Making And Investigating Buffer Solutions Research Essay

Making And Investigating Buffer Solutions Essay, Research Paper

`Aim? ? ? ? ? ? ? ? ? ? ? I will

effort to fix two buffer solutions. ?

The first buffer solution will hold a pH value of 5.2 and will be made

from a mixture of 1.0M ethanoic acid and 1.0M Na acetate solution. ? The 2nd buffer solution will hold a pH

value of 8.8 and will be made from a mixture of 1.0M ammonium hydroxide and 1.0M ammonium

chloride solution. Plan In order to do these buffers, I will necessitate to cipher the

exact proportions of salt solution and acid/alkali to add in order to obtain

the necessary pH value: pH = pKa? log [ HA ] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? [ A- ] Given that: The pKa value for 1.0M ammonium hydroxide and 1.0M ammonium chloride

solution is 9.3. The pKa value for 1.0M ethanoic acid and 1.0M Na

ethanoate solution is 4.8.For the devising of the buffer pH 5.2: Equations for the dissociation of ethanoic acid and Na

acetate severally: CH3COOH + H2O & # 8596 ; CH3COO-

+ H3+O CH3COONa & # 8594 ; CH3COO- +

Na+ Using the equation antecedently stated: 5.2 = 4.8? log [ HA ] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? [ A- ] 5.2? 4.8 = & # 8211 ; log [ HA ] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? [ A- ] 0.4 = & # 8211 ; log [ HA ] ? ? ? ? ? [ A- ] 10-0.4 = [ HA ] ? [ A- ] 0.398 = [ HA ] : [ A- ] CH3COOH + H2O & # 8596 ; CH3COO-

+ H3+O ( 100? ten ) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ten? ? ? ? ? ? ? ? ? ? ? ? ? ? ten = 0.398/1 100 ten 0.398? = 28.46

cm3 salt? ? ? ? ? ? ? ? ? 1.398 Therefore: 100? 28.46 = 71.54 acidFor the devising of the buffer pH 8.8: Equations for the dissociation of ammonium hydroxide and ammonium

chloride severally: NH3 + H2O & # 8596 ; NH2-

+ H3+O NH2Cl & # 8594 ; NH2- + Cl- Using the equation antecedently stated: 8.8 = 9.3? log [ HA ] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? [ A- ] 5.2? 4.8 = & # 8211 ; log [ HA ] ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? [ A- ] 0.5 = & # 8211 ; log [ HA ] ? ? ? ? ? [ A- ] 10-0.5 = [ HA ] ? [ A- ] 0.316 = [ HA ] : [ A- ] CH3COOH + H2O & # 8596 ; CH3COO-

+ H3+O ( 100? ten ) ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ten? ? ? ? ? ? ? ? ? ? ? ? ? ? ten = 0.316/1 100 ten 0.316 = 24.01 cm3 salt? ? ? ? ? ? ? ? ? 1.316 Therefore: 100? 24.01 = 75.99 cm3 acidIn order to do these buffer solutions, I must accurately

step the volumes of the acid and the salt. ?

Unfortunately, the most accurate volumetric measurement equipment

available to me is a burette that is merely accurate to one denary topographic point.

However, this should be sufficient to obtain a pH value correct to one decimal

place. ? I will utilize two burettes, one

filled with acid, the other with salt. ?

I will run the needed sum of acid and salt into a beaker in each

case. ? I will so mensurate the pH utilizing

a digital pH metre, calibrated utilizing buffer solutions of pH 4 and 7. ? Hopefully, the intended values of the buffer

solutions will be the same as the accurate values +-0.1.Results: ? ? ? ? ? ? ? ? ? ? ? I had some

trouble in obtaining an accurate value for the pH of my buffer solution due

to the undependability of the pH metres available to me. ? However, I did pull off to obtain a dependable

pH metre finally and when I measured the pH of my buffer solutions with it I

found that the buffer solution made from the ethanoic acid and the Na

acetate had a pH value of 5.2 +-0.1 as the pH metre

tended to waver between 5.1 and 5.3, and the buffer solution made from the

ammonium hydroxide and the ammonium chloride had a pH of 9.0+-0.1 as

one time more the pH metre tended to waver between 8.9 and 9.1. ? I think that the wrong value of the

2nd buffer solution can be attributed partly to the inaccuracy of the pH

metre, but besides to the inaccuracy of my measurement. ? My burette for the first portion of the experiment had a faulty pat,

I did non gain this until portion manner through, but as I made the ammonium hydroxide

solution foremost, it is likely that this caused the pH of my buffer solution to

be inaccurate.Investigation of my buffer solutions: ? ? ? ? ? ? ? ? ? ? ? I chose to

investigate merely the buffer solution of pH 9.0 after being instructed to merely

investigate merely one buffer solution by my teacher. ? In order to look into the buffering capacity, I will add some

1.0M HCl and NaOH to the buffer solution to see how effectual my buffer is in

battling the debut of acid or base. ?

Harmonizing to buffer theory, the debut of little sums of acid or

base to the buffer solution should hold small consequence on the pH of the

solution due to the nature of the buffer solution. I shall put up two burettes

one filled with 0.1M HCl the other with 0.1M NaOH. ? I shall so utilize a pipette to mensurate out precisely 25cm3

of buffer solution and topographic point it in a little beaker. I shall so reiterate this so

that I will hold two little beakers each incorporating 25cm3 of buffer

solution. ? To the 1 I shall add HCl,

to the other NaOH from two separate burettes. ?

However, I shall add one bead, so 1cm3 and so 5cm3

mensurating the pH after each measure and entering it in a tabular array. ? ? ? ? ? ? ? ? ? ? ? I will besides

look into the consequence of dilution on buffer solutions. ? I will do two solutions, the first will be

a 1/10 dilution, and for this I shall mensurate 10cm3 of buffer

solution and

attention deficit disorder to it 90cm3 of distilled H2O measured out utilizing a

burette. ? The second will be a 1/100

dilution, for this I shall mensurate out 2cm3 of buffer solution and

attention deficit disorder to it 198cm3 of distilled water. ? I shall so prove these dilutions for their consequence on the

buffering capacity of my buffer solution. ?

I shall utilize a pipette to mensurate out precisely 25cm3 of each

dilute buffer solution and topographic point it in a little beaker. I shall so reiterate this

so that I will hold four little beakers each incorporating 25cm3 of a

dilute buffer solution. ? For each dilute

buffer, to one beaker I shall add HCl, to the other NaOH from two separate

burettes. ? Initially, I shall add one

bead, so 1cm3 and so 5cm3 mensurating the pH after each

measure and entering it in a table.Results Vol.

added ( cm3 ) HCl

( undiluted buffer ) NaOH

( undiluted buffer ) HCl

( 1/10 diluted buffer ) NaOH

( 1/10 diluted buffer ) HCl

( 1/100 diluted buffer ) NaOH

( 1/100 diluted buffer ) 0 9.0 9.0 9.0 9.0 9.0 9.0 0.1 8.9 9.0 8.8 9.2 7.8 10.3 1.0 8.7 9.2 8.5 9.7 2.0 11.6 5.0 8.2 9.9 2.0 11.7 1.6 12.2? ? ? ? ? ? ? ? ? ? ? ? ? Decision? ? ? ? ? ? ? ? ? ? ? As

expected, the debut of a little sum of strong acid or base to my

undiluted buffer solution made small difference to its pH. ? However, the debut of even little

sums of strong acid or base to the diluted buffer solutions made a

significant difference to their pH. ? In

a old experiment, I investigated the affect of adding acid or base to

H2O in comparing to a buffer solution, the differences in the alteration in pH

was marked the H2O alterations pH easy with the debut of little sums

of acid or base in contrast to the buffer solution. ? Similarly, as I added more H2O to a diminishing sum of? buffer solution, the buffer? s ability to

cut down the consequence of add-ons of acid or base is besides reduced and the consequence

of the H2O, becomes more outstanding, therefore the pH either beads or rises far

more quickly when the buffers are diluted and the more diluted they become, the

greater the consequence of presenting acid or base to the solution. Therefore, I

can reason that dilution of a buffer solution has an inauspicious consequence on its

buffering capacity. I was besides asked to propose a ground for the likeliness

that the buffer of pH 8.8 may be less stable over a period of clip than many

other buffers. ? I would propose that

this is because the ammonium hydroxide is usually a gas at room temperature. ? As a consequence, it is likely that the liquid

ammonium hydroxide will be unstable and prone to vaporize and go a gas one time

more. ? Blending the ammonium hydroxide liquid with a

solution of its salt will hold no consequence on the unstable nature of the ammonium hydroxide

and therefore the buffer is more likely than other buffers to interrupt down over

clip as the ammonium hydroxide is likely to vaporize therefore cut downing its ability as a

buffer and changing its pH.Evaluation? ? ? ? ? ? ? ? ? ? ? This

experiment was one of the most hard that I have attempted. ? I found it hard chiefly because of the

clip restraints set on me. ? I made my

undertaking more hard by my readying ; I made an initial cardinal error in

the computation of the volumes of acid and salt solution necessary to obtain

the needed pH. ? This resulted in the

pH of my first two solutions being really incorrectly, it was merely when I realised this

error that I was able to rectify it and therefore go on with the experiment. ? This would non hold mattered except that

there was a rigorous clip bound on the experiment. ? This meant that I had to hotfoot the balance of the experiment,

i.e. the dilution of the buffer solution and hence, I did non pass as much

clip look intoing the volumes for the dilution as I would hold liked and I used

mensurating cylinder alternatively of a burette for mensurating out the distilled H2O.

Furthermore, when I was adding acid and base to the buffer, I did non hold

clip to allow the pH metre settle down wholly and I was taking the first stable

reading as correct, as I have discovered this is non ever the case. ? This holding been said, the pH metre that I

finally found after utilizing several different types was really dependable and

accurate and I feel that my consequences are reasonable. ? I do non experience that my consequences are inaccurate, but that they could

possibly be improved if I spent a little more clip taking them. ? If I was to reiterate this experiment, I would

better it by passing a whole twenty-four hours on it, I would carefully do both buffers

and let them to settle before thining them meticulously. ? Finally, I would add acid and base to both

buffers. ? I would contrast their

public presentation with that of H2O and work out their buffering capacity in

comparing to each other and H2O. I would besides meticulously note the pH

alterations of the diluted buffers and work out whether the lessening in pH is

straight relative to the sum of H2O added.