   Chapter 4, Problem 72PS

Chapter
Section
Textbook Problem

Potassium hydrogen phthalate, KHCgH4O4, is used to standardize solutions of bases. The acidic anion reacts with strong bases according to the following net ionic equation:HCgH4O4–(aq) + OH–(aq) → CgH4O42–(aq) + H2O(l)If a 0.902-g sample of potassium hydrogen phthalate is dissolved in water and titrated to the equivalence point with 26.45 mL of NaOH(aq), what is the molar concentration of the NaOH?

Interpretation Introduction

Interpretation:

The molar concentration of NaOH required to titrate with 0.902g sample of Potassium hydrogen phthalate,KHC8H4O4 should be determined.

Concept introduction:

Numberofmole=GivenmassofthesubstanceMolarmass

• The molar mass of an element or compound is the mass in grams of 1 mole of that substance, and it is expressed in the unit of grams per mol (g/mol).
• Concentration of solutions can be expressed in various terms; molarity is one such concentration expressing term.
• Molarity (M) of a solution is the number of gram moles of a solute present in one liter of the solution.

Molarity=MassperlitreMolecular mass

• A solution containing one gram mole or 0.1 gram of solute per litre of solution is called molar solution.
• For chemical reaction balanced chemical reaction equation written in accordance with the Law of conservation of mass.
• Law of conservation of mass states that for a reaction total mass of the reactant and product must be equal.
• Stoichiometric factor is a relationship between reactant and product which is obtained from the balanced chemical equation for a particular reaction.
• Concentrationofsubstance=Amountof substancevolumeofthesubstance
Explanation

Balanced chemical equation for the given reaction is,

HC8H4O4(aq)+OH(aq)C8H4O4(aq)2+H2O(l)

The amount (moles) of KHC8H4O4 available can be calculated as follows,

0.902gKHC8H4O4×1molKHC8H4O4204.44g=0.004412molKHC8H4O4

The balanced equation for the reaction shows that 1mol of KHC8H4O4  requires 1mol of NaOH.  This is the required stoichiometric factor to obtain the amount of NaOH present.

Thus the amount of NaOH can be calculated as follows,

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