QuestionQuestion

You are given 50 mL or Phosphoric Acid (H3PO4) with unknown concentration.

It is recommended that you determine the molar masses of the acids below before lab and write or type up directions for how to accomplish the following objectives. These directions should be in your lab notebook if written, or printed out if typed. The objectives are NOT necessarily written in the best order for completion.

Determine the mass of the solution.

Determine the density of the solution.

Using 0.5 M NaOH, titrate a 10-mL sample of acid to determine its concentration (molarity). Remember how we did titrations in previous labs. Once your titration is complete to your satisfaction, determine the moles of acid, the concentration of your acid, and the mass of acid in your sample.

Identify your acid as organic or inorganic.

Does it contain any polyatomic ions?

Write a balanced chemical equation for the acid-base reaction of your acid.

Identify if anything in your acid undergoes a redox reaction.

What would be pressure be if the acid in your 10-mL sample was vaporized in a 20 L container at the current room temperature? (Hint, use the ideal gas law.)

If the stock volume used to make up your acid was 0.020 L, and was diluted to 1.00 L of your current (discovered) molarity, what was the molarity prior to dilution?

What would the heat of this acid be when heated from the current room temperature to 35° C, assuming the specific heat is the same as that of water? (Hint, find heat in Joules.)

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H3PO4 + NaOH → NaH2PO4 + Ans:
To determine the unknown concentration of phosphoric acid (H3PO4), its titration will be performed by using standardized sodium hydroxide (NaOH) solution.
H3PO4 is a weak acid with pKa1=2.15, pKa2=7.20 and pKa3=12.35. So it is titrated first against methyl orange indicator changing color around pH 4.7 and secondly against thymolphthalein indicator changing color around pH 9.6.
Depending on the indicator used reaction taking place is either:

H2O…. first end point around pH 4.7 (Methyl orange as an indicator)
or
H3PO4 + 2NaOH → Na2HPO4 + 2H2O …… second end point around pH 9.6 (Thymolphthalein as an indicator)

Step 1: Preparation and standardization of a sodium hydroxide solution (0.1 M).
1. Weigh accurately 1 g of sodium hydroxide and transfer to a volumetric flask of 250 mL, dissolve it in 100 mL of distilled water (carbon dioxide free) and finally make up the volume up to 250 mL....

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