Elements from the Sea

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  • Created by: LBCW0502
  • Created on: 21-05-16 11:40
Which group in the periodic table is the most reactive group of non-metals?
Group 7 (Halogens)
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In what form are the halogens found naturally and why?
Halogens are found naturally in compounds e.g. NaCl because they are too reactive (none of them are found naturally in the elemental form)
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What type of bonds are present in diatomic molecules of halogens (e.g. chlorine)
Covalent bonds
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What are the similarities within Group 7?
Non-metals, form negative ions, similar electronic configuration and form diatomic covalent molecules
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How can a halogen atom achieve stability (in terms of bonding)?
In an ionic bond, the gaining of an electron from a metal atom forms a halide ion. In a covalent bond, (outer) electrons are shared from another non-metal atom
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What are the trends in properties down Group 7?
Becomes darker in colour, melting point and boiling point increase, changes from gases to liquids to solids (at room temperature) and becomes less volatile
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What are the trends in properties (in terms of electronegativity and oxidising power) down Group 7?
Electronegativity and oxidising power decreases down the group
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Are the halogens more soluble in water or organic solvents?
More soluble in organic solvents (cyclohexane)
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What are the colours of the solutions of halogens (chlorine, bromine and iodine) when dissolved in cyclohexane?
Chlorine is pale green, bromine is orange/brown/red and iodine is violet
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What are the colours of the solutions of halogens (chlorine, bromine and iodine) when dissolved in water?
Chlorine is pale green, bromine is orange/yellow and iodine is brown
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Which element is the strongest oxidising agent in Group 7?
Fluorine
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Which element is the strongest reducing agent in Group 7?
Iodine
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What is the trend in reducing ability down Group 7 (order of weakest to strongest reducing agent)?
F- < Cl- < Br- < I-
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Which hydrogen halide is a colourless liquid at RTP?
Hydrogen fluoride (boiling point is higher than expected due to hydrogen bonding). At RTP the other hydrogen halides are colourless gases
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What is a displacement reaction?
A more reactive element displaces a less reactive element from a compound
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What is a redox reaction?
Both oxidation and reduction have occurred in the same reaction
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What is a precipitation reaction?
Soluble solutions react to form an insoluble solid (precipitate)
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What are the colours of the precipitates formed when silver nitrate reacts with: chloride, bromide and iodide ions?
Chloride ions form white precipitates, bromide ions form cream precipitates and iodide ions form yellow precipitates
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Which silver halides (chloride, bromide or iodide) are soluble in dilute ammonia solution
Silver chloride
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Which silver halides (chloride, bromide or iodide) are insoluble in dilute ammonia solution
Silver bromide and silver iodide
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Which silver halides (chloride, bromide or iodide) are soluble in concentrated ammonia solution
Silver bromide
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Which silver halides (chloride, bromide or iodide) are insoluble in concentrated ammonia solution
Silver iodide
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What is oxidation?
Gain of oxygen, loss of electrons and an increase in oxidation number
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What is reduction?
Loss of oxygen, gain of electrons and a decrease in oxidation number
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What is the oxidation state of an element?
0
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How do you work out the oxidation state for a simple ion (e.g Cl-)?
In simple ions, the oxidation state is the same as the charge on the ion (e.g. Cl- has the oxidation state -1)
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How do you work out the oxidation states in compounds with no overall charge?
The oxidation states of all the constituent elements must add up to zero (e.g. oxidation state of bromine in BrF3 is +3)
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How do you work out the oxidation state in more complicated ions?
The oxidation state of the constituent elements must add up to the overall charge on the ion (e.g. PO4 3-)
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What is an oxyanion?
A negative ion with oxygen. The name always ends in -ate to show that oxygen is present (e.g. chlorate (I) - ClO-)
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What is a disproportionation reaction?
Simultaneous oxidation and reduction of a species (e.g. chlorine is both oxidised and reduced in a reaction)
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What is electrolysis?
The decomposition of compounds (ionic compounds when molten or in solution) to form its elements using electricity
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Which electrode are the cations attracted to?
Cathode
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Which electrode are the anions attracted to?
Anode
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What type of reaction takes place at the negative electrode?
Reduction
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What type of reaction takes place at the positive electrode?
Oxidation
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What is produced in the electrolysis and sodium chloride solution?
Hydrogen, chlorine and sodium hydroxide solution (hydrogen is produced at the cathode, chlorine is produced at the anode)
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Why is hydrogen produced in the electrolysis of compounds such as sodium chloride?
Sodium is too reactive and large amounts of energy are required to break down the compound to form sodium
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What is produced at the positive electrode in the electrolysis of sulphuric acid?
Oxygen
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What is a dynamic equilibrium?
Concentration of reactants and products stay constant, forward and reverse reactions are both happening and the rate of the forward and reverse reactions are equal to each other (in a closed system)
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What is Kc?
The equilibrium constant
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What does Kc > 1 mean?
There are more products than reactants at equilibrium
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What does Kc >> 1 (greater than 10^10) mean?
The reaction appears to have gone to completion
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What does Kc < 1 mean?
There are more reactants than products
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What does Kc
The reaction appears to not have happened
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Which factors affect Kc?
A change of temperature
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Which factors do not affect Kc?
Changes in concentration (assuming that the temperature remains constant), change of pressure and adding a catalyst (catalysts do not affect the position of equilibrium but equilibrium is reached quicker)
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What are the health risks of chlorine?
Toxic, can irritate eyes skin and respiratory system, affects lung tissue (causes drowning as liquid floods the lungs)
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What are the precautions which need to be taken when transporting chlorine?
Chlorine is stored as a liquid (with an inert gas e.g. nitrogen) under pressure in tanks lined with steel (with pressure release devices). Inside of tank is dry to prevent chlorine from reacting with water to produce corrosive acids
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What are the key aspects when unloading chlorine?
A scrubber unit ensures that air being displaced from the bulk trailer has any chlorine removed from it. Scrubber has sodium hydroxide solution that reacts with chlorine to produce sodium chlorate (I) - bleach can be sold on
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What can be used to check if chlorine is leaking out of the cylinders?
Take a stick with a cloth soaked in concentrated ammonia solution over the end. If a cylinder is leaking then a white cloud of ammonium chloride will be seen
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What are the uses of chlorine?
Production of paper products, plastics, dyes, textiles, medicines, antiseptics, insecticides, solvents paints and bleaches
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What are the uses of bromine?
Water purification, pesticides and flame retardants
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What are the uses of iodine?
Used in pharmaceuticals and disinfectants, inks/ dyes and added in small amounts to table salt, in order to avoid iodine deficiency affecting the thyroid gland. The radioactive isotope iodine-131 is sometimes used to treat cancerous thyroid glands
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What are the main concepts in titration (equipment/key ideas)
Volumetric pipette, burette (rinsed) conical flask, white tile, indicator, meniscus, end point, concordant results, swirling solution
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How do you calculate atom economy?
Mr of desired product / Mr of all reactants used x 100
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What is produced when NaCl reacts with concentrated sulphuric acid?
Hydrochloric acid
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What is produced when NaBr reacts with concentrated sulphuric acid?
Hydrogen bromide, bromine and sulphur dioxide
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What is produced when NaI reacts with concentrated sulphuric acid?
Hydrogen iodide, iodine, sulphur dioxide, sulphur and hydrogen sulphide
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What is the test for hydrogen sulphide?
Smell of rotten eggs
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Which reagent is used to react with sodium bromide (or sodium iodide) to produce a pure hydrogen halide?
Concentrated phosphoric acid
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What is the trend for thermal stability of hydrogen halides down Group 7?
Thermal stability of hydrogen halides decreases (HI is broken at a lower temperature than HCl - bond enthalpy decreases down the group)
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What happens when hydrogen halides (fluoride, chloride, bromide and iodide) are heated?
Hydrogen fluoride and hydrogen chloride isn't broken down into its elements, some brown bromine has is made when hydrogen bromide is heated and large amount of purple gaseous iodine is made when hydrogen iodide is heated
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What are the properties of hydrogen halides (in terms of acidity)?
Very soluble hydrogen halides are all acidic (apart from HF they are strongly acidic), for HCl, HBr and HI there is almost 100% dissociation
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What is produced in the reaction of hydrogen halides (fluoride, chloride, bromide and iodide) with sulphuric acid?
HF and HCl do not react, HBr produces sulphur dioxide and HI produces hydrogen sulfide
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What is Le Chatelier's principle?
If a system is at equilibrium and a change is made in any of the conditions then the system will oppose the change
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Where will the equilibrium position shift to when the concentration of reactants is increased?
Equilibrium position will move to the product side (right)
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Where will the equilibrium position shift to when the concentration of products is increased?
Equilibrium position will move to the reactant side (left)
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Where will the equilibrium position shift to when the concentration of reactants is decreased?
Equilibrium position will move to the reactant side (left)
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Where will the equilibrium position shift to when the concentration of products is decreased?
Equilibrium position will move to the product side (right)
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What happens to the equilibrium position when the pressure is increased?
Increasing the pressure moves the equilibrium to the side of the equation with fewer gas molecules at this tends to reduce the pressure
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What happens to the equilibrium position when the pressure is decreased?
Decreasing the pressure moves the equilibrium to the side of the equation with more gas molecules as this tends to increase the pressure
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What happens to the equilibrium position when the temperature is increased?
Heating a reversible reaction at a equilibrium shifts the reaction in the direction of the endothermic reaction
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What happens to the equilibrium position when the temperature is decreased?
Cooling a reversible reaction at equilibrium shifts the reaction in the direction of the exothermic reaction
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Other cards in this set

Card 2

Front

In what form are the halogens found naturally and why?

Back

Halogens are found naturally in compounds e.g. NaCl because they are too reactive (none of them are found naturally in the elemental form)

Card 3

Front

What type of bonds are present in diatomic molecules of halogens (e.g. chlorine)

Back

Preview of the front of card 3

Card 4

Front

What are the similarities within Group 7?

Back

Preview of the front of card 4

Card 5

Front

How can a halogen atom achieve stability (in terms of bonding)?

Back

Preview of the front of card 5
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