8 Acidity of Gastric HCl A technician in a hospital...

8 Acidity of Gastric HCl A technician in a hospital laboratory obtained a $10.0 \mathrm{~mL}$ sample of gastric juice from a patient several hours after a meal and titrated the sample with $0.1 \mathrm{~m} \mathrm{NaOH}$ to neutrality. The neutralization of gastric $\mathrm{HCl}$ required $7.2 \mathrm{~mL}$ of $\mathrm{NaOH}$. The patient's stomach contained no ingested food or drink at the time of sample harvest. Therefore, assume that no buffers were present. What was the $\mathrm{pH}$ of the gastric juice?

Key Concepts

Acid-Base Titration

Acid-base titration is a common laboratory method used to determine the concentration of an acid or base in a sample by gradually adding a titrant of known concentration until the reaction reaches a neutralization endpoint. This technique relies on the precise measurement of the volume required to completely react with the analyte, which directly informs the mole calculation of the substance being titrated.

Molarity

Molarity is a measure of concentration expressed as the number of moles of solute per liter of solution. It is a fundamental concept in chemistry that allows for the calculation of the exact amount of a substance involved in a reaction, which is essential when relating the volume of titrant used to the number of moles in the sample.

Neutralization Reaction

A neutralization reaction occurs when an acid reacts with a base to produce water and a salt. In the context of titration, this reaction is used to determine the amount of acid or base present in the sample by ensuring that the added titrant completely neutralizes the analyte, leading to a measurable endpoint.

Stoichiometry

Stoichiometry involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. It is used in titrations to relate the volume and molarity of a titrant to the number of moles of the analyte, thereby enabling the calculation of the original concentration of the substance in the sample.

pH Calculation

pH is defined as the negative logarithm of the hydrogen ion concentration in a solution, serving as an indicator of its acidity or basicity. Once the concentration of hydrogen ions is determined through titration and stoichiometric calculations, the pH can be calculated to quantify the solution's acid strength.

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