Question

Which addition would not change the \(\mathrm{pH}\) of \(10 \mathrm{ml}\) of dilute hydrochloric acid? (1) \(20 \mathrm{ml}\) of the same hydrochloric acid (2) \(5 \mathrm{ml}\) of pure water (3) \(20 \mathrm{ml}\) of purc water (4) \(10 \mathrm{ml}\) of concentrated hydrochloric acid

Short answer

Adding 5 ml of pure water (Option 2) would not notably change the \(\rm{pH}\).

Step-by-step solution

Analyze the given solutions

Evaluate each option and its potential impact on the \(\rm{pH}\) of the dilute hydrochloric acid.

Evaluate Option 1

Adding more of the same hydrochloric acid (20 ml) would increase the concentration of hydrogen ions \(H^+\), thus decreasing the \(\rm{pH}\).

Evaluate Option 2

Adding 5 ml of pure water would slightly dilute the solution, potentially increasing the \(\rm{pH}\) a little, but not significantly.

Evaluate Option 3

Adding 20 ml of pure water would significantly dilute the solution, raising its \(\rm{pH}\) noticeably.

Evaluate Option 4

Adding 10 ml of concentrated hydrochloric acid would increase the concentration of hydrogen ions \(H^+\) in the solution, decreasing the \(\rm{pH}\).

Determine the correct answer

The correct choice brings almost no change in the \(\rm{pH}\) level. Among the options, adding 5 ml of pure water is the one that would cause the least change in the \(\rm{pH}\).

Key concepts

pH change

Understanding \(\rm{pH}\) change is crucial in acid-base chemistry. \(\rm{pH}\) is a measure of the hydrogen ion concentration in a solution. The \(\rm{pH}\) scale ranges from 0 to 14. Lower values mean a solution is more acidic, while higher values mean it is more basic. Pure water has a neutral \(\rm{pH}\) of 7.

The \(\rm{pH}\) changes when substances that alter hydrogen ion concentration are added. For instance, adding hydrochloric acid, which releases hydrogen ions, will lower the \(\rm{pH}\). Conversely, adding a basic substance will increase the \(\rm{pH}\) by reducing the hydrogen ion concentration. When evaluating the effects of substances on \(\rm{pH}\), consider their capability to donate or accept hydrogen ions.

dilution effect

Dilution occurs when more solvent, usually water, is added to a solution. This can change the concentration of solutes, impacting the solution's \(\rm{pH}\).

When you dilute an acid like hydrochloric acid, the concentration of hydrogen ions \((\rm{H}^+)\) decreases. This causes the \(\rm{pH}\) to rise, making the solution less acidic. The degree of \(\rm{pH}\) change depends on how much solvent you add. Small amounts might only slightly affect the \(\rm{pH}\), while larger quantities can significantly increase it.

hydrochloric acid

Hydrochloric acid (\rm{HCl}) is a strong acid commonly found in laboratory and industrial settings. It fully dissociates in water, meaning it releases all of its hydrogen ions \((\rm{H}^+)\). This leads to a very low \(\rm{pH}\) and strong acidity.

When you add hydrochloric acid to a solution, it significantly increases the hydrogen ion concentration, lowering the \(\rm{pH}\). Knowing this helps in analyzing how different volumes or concentrations of \rm{HCl} impact the \(\rm{pH}\) of a solution. For instance, adding more \rm{HCl} will further reduce the \(\rm{pH}\), while dilution with water will reduce its acidity.

hydrogen ion concentration

Hydrogen ion concentration \((\rm{H}^+)\) is key in determining the \(\rm{pH}\) of a solution. The relationship is given by the equation: \[\rm{pH} = -\text{log}[\rm{H}^+]\]

In this equation, \([\rm{H}^+]\) represents the molar concentration of hydrogen ions. A high \([\rm{H}^+]\) means a low \(\rm{pH}\), indicating an acidic solution. Conversely, a low \([\rm{H}^+]\) means a high \(\rm{pH}\) and a basic solution.

Understanding these principles helps in predicting how additions of certain substances, like hydrochloric acid or water, can alter the \(\rm{pH}\) by affecting the \([\rm{H}^+]\).