Prepare 100. ml of 0.1 N H2S04 by diluting from original H2S04. Eq. wt. of H,S04 = 98/2=49 . dH2S04= 1.08 Purity =98%

Question

Prepare 100. ml of 0.1 N H2S04 by diluting

from original H2S04.

Eq. wt. of H,S04 = 98/2=49 .

dH2S04= 1.08

Purity =98%

Answer 1

The normality of a solution refers to the concentration of the acid or base component of a solution. In this case, the concentration of the H+ ion after dissolution, which is why the normality here would be double the molarity (H₂SO₄ --> 2H⁺ + SO₄^2- ; notice the 2 H⁺s dissociated for every 1 mole of H₂SO₄).

If the purity of the original H2SO4 is 98%, we can use unit analysis to find our answer. Since 100mL = 0.1L:

Stepwise solution:

1. Since our target volume is 100mL (0.1L) and our target normality is 0.1 N (0.1 mol H+ / Liters solution):
2. 0.1 L x (0.1 mol H⁺ / Liter solution) = 0.01 moles of H+ are needed from stock solution
3. Since equiv. weight says each each 49 grams of H2SO4 imparts 1 mol of ions:
4. 0.01 mol H⁺ x (49 g H₂SO₄ eq. / 1 mol H+) = 0.49 grams of H2SO4 are needed
5. Since the purity (assumed by mass) of the stock H₂SO₄ solution is 98%:
6. 0.49 g H₂SO₄ x (100 g stock / 98 g H₂SO₄) = 0.5 g stock
7. Since the density of H₂SO₄ is 1.08 g/mL (and the stock is mostly H₂SO₄ so its density is approx. the same):
8. 0.5 g stock x (1 mL / 1.08g) ≈ 0.46 mL stock solution needed

Unit analysis continuous solution:

0.1 L x (0.1 mol H+ / Liter solution) x (49 g H₂SO₄ eq. / mol H+) x (100g stock / 98 g H₂SO₄) x (1 mL / 1.08 g) ≈ 0.46 mL stock H₂SO₄ solution

Creating the solution:

1. Obtain a clean, dry 100 mL volumetric flask.
2. Fill approx. 3/4 with deionized water. **This step is a safety measure. Always add acid to water to dilute it immediately, never water to concentrated acid.
3. With gloved hands, prepare a small graduated pipette (markings at least to 0.1 mL, 0.01 preferred) by rinsing the inner walls with stock H₂SO₄ solution (draw up into the pipette using a pipette bulb and release into a waste beaker).
4. Draw up 0.46 mL of the stock solution into the pipette and release it into the volumetric flask, ensuring all acid is dropped into the water. Swirl gently.
5. With a wash bottle, fill the volumetric flask the rest of the way to the 100mL mark.
6. With a gloved hand, cover the opening of the volumetric flask. Swirl gently and invert to mix.
7. Your 0.1N solution is prepared!