Calculate the number of moles of hydrogen peroxide that has reacted: Note: You w

Question

Calculate the number of moles of hydrogen peroxide that has reacted:  Note:  You will need to use stoichiometry to determine this.

Calculate the change in concentration of hydrogen peroxide in each case, i.e., moles of H2O2 reacted per litre of solution.  Hint:   Recall the total volume, and you have calculated the number of moles that reacted, previously.

Calculate the rate of the reaction, which is simply the change in concentration of H2O2 (calculated above) divided by the time it took for the reaction to complete.  i.e., the numbers of moles per litre of peroxide consumed divided by the number of seconds required to react completely.

The following chart will be helpful as a checklist for the preparation of the solutions which will be used in this experiment: Use pipettes to measure the buffer, Na2S203 and the H202 solutions. Use a burette to measure the KI solution and a graduated cylinder for the distilled water. Use the graduated dropper provided to measure the starch. 0.0200 0.1 M Distilled stilledbuffer 0.300 M starch H202 sol'n H2o mL 164.5 162 158 148 128 (mL) KI (mL) (mL)Na,s,O, (mL) Na2S20; (mL) 10 10 10 10 10 10 10 10 20 40 3.5 10 10 10 10 10 Note that the total volume in each case is 200 mL.

Explanation / Answer

The reaction will be

Na2S2O3(aq) + 4H2O2(aq) Na2SO4(aq) + H2SO4(aq) + 3H2O(l)

The above reaction is the balance reaction for the given problem.

So as per the stoichiometry 1 mole of Na2S2O3 will react with 4 moles of H2O2

Moles of  Na2S2O3   molarity X volume = 0.02 X 10 = .2 millimoles

Moles of H2O2 present = 0.1X 10 = 1 millimoles

So moles of H2O2 react will be: 4 X .2 millimoles = 0.8 millimoles

So change in concentration = 1-0.8 / volume = 0.2 / 200 = 0.001 M

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