Choater 20 Flashcards
Brindled lowery acids and bases?
BL ACID is a species that donates a H+ ion
BL base is a species that can ACCEPT A h+ ion
So even in those nucleophikic RESCTION acids, even tho naught be electiphile NUCLEOPHILIC, if they accept or donate they could be acting as acid or base
SO WAYCH OTU
What’s a conjugate acid base pair?
A pair of species that from the inter conversion of a hydrogen ion can become each other, needs BL base and acid
Always pairs
Monobasic dibasic etc?
Refers to the number of Hydogen ions a species can donate in total
H2so4 is dibasic
How does something actually neutralise IN WATER
What’s this ion
Instead of H+ and OH-, the H+ goes to H2o to become H3+O, hydronium ion
Here we nwomally do Hcl + OH becomes water and Cl-
But when usign aqueous soltuon do Hcl + H2O becomes H39+ and cl-
Int his case rhe H3O is BL acid now
How ti write ionic equations, with the exception of a carbonate
Here write split into ions that are aqueous, and then cancel
However group 2 metal carbonates are normally solid but stil, in this case solitaire the, up
Acid reactions
Acid + metal = hydrogen and salt
Acid + alklai = salt + water
Acid +. Teal oxide = salt + water
Acid + metal hydroxide = salt and more water
Acid + metal carbonate = salt water co2
Group one metals normally aqeuous
Ph
Higher conc of H+ determines pH lower
Ph = - log (h+) conc
H+ 10-ph
How ti find Ph for string acids and assumption
What to remember !
Assumptions is as it’s a strong acid all the acid dissociates into h+ ions
To find the cinc of H+ do conc of acid x the fact it’s mono or dibasic
Remember how to do dilution questions, Abbas formula
Moles constant
Upon dilution, moles ar the same
So c1v1 = c2v2
WHY DO WE USE LOGARITIHMIC SCALE
I think because we are dealing with EGATIVE INDIDICES, it’s hard to make comparisons. E tween
Therefore we do PKa and Ph
Eva for weak acids
What does Ka and PKa mean in terms of stentgh of the acid
Weak acids form an EAUILOBRIA as they partially dissociate, therefore we can use an ewuaikoborum constsnt which is KA
Ka is small so we use PKa to compare
The higher the Ka, the STRINGER the weaker acid as more of it disscoates
Therefore the LOWER THE PKA adjust like with pH, the stinger the weaker acid too
What are string acids and weak acids in general
Strongest acids are the shanc
Weakest acids are the cabroylic acids
But still the stringent weakest acid, able to react with carbonate a weak alklai to produce bubbles, but something like phenol can’t
Why is the first disscoation for a weak acid always result in a lower PKa so stinger acid then second isisscistij?
First dissocsiton you’re removing h+ from neutral calm
Second it’s from h+ from an already negative intermediate which is harder, and thus happens less often
Why are there Ka approximations?
Because we can only uses these things once Moles at EQUILBKRUM are found, but because some are very similar to each other we can make approxmstims
What is the Ka equations and what 2 APPROXIMATIONS CAN WE MAKE AND WHY
Ka equatuins is the H+ and A- at equilibrium all / HA at equkibkrum
But we can write Ha at EQUILBKRUM as Ha at start - moles of H+ equkibkrum as this is equal to the change
1) okay so initially , assuming the concentration of H+ from the AQEUOUS WATER IS SMALL, we know that the dissocsiton fi HA will produce H+ and A- in EQUAL QUANTITIES.
= therefore top = H+ 2
2) and we rewrote HA at eqbm to be HA start - H+ at equilibrium
Well it is a weak acid, with a low Ka, the moles of H+ at EQUILBKRUM will be very little compared to moles of the Acid at the start which were j disscoates
So we can IGNORE the H+ at EQUILBKRUM and therefore HA start = HA at EQUILBKRUM
And final equation is KA is riougjly H+ 2 / HA at start for weak acis
When does approximation break down and why?
If the KA IS ACTUALLY BIG
- then the H+ at EQUILBKRUM is no longer negligible, and will have an effect
- if KA is big it mean conc of H+ at EQUILBKRUM is quite decent and so appeimxstiojnbreakdneownn, not justified for STRONGER WEAKER ACIDS
1) for approximation number one assuming the conc of H+ due ti water is very negligible
Now this is true at room temp, where Ph is 7, and conc of h+ due ti water by Kw is 1x 10-7
But when pH is less then 7, now the conc of H+ slowly increases, and this happens at HIGHER TEMPS
Or at DILUTE AFIDS WEAK ACIDS IT BREAK DOWNS
Again approximation 1 and 2 when break down
1 breaks down when very dilute (content of water big) or the pH of water is less than 7 due to temp, as then the contribution of H+ form water actually takes an effect. Doesn’t work for very dilute acids
2 breaks downs when the acid is string, as the KA will be higher and thus moles of H+ at EQUILBKRUM high too, which takes an effect in equation for moles of HA at EQUILBKRUM = HA start £ H+ at equkibkrum
Thus breaks down for high KA acids
Ionic product of water?
How ti find neutral point of water the pH based on info
This is a constant at different tempertaures and controls the Ph of WATEE
At room temp it’s 10-14
We know that at neutral the conc o H+ must be the same as OH-
So we can just say H+2, which = ionic product of water
Rearrange to find H+
You’ll see you get pH 7
But at different temps the pH if neutral water changes as ionic product changes too
How is ionic product of water useful for us in acids alklai etc
Every AQEUOUS SOLUTON THERE WILL BE A NUMBER OF OH - IONS AND H+
If acidic then H+ > Oh-, if ALKLI then less if neutral then equal
Therefore, if we know the temp is room temp, then we can use KW as a constant to find out how much OH- ions there is or H+ if we know one other value
Acidic solutions still contain oH- ions, if pH is 3 at temo 25, then we can figure out how much Pah - there’s we
Must multiply and thus add to give -13
Like string acid what is the appeoximation for strong based
A string base is something that comoeltley dissociates ti form Oh- ions in solution
Therefore how would we find oH if a string base
HWAT TI REMMEBER
oh if a string are, well we can find the Oh cinc first
This is = to conc if base at start x mono / di basic type base
Now we have Oh cinc, use i2 to find H+ conc
And then fidnpah
Why use ph and PKa instead of H+
H+ deals with numbers if negative indicies over a wider range, so using ph allows us to use numbers which are much more comparable
How ti find PERCENTAGE OF MOLECULES DISSOCSTED
Use conc Of H+ / CONC OF ORIGNAL TO GIVE INDICATION HOW MNAY MOLECULES DISSOCed
Why does 0,1 sukfruic acid that disscoates twice, fire tfukly snd then partially give a pH of 0,96
Well if it dislodged fully it would give ph of 0.7 usign dibasic rule
The fact that first disscoation is full but second is partial. Meaning not enough h+ ions will be released in order to reach a ph that low
And thr conc of h+ they say. Well is 0.1 which is not same as 0.2, and this is because if the little disscoation from second ssicostion
Finally go through H+ aprlidmsitins snd why breaks don
1) apoeidmstes h+ from water small enough so we can say h+ = A-
Thing is when very dilute, or oH less than 6 , the ph of water is quite high so appeoximation breakdown
2) appeimxsted the H+ of euaonorum negligee cimaored to Ndowcistrd conc of aha at start as it’s a weak acid, so can just say ha at daub = ha start
Problem with this if the Ka is big then the h + at eqm will Acc bue quire a lot, so the allridmsitoj breaks down and can’t use
So doesn’t work for stringer weaker acid
