A solution of I2 was standardized with ascorbic acid. Using a .1000 g sample of pure ascorbic acid, 25.32 mL of I2 were required to reach the starch end point. A. What is the molarity of the iodine solution? B. What is the titer of the iodine solution?
To find the molarity of the iodine solution and titer, we need to use the equation:
Molarity (M) = (moles of solute) / (volume of solution in liters) ----(1)
Titer = volume of iodine solution used in the titration
First, we need to find the moles of ascorbic acid (solute).
A. Calculation of moles of ascorbic acid:
Given:
Mass of ascorbic acid (solute) = 0.1000 g (grams)
Using the molecular formula of ascorbic acid (C6H8O6), we can find the molar mass:
C = 6 * 12.01 g/mol
H = 8 * 1.01 g/mol
O = 6 * 16.00 g/mol
Molar mass of ascorbic acid = (6 * 12.01) + (8 * 1.01) + (6 * 16.00) g/mol
Now, we can calculate the moles of ascorbic acid using the given mass, molar mass, and the equation:
moles of ascorbic acid = (mass of ascorbic acid) / (molar mass of ascorbic acid)
moles of ascorbic acid = 0.1000 g / (C6H8O6 molar mass)
B. Calculation of Molarity of Iodine Solution:
Using the stoichiometry of the reaction, we know that 1 mole of ascorbic acid reacts with 1 mole of iodine (I2).
Therefore, moles of iodine (I2) = moles of ascorbic acid
Now, we need to find the volume of the iodine solution in liters.
Given:
Volume of iodine solution used = 25.32 mL
Volume of iodine solution used (in L) = 25.32 mL / 1000 mL/L
Now, we can calculate the molarity of the iodine solution using the moles of iodine and the volume:
Molarity of iodine solution (I2) = (moles of iodine) / (volume of iodine solution used in L)
B. Calculation of Titer of Iodine Solution:
Titer = volume of iodine solution used in the titration
Given:
Volume of iodine solution used = 25.32 mL
Therefore, the titer of the iodine solution is 25.32 mL.
Please note that the titer is a measure of the concentration of the iodine solution. It represents the volume of the solution required to react completely with a known amount of the substance being titrated (ascorbic acid in this case).
To find the molarity of the iodine solution, we can use the equation:
M1V1 = M2V2
Where:
M1 = Molarity of the iodine solution
V1 = Volume of the iodine solution (in liters)
M2 = Molarity of the ascorbic acid solution
V2 = Volume of the ascorbic acid solution (in liters)
In this case, we know the values of V1 (25.32 mL = 0.02532 L), V2 (0.1000 g), and M2 (unknown). We need to solve for M1.
To find the molarity of the ascorbic acid solution (M2), we can use the equation:
M = n/V
Where:
M = Molarity of the ascorbic acid solution
n = Number of moles of ascorbic acid
V = Volume of the ascorbic acid solution (in liters)
To find the number of moles of ascorbic acid (n), we can use the equation:
n = m/MW
Where:
m = Mass of ascorbic acid (in grams)
MW = Molecular weight of ascorbic acid
The molecular weight of ascorbic acid is 176.12 g/mol.
Let's calculate the number of moles of ascorbic acid (n):
n = 0.1000 g / 176.12 g/mol
n ≈ 0.000568 mol
Now, let's substitute the values into the equation for M2:
M2 = n / V
M2 = 0.000568 mol / 0.02532 L
M2 ≈ 0.0224 M
Now, let's substitute the known values into the equation M1V1 = M2V2 and solve for M1:
M1 = (M2 * V2) / V1
M1 = (0.0224 M * 0.02532 L) / 0.02532 L
M1 ≈ 0.0224 M
So, the molarity of the iodine solution (M1) is approximately 0.0224 M.
To find the titer of the iodine solution, we can use the formula:
Titer = Molarity of iodine solution * Volume of iodine solution used
Titer = 0.0224 M * 0.02532 L
Titer ≈ 0.000567 mL
So, the titer of the iodine solution is approximately 0.000567 mL.
M = moles/L.
moles ascorbic acid = grams/molar mass.
Plug in moles and L and solve for M.
The "old" definition (meaning years ago when I was in school) titer was defined as N x milliequivalent weight. As far as I know, IUPAC doesn't recognize equivalent weights or normality now; therefore, I don't know if the definition of titer has changed or not. I looked in two or three modern texts and did not find the term; in fact, I had to go back to an old quant book published in 1952 to find it in the appendix, along with a very good description in the text.