16.6
滴定计算：强酸 - 强碱
计算滴定溶液的 pH 值：强酸 / 强碱
对 25.00 mL 0.100 M HCL (强酸) 和 0.100 M 的强碱 NaOH 进行滴定。 添加碱溶液的不同体积的 pH 值可按以下公式计算：
(A) 滴液体积 = 0 mL。 溶液 pH 值是由 HCl 的酸电离引起的。 因为这是一个强酸，电…
当用强碱滴定强酸或反过来滴定时，整个滴定过程中的 pH 值 可通过测定剩余的水合氢离子 或氢氧化物离子的浓度来计算。例如，50 毫升 0.10M 的盐酸 分解成 0.10M 的水合氢离子和氯离子，初始 pH 值为 1。如果加入 25 毫升的 0.10M 氢氧化钠，新的水合氢离子浓度可以 通过从水合氢离子的总摩尔数中减去 氢氧化物离子的总摩尔数 并除以总体积来计算—75 毫升或 0.075 升。50 毫升 0.10M 的盐酸含有 0.0050 摩尔的水合氢离子，而 25 毫升 0.10M 的 氢氧化钠含有 0.0025 摩尔的氢氧化物离子。将这些值代入方程式，得到水合氢离子的浓度等于 0.033M。因此，溶液的 pH 值上升到 1.48。如果继续添加氢氧化钠 至 50 毫升，则盐酸中 的所有水合氢离子 均被中和，达到等值点，此时 pH 值上升至 7。在等值点以上，溶液的 pH 值 由氢氧化物离子决定，因为盐酸已被完全中和。如果向溶液中加入 70 毫升含有 0.0070M 氢氧化物离子的氢氧化钠溶液，氢氧化物离子的最终浓度可以 通过从氢氧化物离子的总摩尔数中减去 水合氢离子的初始摩尔数并除以 溶液的总体积来确定。由于最终的氢氧化物离子浓度为 0.017M，溶液的 pOH 和 pH 值分别等于 1.78 和 12.22。
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Q1: How do you calculate pH before any base is added to a strong acid?
For a strong acid like hydrochloric acid, complete ionization occurs, so the hydronium ion concentration equals the acid's molarity. For example, 0.10 M HCl produces 0.10 M hydronium ions, giving a pH of 1.0. Simply use pH = -log[H+] to find the initial pH of the solution.
Q2: What happens to pH when you add base before reaching the equivalence point?
Before the equivalence point, excess acid remains in solution. Calculate the moles of hydronium ions remaining by subtracting moles of added hydroxide from initial moles of hydronium, then divide by total volume. For instance, adding 25 mL of 0.10 M NaOH to 50 mL of 0.10 M HCl leaves 0.0025 moles of hydronium in 75 mL, yielding pH 1.48.
Q3: What is the pH at the equivalence point for a strong acid-strong base titration?
At the equivalence point, all hydronium ions from the acid are neutralized by hydroxide ions from the base, producing only water and salt. Neither the cation nor anion undergoes acid-base ionization, so only water autoprotolysis generates hydronium ions. The pH equals 7.0, making the solution neutral.
Q4: How do you determine pH after adding excess base past the equivalence point?
Beyond the equivalence point, all acid is consumed and pH is determined by excess hydroxide ions. Calculate the moles of hydroxide remaining by subtracting initial moles of hydronium from total moles of hydroxide, then divide by total volume. Use pOH = -log[OH-] and pH = 14 - pOH to find the final pH.
Q5: Why does pH change more dramatically near the equivalence point in strong acid-strong base titrations?
Near the equivalence point, small additions of base cause large changes in hydronium ion concentration because the buffer capacity is minimal. Before the equivalence point, excess acid resists pH change, but as the equivalence point approaches, nearly all acid is consumed, making the solution sensitive to small base additions.
Q6: What is the relationship between moles of acid and moles of base at the equivalence point?
At the equivalence point, the moles of hydronium ions from the acid equal the moles of hydroxide ions from the base. For monoprotic strong acid and strong base, this means the moles of acid and base are equal. Using the equation moles = molarity × volume, you can determine the volume of titrant needed to reach equivalence.
Q7: How does the volume of titrant added affect the total volume used in pH calculations?
The total volume in pH calculations includes both the initial acid solution and all added base titrant. For example, adding 25 mL of base to 50 mL of acid gives a total volume of 75 mL. This dilution effect is critical because it reduces the concentration of remaining hydronium or excess hydroxide ions, directly affecting the calculated pH.