= Acid-base titration measurement
The institutional experiment The Potentiometric Titration of an Acid Mixture, from Massachusetts Institute of Technology's 5.310 Laboratory Chemistry, determines <hydrochloric acid> and <phosphoric acid> inventories. Dried <potassium hydrogen phthalate> standardizes <sodium hydroxide>. A <volumetric pipette> selects an acid <aliquot>, diluted with <water> in a beaker. A <burette> feeds a stirred sample beside a <glass electrode>; the apparatus isolates the sample from stirrer warming. The <burette> is conditioned with <titrant> and its tip freed of bubbles. Stable <pH> and added <volume (thermodynamics)> are recorded, with smaller additions near the transition. Controls include replicate standardizations, a consistent pale-pink <phenolphthalein> endpoint, and a standard <buffer solution> check between sample runs. The readout supports inventory estimates through known <stoichiometry>; it does not directly count <molecules>.<The Potentiometric Titration of an Acid Mixture (MIT 5.310 laboratory handout)>[The Potentiometric Titration of an Acid Mixture, printed Titration-5–8, §IV.2 and Day \#2; Figure 3; standardization, aliquot, bubbles, stable readings, and buffer check]{ref}
The same protocol requires drainage time for <burette> readings and warns that an undelivered hanging drop spoils the association between <volume (thermodynamics)> and <pH>. Its color-persistence wording differs between the main paragraph and footnote, so a reproducible <titration endpoint> needs an explicitly chosen criterion. Its acid mixture is not the single-<strong acid> ideal model above.<The Potentiometric Titration of an Acid Mixture (MIT 5.310 laboratory handout)>[Printed Titration-6, main endpoint paragraph and footnote 6; Titration-8, hanging-drop warning]{ref}
A distinct control appears in Process Measurement Procedures: Sulfuric Acid Emissions, §1.4.4.2: the <phenolphthalein> standardization is repeated with <water> replacing the acid, matching the sample <aliquot> and indicator quantity. The <volume (thermodynamics)> needed for the same pink endpoint is subtracted from the sample reading.<Process Measurement Procedures: Sulfuric Acid Emissions by R. Maddalone and N. Garner>[Process Measurement Procedures: Sulfuric Acid Emissions, printed pp. 26–27, §1.4.4.2, indicator-blank paragraph, NOTE, and procedure steps 1–3]{ref}
The independent bookkeeping for such a matched blank is $n_A=c_B(V_{\mathrm{sample}}-V_{\mathrm{blank}})$, assuming one-to-one <neutralization> and equal background consumption. A blank cannot correct an unmatched <chemical reaction> or guarantee exact coincidence of endpoint and <equivalence point>. Subtracting <pH> readings would not give this inventory correction, because <pH> is a <logarithm>. Repeatability constrains scatter; an independently known check sample also tests systematic bias. <Carbon dioxide> uptake, incomplete mixing, <electrode> drift, and uncertain <titrant> <concentration> limit the inference.
Back to article page
