[rubystar91]

In general, a buffer solution consist of
a Stong Acid and it's Conjugate Base
a Weak Acid and it's Conjugate Base
a Stong Base and it's Conjugate Acid
a Weak Base and it's Conjugate Acid
-I though it only consists of a weak acid and it's conjugate base, but apparently another one of the answer is correct too but idk which.

Which of the follwing pair makes a buffer
HCl and NaCl
H3PO4 and NaH2PO4
HC3H5O3 (Lactic Acid) and NaC3H5O3 (Sodium Lactate)
CH3NH3 and CH3NH4Cl
KOH and KNO3
-Is it only HC3H5O3 and NaC3H5O3?

[AWK]

a Weak Acid and it's Conjugate Base
a Weak Base and it's Conjugate Acid

This two lines forms a sufficient definition of buffer.

[llagetias]

Like the moderator said above, buffers are made of weak acids or bases and their conjugates. Since a buffer works to keep the pH from changing too much, you wouldn't want a strong acid or base that would cause large changes in pH with just a small amount.

 For the buffer solution pair, choose the one that isn't a strong acid or base. I think the amine will work as well as the lactic acid. Sometimes the second ionization of a strong acid will be a buffer, while the first is not.

Hope this helps.

[AWK]

Sometimes the second ionization of a strong acid will be a buffer, while the first is not

eg. NaHSO₄/Na₂SO₄

[Jorriss]

a Weak Acid and it's Conjugate Base
a Weak Base and it's Conjugate Acid

This two lines forms a sufficient definition of buffer.

I know it's a relative scale, but...

a Stong Acid and it's Conjugate Base
a Weak Base and it's Conjugate Acid

a Weak Acid and it's Conjugate Base
a Stong Base and it's Conjugate Acid

Aren't those more or less the same?

[AWK]

Conjugated bases obtained from strong acids or conjugated acids obtained from strong bases are extremely weak and such solutions show nearly null buffering capacity, hence such solutions are inappropriate as buffers.

[Jorriss]

Conjugated bases obtained from strong acids or conjugated acids obtained from strong bases are extremely weak and such solutions show nearly null buffering capacity, hence such solutions are inappropriate as buffers.

Ya know... I already knew that... I have no idea why I brought it up at all?

[aeacfm]

iam waiting for that for along time
is that practically different or iam confused??

in my work i make buffer pH= 4 by dissolving potassium hydrogen phthalate alone in dist.water

also i  make pH= 6.86 by dissolving diSodium hydrogen phosophate (Na2HPO4) + potassium dihydrogen phosphate (KH2PO4)

i need the explanation ?

[aeacfm]

or these compounds work as the acid and conjugate base at the same time ??

[AWK]

make pH= 6.86 by dissolving diSodium hydrogen phosophate (Na2HPO4) + potassium dihydrogen phosphate (KH2PO4)

H₂PO₄^- (from KH2PO4) - Bronsted acid
HPO₄^2- (from Na₂HPO₄₎ - conjugated Bronsted base

To the poatassium  hydrogen phtalate you should add some amount of strong acid or strong base (in your case  acid) to form buffer with ph 4.0

See buffer B in
http://www.csudh.edu/oliver/chemdata/buffers.htm

[aeacfm]

no i prepare it according to the standard methid of ASTM   and no acid added

[aeacfm]

see these bufferes and explain to me please

...Borax Reference Buffer Solution (pHs= 9.18 at25°C)—
Dissolve 3.80 g of sodium tetraborate decahydrate(Na2B4O7·10H2O) in water and dilute to 1 L.


...Phthalate Reference Buffer Solution (pHs= 4.00 at25°C)—
Dissolve 10.12 g of potassium hydrogen phthalate(KHC8H4O4) in water and dilute to 1 L.

..Tetroxalate Reference Buffer Solution (pHs= 1.68 at25°C)—
Dissolve 12.61 g of potassium tetroxalate dihydrate(KHC2O4·H2C2O4·2H2O)
 in water and dilute to 1 L.

you can find all that in ASTM D 1293  Standard Test Methods for
pH of Water1

many thanks

[AWK]

ASTM 1293 says about solutions for instrument standarizations which are generally called buffers though some of them are hydrolysing salts but not the working buffers. For good instrument standarization you should use two standard solutions that span the range of pH values to be measured.

http://www.ph-meter.info/pH-electrode-calibration-buffers

[aeacfm]

 i am alittle confused here !!!!!!!!!!
is there adifference between calibration buffers and buffers ?
 why this difference occure ? imean why i cant calibrate pH electrode with ordinary bufferes