提出了一种滴定强酸性含Ｆｅ３＋及Ｆｅ２＋体系中游离酸（其游离酸浓度＞１ｍｏｌ／Ｌ）的新方法。实验证明，将Ｋ２Ｃ２Ｏ４作为掩蔽剂时，利用过量的ＫＩＯ３与过量的Ｎａ２Ｓ２Ｏ３在酸性溶液中的氧化还原反应可以测定体系中的游离酸。当体系中存在Ｆｅ２＋时，可利用ＫＭｎＯ４（在强酸性下）或Ｈ２Ｏ２（在弱酸性下）的预氧化来消除Ｆｅ２＋的干扰。在加入过量的Ｋ２Ｃ２Ｏ４（Ｃ２Ｏ４２－与Ｆｅ３＋的摩尔比值为３０）和过量的ＫＩＯ３及Ｎａ２Ｓ２Ｏ３的条件下，其化学反应可以在３０ｍｉｎ内完成。采用Ｉ２回滴法测定游离酸，测试结果的精密度高，测定结果的相对偏差小于３％ A new method for titration of free acid (its free acid concentration> 1 mol / L) in strong acidic Fe3 + and Fe2 + -containing systems was proposed. Experiments show that K2C2O4 as a masking agent, the use of excess KIO3 and excess Na2S2O3 in acidic solution redox reaction can be measured free acid in the system. When Fe2 + is present in the system, the interference of Fe2 + can be eliminated by pre-oxidation of KMnO4 (under strongly acidic conditions) or H2O2 (under weakly acidic conditions). The chemical reaction can be completed in 30 min with an excess of K2C2O4 (molar ratio of C2O42- to Fe3 + of 30) and excess of KIO3 and Na2S2O3. I2 back drop method for the determination of free acid, the test results of high precision, the relative deviation of the measurement results is less than 3%