phenolphthalein is an indicator for titration of weak acid and strong base.
phenolphthalein is an indicator for titration of weak acid and strong base.
indicator for titration of weak acid and strong base?
phenolphthalein
if one reagent is a weak acid or base and the other is a strong acid or base, the titration curve is irregular and the ph shifts less with small additions of titrant near the equivalence point. for example, the titration curve for the titration between oxalic acid (a weak acid) and sodium hydroxide (a strong base) is pictured. the equivalence point occurs between ph 8-10, indicating the solution is basic at the equivalence point and an indicator such as phenolphthalein would be appropriate. titration curves corresponding to weak bases and strong acids are similarly behaved, with the solution being acidic at the equivalence point and indicators such as methyl orange and bromothymol blue being most appropriate.
titration
ammonium ion concentration in the acid solution, and thus the amount of nitrogen in the sample, is measured via titration. if boric acid (or some other weak acid) was used, direct acid-base titration is done with a strong acid of known concentration. hcl or hso can be used. indirect back titration is used instead if strong acids were used to make the standard acid solution: strong base of known concentration (like naoh) is used to neutralize the solution. in this case, the amount of ammonia is calculated as the difference between the amount of hcl and naoh. in the case of direct titration, it is not necessary to know the exact amount of weak acid (e.g. boric acid) because it does not interfere with the titration (it does have to be in excess of ammonia to efficiently trap it). thus, one standard solution is needed (e.g. hcl) in the direct titration, while two are needed (e.g. hcl and naoh) in the back-titration. one of the suitable indicators for these titration reactions is tashiro's indicator.
kjeldahl method