Understanding pH, pOH, and Neutralization

Flashcards covering the fundamentals of pH, pOH, the logarithmic nature of the pH scale, water's equilibrium constant, and chemical definitions of acids, bases, and neutralization.

What is pH a measure of in a solution?

It is a measure of the concentration of hydronium ($H_3O^+$) ions, more commonly called free protons ($H^+$).

How are acids defined in terms of proton behavior?

Acids are defined as proton donors that release $H^+$ ions into a solution.

What are three examples of substances with an acidic pH between $1$ and $3$?

Stomach acid, lemon juice, and vinegar.

What are two examples of substances with a neutral pH of approximately $7$?

Pure water and human blood ($\text{~}7.4$).

What are three examples of substances with a basic pH between $11$ and $14$?

Bleach, soapy water, and drain cleaner.

What does it mean for the pH scale to be logarithmic?

Each step on the scale represents a $10 \times$ difference in $H^+$ concentration from the next.

How much more $H^+$ does a solution at $pH \text{ } 6$ have compared to a solution at $pH \text{ } 7$?

It has $10 \times$ more $H^+$ ions.

What is the difference in $H^+$ concentration between stomach acid ($pH \text{ } 1$) and pure water ($pH \text{ } 7$)?

Stomach acid has $1,000,000 \times$ more $H^+$ than pure water.

What is the mathematical formula for pH?

$$pH = -\text{log}_{10}[H^+]$$

How do concentration values for $pH \text{ } 2$ and $pH \text{ } 13$ compare?

A $pH \text{ } 2$ solution has a very high $H^+$ concentration ($0.01\text{ }mol/L$), while $pH \text{ } 13$ has an extremely low concentration ($0.00000000001\text{ }mol/L$).

What does pOH measure and what is its formula?

pOH measures hydroxide ($OH^-$) concentration and is defined as $pOH = -\text{log}_{10}[OH^-]$.

What is the relationship between pH and pOH in an aqueous solution?

The sum of pH and pOH always equals $14$ ($pH + pOH = 14$).

What is the water ionisation constant ($K_w$) at $25^\text{o}C$?

$$K_w = [H^+][OH^-] = 1 \times 10^{-14}$$

What is the general formula for a neutralization reaction?

$$\text{Acid} + \text{Base} \rightarrow \text{Salt} + \text{Water}$$

How does the Arrhenius definition describe a base?

A base is a substance that produces $OH^-$ ions in water.

How does the Brønsted–Lowry definition describe the interaction between an acid and a base?

An acid is a proton donor and a base is a proton ($H^+$) acceptor.

What happens to the $H^+$ and $OH^-$ ions during Arrhenius neutralization?

The $H^+$ from the acid combines with the $OH^-$ from the base to form water ($H_2O$), eliminating both ions.