Acids & Bases: 29 MCQs with answers

B · They turn blue litmus red

Acids turn blue litmus paper red, while bases turn red litmus blue.

D · 7

A neutral solution has a pH of 7 at 25°C, where [H⁺] = [OH⁻] = 10⁻⁷ M.

C · HCl (hydrochloric acid)

HCl is a strong acid because it completely dissociates in water, while the others are weak acids.

B · NaOH (sodium hydroxide)

NaOH is a strong base that completely dissociates into Na⁺ and OH⁻ ions in water.

C · CH₃COOH

CH₃COOH (acetic acid) is a weak acid because it only partially dissociates in water.

C · Ca(OH)₂

Ca(OH)₂ is a strong base that completely dissociates into Ca²⁺ and OH⁻ ions.

A · True

Lower pH indicates higher acidity, so pH 3 is more acidic than pH 5.

C · 7

The pH is calculated using the formula $\text{pH} = -\log[H^+]$. For $[H^+] = 1 \times 10^{-7}$ M, the pH is 7, indicating a neutral solution.

D · They feel slippery.

Bases are known for feeling slippery to the touch, which is a common characteristic property of basic substances.

C · Hydrogen ions ($H^+$)

According to the Arrhenius theory, acids are substances that increase the concentration of hydrogen ions ($H^+$) in aqueous solution.

C · 0 to 7

Acidic solutions have a pH range from 0 to 7, where lower pH values indicate stronger acidity.

A · Phenolphthalein

Phenolphthalein is a common acid-base indicator that changes color depending on the pH of the solution.

D · Proton donor

The Brønsted-Lowry definition states that an acid donates a proton (H⁺) and a base accepts a proton.

B · HPO₄²⁻

The conjugate base is formed by removing one proton (H⁺) from H₂PO₄⁻, giving HPO₄²⁻.

A · CH₃COONa

CH₃COONa is the salt of a weak acid (acetic acid) and a strong base (NaOH), so its solution is basic due to hydrolysis of the acetate ion.

A · 2

HCl is a strong acid, so [H⁺] = 0.01 M = 10⁻² M. pH = -log(10⁻²) = 2.

C · Al(OH)₃

Al(OH)₃ is amphoteric; it can react with both acids and bases.

C · 11

pOH = -log(10⁻³) = 3. pH = 14 - pOH = 11.

B · False

According to Lewis theory, a base is an electron-pair donor, while an acid is an electron-pair acceptor.

D · pH decreases as hydrogen ion concentration increases.

The pH scale is inversely related to hydrogen ion concentration; as the concentration of hydrogen ions increases, the pH value decreases.

C · HCl and Cl⁻

In the Brønsted-Lowry theory, an acid donates a proton, and its conjugate base is what remains after the acid has donated that proton. HCl donates a proton to become Cl⁻.

D · It completely dissociates in water to produce OH⁻ ions.

A strong base like NaOH completely dissociates in water, producing a high concentration of hydroxide ions, which is characteristic of strong bases.

D · [OH⁻] = 1 imes 10^{-4} M

The pH of a solution is related to the hydroxide ion concentration by the formula: $$pOH = 14 - pH$$. Therefore, $$pOH = 4$$, leading to $$[OH⁻] = 1 imes 10^{-4} M$$.

A · BF₃

BF₃ is a Lewis acid because it has an empty p-orbital and can accept an electron pair.

D · [H⁺] = 3.16 × 10^{-5} M

To find [H⁺], use the formula: [H⁺] = $10^{-pH}$. Thus, [H⁺] = $10^{-4.5} = 3.16 × 10^{-5} M$.

D · [OH⁻] = 1.00 × 10^{-4} M

Use the relationship between pH and pOH: pOH = 14 - pH. Thus, pOH = 5, and [OH⁻] = $10^{-5} M$.

A · pH = 7

HCl and NaOH neutralize each other in a 1:1 ratio, resulting in a neutral solution with pH = 7.

B · It is a strong acid.

H₂SO₄ is a strong acid because it completely dissociates in water to produce H₃O⁺.

D · pH = 5.06

Using the Henderson-Hasselbalch equation: pH = pKa + log([A⁻]/[HA]). After adding NaOH, [A⁻] increases and [HA] decreases, leading to a new pH of approximately 5.06.