Group 7 and Redox Flashcards
Describe fluorine
-yellow gas
-very reactive
-toxic
Describe chlorine
-green gas
-very reactive
-toxic
Describe bromine
-orange liquid
-very reactive
-toxic
-often used as a solution in water-bromine water, Br2(aq)
Describe iodine
-grey crystals
-reactive
-toxic
-easily turns into purple vapour on heating
-used in solution as an antiseptic
What colour is iodine solution?
Brown
Describe the trend in atomic radius of group 7 down the group
-atomic radius increase
-because more shells/more shielding
-so bigger atoms
What is electronegativity?
-the power of an atom to attract the 2 electrons in a covalent bond
Describe the trend in electronegativity down group 7
-electronegativity increases
-bigger atoms/ more shells
-more shielding
-weaker attraction between buckeye and 2 electrons in covalent bond
Describe the trend in melting/ boiling points down group 7
-bigger molecules
-more electrons
-stronger van der waals forces between molecules
-higher mpt/bpt
Describe the trend in 1st ionisation energy down group 7
-1st IE decreases
-atoms get bigger/ more shells
-more shielding
-therefore weaker attraction from nucleus to electron in outer shell
What happens to reactivity going down group 7?
Reactivity decreases because it becomes more difficult to gain an e-
The trend in reactivity enables the halogens to undergo displacement reactions
What happens in the reaction: Cl2(aq) + 2KI(aq) —> I2(aq) + 2KCl(aq)
-Here, a more reactive halogen replaces a less reactive halogen in a halide salt compound
-Chloride had been reduced
-Iodide has been oxidised
-Potassium is a spectator ion
What happens in the reaction between bromine and chloride
no reaction
What gained in the reaction between iodine and chloride
no reaction
What happens in the reaction between chlorine and bromide
yellow solution forms
What is the ionic equation for the reaction between chlorine and bromide
Cl2 + 2Br- —> 2Cl- + Br2
What happens in the reaction between iodine and bromide
no reaction
What happens in the reaction between chlorine and iodide
brown solution forms
What is the ionic equation for the reaction between chlorine and iodide
Cl2 + 2I- —> 2Cl- + I2
What happens in the reaction between bromine and iodide
brown solution forms
What is the ionic equation for the reaction between bromine and iodide
Br2 + 2I- —> 2Br- + I2
Put chlorine iodine and bromine in order of strongest to weakest oxidising power
strongest—chlorine, bromine, iodine—weakest
Explain the order of oxidising power from chlorine(chlorine) to iodine(weakest)
-Halogen atom gains an electron when it oxidises the halide ion
-The smaller the halogen atom, the easier it is to gain an electron as it is smaller and has less shielding
What is an oxidising agent
Oxidising agents accept electrons
Therefore oxidising agents are reduced
What are reducing agents
Reducing agents are electron donors
Therefore, reducing agents are oxidised
In the reaction: 2Mg + O2 —>2MgO , what is the oxidising agent and what is the reducing agent?
Mg- reducing agent
O2- oxidising agent
When writing half equations, where do the electrons go for a reduction reaction and a oxidation reaction
reduction- left
oxidation- right
What are oxidation states
Oxidation states are a method for working out if a substance is oxidised or reduced.
Every element in a compound is given an oxidation number.
Changes in oxidation number indicate if oxidation or reduction is happening
What oxidation number do elements have and why?
0
Because they haven’t lost or gained any electrons
In a simple ion, what is the oxidation number of each element the same as?
it’s charge
What is the overall oxidation number for the uncharged ionic substance? Give examples
0
-NaCl—> Na Ox= +1; Cl Ox=. -1
How do we assign oxidation numbers to covalent molecules
The same way as if they were ionic
What are the general rules for oxidation numbers ?
What is the oxidation number of S in SO4 2-
Oxygen ion is -2
-2 x 4 = -8
The total has to be -2, so the oxidation number of S has to be 6 because -8 + 6= -2
What is the oxidation number of Cr in Cr2O7 2-
Oxygen ion is -2
-2 x 7 = -14
The total number has to be -2, so the oxidation number of Cr2 is 12.
Therefore, the oxidation number of Cr is 6
What are the oxidation numbers of Na and H in NaH?
Usually H is +1, however since it’s joined with a metal, on this occasion, it is -1
And Na is +1
What are the oxidation numbers of H and O in H2O2?
What is one key thing that must be remembered when writing half equations?
all reactants and products must be balanced
What are the steps to ensure that half equations are balanced
-atoms
-ions
-charges
-electrons
(in this order)
Write a half equation for chlorine gas being reduced
How can we tell if a reaction is an oxidation or reduction?
If the change in oxidation number goes down, it is a reduction and if it goes up, it is an oxidation
What are the rules for constructing half equations
You are only allowed to write certain things in half equations:
-the substance you start from snd what it is oxidised or reduced to.
-Hydrogen ions
-Water
-Electrons
(in this order)
Write a half equation for SO4 2- —> S
First try to balance:
Add a 4H20 on the side of the products and a 8H+ on the side of the reactants.
Then calculate the change in oxidation number.
The Ox of S in SO4 2- is +6 and the Ox of S is 0 so therefore the Ox has gone down which means the reaction is a reduction snd the number of electrons needs to go on the left.
6e- + 8H+ + SO4 2- —> S + 4H2O
Write a half equation for IO3- —> I2
First try to balance:
Add a 2 in front of IO3-, a 6H2O on the side of the products and a 12H+ on the side of the reactants.
Then calculate the change in oxidation number
+5–>0
+5–>0
The number goes down so the reaction is a reduction reaction and the electrons go on the left.
12H+ + 2IO3- + 10e- —> I2 + 6H2O
Write a half equation for VO^2+ —>VO2+
First try to balance:
Add a H2O to the side of the reactants and a 2H+ to the side of the products
Then calculate the change in oxidation number
+4—>+5
The oxidation number is going up, therefore the reaction is an oxidation reaction and the electrons need to go on the right hand side
H2O + VO^2+ —> VO2+ + 2H+ + e-
Write a half equation for the oxidation of sodium metal to sodium 1+ ion and write a half equation for the reduction of fluorine gas to fluoride ions. Then combine the equation.
1)Na —> Na+ + e-
2)F2 + 2e- —> 2F-
Then multiply equation 1 by 2 dk that there the same number of electrons in both the oxidation reaction reduction reaction and combine them.
2Na —> 2Na+ + 2e-
2Na + F2 —> 2Na+ + 2F-
Between fluorine, chlorine, bromine and iodine, which one has the highest reducing power and why?
Iodine
Because it has the most shells, most shielding, its the largest ion and has the lowest charge density
When a halide ion acts as a reducing agent, what does it do?
It loses electrons
What type of reaction happens with a chloride ion (NaCl) and sulfuric acid(H2SO4)?
displacement
What is the product from the reaction between NaCl and H2SO4 and what are the observations?
HCl
Steamy fumes
What is the equation for the reaction between NaCl and H2SO4?
NaCl + H2SO4 -> NaHSO4 + HCl
What type of reaction happens between NaBr and H2SO4?
Displacement
What is the product formed from the reaction between NaBr and H2SO4 and what are the observations?
HBr
Steamy fumes
What is the equation for the reaction between NaBr and H2SO4?
NaBr + H2SO4 -> NaHSO4 + HBr
What type of reaction is the reaction between Br- and H2SO4?
Redox
What is the product made in the reaction made between 2Br- , 2H- and H2SO4 and what are the observations?
Br2
Brown fumes
What is the equation for the reaction between Br- and H2SO4?
2Br- + H2SO4 + 2H- -> Br2 + SO2 + 2H2O
What type of reaction is the reaction between Br- and H2SO4?
redox
What is the name of the product between the Br- and H2SO4 and what are the observations?
SO2
colourless gas
What is the name of the reaction between NaI and H2SO4?
displacement
What is the name of the product formed in the reaction between NaI and H2SO4 and what are the observations?
HI
steamy fumes
What is the equation for the reaction between NaI and H2SO4?
NaI + H2SO4 —> NaHSO4 + HI
What type of reaction is the reaction between I-, H+ and H2SO4?
redox
What are the products made in the reaction between I-, H+ and H2SO4 and what are the observations?
I2
purple fumes
What is the equation between I- , H+ and H2SO4?
2I- + H2SO4 + 2H- —> I2 + SO2 + 2H2O
What type of reaction is the relaxation between I- and H2SO4?
redox
What type of reaction is the reaction between 6I-, H2SO4 and 6H-?
redox
