FINAL FINAL FINAL DECK Flashcards
What does 3 bonded pairs around the central atom produce?
Trigonal planar
120 degrees
3 bonded pairs and one lone pair around central atom?
Trigonal pyramidal
Lone pair at the top, everything bellow same structure as tetrahedral
107 degree bond angle
2 bonded pairs and 2 lone pairs around central atom?
nonlinear shape (V shaped) 104.5 degrees
5 bonded pairs around central atom?
Trigonal bipryamidal
Around central atom there is a straight line going through, and perpindicular to this there is a triangle of atoms (use both wedges in this)
Producing 90 degree angles and 120 degree angles)
Formula for moles in gas?
Moles = volume / 24dm^3
However there are 2 exceptions in the rule that ionisation energy increases along a period between group 2 to 3 and group 5 to 6 explain why?
The outer electrons in group 3 elements is a p orbital, rather than an S orbital, which means it’s further away from the nucleus, and has additional shielding from s orbital, theses factors overide the increased nuclear charge
In the group 5 elements, the electron is being removed from a singly-occupied orbital, in group 6 being removed from orbital containing 2 electrons. The repulsion means between 2 electrons in a orbital makes it easy to remove from shared orbitals
What’s a chlorate ion?
ClO-
How do you make bleach?
React chlorine gas with cold dilute aqueous sodium hydroxide in a disproportionation reaction
How is chlorine used to kill bacteria in water?
Cl2 + H2O =(reversible reaction) HCl + HClO
HClO + H2O = (reversible reaction) ClO- + H3O+
Chlorate ions kill bacteria
What order should you do tests to avoid false negatives?
Test for carbonates - no CO2, so no barium carbonate precipitate can form
Test for sulphates - no sulphate to react with silver nitrate to form silver sulphate
Test for halides
What happens to KBr (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes yellow from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes orange from Br2
Bromine water added: no reaction
Iodine solution added: no reaction
What happens to KI (colourless) when in aqueous or organic solution and Chlorine water, Bromine water, and Iodine solution are added?
In aqueous solution:
Chlorine water added: Goes orange/brown as I2 displaced
Bromine water added: Goes orange/brown as I2 displaced
Iodine solution added: no reaction
In organic solution:
Chlorine water added: Goes purple as I2 displaced
Bromine water added: Goes purple as I2 displaced
Iodine solution added: no reaction
What is enthalpy change in terms of bond forming and breaking?
The overall affect of both of them occuring
Average bond enthalpy of breaking bonds - average bond enthalpy of forming bonds
How can enthalpy changes be worked out using the enthalpy change of combustion?
Same method before, however the direction of arrows have changed and so has what’s on the bottom
On the bottom have water and CO2 and both the lines will be going downwards with an amount of oxygen next to them to balance the equation
Work out total distance taking into account second line is going to wrong way
What is the reaction rate?
The change in the amount of reactants or products per unit time
Units are mol dm^-3 s^-1
Explain the iodine clock reaction?
H2O2 (aq) + 2I- (aq) + 2H+ (aq) = 2H2O (l) + I2(g)
Small amount of Sodium Thiosulfate solution and starch are added to an excess of H2O2 (Hydrogen peroxide), and Iodide ions in acid solution (H+)
Starch is an indicator and turns blue/black in presence of iodine
Sodium thiosulfate instantly reacts with any Iodine that forms making it go back to iodide ions
So once the set amount of Sodium thiosulfate is used up solution will go blue/black, so can vary iodide or H2O2 concs to give you different times
All the graphs for conc-time and rate conc?
Conc-time
0- diagonal straight line from y axis
1st Curved line with diagonal gradient from y axis, reaching an asymptote near x axis
Rate conc -
0-Horizontal line from Y axis
1st - Positive gradient for y=x, through the origin
2nd - Positive curve going through the origin, Rate is proportional to concentration^2
Half life for 1st order reactant and second order?
1st - constant
2nd not constant
How do you work out the rate constant of a first order reaction if you know it’s half life?
k = ln2 / half life
Units = s^-1
How do you find the total pressure of a gas mixture?
It’s the sum of all the partial presures
How do you find the partial pressure of a gas?
First find mole fraction of the gas in the mixture using Number of moles of gas / total number of all moles of gas in mixture
The multiply the mole fraction of gas by the total pressure of the mixture
So if they have the same amount of moles in equation will have the same partial pressure
What’s the equation for Kp?
if aA(g) + bB(g) ⇋ cC(g) + dD(g)
Then Kp = p(C^c) x p(D^d) / p(A^a) x p(B^b)
Use the partial pressures instead of concentrations
Units are kPa
NOT SQUARE BRACKETS
Formula to find pKa?
pKa = -log10 Ka
remember that it’s weird one and you are finding it out the same way for pH
Formula to find Ka when you know pKa?
Ka = 10^-pKa
Describe features f Methyl orange indicator?
Colour at low pH is red
Colour at high pH is yellow
Approx pH of colour change is between 3 and 4.5
So useful for strong acid/ strong base and strong acid/ weak base
Describe phenolphthallein?
Colour at low pH is colourless
Colour at high pH is pink
Approx pH of colour change is 8 to 10
So useful for strong acid/ strong base and weak acid/ strong base
How do you calculate entropy?
Entropy = Entropy of products - Entropy of reactants
So entropy has to increase during a reaction for it to be feesible
What are the 2 half equations for the redox titration of Acidified Potassium manganate oxidising Fe(2+) to Fe(3+) and the colour change and what does this titration tell us?
MnO4(-) + 8H(+) + 5e- = Mn(2+) + 4H2O
5Fe(2+) = 5Fe(3+) + 5 e-
So equals MnO4(-) + 8H(+) + 5Fe(2+) = Mn(2+) +4H2O + 5Fe(3+)
Once the reaction has finished will see a colour change from purple to colourless as MnO4(-) is pink and {Mn(H2O)6}(2+) is colourless
How much Oxidising agent we need to reduce the species
Can work out both half equations by: MnO4 - = Mn(2+) MnO4- = Mn(2+) + 4H2O MnO4- + 8H+ = Mn(2+) + 4 H2O MnO4- + 8H+ + 5e- = Mn(2+) +4H2O
Fe(2+) = Fe(3+) Fe(2+) = Fe(3+) + e- 5Fe(2+) = 5Fe(3+) + 5e-
What are the 2 half equations for Potassium dichromate solution K2Cr2O7 oxidising Zn to Zn(2+) and the colour change and what does this titration tell us?
Cr2O7(2-) + 14H+ + 6e- = 2Cr(3+) + 7H2O
3Zn = 3Zn(2+) +6e-
So equals Cr2O7(2-) + 14H+ + 3Zn = 2Cr(3+) + 7H2O + 3Zn(2+)
Colour change when reaction is finished will be orange to green as Cr2O7(2-) is orange and {Cr(H2O)6}(3+) looks green
How much Oxidising agent we need to reduce the species
Can work out by: Cr2O7(2-) = 2Cr(3+) Cr2O7(2-) = 2Cr(3+) + 7H2O Cr2O7(2-) +14H+ = 2Cr(3+) + 7H2O Cr2O7(2-) +14H+ +6e- = 2Cr(3+) + 7H2O
Zn = Zn(2+) Zn = Zn(2+) +2e- 3Zn = 3Zn(2+) + 6e-
All the steps and equations for a sodium thiosulfate titration to find the concentration of an oxidising agent?
Use a certain volume Potassium Iodate solution to oxidise an excess of KI
IO3(-) + 5I(-) + 6H+ = 3I2 + 3H2O
To work out:
IO3(-) 5I(-) = 3I2
IO3(-) 5I(-) = 3I2+3H2O
IO3(-) 5I(-) +6H(+) = 3I2+3H2O
Find out how many moles of iodine have been produced, by titrating the resulting solution with a known concentration of Sodium Thiosulfate (Na2S2O3), when the solution goes pale yellow showing it’s near to the end point, add starch solution, which will show that Iodine is still present by being blue/black, will know reaction is finished when blue/black dissapears
I2 + 2S2O3(2-) = 2I- + S4O6(2-)
Find the moles of Iodine from second equation, then input it into first equation to find moles of oxidising agent ( divide by 3) and then can find concentration
