6 khp acid-base

8/13/2019 6 KHP Acid-Base

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Volumetric Determination of KHP(Acid-Base Titration)

(Experiment 6)

INTRODUTION

The object of this analysis is to determine the amount (mass percentage) of "KHP" in a solidsample by direct acidbase titration !ith a standard solution of a#H$ KHP is actually

"potassium hydrogen phthalate" !hich is the mono potassium salt of phthalic acid% a diprotic

organic acid$ &s illustrated belo!% KHP is amphoteric it reacts !ith acid to reform the

diprotic acid H'P or !ith base (e$g$% a#H) to produce the salt of its dianion (e$g$% KaP)$

#K

#H

#

#

#H

#H

#

#

#K

#a

#

#

*H6#+,- . /66$/0phthalic acid

(a diprotic acid)"H'P"

*H1K#+,- . '2+$''

potassium hydrogenphthalateor potassium biphthalate

"KHP"

K#H

H H

a#H

*H+Ka#+,- . ''6$'2

potassium sodium phthalate

(a salt of dianion P')"KaP"

Pure KHP meets all of the criteria of a primary standard grade reagent$ &s such% it !ill be

used to standardi3e a solution of a#H 4 2$/ -) that% in turn% !ill ser5e as the titrant in the

determination of the KHP unno!n$

Teamwork. &lthough each student !ill prepare their o!n standard a#H solution and

analy3e their o!n unno!n (and be graded indi5idually as usual)% this experiment alsoin5ol5es !oring in assigned groups of four to accomplish some common goals$ ,or

example% !ithin the group% each person !ill chec the standardi3ation of their teammate7s

a#H solutions and !ill also analy3e their teammate7s unno!n KHP samples$ This !illallo! us to pool the data and do a meaningful statistical analysis of the results$ There is a lot

of !or to be done here including many extra !eighings% solution preps% and titrations% etc$

Thus% it is critical that teams coordinate their efforts and plan their work in advance ! 8e

!ill spend two weekson this experiment roughly one for preparation and standardi3ationof solutions and one for the unno!n KHP determination$

UNKNO"N

The unno!n pro5ided !ill be a !hite po!dery solid containing some amount of KHP

(typically% 0161 9 by mass) and inert impurities$ Each member of a team !ill ha5e a

different unno!n sample that they !ill analy3e themsel5es (+ trials) and that !ill also beanaly3ed by each other team member (/ trial each)$ Thus% there !ill be a total of : results

generated for each unno!n$


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R#A$#NT% and %TANDARD %O&UTION%

Primary standard grade KHP. ;ry 4 * g of KHP at //2 for one hour and store in a

desiccator$ oil another liter of ;= !ater for about 1 minutes to remo5e

#'and cool$ Pour the !ater into a polyethylene bottle% !hich should be tightly capped

!hene5er possible to minimi3e absorption of #' from the air$ &dd 4 1$0 m? of 129

a#H to a /? 5olumetric flas and fill to the mar !ith #'free !ater$ The exact

5olumes are not critical here since the solution !ill be standardi3ed$ -ae sure that the base

solution is thoroughly mixed and then allo! it to cool to room temperature before performing

the standardi3ation$

&tandardi'ation of !a"H solutions. =n the follo!ing procedures% your individual NaOHsolution will be standardized in ten separate titrations- 4 done by you and 2 done by each of

your 3 teammates. &ll /2 results must be recorded in your noteboo and !ill be re@uired for

the lab report$

(a) *our own !a"H solution. 8eigh (to the nearest 2$/ mg) four 2$1/ g portions of dry

KHP and dissol5e each in 4 '1 m? of preboiled !ater in either a '12 m? beaer orconical flas$ Cinse your buret !ith ' or 0 small portions (4 01 m?) of your a#H


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solution$ The buret should ha5e a loosely fitted cap to minimi3e entry of #'$ &dd +1

drops of phenolphthalein indicator to each KHP solution$ Titrate each !ith your a#Hsolution to the phenolphthalein endpoint !hich is the first appearance of pin color that

persists for /1 seconds$ (Each sample should re@uire 4 '202 m? of 2$/ - a#H in the

titration$) The indicator color !ill slo!ly fade as #'from the air dissol5es in the

solution$ alculate the a#H molarity (to + sig figs) for each trial% the a5erage% and the

standard de5iation$ The three closest 5alues should agree to !ithin D 2$'9$ =f necessary%titrate another KHP sample$

($) Teammate+s !a"H solutions. #btain about :1 m? of standard a#H solution from

each of your teammates$ (They should #T tell you the concentration of their solution)

-ae sure that you obtain each of these solutions in a clean and ,-*flas or bottle inorder to not alter the a#H concentration$ ?abel each solution !ith the o!ner7s name

and $e very careful to keep track of who+s solution you are working with at all times

y means of the follo!ing procedures% your individual KHP unknown will beanalyzed in seven separate titrations - 4 done by you and by each of your 3

teammates. &ll : results must be recorded in your noteboo and !ill be re@uired for

the lab report$

/$ ;ry your KHP unno!n sample for at least an hour at //2 G$ ool in desiccator$

'$ 8eigh (to the nearest 2$/ mg) four 4 2$12$6 g samples of your KHP unno!n$ ;issol5e

each in 4 '1 m? of preboiled ;= !ater and add +1 drops of phenolphthalein indicator to

each solution$ Titrate each one !ith your standard a#H solution to the pin endpoint as

described abo5e$

0$ alculate the moles of KHP in each unno!n sample by noting that one mole of a#H

neutrali3es one mole of KHP$ alculate the mass percentage of KHP in your unno!n

for each trial and the a5erage$ The three best 5alues should agree !ithin D 2$'9$ =f

necessary% titrate another sample$


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+$ #btain a portion of KHP unno!n from each of your teammates$ 8eigh (to the nearest

2$/ mg) a 4 2$12$6 g sample of each unno!n% taing special care not to mix them up$

(oth reports !ill be submitted electronically$

Part One =ndi5idual data and KHP unno!n results$

This includes the data and results that you obtained yourself for your o!n a#H

standardi3ation and KHP unno!n analysis$ & standard report form !ill be pro5ided$

Part To ombined data and results$

>y combining the team data% each person !ill prepare a report% including an Excel

spreadsheet% that summari3es and analy3es the a#H standardi3ation data and KHP

results$ &dditional details and a blan spreadsheet template !ill be pro5ided$

NOTE: This entire experiment requires very careful attention to

detail and excellent organization, both individually and as a team.

or! closely "ith your teammates to insure that no solutions,

un!no"ns, etc. get mixed up. #$$ data that you obtain yourself %%

regardless of "hether it pertains to your o"n solutions and

un!no"n or your teammates %% must be accurately recorded in

your lab noteboo!. &ata provided by a teammate must also be

recorded along "ith a notation as to "ho provided it. e "ill

definitely be chec!ing noteboo!s on this one'

6 khp acid-base

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