Acid-Base Reactions and Buffers - AP Chemistry

pH = 7. Equal concentrations of $H^+$ and $OH^-$ ions.

$pK_w = pH + pOH$. Sum equals 14 at 25°C for aqueous solutions.

Hydrochloric acid ($HCl$). Strong acid with 100% ionization in water.

$K_b = \frac{[NH_4^+][OH^-]}{[NH_3]}$. Products over reactants for base ionization equilibrium.

Ammonia ($NH_3$). Weak base component that partially ionizes.

p$OH = -\text{log}[OH^-]$. Negative log transforms $OH^-$ concentration to pOH scale.

$NH_4^+$. Gains a proton from $NH_3$ to form ammonium ion.

pH decreases slightly. Buffer components neutralize added acid effectively.

Sodium hydroxide ($NaOH$). Strong base with 100% dissociation in water.

To maintain stable pH. Prevents large pH changes in chemical systems.

$K_a \times K_b = K_w$. Product equals water's ionization constant at 25°C.

Minimal pH change. Buffer capacity prevents large pH shifts effectively.

pOH = 4. pOH = $-\log(1.0 \times 10^{-4}) = 4$.

$pK_a = 5$. $pK_a = -\log(1.0 \times 10^{-5}) = 5$.

pH = 1. Strong acid completely ionizes: $[H^+] = 0.1$ M.

$ \mathrm{pH} = \mathrm{p}K_a + \log \frac{[A^-]}{[HA]} $. Relates buffer pH to acid strength and base ratio.

Partial ionization. Incomplete dissociation provides buffering capacity.

Acetic acid ($CH_3COOH$). Weak acid component that partially ionizes.

Hydrogen ion ($H^+$). Higher $H^+$ concentration means more acidic solution.

Proton acceptor. Bases accept protons from other species in solution.

$H_3O^+$. Water gains a proton to form hydronium ion.

$Cl^-$. Loses a proton from $HCl$ to form chloride ion.

Minimal change in pH. Buffer ratio remains constant during dilution process.

Resists changes in pH upon addition of acid or base. Weak acid-base pair maintains stable pH range.

$1.0 \times 10^{-4} M$. $[H^+] = 10^{-4} = 1.0 \times 10^{-4}$ M.

$OH^-$. Water loses a proton to form hydroxide ion.

$H_2PO_4^-$. Loses one proton from phosphoric acid.

$NH_3$. Gains a proton to form ammonia from amide ion.

pH = 9. pOH = 5, so pH = 14 - 5 = 9.