The equation for the reaction of KHP and NaOH shows a 1:1 ratio for the two reac

Question

The equation for the reaction of KHP and NaOH shows a 1:1 ratio for the two reactants Experimentally, how do you know that the base solution that you delivered from the buret had just as many moles as were in the KHP sample that you weighed out in the beginning of the experiment? What might happen to your calculated NaOH molarity if you use tap water rather than deionized (purified) water to dissolve the KHP crystals or to rinse down the walls of the flask during the titration? (Tap water contains some calcium bicarbonate.) Write and balance the equation for a neutralization of a phosphoric acid solution of unknown concentration by sodium hydroxide. Calculate the molarity of an unknown phosphoric acid solution if a 25.0-mL sample of the acid solution consumes 27.2 mL of 0.138 M NaOH solution in a titration.

Explanation / Answer

2. The function of Phenolphthalein indicator is to inform of the end point of the titration (i.e when the base or alkali has just neutralized the acid or vice versa). The indicator will turn a different colour at this point, so inform you that the titration can be stopped and no more base needs to be added.

3. Molarity of NaOH decreases if we use normal water. Because sodium hydroxide involve in the process of converting CaCO3 to Ca(OH)2

CaCO3+NaOH     à Ca(OH)2+ Na2CO3

4.

H3PO4+ 3KOH   à 3H2O+ K3PO4

(M1V1/n1)H3PO4= (M2V2/n2)KOH

(M1*25/1)H3PO4= (0.138M*27.2/3)KOH

M H3PO4 = 0.05M

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