Chemistry Unit 3 Revision

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In the early 1800s what did they base the periodic table on?
Atomic mass
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In what ways do we currently base the table on?
1- their physical and chemical properties 2- their relative atomic mass
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When were protons and neutrons discovered?
20th century
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What is Newlands' Law of Octaves based upon?
Every 8th element had similar properties, and so he listed some of the known elements in rows of seven.
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Why was Newlands work criticized?
His groups contained elements that didn't have similar properties/He mixed up metals and non metals/He didn't leave any gaps for elements that hadn't been discovered yet
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What was Mendeleev' theory?
Put the elements in order of atomic mass, however he had to leave gaps in order to keep elements with similar properties in the same groups. He left gaps for undiscovered elements, which were discovered later on
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What do elements in the same group have?
The same number of electrons in the outer shell. The group number is the number of electrons which occupy the highest energy level
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Why do group 1 metals get more reactive as you go down the group?
The combination of increased distance and increased shielding means that an electron in a higher energy level is more easily lost because there's less attraction from the nucleus holding it in place.
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Why are group 7 elements less reactive going down the group?
Increased distance and shielding also means that a higher energy level is less likely to gain an electron as there's less attraction from the nucleus pulling electrons into the atom.
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Trends in the alkali metals:
-Metals with low densities -React with non metals to form ionic compounds (metal +1) White solids that dissolve in water to form colourless solutions -react with water producing hydrogen -Form Hydroxides that dissolve in water to give alkali solution
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The further down group one you go the element is....
More reactive + Lower melting and Boiling point
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Compared with the elements in Group 1, transition elements..
Have higher melting points (except mercury) and higher densities. Are stronger and harder. Are much less reactive and so do not react as vigorously with water or oxygen
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What are transition elements useful for?
Useful catalysts and have ions with different charges
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The further down group 7 you go the elements are:
Less reactive the element and the higher the melting points and boiling points
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How can the trends in reactivity within groups be explained.
The higher the energy level of the outer electrons the more easily electrons are lost and the less easily electrons are gained.
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What does soft water form?
Readily forms lather with soap
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What does hard water form?
Reacts with soap to form scum and so more soap is needed to form lather
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What dissolved compounds does hard water contain?
Calcium or magnesium. They dissolve when water comes into contact with rocks
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What are the 2 types of hard water?
Permanent and temporary.
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What is the difference between temporary and permanent hard water?
Permanent remains hard when it is boiled and temporary is softened by boiling
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Temporary hard water contains hydrogencarbonate ions and that decompose on heating. What does this produce?
Carbonate ions which react with calcium and magnesium ions to form precipitates
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Why does using hard water can increase costs?
More soap is needed
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What are some benefits of hard water?
Calcium compounds are good for the development and maintenance of bones and teeth and also help to reduce heart disease
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How can you make hard water soft?
By removing calcium and magnesium ions.
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How can you remove the calcium and magnesium ions?
Adding sodium carbonate, which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate. Also using commercial water softeners such as ion exchange columns containing hydrogen ions or sodium ions
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What do water filters contain?
Carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality
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How can pure water be produced?
Distillation
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What is energy normally measured in?
Joules (J)
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How is the amount of energy releases or absorbed by a chemical reaction in a solution can be calculated, how can it be calculated?
From the measured temperature change of the solution when the reagents are mixed in an insulated container. This method can be used for reactions of solids with water or for neutralisation reactions
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What must there be during a chemical reaction?
Energy must be supplied to break the bond and energy is released when bonds are formed
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What happens in an exothermic reaction?
The energy released from forming new bonds is greater than the energy needed to break existing bonds
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What happens in an endothermic reaction?
The energy needed to break bonds is greater than the energy released from forming new bonds
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What does a catalyst provide?
A different pathway for a chemical reaction that has a lower activation energy
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What can be used to identify metal ions?
Flame tests
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What colour does lithium compounds burn?
Crimson red
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What colour does sodium compounds burn?
Yellow
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What colour does potassium compounds burn?
Lilac
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What colour does calcium compounds burn?
Red
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What colour does barium compounds burn?
Green
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What ions form white precipitates with sodium hydroxide solutions?
Aluminium, Calcium and Magnesium
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What precipitate dissolves in excess sodium hydroxide solution?
Aluminium Hydroxide
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What ions form coloured precipitates with sodium hydroxide solution?
Copper(II) = Blue, Iron(II) = Green, Iron(III) = Brown
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Carbonates react with dilute acids to form carbon dioxide. What does this produce?
C02 produces a white precipitate with lime-water. This turns lime-water cloudy
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Halide ions in solution produce.... with silver nitrate solution in the presence of dilute nitric acid
Precipitates
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What can be done if the concentration of one of the reactants is known?
The results of a titration can be used to find the concentration of the other reactants
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What are the raw materials of the Haber process?
Nitrogen and hydrogen
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How are nitrogen and hydrogen obtained?
Nitrogen is obtained from the air and the hydrogen may be obtained from natural gas or other sources
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To make ammonia what is done to the purified gases?
They're passed over a catalyst of iron at a high temperature (450^0C) and a high pressure (200 amps). Some of the hydrogen and nitrogen reacts to form ammonia. Its a reversible reaction.
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How is the production of ammonia reversible?
Ont he cooling the ammonia liquefies and is removed, the remaining hydrogen and nitrogen are recycled
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When is an equilibrium reached?
When the reactions occur at exactly the same rate in each direction in a reversible reaction
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What does the relative amounts of all the reacting substances at equilibrium depend on?
The conditions of the reaction
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What happens if the temperature is raised in a reversible reaction?
The yield from the endothermic reaction increases and the yield from the exothermic reaction decreases
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What happens if the temperature is lowered in a reversible reaction?
The yield from the endothermic reaction decreases and the yield from the exothermic reaction increases
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What happens in a gaseous reaction if there is an increase in pressure/
It will favour the reaction that produces the least number of molecules as shown by the symbol equation for that reaction
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What is the functional group of alcohols?
-OH.
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What are the properties of Methanol, Ethanol and Propanol?
Dissolve in water to form a neutral solution, React with sodium to produce hydrogen, Burn in air, Are used as fuels and solvents and ethanol is the main alcohol in alcoholic drinks
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How can ethanol turn into ethanoic acid?
Oxidised, either by chemical oxidising agents or by microbial action
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What is the functional group of carboxylic acids?
-COOH
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What are the main properties of carboxylic acids?
Dissolve in water to produce acidic solutions, React with carbonates to produce carbon dioxide, React with alcohols in the presence of an acid catalyst to produce esters. Do not ionise completely when dissolved in water and so are weak acids
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What is ethyl ethanoate?
The ester produced from ethanol and ethanoic acid.
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What is the functional group of Esters?
-COO-
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What are the properties of ester?
Volatile compounds with distinctive smells and are used as flavourings and perfumes
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In what ways do we currently base the table on?

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Card 3

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Card 4

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Card 5

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Why was Newlands work criticized?

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