Preparation of standard buffer for calibration of a ph meter the glass electrode used in commercial ph meters gives an electrical response proportional to the concentration of hydrogen ion. to convert these responses to a ph reading, the electrode must be calibrated against standard solutions of known h+ concentration. determine the weight in grams of sodium dihydrogen phosphate (nah2po4 · h2o; fw 138) and disodium hydrogen phosphate (na2hpo4; fw 142) needed to prepare 1 l of a standard buffer at ph 7.00 with a total phosphate concentration of 0.100 m

Explanation:

Keeping in mind the equilibrium:

H₂PO₄⁻ ↔ HPO₄⁻² + H⁺

We use the Henderson-Hasselbalch equation (H-H):

pH = pka +

For this problem [A⁻] = [HPO₄⁻²] and [HA] = [H₂PO₄⁻]

From literature we know that pka = 7.21, from the problem we know that pH=7.00 and that

[HPO₄⁻²] + [H₂PO₄⁻] = 0.100 M

From this equation we can express [H₂PO₄⁻] in terms of [HPO₄⁻²]:

[H₂PO₄⁻] = 0.100 M - [HPO₄⁻²]

And then replace [H₂PO₄⁻] in the H-H equation, in order to calculate [HPO₄⁻²]:

With the value of  [H₂PO₄⁻], we calculate [HPO₄⁻²]:

[HPO₄⁻²] + 0.0381 M = 0.100 M

[HPO₄⁻²] = 0.0619 M

Finally, using the concentrations, the volume, and the molecular weights; we can calculate the weight of each substance:

explanation:

metals have excess of electrons whereas non-metals have deficiency of electrons. thus, in order to gain stability metals easily donate their electrons to the non-metals.

for example, electronic configuration of sodium is and electronic configuration of phosphorous is .

when a phosphorous atom and sodium atom combine together then sodium will donate is extra one electron to the phosphorous atom. as a result there will be formation of ionic bond between sodium and phosphorous.

the reaction will be as follows.

there, are three sodium sodium atoms and each of them will donate its one extra electron to phosphorous atom. thus, the sub-shell of phosphorous gets completely filled.  

thus, we can conclude that electrons are transferred from atoms of sodium to atoms of phosphorous. this transfer makes the sodium atoms donate one electron and the phosphorous atoms to gain one electron. as a result, the sodium and phosphorus atoms strongly attract each other.