CHAPTER 1751 WORKSHEET

17.1; THE COMMON-ION EFFECT

Common-Ion Effect: Whenever a weak electrolyte and a strong electrolyte contain a common ion. the

weak electrolyte ionizes less than it would if it were alone in solution.

What is the common ion in the following

1'3D+1) Hydrochloric acid and Hydrofluoric acid __ .:...-....H:::-..= _

2) Nitrous Add and Potassium Nitrite NO '2..-

Calculating tne pH wnen a common ion is involved

r>:\

'-

3) Calculate the pH of a solution made from equal amounts of 0.30 M hydrofluoric acid and 0.70 M )sodium fluoride. K. = 7.1 x 10" H F ~ H of + f - 7H~ -) 0 5~.:..Ol!.')( \0-4

"I- O. ~L) 0 0.10 nrt = P3'~®c... -)( -t '( 1- ~ r, --__~ 0.307',( -t x () .10 ~

'l.\~\a-'4:. (\-\t][o."1iY] I .i' ·.{'l.hdD-yXD.'3D)-=.O,lCU+""]Co.3Ql - ].04 x. \Lf~ =- [/.+ tJ

4) A buffer solution was prepared which had a concentration of 0.20 M in acetic acid and 0 10 Min sodium acetate. If the Ka for acetic acid is 1.74 x 10.5, calculate the ttleoretical hydrQgen ion _ ~ ,concentration and pH of the buffer solution. i:t\+:l-:,"34~:Hsx'iC S';L ~.3 (.Ol)1-\ ~ t1 -+- + Ct1~c:..ro- \,'\ l..\ x_ ra-S".:- ~..,. (0, \0) ... _ -~.~ ... 11-

.L 0, '20 0 0."1.0 (0.'2..0) tP.tt.-~~~-~c -'I.... -t'l{ -t~ (Ll'tx..\D-rxo. La)~ o.\O(r\-t")l. 'l). 7.0 ~ «: O.1.0~ c3.Y ~ x.IO-S - H-t

Calculating Ion concentrations when a common ion is involved

(5) Calculate the fluoride ion,concentration and pH of a solution that is 0.2SM in HF and 0.10M in HCI

Ka HF = 6.8 x10'"

~r: ~ H-t-t~ - ~.~x \D-Y ~ [D.:lOJ (\=-j1. 0,'1.$ o.vc -0 D. '2S":: - ¥-. ""t 'f... +" (~ <6 y._ \ 0-4 ) ( D. 'LS) -:.O~ () ~ -~ D."2..5 0·10 0 \. TC'~=--~"""1~\1'l.-.i-~,

6) Calculate the formate ion concentration of a solu'tion that is1r.b2~f$1n fOrmic-acid ( HCOOH; Ka = 1.8

x 10") and O.ISM in HN03.

t-\(CD~ ~ rt -t -+ t-\C'..,DO-I 0.0'25 O.\S- 0

',-

. we.~ ba...J")(_ - I....1J..n d LLk-...O ..oo...u-/ lA.J(.b..l' u.(.L_d ~ u.3LD ~ It

17.2 BUFFEREDSOlUTtONS ~ l.A.(..£U; £t.u._d I (..O(\jU-ljcJ(., b~ ~_). l', ' vvt-D.lL. b~1 (_.Oi\.-\LlA o.k CtCA-t1

Solutions which contain a weak conjugate acid-base pair, ca'(resfst drastic changes in pH upon the

addition of small amounts of strong acid or strong base

Buffer Capacity is the amount of acid or base the buffer can neutralize before the pH begins to change

to an appreciable degree.

pH range of any buffer is the pH range over which the buffer acts effectively. Range of pH = pKa +/- 1.

Which of the following conjugate acid - base pairs will or will not function as a buffer

1) C2HsCOOH AN.D C,H~OO' '/ e.S

3) HCID AND CIO- 'ie~5) HND3 AND NaND1 1\10

2) HCI AND cr NO

CALCULATING THE pH OF A BUFFER

USETHE HENDERSON-HASSELBACHEQUATION Pt\ ':. 'PKG.... + l03 ~J;-6) The Ka of acetic acid is 1.76 x 1O-~. The pH of a buffer prepared by combining 50.0 mL of 1.00 M

potassium acetate and 50.0 mL of 1.00 M acetic acid is _

l.OOI.DD

pH-~ Y,1S-\- \03~p-~~-~..1-S,:

/7) Calculate the pH of a solution prepared by dissolving 0.370 mol of formic acid (BCO)!) and 0.230

mol of sodium formate (NaC02H) in water sufficient to yield 1.00 L of solution. The Ka of formic acid is

1.77 x 10 ,1.

'P\-\- -:; 3,15 -t '05 0, ~,3g___ ..__..... D.r~~~3.sTtlCALCULATING CONCENTRATIONS OR MOLES OF A BUFFER SOLUTION

/s) How many moles of sodium hypobromite, NaSrO, should be added to 1.00 L of 0.200 M hypobromous

acid, HSrO (K" = 2.5 x 10 \ to form a buffer solution of pH 8.80? Assume that no volume change occurs

when the NaSrO is added. f\. D., '20 _ ~C,~O-:..<g.LDO-t\DQ - 'j._ ID - o."2.00~~-:';'''7'.llj}----''\·:l; -.J D. 'LDO / '\' ,....- v.Jl- MDD. '2.0 ~ \O~ TI~OO (._l' '5~X_O. '2..0).;-::. )'(

9) You need to make a buffer with a pH of 3.50 from citric acid and sodium dihydrogen citrate. If you

ignore all higher ionizations of the dihydrogen citrate ion, what concentration of sodium dihvdrogen

citrate needs to be added to 0.40 M acid (Ko = 7.4 x 10 4)?/

( 2,34 )(0 .L\O)::- .;...'''0/ -----o--? '3--~-rV\- ~1/'1.... _. ..':1

..----------------------------.---

CALCUlATING pH CHANGES IN BUFFERS

~O) What is the final pH if 0.020 mol uo is added to 0.500 l of a 0.28 M NH) and 0.22 M NH.CI buffer

solution (K" (NH3) = 1.8 x 10'~)? . :_S,_::<"::,__'Bc.~ O.i~ D,~:'_~

A.cl-Md. 1-D,O'2. - 0,0'2.o. :1('2..

11) A buffer contains 0.30 M acetic acid and 0.20 M sodium acetate. What is the pH of the buffer after

iI!U9Q~ Q)QOtQ)dA a:itiAr 0.030 mol/l of a strong base are added (Ko = 1.8 )( 10'~)?A 'd~c...fDf"C.. D.~b 0.'2.0 'PH-~Y.'lY+\o'3 D,'2~

~. -D.D3 +D,03 Ol'2..1f\~-\(f 0, 'l.1 0. '2,3 ~H -::;-~'-t_~~~17.3 ACID-BASE TITRATIONS

Titration: The process of reacting a solution of unknown concentration with one of known concentration

("\", .-'

Equivalence Point: The point in a titration at which the added solute reacts completelv with the solute

present in the solution.

TItration Curve: A graph of pH as a function of added titrant

Draw the titration curve for the following:

:;·····-ni

II ---- I~ ~ ~ . ~ ~ ~ ~ ~

.,,'" ,,- ....~

'" ,.•

Strong Acid- Strong Base

Equivalence Point: pH 1.00

-. - - ----_.-----

,'i. -.

".~ ..

"'...'- .... ,

Strong Base to a Weak Acid Strong Acid to a Weak Base

pH= <. 1.DOk~ Y>-'-\

-------------------------------- '-- --'-- ----

~ Calculating Equivalence Point ~/\:1 V1.:: tv') '2. V2-

J12) A 25.0 mL sample of an acetic acid solution is titrated with a 0.175 M NaOH solution. Theequivalence point is reached when 37.5 ml of the base is added. The concentration of acetic acid in the

sample was M. ( O. \\ S )~'5 '151..) -e, (0. 0'25"') lM f2,)

'-(0~ '[(0"3 tJ\(

13) A 50.0 mL sample of an aqueous H}SO~ solution is titrated with a 0.375 M NaOH solution. The

equivalence point is reached with 62 5 mL of the base. The concentration of H2S04 is M."'2.S0,-, + 2_~QOH -;:> Na'2~O,-\ -t-~\-\'2.D)

... \ I l j_'CV'\D \ H"2,SU4 -(:O,.?/1$ M)(D.O~'lSL -=. D. O'2.3Y~\\~aDn ~o I -

O.Dl"MO\ = D. 'Z.3L.t"vtlCalculating the pH at the Equivalence Point 0 l OS0 L..

~~ ~'() 14) Calculate the pH at the equivalence point when (A) 40.0ml of 0.025M benzoic acid (Ka= 6.3 x 10.5) is

~~,?~'(1)-0/ titrat~~,with O.OSOMNaOH; 1:1 ~ I:Y'()\~S ~ 1..,0~ 'D -$('f\~\.w.) 0.0'2. L'O¥I\)? Q.,~ "01£ '0- 3 O. OS D l"\,...-_- __r: '() i"b+a..\ VO\LAmc:...~ O.O\PL ~"'J= "t.51)f'O"'IO)-(-O-tO-\~1)

:: 0,D-i ~'1 M -jH::' ,[, 'L:-1' ~S15) 4D.Oml of O.l00M NH3 is titrated with O.l00M HCI. \<"b N3 :. \ ._i_x_' _O -_

L.{ ,0)(.10 '3f'()O~ 0.0'-\ L '"\ - 15 5toKID I~(0 Dr)0.'1..00 - [\1+..)-- -y: . ·

D't._.,Y ,0)( \0- 3 _ _ C l+ ofJ -=- 6 l' 'I:'1 '/..\to. 0<6 L - (D1.1>5 :-pw ~ - 5,u v

Calculating pH for a Strong Acid -Strong Base Titration

--------------------- --_._ .. - ---- - -------_-_----_---

Calculating pH for a Weak Acid- Strong Base Titration

17) A 3S.0ml sample of 0.150M acetic acid is titrated with 0.159M NaOH solutio~: Calculate the pH att,e.t

the following volumes of ~.a.s.eshas been added: A) Oml B) r7.5ml 4 F e) 35.0ml Iii) b'l.sf"

2,1.5><.10-3

DI6~S'----:O. D'2.I.!J5"._?.9!!~ __\ ~S~ .tyt ...~..dt't ... ~·

l'.4S0LUBIUTYEQUIUBRIA -/"'5.510 ~ \O'D )(D.Ol5" )CDl4-J ~ (g. 4 (P'i \O-lD fg\f-:'6.Krl

Solubility-Product Constant: (Ksp) An eqUinEffium constant relateOlo the eQUllbrium b€twe a solid

salt and its ions in solution. It provides a quantitative measure of the solubility of a slightly soluble salt.

~--5.flS'I. \()-30, '0 -u.) :

[O\-\-J = 0.015

The solubility product of a compound equals the product of the concentration of the ions involved in the

equilibrium, each raised to the power of its coefficients in the equilibrium equation.

The magnitude of Ksp is a measure of how much of the solid dissolves to form a saturated solution.

The larger the Ksp, the greater is the molar solubility

Calculating Ksp from Solubility

JS) If the molar solubility of CaF2at 35.0·C is 1.24 x 10.3 mol/l, what is Ksp at this temperature?C.o,F1. ___;) c..0. '2- + -+ '2. l= -

-er: \'. '2 ~ X ID- 3 '2 ( \ . '2.4 x ID- ~ )"2.

!'\'\S'?~"'~G~'1( \ D- 9 ~

19) The molar solubility of PbBr} at 25.0·C is 1.0 x 102 mol/l . Calculate Ksp.

'TVBr-2 --- '> \.D~~;;-+ -~~~~Y.IO·'Z)~

d{5p~ ~~Lb-x.\D~~/20) A 1.00-l solution saturated at 25.0·( with calcium oxalate ( CaC20.) contains 0.0061g of calcium

, .,-..... oxalate. Calculate the solubility-product constant for this salt at~C. f\ 2...... o 1"\•• 2.-""_'/ ~ c"'2Oy <:::" La + '-2.\oA.{ _\-

ea.e_l~:: \'2.~.i ~"L'l~)('O-S" '-{.11oY\O

rKsp: 2. '2.1 )l '0- ~..

, Calculating Solubility from Ksp

21) The Ksp for laF1 is 2.0 x 10 19 • What is.the solubility of laF~ in water in moles per liter?

Let r-3 ~ La. 3+ + 3 \= -)( 3X3

2- .Ox 16'1'1 -:: Q1J( 'i

V '2.0)( 1O-l4 !:x.-~-q~i~)(_ ) 0 -c:~2) The concentration of iodide ions in a sattft?at'ld solution of I~ad {,i) iodide is····· M. The

solubility product constant of PbI, is 1.4 x 10 M.

Pb1 '2..- -:;;;:. \lb'l.:T -+}(_

17.5 FACTORS THAT AFFECT SOLUBILITY

Common-Ion Effect: The solubility of a slightly soluble salt is decreased by the presence of a second

solute that furnishes a common ion.

Solubility and pH: In general, if a compound contains a basic anion( the anion of a weak acid), its

solubility will increase as the solution becomes more acidic.

The solubility of slightly soluble salts containing basic anions increases as [H+)

increases{ as pH is lowered). \ thl'- "I-f -tn~rc u..o 0. J'\.u..mbe.r ~1'\o.e(" C

Calculating the Effect of a Common Ion on Solubility spc.C.i e,~ (Y1\ ':1 <..A~ t-h'- a::£:~. CJ)..,

a..:~\L\-€ "- pot'D rtf", @'nDT n-\ vJl-hf> V23) Calculate the solubility of AgBr in A} 3.0 x 10.1 MAgNO] solution Ksp for AgBr 5.0 x 1013

A9 B~ > ~+- -t' "B ( - -::cB.Dx\D-~ X. -'3 - -- .-.__.-_. -'-,~~': $,..0 ~\D, '2. -:.~L to'1 x. lD~"tv\~

3,O){ \D

24) 0.10M NaBr solution.

_----- .- - -' ~Y'2. ~1K -;.$S.O)\. \0 .

--_-----_ .._ .._-

r">; calculatine the effect of pH on Solubllty

25) Calculate the solubility of Mn(OHh in moles per liter when buffered at pH 9.S

Ksp for manganese (II) hydroxide: 1.6 x io"Mn (0 f·n'2.. -=:: ~ }It(\ '2-+ + '2...D~ - 2-

)( (3, \(ox \c> -$")(.Lx 10-'3 ::(><)({,OxIO-'1)

~-- - -- ..---- ._. _.-.-;'-4-L~.X.=. j_, ~ X.\ D j'

26) Calculate the molar solubility of Fe(OHh when buffered at pH 8.0

Ksp for iron(lI) hvdroxide:7.9 x 10.16

Ft{o~)'2 ~ F~ '2.+ + 'lOt{ ~~)'L"A. (l.Ox \D

1,~~\D-1L, :: )( ( \. Dx \D-\'2.)'i- -= '1l~ ~ 10-'-t

Concept Questions

27) The molar solubility of is not affected by the pH of the solution.

28) In which of the following aqueous solutions would you expect AgCI to have the lowest solubility?Highest? 1h1..._more. o+-\-he. CJ)rY\rn~ ~on - -\-Yu LQ:)\u...b~~t o:s> i~~~. .

®ure water B) 0.020 M BaCI2 C) O.OlS NaCI D) 0.020 AgNO~ E)0.020 KCI

17.6 Precipitation and Separation of Ions

If Q > Ksp, precipitation occurs until Q = Ksp

If Q = Ksp, equilibrium exists (saturated solution)

If Q < Ksp, solid dissolves until Q =- Ksp

------_._._--- _ ...-