes?
Because many of them have pleasant smells
What are the bad things about esters?
Many of them are flammable or even highly flammable so their volatility also makes them potentially dangerous. They also don’t mix well with water (they’re not nearly as soluble as alcohols or carboxylic acids)
What do esters mix well with?
Alcohols and other organic solvents
What are esters used for?
Perfumes, flavourings, aromas (there are some that smell or taste of Apple, orange, banana etc), ointments and solvents for paint, ink, glue and in nail varnish remover
What are the dangers of using esters?
Inhaling the fumes can irritate mucous membranes in the nose and mouth. They are heavier than air and very flammable (flammable vapour + naked flame = flash fire) some are toxic especially in large doses so some health problems occur associated with synthetic food additives such as esters.
What are esters not as volatile or toxic as?
Other organic solvents as they don’t release nearly as many toxic fumes as some of them. Esters have replaced solvents such as toluene in many paints and varnishes
