2. A 0.1967 g sample of pure ascorbic acid is weighed out and dissolved in 50.0 mL of distilled water in an

Erlenmeyer flask. One week later, when about one third of the water in the flask has evaporated, this
solution is titrated against 0.01735 M KIO3 solution and requires 18.75 mL of it to reach the end point.

(a) What mass of ascorbic acid has been oxidized by the air over the weeklong waiting period?

(b) Has the concentration of the ascorbic acid solution increased or decreased as a result of the
evaporation? Show calculations to support your answer. Hint: Remember that oxidation has
occurred as well as solution evaporation.

(a) Well, it seems like the air had quite an appetite for ascorbic acid over the week! To find out the mass of ascorbic acid oxidized, we first need to figure out how much ascorbic acid was initially present.

We know that the mass of the sample before evaporation was 0.1967 g. Assuming no ascorbic acid was lost during evaporation, this is also the mass of ascorbic acid present after evaporation.

Now, we need to calculate the mass of ascorbic acid that reacted with the air. To do this, we can use the balanced chemical equation for the oxidation of ascorbic acid:

C6H8O6 + I2 = C6H6O6 + 2HI

From the equation, we can see that 1 mole of ascorbic acid is oxidized to form 1 mole of dehydroascorbic acid (C6H6O6). The molar mass of ascorbic acid is approximately 176.12 g/mol.

First, let's find moles of ascorbic acid used in the reaction:

Moles of ascorbic acid = Mass / Molar mass
= 0.1967 g / 176.12 g/mol

Now, since the reaction is 1:1, the moles of ascorbic acid oxidized are the same as the moles of dehydroascorbic acid formed.

Finally, calculate the mass of ascorbic acid oxidized by multiplying the moles of ascorbic acid oxidized by its molar mass.

Mass of ascorbic acid oxidized = Moles of ascorbic acid oxidized x Molar mass of ascorbic acid
= Moles of ascorbic acid x 176.12 g/mol

(b) Ah, the concentration conundrum! To determine if the concentration of ascorbic acid solution increased or decreased, we need to consider the changes in volume and moles of ascorbic acid before and after the evaporation.

Initially, the solution had a volume of 50.0 mL. After one-third of the water evaporated, the volume decreased to (2/3)*50.0 mL.

The moles of ascorbic acid present before evaporation can be calculated using the formula:

Moles of ascorbic acid = (Mass of ascorbic acid) / (Molar mass of ascorbic acid)

However, during the weeklong waiting period, some ascorbic acid got oxidized, so we have to account for this in our calculations. We already know the mass of ascorbic acid oxidized, so we can calculate the moles of ascorbic acid oxidized using:

Moles of ascorbic acid oxidized = (Mass of ascorbic acid oxidized) / (Molar mass of ascorbic acid)

The moles of ascorbic acid after evaporation and oxidation can be found by subtracting the moles oxidized from the moles initially present.

Now, to calculate the new concentration of the ascorbic acid solution, we use the formula:

Concentration = (moles of ascorbic acid after evaporation and oxidation) / (volume of solution after evaporation)

Compare this concentration with the initial concentration to determine if it increased or decreased.

To solve this problem, we can use the concept of stoichiometry and the balanced chemical equation for the reaction between ascorbic acid (C6H8O6) and KIO3.

First, let's calculate the number of moles of KIO3 used in the titration:

Moles of KIO3 = Volume of KIO3 solution (in L) x Molarity of KIO3 solution
= 0.01875 L x 0.01735 mol/L
= 0.00032456 mol KIO3

Now, let's determine the balanced chemical equation for the reaction between ascorbic acid (C6H8O6) and KIO3:

C6H8O6 + 6I- + 6H+ → C6H6O6 + 3I2 + 3H2O

From the balanced equation, we can see that one mole of ascorbic acid (C6H8O6) reacts with 1 mole of KIO3.

Therefore, the number of moles of ascorbic acid oxidized is also 0.00032456 mol.

(a) To calculate the mass of ascorbic acid oxidized, we need to use the molar mass of ascorbic acid:

Molar mass of ascorbic acid (C6H8O6) = (6 x 12.01 g/mol) + (8 x 1.008 g/mol) + (6 x 16.00 g/mol)
= 176.12 g/mol

Mass of ascorbic acid oxidized = Number of moles of ascorbic acid oxidized x Molar mass of ascorbic acid
= 0.00032456 mol x 176.12 g/mol
= 0.05711 g

Therefore, approximately 0.0571 g of ascorbic acid has been oxidized by the air over the weeklong waiting period.

(b) To determine whether the concentration of the ascorbic acid solution has increased or decreased, we need to consider the change in volume and the stoichiometry of the reaction.

The original volume of the solution was 50.0 mL (or 0.0500 L). Since about one-third of the water in the flask has evaporated, we have 2/3 of the original volume remaining.

Remaining volume of the solution = (2/3) x 0.0500 L
= 0.0333 L

Since the volume of ascorbic acid solution has decreased, the concentration of the solution has increased.

To calculate the new concentration, we need to use the number of moles of ascorbic acid that remained after oxidation:

Moles of ascorbic acid remaining = Moles of ascorbic acid - Moles of ascorbic acid oxidized
= 0.00032456 mol - 0.00032456 mol
= 0 mol

However, since no ascorbic acid remains, the concentration of the ascorbic acid solution is now 0 mol/L (or 0 M).

In conclusion, the concentration of the ascorbic acid solution has decreased to 0 M as a result of both oxidation and solution evaporation.

To solve this problem, we need to follow a step-by-step approach. Let's start with part (a).

(a) To calculate the mass of ascorbic acid oxidized over the weeklong waiting period, we need to first determine the number of moles of KIO3 that reacted with the ascorbic acid. Then, we can use the stoichiometry of the reaction between ascorbic acid (C6H8O6) and KIO3 (potassium iodate) to find the number of moles of ascorbic acid oxidized.

1. Calculate the number of moles of KIO3 used in the titration:
- Volume of KIO3 solution used = 18.75 mL (given)
- Concentration of KIO3 solution = 0.01735 M (given)
- Convert mL to L: 18.75 mL * (1 L / 1000 mL) = 0.01875 L
- Calculate moles of KIO3: moles = volume (L) * concentration (M)
moles of KIO3 = 0.01875 L * 0.01735 M = 0.000325 mol

2. Determine the stoichiometry of the reaction between ascorbic acid and KIO3:
The reaction between ascorbic acid and KIO3 is as follows:
3 C6H8O6 + KIO3 → 3 C6H6O6 + 3 I2 + 3 H2O
From the balanced equation, we see that it takes 3 moles of ascorbic acid (C6H8O6) to react with 1 mole of KIO3.

3. Calculate the number of moles of ascorbic acid oxidized:
Since the ratio of ascorbic acid to KIO3 is 3:1, the moles of ascorbic acid oxidized will be three times the moles of KIO3 used.
moles of ascorbic acid oxidized = 3 * moles of KIO3 = 3 * 0.000325 mol = 0.000975 mol

4. Calculate the mass of ascorbic acid oxidized:
- Formula mass of ascorbic acid (C6H8O6) = 176.12 g/mol
- Calculate the mass of ascorbic acid oxidized: mass = moles * formula mass
mass of ascorbic acid oxidized = 0.000975 mol * 176.12 g/mol = 0.1713 g

Therefore, approximately 0.1713 g of ascorbic acid has been oxidized over the weeklong waiting period.

Moving on to part (b),

To determine whether the concentration of the ascorbic acid solution has increased or decreased as a result of evaporation, we need to consider the change in the number of moles of ascorbic acid due to both oxidation and evaporation.

1. Calculate the original moles of ascorbic acid:
- Mass of ascorbic acid weighed out = 0.1967 g (given)
- Formula mass of ascorbic acid (C6H8O6) = 176.12 g/mol
- Calculate the moles of ascorbic acid: moles = mass / formula mass
moles of ascorbic acid = 0.1967 g / 176.12 g/mol = 0.001115 mol

2. Calculate the final moles of ascorbic acid after oxidation and evaporation:
- As determined in part (a), 0.000975 mol of ascorbic acid was oxidized.
- Since one-third of the water evaporated, the final volume of the solution is (1 - 1/3) * 50.0 mL = 33.3 mL.
- Convert mL to L: 33.3 mL * (1 L / 1000 mL) = 0.0333 L
- Calculate the new concentration of the ascorbic acid solution: concentration = moles / volume
new concentration of ascorbic acid = (0.001115 mol - 0.000975 mol) / 0.0333 L = 0.004209 M

The concentration of the ascorbic acid solution has increased as a result of evaporation and oxidation. It is now approximately 0.004209 M.

Remember to double-check the calculations and units of measurement.