Calculate the pH of a 25 mL of 5.45 × 10 −2 M LiOH solution.

Calculate the pH of 25 ml's of 5.45 times 10 to the negative 2 molar lithium hydroxide solution. Now, lithium hydroxide represents a strong base, and what we need to see here is that we have both the volume and the concentration of my strong base. But here's the thing, we don't need to use the volume. We only use the volume of this base if it were being titrated with an acid. That volume is just placed there to kind of throw you off. Because it's just a base by itself, we focus on the concentration. Here, when it ionizes completely it breaks up into lithium ion plus 1 hydroxide ion. Here, each of these ions would have the same concentration as the strong base itself. And since there's only 1 hydroxide ion here, it'd just be 5.45 times 10 to the negative 2 molar. So we know the concentration of my hydroxide ion. With that information I can first find pOH. Remember pOH equals negative log of Oh minus, So it's equal to negative log of 5.45 times 10 to the negative 2. When I put that into my calculator I'm gonna get 1.264 as my pOH. Now that we know our pOH we can find our pH, because they're connected together by the fact that pH, plus pOH equals 14. So, here when I subtract pOH from both sides we see that pH equals 14 minuteus pOH. So plug in what we just found for pOH and we'll have our answer. So, 14 minus 1.264 gives me 12.736 as the pH for this very strong base. It's a pretty concentrated strong base, so we'd expect the pH to be pretty high.

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10. Acids and Bases

pH of Strong Acids and Bases

GOB Chemistry

10. Acids and Bases

pH of Strong Acids and Bases

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Multiple Choice

Calculate the pH of a 25 mL of 5.45 × 10⁻² M LiOH solution.

1.264

12.736

0.338

11.134

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Verified step by step guidance

Identify that LiOH is a strong base, which means it dissociates completely in water to produce OH⁻ ions.

Calculate the concentration of OH⁻ ions in the solution. Since LiOH dissociates completely, the concentration of OH⁻ ions is the same as the concentration of LiOH, which is 5.45 × 10⁻² M.

Use the formula for pOH: \( \text{pOH} = -\log[\text{OH}^-] \) to find the pOH of the solution.

Convert the pOH to pH using the relationship: \( \text{pH} + \text{pOH} = 14 \). Solve for pH.

Ensure the final pH value is reasonable for a basic solution, which should be greater than 7.