Chaoter 21

Question 1

What is a buffer soltuon exact definition

2 marks

Answer 1

A buffer soltuon sis a soltuon that MINIMISES THE CHANGE IN Ph when only SMALL amounts of acid or base are added
Or diluted a bit

Minuses , small

Question 2

What is a buffer made out of

Answer 2

A weak acid and it’s CONJUGATE BASE

These exist in an EQUilinrium, designed that if acid is added shifts if alkali added shifts

Question 3

What happens when a component of the buffer is used up

Answer 3

If a component is used up, then the buffer soltuon will stop working

Question 4

Oh an in general can yiu say the ph changes when a small amount of acid and alkali added?

Answer 4

YES THE PH VHANGES OFC, BUT JUST THE CHANGE IS MINISIED THATS IN THE DEFINITON

Question 5

How is first way of making a base

Answer 5

Using an acid and it’s conjugate base to make the components

1) ethanoic acid weak acid so barely dissociates, thus ethnaoic acid is thr source of thr wrka acid
2) if you use a salt of the acid, and then dissocsted that into water, that will produce a lot of Ethanoate ions, which is the cinjugwte base, as the salt dissocsted into ions comoletley

As a result, the salt is the source for the consjugste base, once combine their two compientnd you can get an buffer

Question 6

2nd way of producing a buffer with ethnaoic acid

If there is a question with this must use the BUFFER KA EQUATIONS NOT KA

Answer 6

BY WAY OF PARTIAL NEUTRIKISARIOM OF WEAK ACID

Int think mix excess weak acid with AN ALKLAI like NaOH

Acid being in excess means ALL THE ALKLAI IS READRED, which produces source of conjugate base

And some of the ethanoic acid is remaining which is source of weak acid

Question 7

What is basiclaly do equilibrium produced for a buffer

Answer 7

Ed at,y the same as a weak acid

Ha = Hc cA-

Question 8

What happens when an acid is added to the buffer

And when alklai?

Answer 8

• increases H+ conc
• H+ will react with A-
• EQUILBKRUM will shift to the left by le chatlelkeir
  -producing more HA
  , H + ions attempted it be restored, Oh is minised
  2)

When alkali added, this will REACT with H+ conc, reducing H+ conc
- the HA thus dissocgsed to produce more H+
- EQUILBKRUM shifts to the right

H+ ions restored, pH is minised

Question 9

Again exact structure for dice ring EQUILBKRUM with buffers and even indicative

Answer 9

1) alkali added, this reavts with H+ conc, reducing the conc
2) the Ha thus dissocsted, producing more H+ conc
3) EQUILBKRUM shifts ti right

H+ conc increased, pH change is minised

Or increase acid increases h+ conc
Reavts with A- to form more HA
Eaukibkrum shifts ti the left,
Reduced H+ conc and so oH change is mimisnied

Question 10

What is the BEST EFFECTIIVE BUFFER concentrations

What does PKa=

Answer 10

This is achieved when HA conc = A- conc

At this point they cancel in the Ka expression such that Ka = H+
Thus PKa = pH at this point

Question 11

What does operating pH of a buffer mean and what is the range typically

Answer 11

This is the range in which the buffer MUST BE AT TO WORK

Typically it’s +-1 pH from the standard oH

The standard pH is it’s OPTIMAL pH

This is when HA and A- are equal etc and PKa = ph

Question 12

HOW TO DO BUFFER QUESTIOSN WNAT EQUATION AND WHY

Answer 12

although it still is weak acid, this time the A- HAS A WHOLE COMPONENT WHICH WE NORMALLY IGNIRE

THUS NEED TO USE FULL KA EQUATION

Question 13

How to do buffer question where they give you conc and volume of each component, what special thing have to do

Answer 13

Need to find NEW CKNCENTRATIONS OF ESCH COMOONENT

Do thst by doing n = cv ti find moles of each

Then divide the n by TOTAL VOLUME To find nee concs as it’s a MIXTURE

Then use this in the equations

Question 14

And how ti do PARTIAL NEUTRIKSIAIRON AUESTION

Answer 14

easy, find moles of each first

Now see limiting reagent

Now write down the mole of conjugate base that will be formed due to limiting

Now all the lining moles will BE REACTED, so they go to 0, from the excess sreganer, subtract moles of limiting reagent

These are you final mole values, divide each by TOTAL VOLUME to get concs, out them into Ka equation

Remmeber they Ishtar just give an EQUATUIN like this without mentioning it’s a buffer

Question 15

Why must pH be controlled in Hama body

Answer 15

This is because we run using enzymes which all follow a narrow lH range

If you exceed or go under this range, then they denature and you can die

Question 16

What oH should blood plasma normally be at and what range

Answer 16

Healthy blood = 7.4

Range is 7,34 to 7.45

Question 17

What happens if goes below 7.35 and above 7.45, why is it deep even tho the change isn’t

Answer 17

It’s deep because this is logarithmic scale, so a small change actually represents a huge change of h+ cinc

Anyways go low acidosis high alkalosis smith are dangerous and potential death

Question 18

Okay so what’s the BUFFER IN BLOOD CALLED AND WHAT COMOENTDNT

How does sdiwiton go alkali acid , ph still minisied using EQUILBKRUM lit ideadnfiek before

Answer 18

Carbonic acid hydrogen cwbdiante ion buffer
Weak acid is carbonic acid and conjugate base it the hydrogen csbrinste

Icncrease acid, h+ increase, reavts with conjugate base, ewuaikoborum shifts to left, h+ decrease oh minised

Additoj Oh# ions alkali, reavts with h+ , reduced the h+ conc, so HA dissocsted moved to right and then the h+ increased and oH minised

Question 19

How ti find ratios ( to that hard)

Answer 19

Jsutnrearmaged rhe eauation ti give the denim storm and workmout unknowns

IF ONE AT BOTOTM, LEABE IT THERE

Question 20

How to use a Ph meter

How to do continous monitoring if pH, what equipment to get data easily

Answer 20

Ph probe
Put acid in concixla flask measure

Add one drop at a time and measure pH

You can resend with water esch tube and do it again

Use an AUTOMATIC DATA LOGGER to log the pH , connected it to the pH probe

Foe even more easy, use MAGENTIC stirrer

Question 21

What is the EQUIVALNCE POINT OF A GRAPH and what does this value mean

Answer 21

This value is directly the vertical value

It’s when the volume of one acid reacts exactly with the volume of another base

You use this value when doing stoichemtry calculations , as it’s the exact

Often we confused this with end point, in reality the end point is very close to the equivalence point pretty kuch

Question 22

What is an ACID BAS INDUCATOR max out of

What is end point thus

Answer 22

Badicsllt made out of a buffer

Weak acid and conjugate base

The weak acid will have one colour, conjugate base another

The end point is when the concs of the weak acid = the cicn if the cinjugwte base

At this point the colour observed will be half between the extremes!

Question 23

How does the colour change stuff works with equikbira

Answer 23

Initally, if you have a base or acid present and put idncistor in, it will give a colour based on what.

If it’s acidic, then conc shift to left, but say the EQUILBKRUM lies at the elft ti begin with disoakhign this colour

If alklai EQUILBKRUM starts at the right

Anyways on the additoj of acid , again h+ increase reavts with a- shifts ti left , colour starts ti changing

Adding alklai reavts with h+ reduces it caused it drive shif to to right colour show dot eirght side more

WHEN THE SIFT HAPPENS, THE COLOUR WILL PASS THROIGH THE END POINT THUS IT WILK BRCOME MIXTURE FIRST

anyways that’s why when acid and alkali equivalence point meet normally it’s around end point but off by a bit. Here the equal amount fi acid and base cause equal amounts of eauoabira to be felt too, so we attribute them

In reality there off by maybe 0,5cm2, so we often go for concord and results for this reason

Question 24

Again what happens at the end point of an I’d castor in terms of itd oh and PKa

Answer 24

Again end point c angel thr ha and a- form ma equation, and thus thr pH = PKa

Question 25

So why do we choose an idncistor that PH RANGE FALLS IN THE VERTICAL SECTION OF THE GROAHN

Answer 25

This is bevause thr berticla section is when the stoichemtry is equal, so the pH change must fall in this berticla section ti actually mean something ti us

It’d not to say colours wont be seen bevause they will, jt it won’t mean a hot jt.

So yeah must choose inductor that falls in the range

Question 26

All 4 tritwtion curve shapes

Answer 26

String acid string alkali

Starts low goes high to Alamo curved there

String acid weak alkali
Starts low end like 9 10

Weak acid and string alkali
starts highs like 34, and CURVES A BIT as it TEMPROWTILY ACTD SS A BUFFER , as here there is a weak acid and cinjugwte base , si oh is minised

Then finished high

Finally WEAK ALAKLAI WEAK ACID

starts high, finished low,
Vertical section is VERY SMALL AND NO ISNCISTOR FITS IT

Question 27

Why does no idncistor fit thr WEAK AKLAI WEAK ACID

Answer 27

Bevause ther vertical section does not 8ntersevt any range of any idncistor so never any idncistor is suitbsle

Question 28

AND ALSO SEEN IN WAK ACID WEAK ALAKLI THE START

Answer 28

AGAIN DURVED UP A BITA

AGAIN ACTS AS A BUFFER
DONT LACK

Question 29

So for curve questions how will curve look like if
Conc changes
If dibasic instead of Monobasic

Answer 29

Always write EQUATUIN if scared
But generally if you half conc, then thr volume needed will half too, so equivalence point drops

And if it’s dibasic, you’ll probably need twice the volume , so don’t lack for they