Chemistry

posted by .

"An aqueous sodium borate solution is titrated to the second endpoint with 0.225 mol/l nitric acid in the presence of a suitable indicator. If an average of 12.6mL of titrant are required to reach the second endpoint for a 25.0 mL sample, what is the base concentration?"

My calculations:

nHNO3: (0.225 mol/l)(12.6 mL)/1000
= 2.835 x 10^-3 mol

nNa3BO3: (2.835 x 10^-3 mol)(1/3)
= 9.45 x 10^-4 mol

[Na3BO3]: (9.45 x 10^-4 mol)/(25 mL)(1000)
= 0.0378 mol/L

Is this correct? Because the answer given is different (0.0567 mol/L).

  • Chemistry -

    nHNO3: (0.225 mol/l)(12.6 mL)/1000
    = 2.835 x 10^-3 mol
    This step is ok.

    nNa3BO3: (2.835 x 10^-3 mol)(1/3)
    = 9.45 x 10^-4 mol
    This step is in error. The problem says that Na3BO3 was titrated to the second end point (meaning two H ions were added) but you divided by 3. You should have divided by 2

    [Na3BO3]: (9.45 x 10^-4 mol)/(25 mL)(1000)
    = 0.0378 mol/L

    Is this correct? Because the answer given is different (0.0567 mol/L).
    Another way to approach the problem is to say if 12.6 mL were used to add 2 Hs, then 6.3 would have been used to add 1 H, then go through the remainder of the calculation. I think the answer of 0.0567 M is correct.

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. chemistry

    If 0.1200g of sodium carbonate is dissolved in 50 mL of water and titrated with 0.1000 M HCl, how many mL of HCl will be required to reach the second endpoint?
  2. chemistry(Urgent Please help)

    A student is asked to standardize a solution of barium hydroxide. He weighs out 0.945 g potassium hydrogen phthalate (KHC8H4O4, treat this as a monoprotic acid). It requires 33.9 mL of barium hydroxide to reach the endpoint. A. What …
  3. Chemistry

    A student has 100.0 mL of an unknown solution of Vitamin C. She removes 1.00 mL of this solution, dilutes it to 50.0 mL, and titrates this second solution with an iodine solution that is 8.5 × 10-4 M. 6.60 mL of iodine solution is …
  4. chemistry

    A nitric acid solution of unknown concentration is used to titrate 0.771g of sodium tyrosinate (NaC9H10NO3). If the endpoint is reached when 32.79mL of nitric acid has been added, what is the concentration of the unknown nitric acid …
  5. chemistry

    an aqueous solution solution of sodium borate is sometimes used to to fire-proof wood. a. what is the molarity of 2.50 L of solution that contains 1.85 moles of sodium borate?
  6. Chemistry

    A 5.00-mL sample of a sulfuric acid solution of unknown concentration is titrated with a 0.1401 M Sodium Hydroxide solution. A volume of 5.99 mL of the base was required to reach the endpoint. What is the concentration of the unknown …
  7. Chemistry

    A 10.00mL sample of 0.02141mol/L potassium iodate was treated with excess iodide ion and titrated with sodium thiosulfate. If 32.33 mL of a Na2S2O3 solution was requried to reach the colorless endpoint (after addition of starch indicator) …
  8. Chemistry

    A solid weak acid is weighed, dissolved in water and diluted to exactly 50.00 ml. 25.00 ml of the solution is taken out and is titrated to a neutral endpoint with 0.10 M NaOH. The titrated portion is then mixed with the remaining untitrated …
  9. general chemistry

    a solution of sulfuric acid was titrated with sodium hydroxide. if you took 23.7 mL of .025 M NaOH to reach the endpoint with a 5.0 mL sample of the acid what was its concentration?
  10. Chemistry

    A 0.1818 g sample of sodium oxalate required 28.12 ml of a potassium permanganate solution to reach the endpoint (assume the reaction was carried out in excess acid). A 5.000 g sample of tin (II) sulfate containing potassium sulfate …

More Similar Questions