A 1.0-mL volume of 0.010 M H2SO 3 is added to a mixture of 6 drops of 0.010 M
HIO3, 14 drops of deionized water, and 1 drop of starch solution. A color change in the reaction mixture occurred after
56 seconds.
a. Assuming 20 drops per milliliter for all solutions, determine the initial molar concentration of HIO3 after the mixing
but before any reaction occurs (at time = 0). Hint: Units are .
b. The rate of the reaction is measured by the disappearance of HIO3. For the reaction mixture in this question, what is
the reaction rate? Express the reaction rate in units of to the correct number of significant figures
a. To determine the initial molar concentration of HIO3, we need to calculate the amount of solution added in drops and convert it to milliliters.
The total volume of the mixture is 6 drops HIO3 + 14 drops water + 1 drop starch solution = 21 drops.
Since there are 20 drops per milliliter, the total volume of the mixture is 21 drops / 20 drops/mL = 1.05 mL.
Since we added 1.0 mL of the H2SO3 solution, the initial volume of HIO3 is 1.05 mL - 1.0 mL = 0.05 mL.
Now we can calculate the initial molar concentration of HIO3 using the formula:
Initial molar concentration (M) = amount (mol) / volume (L)
Since the amount is not given directly, we need to calculate it using the relationship:
amount (mol) = volume (L) x concentration (M)
The volume in liters is 0.05 mL / 1000 mL/L = 0.00005 L.
The concentration of the H2SO3 solution is 0.010 M.
Therefore, the initial molar concentration of HIO3 is:
Initial molar concentration (M) = 0.00005 L x 0.010 M / 0.05 L = 0.00001 M
b. The reaction rate can be determined by the change in concentration of HIO3 over time. In this case, the HIO3 concentration decreases from the initial concentration to zero (as it is completely used up in the reaction).
The reaction rate is defined as the change in concentration of a reactant or product per unit time. In this case, the reactant HIO3 is disappearing, so the reaction rate is the negative of its change in concentration over time:
Reaction rate = - (concentration change of HIO3) / time
The concentration change of HIO3 is the initial concentration minus the final concentration, since it is completely used up in the reaction.
The final concentration of HIO3 is zero, as it is completely used up.
The time is given as 56 seconds.
Therefore, the reaction rate is:
Reaction rate = - (0.00001 M - 0 M) / 56 s = -0.00001 M / 56 s = -1.79 x 10^-7 M/s (rounded to the correct number of significant figures)