QuestionAnswers 4Similar questionsResearch that mentions ReagentsQuestionAsked 25 July 2018Aishwarya Navnath Markad
Fergusson College
How to standardize 2M NaOH using KHP or HCL? I want to prepare DNSA reagent for that I have to use 2M NaOH.I want to know if it is necessary to standardize NaOH? If yes, then how much amount of KHP or HCL will I need for it? ReagentsShare Facebook Twitter LinkedIn Reddit
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James DemersCittone, Demers & Arneri LLPNaOH is in vast excess over the DNSA in the reagent, so there's really no need to titrate it at all. Many preparations are based on simply weiging out the solids.If you do want to titrate it, a weak acid is fine - with phenolphthalein indicator, anything with a pKa below 8 will do. (The pKa of KHP is about 5.5.)Cite
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Maurice EkpenyongUniversity of CalabarHello, of course it is necessary to standardize your NaOH solution. Your KHP is potassium hydrogen phthalate, so I suppose you are trying to standardize sodium hydroxide against a primary standard acid. You therefore need phenolphthalein as indicator. Since NaOH solutions cannot be prepared by mass to be an exact concentration (solid NaOH is too reactive), you then standardize your NaOH solution by titrating weighed samples of a primary standard acidic substance, potassium hydrogen phthalate (KHC8H4O4, "KHP", molar mass 204.2 g). KHP has one acidic hydrogen atom and reacts with NaOH on a 1:1 stoichiometric basis: KHC8H4O4 + NaOH = NaKC8H4O4 + H2O. Since all the reactants and products of this neutralization reaction are colorless, a few drops of an indicator (phenolphthalein) should be added to each KHP sample to be titrated. Phenolphthalein is colorless in acidic solution, but turns red in basic solution. When one drop more NaOH is added than is required to react with the KHP in a sample, the sample becomes basic and the indicator changes color. We take the point where the indicator color first appears as an indication that we have added NaOH in an equivalent amount to the KHP present in the sample. Cite1 RecommendationAndrew PingitoreSaudi Basic Industries Corporation (SABIC)Maurice is spot on with that answer. I would just like to add, that, the reason we cannot directly prepare NaOH solutions by mass is do to the fact that NaOH is very hygroscopic (absorbs water from the air). It also can, when exposed to air, react with CO2 to form sodium carbonate.CiteYurii V GeletiiEmory UniversityNo, you don't need to use "standardized" solution of NaOH, (2+-0.2) M NaOH would be OK.Dear Maurice, KHP is buffering agent with respect to NaOH. You can't titrate NaOH by KHP. For titration of a strong base you should use a strong acid such as HCl. CiteJames DemersCittone, Demers & Arneri LLPNaOH is in vast excess over the DNSA in the reagent, so there's really no need to titrate it at all. Many preparations are based on simply weiging out the solids.If you do want to titrate it, a weak acid is fine - with phenolphthalein indicator, anything with a pKa below 8 will do. (The pKa of KHP is about 5.5.)Cite
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Aishwarya Navnath Markad
Aishwarya Navnath Markad
James DemersCittone, Demers & Arneri LLPNaOH is in vast excess over the DNSA in the reagent, so there's really no need to titrate it at all. Many preparations are based on simply weiging out the solids.If you do want to titrate it, a weak acid is fine - with phenolphthalein indicator, anything with a pKa below 8 will do. (The pKa of KHP is about 5.5.)Cite
Yasser Fakri Mustafa
Abdelkader BOUAZIZ
Frank T. Edelmann
Adam B Shapiro
Moaed E. Algazally
Maurice EkpenyongUniversity of CalabarHello, of course it is necessary to standardize your NaOH solution. Your KHP is potassium hydrogen phthalate, so I suppose you are trying to standardize sodium hydroxide against a primary standard acid. You therefore need phenolphthalein as indicator. Since NaOH solutions cannot be prepared by mass to be an exact concentration (solid NaOH is too reactive), you then standardize your NaOH solution by titrating weighed samples of a primary standard acidic substance, potassium hydrogen phthalate (KHC8H4O4, "KHP", molar mass 204.2 g). KHP has one acidic hydrogen atom and reacts with NaOH on a 1:1 stoichiometric basis: KHC8H4O4 + NaOH = NaKC8H4O4 + H2O. Since all the reactants and products of this neutralization reaction are colorless, a few drops of an indicator (phenolphthalein) should be added to each KHP sample to be titrated. Phenolphthalein is colorless in acidic solution, but turns red in basic solution. When one drop more NaOH is added than is required to react with the KHP in a sample, the sample becomes basic and the indicator changes color. We take the point where the indicator color first appears as an indication that we have added NaOH in an equivalent amount to the KHP present in the sample. Cite1 Recommendation
Andrew PingitoreSaudi Basic Industries Corporation (SABIC)Maurice is spot on with that answer. I would just like to add, that, the reason we cannot directly prepare NaOH solutions by mass is do to the fact that NaOH is very hygroscopic (absorbs water from the air). It also can, when exposed to air, react with CO2 to form sodium carbonate.Cite
Yurii V GeletiiEmory UniversityNo, you don't need to use "standardized" solution of NaOH, (2+-0.2) M NaOH would be OK.Dear Maurice, KHP is buffering agent with respect to NaOH. You can't titrate NaOH by KHP. For titration of a strong base you should use a strong acid such as HCl. Cite
