Question

Na Title: Sample Measured pH of Solution. Additions of 1.OM HCI Initial 3 drops 6 drops 9 drops 12 drops A pH Water 6.43 2.25 2.10 1.98 1.82 Weak Acid: 4.58 3.15 2.85 2.62 241 Weak Base 9.15 9.00 8.878.72 8.64 Buffer: 6.96 6.90 6.78 6.696.55 ApH-Final pH. Initial pH Title: Sample Measured pH of Solution. Additions of 1.0M NaOH 0 drops 3 drops 6 drops 9 drops 12 drops A pH Water 6.49 11.32 11.65 11.79 11.88 Weak Acid: 5.316.026.296.536.71 Weak Base: 8.95 10.69 10.96 11.13 11.27 Buffer. 6.98 2.07 7.127.14 7.16 Buffer System Addition of 1.OM HC1 Addition of 1.0M NaOH Weak Acid Conjugate pKa Initial pH|Final pH a pH Initial ph Final pH A PH Rose Sodium Sodium Hydrogen Hydrogen 69 696 6.55 6 .987.16 Phosphate, Phosphate, MopobasicDihasie 4.78 4.90 Acetate Arginine 8.929.36 Acetic Acid Sodium 89 897 Hydrochloridel Arginine Sodium Tartaric Acid 2.9 289 Bitartrate 2.49 2.87 3.13 Trizma Hydrochloridel Trizma 8.1 8.35 8.11 8.34 8.62 Sodium Sodium L a Bicarbonate Carbonate 10. 3 9.90 9.64 9.88 10.11 Discussion (Answer the following questions in paragraph form, be sure to discuss specifics from your data and the class data and include any thoughts patterns/ideas etc. discovered from this data and inferences; in addition, answer the additional questions listed after this) 1. Did the buffer keep the pH near the initial value when a moderate amount of hydrochlorie acid (HCI) was added? When a moderate amount of sodium hydroxide (NaOH) solution was added? Provide evidence to support your conclusions.

Answer 1

Lets reconstruct the table containing just Name of system and difference in pH (positive value is indicated)

Sample	$\Delta pH$ (0 drops-3 drop) (HCl)	$\Delta pH$ (0 drops-12 drop) (HCl)
water	4.18	4.61
weak acid	1.43	2.17
weak base	0.15	0.51
buffer	0.06	0.41

Sample	$\Delta pH$(3 drops - 0 drops)(NaOH)	$\Delta pH$ (12 drops-0 drop) on addition of NaOH
water	4.83	5.39
weak acid	0.71	1.4
weak base	1.74	2.32
buffer	0.09	0.18

System	pKa	$\Delta pH$(HCl addition)	$\Delta pH$(NaOH additionl
Phosphate	6.9	0.41	0.18
acetate	4.8	0.31	0.12
arginine	8.9	0.15	0.44
tartarate	2.9	0.4	0.26
trizma	8.1	0.24	0.28
bicarbonate	10.3	0.26	0.23

Answer to Question 1

Yes, buffer was effective when moderate amount of HCl or NaoH was added as it is evident from the $\Delta pH$ value when 3 drops of HCl and NaOH were added in the buffer system as mentioned in table 1 and 2 respectively

Answer to Question 2

When HCl was added, in case of weak base the change in pH was considerably less (however it is not as less as observed in buffer system, as we can see in table 1 on addition of 3 drops of acid, change in pH in weak base = 0.15 while in buffer is 0.06), this is due to the fact that weak base on partial neutralisation with strong acid results in inhouse buffer which will resist the change in pH

Similarly when NaOH was added, change in pH was quite less in case of weak acid (not as less as in buffer of course). The reasoning is same as above.

Answer to Question 3

Yes, buffer was effective, buffer is considered to be effective as long as addition of strong acid and strong base do not change its pH by 1 unit. So, in this aspect we can see even when 12 drops of strong acid and strong base was added change in PH is less than 1 unit while change in Ph of pure water is drastically very high thus yes buffer is effective.

Answer to Question 4

Since the

Since the "Class Data" is not given here i am not able to comment on that.

Answer to Question 5

Different buffer system has different pka value and these buffers have effective buffer capacity in the narrow region of their pka value. According to the Henderson Hasselbalch equation

pH = pka + logio con jugatebase Tweakacid
for acidic buffer, and buffer capacity is found to be maximu when [conjugate base] = [weak acid] and also, the given buffer is effective in buffering the pH range from pka - 1 to pka + 1. i.e. $pk_a\pm 1$ . Thus, ratio of [conjugate base] and [weak acid] determins the pH and buffering power is maximum when pH = pKa.

Similarly for basic buffer $pOH = pk_b+ log_{10}\frac{[conjugate acid]}{[weak base]}$ and here effective pOH range is $pk_b\pm 1$

Thus, overall ratio of conjugate acids and bases and their pka does determine buffering capacity of buffer.

Answer to Question 6

This has been already discussed in question no. 5.

In case of acidic buffer, relation is

pH = pka + logio con jugatebase Tweakacid

In case of basic buffer, relation is
pH = pka + logio con jugatebase Tweakacid
and pH = 14 - pOH at $25^0C$

Additional questions

In our body, ph is about 7.4 and needs to be maintained at that value so, best buffer is the one with pka closes to this value. So from the table given sodium hydrogen phosphate monobasic and sodium hydrogen phosphate dibasic is the best to use.

In stomach, ph is acidic (1.5 to 3.5) thus above buffer is not suitable there, here tartaric acid sodium bitartarate can be used.

For yeast acidic pH must be maintainet thus the buffer system with pka in acidic region is ideal for yeast. If the yeast thrive in ph range of 4 to 4.5 then acetic acid buffer is suitable for it

for alkaliphilic microorganisms, the buffer system with pka value in basic range is suitable for example sodium bicarbonate and carbonate system.