= Glycine titration experiment
The Amrita Virtual Lab procedure uses $0.1\,\mathrm{mol\,L^{-1}}$ <glycine>, <hydrochloric acid> and <sodium hydroxide>, two <burettes>, a <pH> meter, beaker and stirrer. A <pipette> transfers $20\,\mathrm{mL}$ of <glycine> into a $100\,\mathrm{mL}$ beaker. Calibrate the meter with standard <buffer solutions> at <pH> $4$, $7$ and $10$, then record the starting <pH>. Add <hydrochloric acid> in $0.3\,\mathrm{mL}$ increments, recording <pH> after each addition until $1.6$. Rinse the <electrode> in distilled <water>, take a separate fresh $20\,\mathrm{mL}$ portion, and add <sodium hydroxide> in $0.3\,\mathrm{mL}$ increments until <pH> $12.5$. Its observed readout is paired added <volume (thermodynamics)> and <pH>, plotted as an <acid-base titration> curve; it does not measure each <glycine> form directly. <Titration Curves of Aminoacids, Amrita Virtual Lab/Procedure>[Materials Required, items 1–8; Working steps, items 1–9: separate acid and base titrations]{ref}
These are two titrations from the starting <glycine> <chemical solution>, rather than the single acidified-sample protocol assumed by the solid curve in <glycine titration>. Retain each portion's initial <volume (thermodynamics)> and the signed added acid/base <amount of substance>; do not concatenate raw <burette> readings and assume the result begins at $b=0$. For this procedure's $0.00200\,\mathrm{mol}$ of <glycine>, each $0.3\,\mathrm{mL}$ addition supplies $0.000030\,\mathrm{mol}$ of acid or base, a $0.015$ increment relative to the <glycine> inventory. This calculated resolution is not a reported measurement.
Useful additional controls are a fresh repeat portion, independently checked acid/base <concentrations>, a <water> blank, and a calibration-check <buffer solution> after the run. Stir without striking the <glass electrode>, keep its sensing region immersed and wait for stable readings; record <temperature> and background salts. Reduce addition size near a steep <pH> change. These are suggested controls for testing the model, beyond the published steps. A <water> blank can reveal contamination but must not be subtracted directly from <pH>, which is a <logarithm>.
The standards at <pH> $4$, $7$ and $10$ do not bracket either endpoint of this protocol. Extreme readings therefore require independently checked instrument performance, and alkaline samples are sensitive to atmospheric <carbon dioxide> uptake. <Electrode> drift, incomplete mixing, <volume (thermodynamics)> error, <dilution> and changing <ionic strength> can shift apparent <pKa> values. A titration constrains the acid/base model; it cannot establish <chirality (chemistry)> or separate every microscopic <protonation> form. The two original diagrams show calculated predictions to compare with measured points, not reconstructed experimental data.
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