alculations: . Find the number of moles of NaOH used (Molarity x Liters moles) 9

Question

alculations: . Find the number of moles of NaOH used (Molarity x Liters moles) 9. Find the number of moles of citric acid titrated: Use the mole ratio in the equation in the discussion. If your juice had been diluted, you must include the dilution factor. 10. Find the Molarity of the citric acid (moles citric acid/Liters of juice) 12. Write the equilibrium expression for the ionization of citric acid in water (see equation l) e the Ka in the discussion, and the Molarity of the citric acid to find [H,O'] present in the Use the Ka in the discussion, and the Molarity of the citric acid to find [H,O'] present in uice. 13. Find the pH of the juice. (pH =-log [H30'])

Explanation / Answer

1. Nmber of moles of NaOH used = weight/molar mass;

weight = (Molarity x molar mass x volume )/1000

= (0.5 x 40 x 3.8) / 1000

= 0.076;

Number of moles = weight/molar mass = 0.076/40 = 0.0019 moles

2.Generally citric acid is a molecule with three carboxylic acid functional groups. That means three moles of NaOH are literally required for titrating one citric acid molecule.

So num,ber of moles of citric acid = number of moles of NaOH/3

= 0.0019 / 3

= 0.00063 moles.

3. Molarity of citric acid = number of moles x (1000/volume in ml)

= 0.00063 x (1000/20)

Molarity of citric acid = 0.0315 M

4.

C6H8O7 <======> C6H5O73- + 3H3O+

Ka = [C6H5O73-] x [H3O+]3 / [C6H8O7]

Ka = x4 / 0.0315 = 4.0 x 10-6

x4 = 0.0315 x 4.0 x 10-6

= 1.26 x 10-7

x = [C6H5O73-] = [H3O+] = 0.0188M

5. pH = -log[H3O+] = -log0.0188

= 1.725

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