Module 5 Memorisiation

Question 1

Why is Rate determining step features thing from rwte equation only

What speed is the rate determine step?

Answer 1

As rate derminign step controls the rate, only the substances that appear in the rwte equation which are substances that affect the rwte can be present

Substances that don’t appear in the rate equation have no affect on the rate at all

2) SLOW STEP because limiting

Question 2

Why can’t you determine the order of something typically

Answer 2

Because it’d in EXCESS, and thus varying the concentration and seeing effect on rwte is hard

Question 3

Why is the order of something virtually zero

Answer 3

Because it’s in excess, so changing conc barely will have an effect on reaction , so virtually 0 order

Question 4

Remember if heterogenous equilibrium , what to do for KC

Answer 4

Conc of solid and liquid is constsnt, so omit that from kc expresdiom as they automatically incorporated into the Kc

Question 5

How can you ensure something has reached equiloborum?

How to use titration to know the ewuaikoborum conc of acid

Answer 5

Leave it for some time, check the moles, leave it for longer check again and if constsnt then good

2) do a titration to find total moles of acid and SUBTRAVT it from the control , the caltyst will remain cinstsnt

Question 6

Remember if a catalyst is aqueous , water component not part of the catalyst, does that add tk equation

Answer 6

Yes don’t lack

Question 7

What things are in a kp expression state

Answer 7

Only gases, ignore everything else even if there is only one

Question 8

How to explain le chatelier change for temp? (If forward endo / exo)

Answer 8

1) look at whether kp will increase / decrease based in change
2) use that to answer “as kp increases with temp increase, this means this has to increase and that decrease , so shift is this way”

Question 9

How to explain CONC change le chatelier move using kc kp?

Answer 9

As these are constsnt, say now that reactant increase, this gives a value greater or less than kc. To go back to kc, the resvtnat must decrease and product increase, thus shift is to the right etf

Question 10

How to explain le chstfleir for pressure using kc kp EXACT wording + Whars different here

Answer 10

If you increase pressure or the system, You increase pressure of BOTH REACTANTS AND PRODUCTS.A

Show kc expression and state it is CONSTANT
1) increasing pressure increases conc terms more at top or bottom due to molar ratios
2) this makes kc smaller than should be whatever , change needs to happen
3) reactants products change to return to kc
4) this makes an OVERALL SHIFT TO THE RIGHT OR LEFT

Must say last concksuoj

Question 11

1) approximation for KA eauation , why can’t we straight away say H+ = A- even tho Ha dissociated equally?
2) what can we assume
3) when does this fail (2 reasons )

Answer 11

Because there will be some H+ conc due to the disscoation of water as the acid is AQEUOUS

• however if we assume the disscoation of this is NEGLIGIBLE , then we can assume H+ = A-

3) this assumption fails when the
- temp of water is high as high temp increases Kw which means higher Conc of H+
- when acid very dilute / very weak acid (as this means there will be a lot of water so that H+ conc is high from it)

Question 12

2) approximation 2 for Ka

How can we apprismste Ha at start to be Ha at equiliborum?

WHEN DOES APPROXIMATION BREAK DOWN AND WHY

Answer 12

HA at equilibrium = Ha start - H+ EQUILBKRUM
- however remember this is a weak acid, from like 1000 HA if 1 dissocsted, then it will be the same thing pretty much
- therefore disscoation of H+ small as it’d a weak acid means can assume negkible, thus Ha start = Ha equilibrium

2) breaks down when KA acc high, meaning it’s a string weak acid . Therefore can’t say dissociation of H+ from weak acid is negligible
- this value is normally -2 order

Question 13

Why in an acidic soltuoj is there still Oh- ions?

Answer 13

In any AQUEOS solution there is always Oh and H+ ions
If more H+ then OH- then acidic, if less then basic, if same then neutral

Therefore an acidic soltuion can still have Oh-ions

Question 14

What states are group 1 carbonates normally

Answer 14

Aqeuous, so make sure tk remember and put that sign

Question 15

Why is 2nd disscoation always harder than first for a dibasic thst dissocsted twice

Therefore how to explain why the pH of this is higher than when we assume it dissociates like a strong acid dibasic

Answer 15

1) as harder to remove protom from negative charge then neutral

Say that we think pH will be (work it out) when it’s actually thid, thid bevause of partial disscoation

Or say we think H+ is thid when it’d actually (work out), and that’s lower because partial

Question 16

Why is using pH better than H+conc to compare

Answer 16

H+ deals in NEGATIVE INDICES OVER A HIGH RANGE

So hard to compare

Question 17

Buffer solution DEFINITON 2 marks

Answer 17

A solution that MINIMISES the CHNAGE in pH when small amounts of acid or base are added (/ diluted)

Question 18

What’s in every buffer solution

Answer 18

A weak acid and it’s conjugate base

Question 19

2 ways of making buffers

Where does each part come from

Answer 19

1) weak acid and one of its SALTS
- weak acid partially disscoates so that forms weak acid component
- salt completely dissocsted into conjugate base , this is component of conjugate base

2) partial neutrilisation of the weak acid
- mix weak acid with a base like NaOH
- some weak acid stays, some becomes conjugate base, both components here

Question 20

When is buffer most effective

At this point how are PKa and pH related!

Answer 20

When weak acid conc = conjugate base conc

At this point Ka = H+ so PKa = pH

Question 21

What is the pH of blood that must be maintained range

Answer 21

7.35 to 7.45

Question 22

How to explain how each pH minimised in buffer solutions

Use body one with acid additon

Answer 22

1) as acid added, the cinc of H+ increases
2) the H+ ions will react with the hydrogen carbonate ions , and the EQUILBKRUM will shift to the left
3) this will produce more carbonic acid and reduced the H+ conc, such thst pH is maninted

(Say what happens at each step, with alklai say carbonic acid dissociates etc)

Question 23

EQUIVALNCE vs end point

Why do we use end point as marker for equivalnce point

Answer 23

Equivalence point is the point at which a certain amount of volume of one solution is COMPLETELY neutilised by a volume of another
- the point on the graph is on the VERTICAL SECTION

2) However end point refers to indicator, where the conc of weak acid = conc of conjugate base

3) Normally these are very close to each other and end point gives us a visual change to know when done , BUT not the same, we do concodrant titres to help their

Question 24

What isnpH and PKa at end point of a indicator (which is basically a buffer) ?

What is colour at this point

Answer 24

The same remember as conjugate acid = weak base

Colour is half way between extremes

Question 25

How will weak acid string base look like

Weak acid weak base

Answer 25

1) starts high, acts as BUFFER FOR A BIT, then vertical section ends high
2) starts high, acts as a buffer for a bit, very small vertical section nothing can indicate it, ends low

Question 26

Lattice enthlapy DEFINITON

Answer 26

the enthlapy change that accompanied the formation of 1 mole of ionic lattice from its consistent ions in GASEOUS form

Under standard condition with everyhting in standard state

This is Na + cl + NaCl that one

Question 27

Base case for lattic enthlapy questions

What are the 2 routes

Answer 27

Base case is elements in standard state
- route 1 have to atomise , then ionise then can do lattice enthlapy
- route 2 is just formation

Equate these

Question 28

What is the enthlapy change of soltuion definition

Answer 28

Is the enthlapy change that accompanies one mole of solute dissolving ti become constituent ions

Question 29

Is enthally change of solution exo or endothemrif (we know lattice is always exo)

Answer 29

This one it can be BOTH!

Question 30

How to find the enthalpy change of solution using lab

Answer 30

Mix the water or whatever solvent with the solute and measure mass of solute and water
- measure temp of water and temp after added , max or min temp achieve
1) now do q = MCAT, but this time Mass of the solute is given with water, so they BOTH HEAT UP
- however in AS, the thing was in excess and they didn’t tell us that mass so we can’t use it

DONT LACK HERE

Question 31

Enthlapy change of hydration exact DEFINITON

Answer 31

The enthally change that accompanies one mol of gaseous ion dissolving ti become one mol of AQEOUS ion

Question 32

Base case and target for dissolving ionic lattice

Answer 32

Base case is GASEOUS IONS ! Target is dissolved ions
ROUTE 1
- gaseous ions lattice enthakly ti ionic lattice
- ionic lattice enthalpy solution to aqueous ions

ROUTE 2
- gaseous ions indicually ine by one hydration enthalpy to aqueous ions

Equate and solve

Question 33

Why is hydration enthally always EXOTHERMIC

Answer 33

Bevause rhe gaseous atoms making bonds with water to become aqueous, and this RELEASES ENERGY OUT

Question 34

How does raidus and ionic charge affect lattice enthalpy and thus melting / boiling points

Answer 34

Radius
- decreasing radius increases attraction between ions
- stringer attraction means higher energy released, so more negative lattice enthlapy
- therefore higher boiling melting

Charge
Increase ionic charge (difference) increases attraction
-thus more negative lattice enthalpy
- thus more boiling melting

Question 35

How does radius and charge affect hydration enthalpy

Answer 35

Raidus
- decease means attraction between ions and WATER MOLECULES increase
- thus more energy released, and more negative hydration enthally

Charge
- increase charge increase attraction between ions and water molecules
- so energy release, more negative hydration enthalpy too

Question 36

Entropy DEFINITON

The greater rhe entropy …

Answer 36

Measure of dispersal if energy in a system.

The greater the entropy of a system, the more disordered it is

Question 37

GIBBS energy equation

What is cinditon for feasible ?

How to find min temp for feasibility

Answer 37

Free energy = change in enthalpy - temp (k) x entropy value

Make sure units all consistent , enthalpy normally in kJ

2) free enerby less than 0

3) lowest GIBBS energy had to be is 0, so set it to 0, rearrange for temp

Question 38

WHAT IS THE UNIT OF GIBBS

Answer 38

Must be kilojoules, so make everything that or else got wacky number

Question 39

Limitation of free eneby equations (why is everything else than 0 not actually happening)
2 things

Answer 39

Does not take into account kinetics
- such as rate of reaction and ACTIVATION ENERGY

Can have really high AE so even tho it can happen it barely does, or happens incredibly slow,h

Question 40

What is Haemoglobin and why so necessary

Answer 40

Each red blood cell has the Haemoglobin molecule which is 4 protein chains each containing haem groups.
# each haem group has a central Fe 2+ ion
- it is this ion that can form complexes with oxygen to carry oxygen around the body
- and also carbon dioxide ti carry to lungs to be exhaled

Thus we need Haemoglobin for transport of gases around body

Question 41

What happens when CO is breathed in and why

2) why is this fatal

Answer 41

• CO much stringer bonds to Haemoglobin , and thus when breathed in a LIGAND SUB happens with oxygen
  2) this bind so string that irreversible. Thus if Co is breathed in the amount of functioning Haemoglobin now just reduces

This leads to death