Question

properties unit test

a small amount of sodium hydroxide is added to water. when the chemical reaction reaches equilibrium, the ph is 12. which statement and conclusion about sodium hydroxide is correct? (1 point)

the negative log of the concentration of oh– ions is 2. sodium hydroxide is a strong base.

the negative log of the concentration of oh–ions is 12. sodium hydroxide is a strong acid.

the negative log of the concentration of oh– ions is 12. sodium hydroxide is a strong base.

the negative log of the concentration of oh– ions is 2. sodium hydroxide is a strong acid.

Explanation:

1. Recall the relationship between pH and pOH: \( \text{pH} + \text{pOH} = 14 \). Given \( \text{pH} = 12 \), we calculate \( \text{pOH} = 14 - 12 = 2 \). The pOH is the negative log of the hydroxide ion (\( \text{OH}^- \)) concentration, so \( \text{pOH}=-\log[\text{OH}^-] = 2 \).
2. Sodium hydroxide (\( \text{NaOH} \)) dissociates in water to produce \( \text{OH}^- \) ions (\( \text{NaOH}

ightarrow\text{Na}^+ + \text{OH}^- \)). Bases produce \( \text{OH}^- \) ions, and strong bases dissociate completely. Since \( \text{NaOH} \) produces \( \text{OH}^- \) and has a high pH (12, basic), it is a strong base.

1. Analyze the options:

• Option 1: "The negative log of the concentration of \( \text{OH}^- \) ions is 2. Sodium hydroxide is a strong base." matches our calculations (pOH = 2, strong base).
• Option 2: Claims \( \text{pOH}=12 \) (incorrect, pOH is 2) and calls \( \text{NaOH} \) a strong acid (incorrect, it's a base).
• Option 3: Claims \( \text{pOH}=12 \) (incorrect).
• Option 4: Calls \( \text{NaOH} \) a strong acid (incorrect, it's a base).

Answer:

The negative log of the concentration of \( \text{OH}^- \) ions is 2. Sodium hydroxide is a strong base.