Postlab problems A solution of NaOH was standardized by the procedure described

Question

Postlab problems A solution of NaOH was standardized by the procedure described in this laboratory. An average of 32.12mL of the base was required to titrate 10.00mL of 0.3501M HCI standard to a phenolphthalein end point. Calculate the concentration of an unknown H2SO4 solution if 10.00mL of the unknown HSO solution required an average of 39.87mL of the standardized NaOH solution. 1. A solution of NaOH was standardized by the procedure described in this laboratory. An average of 42.12mL of the base was required to titrate 15.00mL of 0.2878M HCI standard to its end point. The base was then used to determine the concentration of an unknown citric acid solution. Citric acid has three acidic protons and can be abbreviated HyCit. Calculate the concentration of the unknown H,Cit solution if 10.00mL of the solution required an average of 46.87mL of the standardized base. (Assume that all three protons in HyCit are titrated in the experiment.) 2.

Explanation / Answer

Q1

mmol of acid = MV = 10*0.3501

mmol of acid = 3.501

then

mmol of base = 3.501

[Base] = mmol/V = 3.501 / 32.12 = 3.501/32.12 = 0.1089 M

Now, after using in in H2SO4

mmol of NaOH =MV = 0.1089*39.87= 4.341843mmol of NaOH

mmol of H2SO4 = 1/2*4.341843= 2.1709 mmol of acid

[H2SO4] = mmol/ V = 2.1709 / 10 = 0.21709 M of H2SO4

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