Elements from the Sea Flashcards
State the appearance and state of Chlorine at room temperature.
Halogens
Pale yellow/ green gas.
State the appearance and state of Bromine at room temperature.
Halogens
Brown/ orange/ red liquid.
State the appearance and state of Iodine at room temperature.
Halogens
Dark grey solid.
What do oxidation states show?
Oxidation states
An atom’s oxidation state tells us how many electrons it has donated or accepted to form an ion or a bond.
Why does an ionic substance need to be molten or in solution before you can electrolyse it?
Electrolysis
An electric current can only pass through an ionic substance when its ions are free to move about.
Describe how you would set up the equipment for the electrolysis of a solution of aqueous copper sulfate.
Electrolysis
- Connect each electrode to the power supply.
- Place the electrodes into a beaker containing a solution of aqueous copper sulfate, making sure that the electrodes aren’t touching each other.
- Turn the power supply on.
What is formed at the anode when a concentrated halide solution is electrolysed?
Electrolysis
The halogen will be formed at the anode.
Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.
What would you see happening at the anode? Explain your answer.
[2 marks]
Electrolysis
At the anode, you would see bubbles of gas appearing because chloride ions are losing electrons to form chlorine.
Two carbon electrodes are placed into molten copper chloride and the power supply is turned on.
What would you see happening at the cathode? Explain your answer.
[2 marks]
Electrolysis
At the cathode, you would see the electrode being plated because copper ions are gaining electrons to form copper metal.
What is brine?
Electrolysis
- a solution of water with high concentrations of salts - mainly sodium chloride, but also some bromine and iodine salts
- occurs naturally in salt lakes and seawater, and can be made by dissolving rock salt in water
Describe what occurs at the cathode.
Electrolysis
positive cations move to the negative electrode, the cathode, and gain electrons. REDUCTION
Describe what occurs at the anode.
Electrolysis
negative anions move to the positive electrode, the anode, and lose electrons.
OXIDATION
How do you calculate percentage atom economy?
molecular mass of desired product / sum of molecular mass of all reactants
x100
What does REDOX stand for?
Redox reactions
Reduction is Gain of electrons.
Oxidation is Loss of electrons.
What happens to the oxidation state of a substance when it’s reduced?
Redox reactions
The oxidation state will decrease.
During a redox reaction, an oxidising agent _____ electrons and is _____.
Redox reactions
During a redox reaction, an oxidising agent gains electrons and is reduced.
What is a reducing agent?
Redox reactions
A substance that is oxidised. It donates electrons.
What happens to the oxidation state of a substance when it’s oxidised?
Redox reactions
The oxidation state will increase.
During a redox reaction, a reducing agent ____ electrons and is ______.
Redox reactions
During a redox reaction, an oxidising agent loses electrons and is oxidised.
What is an oxidising agent?
Redox reactions
A substance that is reduced. It accepts electrons.
Use oxidation states to balance this redox reaction:
Ca(s) + Al³⁺(aq) → Ca²⁺(aq) + Al(s)
[1 mark]
Redox reactions
3Ca(s) + 2Al³⁺(aq) → 3Ca²⁺(aq) + 2Al(s)
What colour solution is formed when iodine dissolves in cyclohexane?
Halogens
purple
What colour solution is formed when bromine dissolves in cyclohexane?
Halogens
Red/ brown
What colour solution is formed when chlorine dissolves in cyclohexane?
Halogens
Pale green
What colour is Fluorine gas/ vapour?
Halogens
Colourless gas.
What colour is Chlorine gas/ vapour?
Halogens
Pale yellow/ green gas
What colour is Bromine gas/ vapour?
Halogens
brown/ orange/ red gas
What colour is Iodine gas/ vapour?
Halogens
Purple gas
What colour is Astatine gas/ vapour?
Halogens
Dark purple gas.
What colour solution is formed when chlorine dissolves in water?
Halogens
Pale yellow/ green solution.
What colour solution is formed when bromine dissolves in water?
Halogens
Brown/ orange/ red solution.
What colour solution is formed when iodine dissolves in water?
Halogens
Brown solution
How are hydrogen halides made?
Hydrogen Halides
Hydrogen halides can be made by adding a concentrated acid to a solid, ionic halide.
What type of reactions can reach a dynamic equilibrium?
Equilibrium
Reversible reactions.
Kc is dependent on what?
Equilibrium
Temperature.
what is volatility?
a measure of how easy it is to vaporise something (turn something from a liquid to a gas)
What specific risks does chlorine pose to humans?
Halogens
Toxic:
- Irritation of eyes, skin, respiratory system
- Reacts with water in mucus, in lungs, to form HCl, causing drowning
Chlorine is transported in pressurised tanks which are usually lined with steel. Why is it essential that the interior of a tank is dry?
Halogens
Chlorine reacts with water to produce corrosive acids.
What are the 2 main uses of chlorine?
Halogens
- Sterilising water by killing bacteria
- Making bleach
Explain the difference between a co-product and by-product.
- Co-product: from intended reaction. Useful
- By-product: from side reactions. Not useful
What is the strongest oxidising agent in group 7?
Halogens
Fluorine
State and explain the trend in thermal stability of the hydrogen halides, down the group.
Hydrogen Halides
Thermal stability decreases down group
- Bond enthalpies decrease because:
- Halide ion becomes larger
- Outermost bonding electrons become further from nucleus
- Weaker electrostatic attraction
What is the oxidation state of uncombined elements or elements made of the same atom? e.g. H₂
Oxidation states
Oxidation state = 0
Rule for oxidation state of a simple/ monatomic ion. e.g Na+ and Mg2+
Oxidation states
The oxidation state is the same as its charge. So oxidation state of Mg2+ is +2.
Rule for oxidation state of a complex ion. e.g. SO4 2-
Oxidation states
The overall oxidation state is the same as the overall charge of the ion. e.g. the oxidation states of the individual atoms will add up to the overall oxidation state.
Rule for oxidation state of a neutral compound.
Oxidation states
Overall oxidation state = 0
State the oxidation state of hydrogen, H and give the exception.
Oxidation states
+1
except in metal hydrides where it is -1.
State the oxidation state of hydrogen, H₂
Oxidation states
0
State the oxidation state of oxygen and give the exceptions.
Oxidation states
Usually -2.
Exceptions:
Peroxides = -1
OF₂ = +2
O₂F₂ = +1
State the oxidation state of group 1 elements.
Oxidation states
Always +1
State the oxidation state of group 2 elements.
Oxidation states
Always +2
State the oxidation state of Aluminium, Al.
Oxidation states
Always +3
State the oxidation state of fluorine.
Oxidation states
Always -1
State the oxidation state of chlorine.
Oxidation states
-1
Except if in a compound with F and O - it will have a positive value.
