Redox Flashcards
What is oxidation?
- The loss of electrons
- The gain of electrons
- Increase in oxidation number
What is reduction?
- The gain of electrons
- The loss of oxygen
- Decrease in oxidation number
What is an oxidation number?
Oxidation numbers are assigned to elements to show the extent to which they have been oxidised or reduced
What is the oxidation number for an uncombined element?
0 e.g. Fe
What is the oxidation number for a group 1 metal?
+1 e.g. Na
What is the oxidation number for a group 2 metal?
+2 e.g. Mg
What is the oxidation number for aluminium?
+3
How do you figure out the oxidation number for other metals?
- Look to the group number for the theoretical maximum
- E.G Mn is Group 7 so the maximum it could be is +7
When is the oxidation number for oxygen not -2?
- In peroxides
2. In compounds with fluorine
When is the oxidation number for chlorine not -1?
- In compounds with fluorine or oxygen
How do you figure out the oxidation number for other non-metals?
- As with metals, look at the group number for the theoretical maximum
What does the sum of the oxidation states in a neutral molecule always add up to?
- Zero
- One element must have a positive oxidation states and the other must be negative
- If neither atom has a fixed oxidation number, the more electronegative species will have the negative value
- Plug in numbers you know are fixed
What does the sum of the oxidation states in a compound ion always add up to?
- The overall charge on the ion e.g. negative one or positive 2
What is the role of oxidation numbers in naming compounds?
- If a compound contains an element that does not always have the same oxidation number (e.g. a transition metal), the oxidation number of this element is shown as a Roman numeral in brackets as part of the name of the compound e.g. iron (III) hydroxide
- Roman numeral’s after the negative compound ion e.g. sulphate (VI)
What is the first ionisation energy down group 2 like?
Decreases
What is the reactivity down group 2 like?
Increases
What is the atomic radius down group 2 like?
Increases
What is the alkalinity down group 2 like?
Increases
What is the solubility down group 2 like?
Increases
What is the electronegativity down group 2 like?
Decreases
What is the melting point down group 2 like?
Decreases
What does group 2 metal and oxygen form?
- Metal oxide
- Redox Reaction
- Increasing reactivity down the group
What is the flame colour of magnesium?
Bright white
What is the flame colour of calcium?
Brick red
What is the flame colour of strontium?
Crimson red
What is the flame colour of barium?
Apple green
What does group 2 metal and water form?
- Metal hydroxide and hydrogen gas
- Redox Reaction
- Reaction becomes more vigorous (remember for observe you don’t see hydrogen you see bubbles!) and no more hydrogen is produced it is just more vigorous!
What does group 2 metal oxides and water form?
- Metal hydroxides (this reaction does not result in the formation of hydrogen gas!)
- NOT Redox Reaction
- Better to go through two steps of make metal oxide and then react with water then straight with water as it is safer as no hydrogen is produced
How does magnesium reaction with steam?
1, Magnesium only reacts very slowly with cold water, hot water is required to make magnesium hydroxide and hydrogen
2. In contrast magnesium will react violent with steam ti takes magnesium oxide and hydrogen
Why does the solubility of group 2 hydroxides increase down the group?
- The IONIC RADIUS of M2+ increase
- Charge density of M2+ increases
- The attraction between the M2+ and OH- decreases
- The lattice will break up and solvate? more easily
How is calcium hydroxide used?
- Neutralises acidic soils
2. Used as lime water
How is magnesium hydroxide used? (and CaCO3)
- ‘anti acids’, intreating indigestion as they neutralise stomach acid
What does group 2 and acids form?
- Salts and hydrogen
- Redox Reaction
- metal and HCL, metal chloride and hydrogen
How does the reactivity change down group 7?
Decreases
How does the atomic radius change down group 7?
Increases
How does the electronegativity change down group 7?
Decreases
How does the melting point change down group 7?
Increases
How does the ability to be an oxidising agent change down group 7?
Decreases
Why is there this trend of melting point in group 7?
- Larger molecules, as atomic radius increases
- More electrons
- Chance of instantaneous dipoles forming increases
- Increased number of induced dipoles
- Increased number of London forces
- Increase in boiling and emptying point / decreases in volatility
Why is there this trend in oxidising power?
- larger molecules, so atomic radius increases
- More electrons
- More full inner shells, so shielding is increased
- Incoming electron is therefore less attracted to the nuclear charge
- Reactivity / oxidising ability decreases
What is an oxidising agent?
An oxidising agent is a substance that will accept electrons. The ability of halogens to accept an electron to from a halide ion makes them very good oxidising agents
What is the rule in displacement reactions?
- A more reactive halogen will displace a less reactive halogen from a solution of its halide ions
- Loose halogens give colour of solution not salts!
What colour is chlorine in hexane (non-polar solvent)?
colourless
What colour is bromine in hexane?
orange
What colour is iodine in hexane?
purple
What colour is chlorine in water?
colourless
What colour is bromine in water?
orange
What colour is iodine in water?
brown
What are the three displacement reactions and what is the colour change in each?
- 2KBr + Cl2 –> 2KCl + Br2
- Water: colourless to orange
- Hexane: colourless to orange - 2KI + Cl2 –> 2KCl + I2
- Water: colourless to brown
- Hexane: colourless to purple - 2KI + Br2 –> 2KBr + I2
- Water: orange to brown
- Hexane: orange to purple
What is a disproportionation reaction?
A reaction in which the same element is both oxidised and reduced
What are some examples of a disproportionation reaction? Where are they used?
- Chlorine and water, in water purification and is used to STERILISE drinking water
- Chlorine and (cold, dilute, aqueous) sodium hydroxide, used to from bleach as active ingredient in bleach is the NaClO
How do you test for halide ions? What are the results?
-Aqueous halide ions can be tested for using by adding an aqueous solution of silver nitrate
1. Halide: Cl-
Precipitate Colour: Silver chloride, white
2. Halide: Br-
Precipitate Colour: Silver bromide, cream
3. Halide: I-
Precipitate Colour: Silver iodide, yellow
How do you test the solubility of a silver halide?
- The relative solubility in ammonia can be used to double check
1. AgCl : soluble in DILUTE NH3
2. AgBr: soluble in CONCENTRATED NH3
3. AgI: insoluble in dilute and concentrated NH3
What are the benefits and risks of using chlorine in water treatment?
- B: Kills bacteria
- R: hazards of toxic chlorine gas and possible risks from formation of chlorinated hydrocarbons
- However, the overall risk to health of not adding chlorine to the water supply is far greater than the risk posed by chlorinated hydrocarbons, as the quality of drinking water would be compromised and sieges such as typhoid and cholera might break out
Why does magnesium gave a greater second ionisation energy than strontium?
- Ionic radius increases
- Shielding increases
- Attraction between the nucleus and outermost electron decreases
- Mg+ –> Mg2+ + e-
Why is calcium nitrate a salt?
The H+ ion in an acid has been replaced by a metal ion
Why does the hydroxide ion in aqueous calcium hydroxide acts as a base when it neutralises dilute nitric acid
It accepts a proton/H+
Explain the decrease in atomic radio acids the period from Na to Cl
- Nuclear charge increases
- Electrons added to the same shell and shielding remains the same
- Greater attraction
