Vitamin C ascorbic acid (C6F1806), is a reducing agent. One way to determine the ascorbic acid content of a sample is to mix the acid with an excess of iodine C6H8O6 + I2 + H2O C6H6O6 + 2H3O + 2I-
and then titrate the iodine that did not react with the ascorbic acid with sodium thiosulfate. The balanced, net ionic equation for the reaction occurring in this titration is
I2+ 2 S2O32-(a9) —) 2 I-(a9) + S4O62-(a9)
Suppose 50.00 mL of 0.0520 M 12 was added to the sample containing ascorbic acid. After the ascorbic acid/I2 reaction was complete, the 12 not used in this reaction required 20.30 mL of 0.196 M Na2S2O3 for titration to the equivalence point. Calculate the mass of ascorbic acid in the unknown sample.

The mass of ascorbic acid in the sample is 0.1076g

Explanation:

In other words to determine ascorbic acid in a sample:

You are adding an amount of I₂. One part is reacting with ascorbic acid and the other with sodium thiosulphate. First, we need to calculate how much thiosulphate reacts to know the iodine that reacts with thiosulphate.

I₂ that reacts with S₂O₃²⁻:

Moles S₂O₃⁻: 0.02030L × (0.196mol / L) = 3.979x10⁻³ moles S₂O₃²⁻.

As 2 moles of S₂O₃²⁻ reacts per moles of I₂, moles of I₂ are:

3.979x10⁻³ moles S₂O₃²⁻ ₓ (1 mole I₂ / 2 moles S₂O₃²⁻) = 1.989x10⁻³ moles I₂

Now, initial amount of I₂ added to the sample is:

0.0500L ₓ (0.0520mol I₂ / L) = 2.600x10⁻³ moles I₂

That means moles of I₂ that react with ascorbic acid = Moles of ascorbic acid are:

2.600x10⁻³ moles I₂ - 1.989x10⁻³ moles I₂ =

6.11x10⁻⁴ moles I₂ = Moles C₆H₈O₆.

To convert moles of substance to mass we need to use molar mass of the substance (176.12g/mol for ascorbic acid):

6.11x10⁻⁴ moles C₆H₈O₆ ₓ (176.12g / mol) =

most historians agree that gabriel mouton, the vicar of st. paul’s church in lyons, france, is the “founding father” of the metric system. he proposed a decimal system of measurement in 1670. mouton based it on the length of one minute of arc of a great circle of the earth (now called a nautical mile, 1852 meters). he also proposed the swing-length of a pendulum with a frequency of one beat per second as the unit of length (about 25 cm). a pendulum beating with this length would have been fairly easy to produce, thus facilitating the widespread distribution of uniform standards. over the years, his work was revised, improved, and extended by a number of french scientists.

the political sponsor of weights and measures reform in the french revolutionary national assembly was the bishop of autun, better known as talleyrand. under his auspices, the french academy appointed several committees to carry out the work of developing a usable system of weights and measures for france. one of the committees recommended a decimalized measurement system based upon a length equal to one ten-millionth of the length of a quadrant of the earth’s meridian (i.e., one ten-millionth of the distance between the equator and the north pole).

it is stable as it is in group 0 which have full outer shells of electrons