Chemistry 3

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  • Created by: Emily
  • Created on: 14-05-13 20:06
What were the two obvious ways to categorise elements on the Periodic Table in the 1800's?
1) Their physical and chemical properties. 2) Their relative atomic mass.
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What did Newlands discover?
That every eighth element had similar chemical properties.
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Three ways in which Newlands work was criticised.
1) His groups contained elements that didn't have similar properties (e.g. carbon & titanium). 2) He mixed up metals and non metals (e.g. oxygen and iron). 3) He didn't leave any gaps for undiscovered elements.
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What did Dmitri Mendeleev do that Newlands didn't?
Left gaps for unknown elements.
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What was Mendeleev able to do because of the structure of his Periodic Table?
Predict the atomic mass and chemical properties of undiscovered elements.
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Why did scientists change their mind about the usefulness of the periodic table in the late 19th century?
To start with, there wasn't much evidence about any elements that would fit into the gaps. But in the late 19th century, scientists discovered protons, neutrons and electrons and the periodic table matched up well with the structure of the atom.
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How is the modern Periodic table structured? Refer to the columns.
By the elements' electronic structure. The vertical columns are called 'groups' which correspond to the number of electrons on the highest occupied energy level (outer shell).
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What happens to the electrostatic attraction between the nucleus and the outer electron(s) as shielding increases?
It decreases.
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Why is group one called 'the alkali metals'?
Because when they react with water they release hydroxides (alkali) solution - turning the colour of a universal indicator purple.
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What happens as you go down group one?
They become more reactive. They have lower melting and boiling points.
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Why is Lithium less reactive than Sodium?
There is a higher electrostatic attraction between the outer electron in Lithium because there is less shielding so the one outer electron is less easily lost. Whereas sodium has more shielding so the attraction is weaker in comparison.
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Describe the bonds alkali metals make.
They form ionic bonds with non-metals. They loose one electron so they for a 1+ ion, causing there to be a oppositely charged attraction between the negatively charged metal and the positively charged non-metal.
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What gas do alkali metals produce when they react with water?
Hydrogen.
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What happens when you go down group seven?
They become less reactive. They have higher melting and boiling points.
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Describe the bonds Halogens make.
They form ionic bonds with metals. They gain one electron so they from 1- ions (called halides).
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Explain how halogens can displace one another.
More reactive halogens can displace (move/take over) a less reactive halogen from an aqueous solution of its salt.
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Four properties of transition metals.
1) Good conductors [of heat and electricity]. 2) Very dense. 3) Strong. 4) Shiny.
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Three differences of transition metals compared to alkali metals.
1) Less reactive than alkali metals (don't react as vigorously with water or oxygen). 2) Denser stronger and harder. 3) Much higher melting points (apart from mercury).
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Three examples of when (and what) transition metals are used as a catalyst.
1) Iron is used in the haber process. 2) Manganese(IV) oxide in the decomposition of hydrogen peroxide. 3) Nickel in turning oils into fats for making margarine.
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What do the two different types of water produce when mixed with soap?
Hard water: produces scum and scale. Soft water: produced a 'nice' lather.
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What happens when hard water is heated, and why is the product bad?
Scale is produced. It can build up, blocking pipes. It is also a thermal insulator - so heating appliances loose efficiency if there is a large amount of scale surrounding it.
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What is hardness caused by and why are they there?
Ca^2+ and Mg^2+ ions in the water because of infiltration through certain types of rock (e.g. limestone, chalk and gypsum).
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Two advantages of hard water.
1) Ca^2+ ions are good for healthy teeth and bones. 2) Studies have found that the minerals in hard water reduce the risk of someone developing heart disease compared to someone drinking soft water.
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What is temporary hardness caused by and how can it be removed?
The hydrogencarbonate ion, HCO[3]^- in Ca(HCO[3])[2]. It can be removed by boiling.
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Describe what happens when temporary hard water is boiled.
The calcium hydrogencarbonate decomposes to form calcium carbonate ('limescale') which is insoluble.
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What two ways can remove both types of hardness?
1) Adding washing soda (sodium carbonate). 2) Running the water through ion exchange columns.
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Describe how washing soda softens hard water.
The added carbonate ions react with the Ca^2+ and Mg^2+ ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. Both original ions are no longer dissolved in the water so they can't make it hard.
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Describe how ion exchange columns.
The columns contain lots of sodium (or hydrogen) ions and 'exchange' them for calcium or magnesium ions in the water that runs through them.
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Name the four stages of water treatment.
1) Screening. 2) Removal or solids and microbes. 3) Filtration. 4) Chlorination.
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Describe the processes of water treatment.
Passes through a mesh screen to remove large debry. Chemicals are added to make solids and microbes stick together and fall to bottom. The water is filtered through gravel beds to removed solids. Chlorine is added to remove any remaining microbes.
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What can people buy to improve their own water quality and how do they work?
Buy filters that contain carbon or silver to remove substances from their tap water. Carbon in the filters removes the chlorine taste and silver kills bugs.
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Two advantages of adding Fluoride and Chlorine to water.
1) Fluoride is known to prevent and reduce tooth decay. 2) Chlorine is added to kill of harmful microbes which prevents disease.
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Three disadvantages of adding Fluoride and Chlorine to water.
1) Chlorine can react with other natural substances in water to produce a toxic by-product which has been linked to cancer. 2) Fluoride can cause bone problems and cancer in high doses. 3) Some people disagree with mass medication.
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What is a reversible reaction?
A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants.
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What is an equilibrium and when does it happen?
When the reactions are taking place at exactly the same rate in both directions so the overall effect is nil because the forward and reverse reactions cancel each other out.This can only happen in a closed system.
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How does changing the temperature change reversible reactions?
If the temperature is increased, the endothermic reaction will increase to use up the extra heat. If the heat is decreased, the exothermic reaction will increase to give out more heat.
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How does changing the pressure change reversible reactions?
If the pressure is increased, the reaction which produces less volume will be encouraged. If the pressure is decreased, the reaction which produces more volume is encouraged.
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What happens if a catalyst is added to a reversible reaction?
The reaction reaches equilibrium quicker, but the amount of product produced is the same as the reaction without the catalyst.
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Where do the gases for the haber process come from?
Nitrogen is obtained from the 78% nitrogen air. Hydrogen comes from natural gas or from other sources like crude oil.
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What are the industrial conditions for the haber process and why are they like this?
Pressure of 200atms: favours the forward reaction (lower volume), higher pressure plant is too expensive. Temperature of 450'C: compromise between maximum yield and speed of reaction. Catalyst is iron: speed up the reaction (without raising temp).
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What is the general formula of an alcohol?
C H OH
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What are the first three alcohols in the homologous series?
Methanol, Ethanol and Propanol.
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Three similar properties of the first three alcohols.
1) Flammable. 2) Dissolve completely in water to form neutral solutions. 3) React with sodium to give hydrogen and alkoxides.
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Why are alcohols useful in industry?
They dissolve most substances that water dissolves, but they also dissolve substances water cant like hydrocarbons, oils and fats.
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Three things alcohols are used for.
Perfumes, fuels and cleaners.
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Three advantages of using ethanol in fuel.
1) Clean burning - less pollution. 2) Doesn't smell bad. 3) Can be produced by fermenting sugar cane which is a renewable resource.
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What is the functional group of Carboxylic acids?
-COOH
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What are the first three Carboxylic acids?
Methanoic acid, ethanoic acid, propanoic acid.
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What do carboxylic acids produce when reacted with carbonates?
Carbon dioxide and salts ending in '-anoate'.
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Explain why carboxylic acids produce weak acidic solutions when dissolved in water.
When they dissolve, they ionise and release H+ ions which make the solution acidic. But they don't ionise fully/completely (not many H+ ions are released) so they have a higher pH (less acidic) than strong acids of the same concentration.
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What is the difference between acidic concentration and acidic strength?
Concentration is how watered down the acid is. Strength is how well it has ionised in water.
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How can ethanoic acid be made?
Oxidising ethanol.
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What is ethanoic acid used for?
Dissolved in water to make vinegar which is used for preserving food and flavouring.
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How can citric acid be useful?
Manufactured in large quantities to make fizzy drinks. It can also be used to get rid of scale.
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Three things carboxylic acids are used for.
Soaps/detergents, preparation of esters, solvents.
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What is the functional group of Esters?
-COO-
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What do you get when you react methanol and propanoic acid?
Methyl Propanoate and water.
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Two reasons why esters are good to use as perfumes.
1) Smell good - sweet and fruity. 2) Volatile.
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What do esters mix well with (and not with)?
They mix well with alcohols and organic solvents. They don't mix well with water.
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Three ways (other than perfumes) esters are used.
1) Flavourings. 2) In ointments. 3) Solvents.
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Three disadvantages of Esters.
1) Irritate mucous membranes in the nose and mouth. 2) Very flammable. 3) Some are toxic in high quantities.
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How many molecules are there in one mole of an element?
6.023 x 10^23
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What is the formula for finding out the concentration of a substance in a titration equation?
Concentration = number of moles / volume in dm^3
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What is the formula for finding out grams per dm^3 in a titration equation?
Mass = number of moles x relative formula mass.
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Five pieces of equipment needed to measure energy transfer.
1) Thermometer. 2) Polystyrene cup. 3) Lid. 4) Cotton wool. 5) Reaction mixture.
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What makes a reaction exothermic?
The energy released in bond formation is greater than the energy used in breaking old bonds. So it gives out energy to the surroundings (e.g. combustion).
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What makes a reaction endothermic?
The energy required to break old bonds is greater than the energy released when new bonds are formed. So it takes in energy from it's surroundings (e.g. photosynthesis).
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What is calorimetry ?
Measuring how much energy is released from a source.
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What is the formula for working out energy transferred?
Mass of water (g) x specific heat capacity of water (4.2) x temperature change ('C)
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In energy level diagrams, what is the 'peak' of the graph?
Activation energy - the amount of energy needed to break the old bonds.
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Advantages of using hydrogen as a fuel.
Because it reacts with oxygen to give water - which is 'clean burning' (not a pollutant).
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Disadvantages of using hydrogen as a fuel.
The specialised engines are expensive. Also, hydrogen requires energy to be made and it has to be stored safely because it's highly explosive.
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What is a fuel cell?
An electrical cell that is supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity.
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Advantages of a fuel cell.
Doesn't run down or need recharging from the mains. It will produce energy in the form of electricity and heat as long as fuel is supplied.
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Precise flame test colours (positive ions test) : Lithium, Sodium, Potassium, Calcium and Barium.
Lithium: crimson. Sodium: yellow. Potassium: lilac. Calcium: red. Barium: green.
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Colours of precipitates formed when these positive metal ions react with sodium hydroxide: Calcium, Copper(II), Iron(II), Iron(III), Aluminium and Magnesium.
Calcium: White. Copper(II): Blue. Iron(II): Green. Iron(III): Brown. Aluminium: White and then dissolves in excess NaOH into a colourless solution. Magnesium: White.
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How do you test for Halides?
Add dilute nitric acid followed by silver nitrate solution.
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What colour precipitates do iodide, bromide and chloride give when testing for Halides?
Iodide: yellow precipitate of silver iodide. Bromide: cream precipitate of silver bromide. Chloride: white precipitate of silver chloride.
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How to test for sulfate ions.
Add dilute hydrochloric acid, followed by barium chloride solution. If a white precipitate, barium sulfate, forms - the original compound was a sulfate.
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Card 2

Front

What did Newlands discover?

Back

That every eighth element had similar chemical properties.

Card 3

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Three ways in which Newlands work was criticised.

Back

Preview of the front of card 3

Card 4

Front

What did Dmitri Mendeleev do that Newlands didn't?

Back

Preview of the front of card 4

Card 5

Front

What was Mendeleev able to do because of the structure of his Periodic Table?

Back

Preview of the front of card 5
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