Estimation of Hydrogen Peroxide via Iodometry

Vocabulary based flashcards covering the chemicals, reactions, procedures, and safety notes for the iodometric estimation of hydrogen peroxide.

Iodometry analysis

A method used to measure the presence of hydrogen peroxide ($H_2O_2$) through titration of liberated iodine with thiosulfate.

Reaction Step 1 (Oxidation)

$$H_2O_2 + 2 KI + H_2SO_4 \rightarrow I_2 + K_2SO_4 + 2 H_2O$$

Reaction Step 2 (Titration)

$$I_2 + 2 Na_2S_2O_3 \rightarrow Na_2S_4O_6 + 2 NaI$$

Ammonium molybdate Catalyst

In step 1, a catalyst added to the analyte under acidic conditions to facilitate the oxidation of iodide to iodine by $H_2O_2$.

Starch Indicator

An indicator that forms a deep, dark blue complex with minute amounts of triiodide ions in the presence of both Iodine and Iodide.

Pale yellow color

The color reached in the final stages of titration at which point the starch indicator should be added.

Permanent binding error

The reason starch should not be added early in the titration, as it can bind permanently with some iodine/iodide species and affect accuracy.

Potassium Iodide ($KI$) Molar Weight

$$166.0028\,g/mol$$

Ammonium Molybdate ($(NH_4)_6Mo_7O_{24} \cdot 4H_2O$) Molar Weight

$1163.9\,g/mol$ (standard) or $1235.86\,g/mol$ (tetrahydrate)

Sulfuric Acid ($H_2SO_4$) Molar Weight

$$98.079\,g/mol$$

Sodium Thiosulfate ($Na_2S_2O_3$) Molar Weight

$158.11\,g/mol$ (anhydrous) or $248.18\,g/mol$ (pentahydrate)

Potassium iodide solution (2 wt%) prep

Dissolve $2.0\,grams$ $KI$ into $100\,mLs$ demineralized water; store capped away from light.

Air oxidation of $KI$

Indicated by a yellow-orange tint in the solution, which can be removed by adding 1-2 drops of dilute sodium thiosulfate.

Ammonium molybdate solution prep

Dissolve $9\,grams$ ammonium molybdate in $10\,mLs$ $6N\,NH_4OH$, add $24\,grams\,NH_4NO_3$, and dilute to $100\,mLs$.

Iodometry Resolution Limit

Yields good resolution for peroxide amounts above $\sim 10\,\mu mol$.

Ammonium paramolybdate Safety

Harmful if swallowed or inhaled; causes irritation to the eyes, skin, and respiratory tract.

Stoichiometric Calculation for $H_2O_2$

$$n(H_2O_2) = \frac{1}{2} \times V(Na_2S_2O_3) \times c(Na_2S_2O_3)$$