Question

A mixture contain 1 mole of each of naoh,na2co3 and nahco3.When mixture is titrated with hcl

Answer 1

Explanation:

Double indicator acid-base titration:

In the acid-base titration the equivalence point is known with the help of indicator which changes its color at the end point. In the titration of polyacidic base or polybasic acid there are more than one end point. One indicator is not able to give color change at every end point. So to find out each end point we have to use more than one indicator. For example in the titration of Na2CO3 against HCl there are two end points.

Na2CO3 + HCl → NaHCO3 + NaCl

NaHCO3 + HCl → H2CO3 + NaCl

When we use phenolphthalein in the above titration it changes its color at first end point when NaHCO3 is formed and with it we cannot know second end point. Similarly with methyl orange it changes its color at second end point only and we cannot know first end point. It is because all indicator changes color on the basis of  pH  of medium. So in titration of  against acid phenolphthalein cannot be used.

A sample contains NaOH, Na2CO3& NaHCO3. This solution is titrated with HCl or H2SO4

(i) When phenolphthalein (HPh) is used as indicator the reaction are given below.

Na2CO3 + HCl → NaHCO3 + NaCl

This is the half neutralization of Na2CO3

NaHCO3 + HCl → X

NaOH + HCl → NaCl + H2O

Hence

Meq. Of HCl = Meq. Of NaOH + (1/2) Meq. Of Na2CO3

(ii) When methyl orange (MeOH) is used as indicator

Na2CO3 + 2HCl → 2NaCl + H2O + CO2

This is the complete neutralization

NaHCO3 + HCl → NaCl + H2O + CO2

NaOH + HCl → NaCl + H2O

in this case

Meq. Of HCl = Meq. Of NaOH + Meq. Of Na2CO3 + Meq. Of NaHCO3

(iii) If MeOH is added after the first end point obtained from HPh

NaHCO3 + NaHCO3 + HCl → NaCl + H2O + CO2

Produced original

Meq. Of HCl = Meq. Of NaHCO3(produced) + Meq. Of NaHCO3(original)

Note:

When we carry out dilution of solution, Meq eq. Milli mole or mole of substance does not change because they represent amount of substance, however molar concentration may change.

Answer 2

Answer:

acid base titration analysis of misture of naoha and na2co2