chemistry unit 2

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how can you tell that the compound h2o has a covalent bond?
its made up of non-metals
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which of these compounds have ionic bonding? KBr HCl h2S Na2O Cl2O MgO
KBr Na2O MgO
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why is the formula of sodium chloride NaCl but magnesium chloride is MgCl2?
sodium ions have a single positive charge they are Na+ and magnesium have a double positive charge: they are they are Mg2+ (chlorine have a single negative charge meaning 2 chlorine are needed for magnesium)
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what are formulas for these compounds: calcium fluoride, sodium sulphate, magnesium nitrate, copper(ll) chloride,
CaF2, Na2SO4, Mg(nO3)2, CuCl2, Fe(OH)3
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how are atoms arranged in metal?
in a giant structure, closely packed together, in layers with a regular pattern
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why do ionic solids have high melting points?
they have giant structures with strong electrostatic forces that hold the ions together, and a lot of energy is needed to over come the forces
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why can ionic substances conduct electricity when molten or in solution?
the ions can move freely and carry the charge
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why does petrol not conduct electricity?
becuase the molecules in petrol have no overall charge
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why are substances with large molecular more likely to be liquids or solids at room temperature?
the intermolecular forces are stronger for larger molecules
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why do substances with giant giant covalent structures have very hight melting points?
every atom is joined to several other atoms, many strong covalent bonds have to be broken
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give 2 similarities and differences between diamond and graphite?
similarities: both forms of carbon, both giant structures. differences: diamond has 4 covalent bonds and graphite only has 3. diamond is very hard and graphite is soft.
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why can metals be made into wires?
when stretched the atoms slide into a new position without breaking apart
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why are alloys better than pre metals?
they are harder than pure metals, they can be made and designs to have different properties.
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why are metals good conductors of electricity?
delocalised electrons move rapidly through the structure carrying the electricity with them
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why do LD and HD poly(ethene) have different properties?
thye are made using different reaction conditions , they have different structures or differently shaped molecules
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what is the main difference in structures between thermosetting and thermosoftening plastics?
thermosoftening polymers have no cross-links or covalent bonds between the polymer chains, and thermosetting polymers have cross-links and covalent bonds.
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what allows thermosoftening polymers to be remoulded?
the weak intermolecular forces between the chains are overcome by heating
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what is a nano-particle?
a very small particle that is only a few nanometres in size
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scientists have developed a new deodorant using nano particles. what should be done before it is sold for people to use?
its effects in people and the environment should be researched and tested
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why do we count only protons and neutrons to calculate the mas number of an atom?
the mass of an electron in very small compared to protons and neutron
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how many protons neutrons and electrons are there in an atoms of 19F9?
9 protons, 9 electrons, and 10 neutrons
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what are isotopes?
atoms of the same element or atoms with the same atomic number that have different numbers of neutrons
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what is the mass of one mole of sodium atoms?
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why is the relative atomic mass of chlorine not a whole number?
it has isotopes and the relative atomic mass is and average value of the isotopes
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why is it not usually possible to get 100% yield from a chemical reaction?
reactions may not go to completion, other reactions may happen during, some product may be lost when separated or collected
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why should chemical manufacturers use reactions with high yields?
to help conserve resources, reduce waste product and/or pollution.
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what is a reversible reaction?
a reaction that can go both forward and backwards, or both ways
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what method can be used to analyse the colours in food?
paper chromatography
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what is the main purpose of the gas chromatography column is gs-ms analysis
to separate the compounds
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how is the relative molecular mass shown in a mess spectrum?
from the molecular ion peak or the peak with the largest mass
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what two types of measurements must be made to find the average rate of a reaction?
amount of a reactant or product and time taken for the reaction to take place
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how can we use a graph of amount of product against time to tell us the rate of reaction at a given time?
the gradient of the line at a given time gives the rate at that time
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what do we call the minimum energy needed for particle to react?
activation energy
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list the factors that increase the rate of reaction?
temperature, concentration of solutions, pressure of gasses, surface area of solids, using a catylist
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why do powders react faster than larger pieces of solid?
powders have a greater surface area than large lumps of solid, and this increases the chance of collisions
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why does a small change in temperature have a large effect on rate of reaction?
it increases the frequency of collisions and the energy of the particles
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why do reactions in solutions go faster at a higher concentrations?
it increase the frequency of collisions
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why does increasing the pressure increase the rate of reaction of 2 gasses?
the frequency of collisions increases because there are more molecules in the same volume
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why can catalysts be used over and over again?
because they're not used up in the reaction
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why do different reactions need different catalysts?
catalyst often work with only one type of reaction
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what are the benefits of using catalysts in industrial processes?
they reduce the energy needed nd the time needed for the reaction to take place and therefore reduces costs
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give one disadvantage of transition metal catalysts?
they may be toxic or expensive
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what 2 areas of research offer possibilities for new better catalysts?
nano-science and enzymes
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how can you tell that burning natural gas is an exothermic reaction?
it transfers energy to the surroundings
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what are the 2 ways of showing that a reaction is endothermic?
it either cools the surroundings or needs heat of keep the reaction going
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why must copper sulphate be heated continuously to change is into anhydrous copper sulphate?
because is an endothermic reaction
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why does adding water to anhydrous copper sulphate cause the mixture to get hot?
because it is an exothermic reaction
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suggest one advantage and disadvantage of a re-usable hand warmer compared with a single use hand warmer?
advantages: less waste, less resourses used. disadvantages:had to be heated or needs energy so it can be used again, slower reaction, smaller temperature rise
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which ions are produced by acids when they are added to water?
hydrogen ions H+
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what is an alkali?
a soluble base or substance that produce hydroxide ions OH-
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which indicators can tell us the PH of a solution?
universal indicators or full-range indicators
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name a metal other than zinc that can safely react with an acid to produce a salt?
any metal that is more reactive that hydrogen but less that calcium e.g lead tin iron
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wh do we ad excess of base when making a salt?
to use up all the acid, or to neutralise al of the acid
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name the products when (a) nitric acid reacts with magnesium (b)hydrochloric acid reacts with copper hydroxide?
(a)magnesium nitrate and hydrogen (b) copper chloride and water
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what compound is produced in every neutralisation reaction?
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zinc carbonate is insoluble in water. what would happen when sodium carbonate solution is added to zinc sulphate solution?
zinc carbonate would be produced as a precipitate and sodium sulphate would remain in the solution
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what must be done to ionic compounds before they can be electrolysed?
they must be melted or dissolved in water
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molten zinc chloride is electrolysed. name the substance produced at (a) the positive electrode? (b) the negative electrode?
(a) chlorine (b)zinc
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what type of change happens at the negative electrode when sodium ions become sodium atoms?
reduction or positive sodium ions gain electrons
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name the products at (a) the positive and (b) negative electrodes when aqueous copper sulphate is electrolysed using carbon electrodes?
(a)oxygen (b)copper
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why is aluminium oxide mixed with cryolite in the electrolysis cell?
to lower the melting temperature
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what are the final products of the electrolysis cell?
aluminium and carbon dioxide
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why is hydrogen produced when sodium chloride solution is electrolysed?
the solution contains hydrogen ions which are discharged in preference for sodium ions because sodium is more reactive then hydrogen
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why is electrolysis of brine an important industrial process?
the three products have many important uses
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why are some knives, forks and spoons silver-plated?
to make them look attractive, to protect the other metal from corrosion and /or reduce the cost
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Card 2


which of these compounds have ionic bonding? KBr HCl h2S Na2O Cl2O MgO


KBr Na2O MgO

Card 3


why is the formula of sodium chloride NaCl but magnesium chloride is MgCl2?


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Card 4


what are formulas for these compounds: calcium fluoride, sodium sulphate, magnesium nitrate, copper(ll) chloride,


Preview of the front of card 4

Card 5


how are atoms arranged in metal?


Preview of the front of card 5
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