Ascorbic acid (vitamin C) is a diprotic acid having the formula H2C6H6O6. A sample of a vitamin supplement was analyzed by titrating a 0.2894 g sample dissolved in water with 0.0215 M NaOH. A volume of 10.83 mL of the base was required to completely neutralize the ascorbic acid. What was the percentage by mass of ascorbic acid in the sample?
______________% ascorbic acid
1. Write the equation and balance it.
2. moles NaOH = M x L = ?
3. Using the coefficients in the balanced equation, convert moles NaOH to moles ascorbic acid.
4. moles asc acid x molar mass asc acid = grams ascorbic acid.
5. %ascorbic acid = (grams ascorbic acid/mass sample)*100 = ?
Suppose 15.0 mL of 0.315 M NH4Cl is combined with 10.0 mL of 0.430 M (NH4)3PO4. Assume the volumes are additive, and no chemical reaction takes place. What is the total cocentration of ammonium ions in this mixture?
9.33 * 10^22 ions NH4
4M
To find the percentage by mass of ascorbic acid in the sample, you need to determine the moles of ascorbic acid and calculate its mass as a percentage of the total sample mass.
First, let's calculate the moles of NaOH used in the titration:
moles of NaOH = concentration of NaOH (mol/L) x volume of NaOH (L)
moles of NaOH = 0.0215 mol/L x 0.01083 L
Next, let's determine the moles of ascorbic acid that reacted with the NaOH. Since ascorbic acid is diprotic, it can donate two moles of H+ ions per molecule, meaning that each mole of ascorbic acid reacts with two moles of NaOH:
moles of ascorbic acid = 2 x moles of NaOH
Now, let's calculate the molar mass of ascorbic acid:
molar mass of ascorbic acid (H2C6H6O6) =
2 x atomic mass of hydrogen (H) + 6 x atomic mass of carbon (C) + 6 x atomic mass of oxygen (O)
molar mass of ascorbic acid = (2 x 1.008 g/mol) + (6 x 12.01 g/mol) + (6 x 16.00 g/mol)
Finally, let's calculate the percentage by mass of ascorbic acid in the sample:
mass percentage of ascorbic acid = (moles of ascorbic acid x molar mass of ascorbic acid) / mass of sample x 100%
mass of sample = 0.2894 g
Putting it all together, we have:
moles of ascorbic acid = 2 x (0.0215 mol/L x 0.01083 L)
molar mass of ascorbic acid = (2 x 1.008 g/mol) + (6 x 12.01 g/mol) + (6 x 16.00 g/mol)
mass percentage of ascorbic acid = (moles of ascorbic acid x molar mass of ascorbic acid) / mass of sample x 100%
Solve these equations to find the answer.