Experiment 4 Common Ion Effect and Buffers C. Grefaldia1 1
College of Home Economics, University of the Philippines, Diliman, Quezon City 1101
Performed 15 June 2017 !u"mitted 1# June 2017
Answers to Questions Questions
$!ee ta"le 1.1%. !olution 1 in met&'l oran(e is !almon Pin) *&ereas !olution 2 is 'ello*.
Figure 1 !tructural formula of methyl"orange #1$ If 'ou loo) at +i(ure 1, one mi(&t t&in) t&at if 'ou add an acid $-%, it *ould automaticall' attac&ed itself to / in t&e formula, &o*eer, it doesnt, instead it attac&es itself to t&e nitro(ennitro(en dou"le "ond *&ic& (ies t&e met&'loran(e its red colour in acidic solution. !olution 1 contains onl' a *ea) acid, t&erefore it doesnt completel' form into t&e red form of met&'l oran(e, t&us t&e colour salmon pin). 31. !olution 2, &o*eer is 'ello*. &us, t&e indicator &as t&e 'ello* formula of met&'l oran(e. Figure %& E'uli(rium (et)een t)o forms of methyl"orange in*icator #1$ 6i(ure 2 s&o*s t&at t&e indicator is red in acidic solution and 'ello* in al)aline solution. !olution in P&enolp&talein is 8a(enta *&ereas solution 4 is li(&t pin). Figure +& E'uili(rium (et)een t)o forms of phenolphthalein in*icator #1$
other hand, CH 3COOH only partially ionizes. When it was divided into three portions, the same reaction as that of Sol Solti tion on !a and and Sol Solti tion on !" happ happen enss with with the the Sol Solti tion on #a and and #". #". Sinc Sincee ther theree is a comm common on ion ion CH3COO , the chan$e in the pH of the soltion will "e mini minima mall comp compar ared ed to Sol Solti tion onss !a and and !" sinc sincee CH3COO will will react react with with the added added stron$ stron$ acid, and CH3COOH will react with the added stron$ "ase. %he same principle is applied to soltions 3 and &. 'ased on the ta"les, the pH vales and the calclated theoretical pH vales are different from each other which cold possi"ly "e a reslt of hman error and the accracy of measrin$ e(ipment. However, the trend in pH of "oth measred and calclated are the same. )isa isall indi indica cato tors rs are are sa sall lly y the the leas leastt accrate in measrin$ pH, the "est measrement of pH yo can possi"le $et from visal indicators is the ran$e or only to determine whether the soltion has trned acidic, "asic or netral *3. lso, it relies so mch on hman d$ment which is why this is the least relia"le. pH meters are the ones that sally $ive a more precise measrement for pH. However, as evident in the ta"les, calclated and measred pH are still different from each other. %herefore, we cold find a more accrate way of measrin$ pH to $et a more relia"le data and avoid errors. Table 1. pH p H using Visual Indicators and pH meter Colour of !olution p!olutions readin( 8et 8et&'l oran oran( (e P&en P&enol olp& p&ttalei alein n
6i(ure s&o*s t&e e9uili"rium of p&enolp&t&alein indicator and s&o*s t&at it is colourless in acidic solution *&ereas it is "ri(&t pin) in "asic:al)aline solution. ;&en 'ou add - t&e e9uili"rium s&ifts to t&e left, a colourless solution, *&en 'ou add /- it s&ifts to t&e ri(&t, ma)in( t&e solution appear pin). &e solutions *ere split into portions, in portion a, drops of 1.0 8 -Cl *as added, in portion ", drops of 1.0 8
completely dissociates into Na + and CH 3COO-. On the
1
!almon pin)
2.==
2
'ello*
4.1
8a(enta
#.70
4
>i(&t pin)
=.#
Table 1.1 pH using Visual Indicators and pH p H meter, meter, HCl, NaOH added to solutions A and B, C is a control Estimated p- ran(e p!olutions readin( 8et& 8et&' 'l oran oran(e (e P&en P&enol olp& p&ta tale lein in 1
2
a " c a " c a " c
?.1 .14.5 .14.5 @4.5 @4.5 @4.5
@10 @10 @10
2.== .# 2.== 4.1= 4.# 4.1 =.A5 11.04 #.70
4
a " c !olutions 1 a " c 2 a " c a " c 4 a " c
=.10 @10 @10 &eoretical p- alue 2.27 .47 2.=A 4.70 4.7# 4.74 10.5 11.7 11.12 #.2 #.0 #.2A
=.20 =.51 =.#
Table ! T"eoretical pH #alues based on calculations $e%erences &Cambria 1', Bold( 31) Clar*, +im &''( AcidBase Indicators. -eb ! "ttp!www.c"emguide.co.u*p"/sicalacidbasee0iai ndicators."tml $etrie#ed! 1 +une '1 2) 3auling, 4. &15'( 6eneral C"emistr/. 78! 9o#er 3ublications 2:) -"itten, ;. -., et al. &''<( 6eneral C"emistr/, t" ed. 78! Broo*sCole
