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Chapter 4: Q94E (page 225)

Potassium acid phthalate, KHC6H4O4or KHP, is used in many laboratories, including general chemistry laboratories, to standardize solutions of base. KHP is one of only a few stable solid acids that can be dried by warming and weighed. A 0.3420-g sample of KHC6H4O4 reacts with 35.73 mL of a NaOH solution in a titration. What is the molar concentration of the NaOH?

\({\rm{KH}}{{\rm{C}}_6}{{\rm{H}}_4}{{\rm{O}}_{4({\rm{aq}})}}{\rm{ + NaO}}{{\rm{H}}_{({\rm{aq}})}}{\rm{ }} \to {\rm{ KNa}}{{\rm{C}}_6}{{\rm{H}}_4}{{\rm{O}}_{4({\rm{aq}})}}{\rm{ + }}{{\rm{H}}_2}{{\rm{O}}_{({\rm{aq}})}}\)

Short Answer

Expert verified

The molar concentration of sodium hydroxide is \({\rm{5}}{\rm{.3 }} \times {\rm{ 1}}{{\rm{0}}^{ - 3}}\;{\rm{M}}\)

Step by step solution

01

Moles of sodium hydroxide

According to the question, it is given that

The mass of KHC6H4O4 is 0.3420 g

The molecular mass of KHC6H4O4 is \(39\,{\rm{ + }}{\rm{5 }} \times {\rm{ 1 + }}{\rm{12 }} \times {\rm{ 6 + }}{\rm{16 }} \times {\rm{ }}4\;{\rm{ = 180 g/mol}}\)

Thus, the number of moles of KHC6H4O4 will be given by:

\(\begin{array}{l}{\rm{Moles = }}\frac{{{\rm{Mass}}}}{{{\rm{Molecular mass}}}}\\{\rm{Moles = }}\frac{{0.3420}}{{{\rm{180}}}}{\rm{ = 0}}{\rm{.0019 moles}}\end{array}\)

Now, from the reaction we can determine that when 1 mole of KHC6H4O4 reacts with sodium hydroxide it requires 1 mole of NaOH, thus the number of moles of sodium hydroxide will be:

\({\rm{1 }} \times {\rm{ 0}}{\rm{.0019 = 0}}{\rm{.0019 moles}}\)

02

Molar concentration of sodium hydroxide

The molar concentration of a compound, also known as molarity, is a method of determining the concentration of a substance in a solvent. As the number of moles of sodium hydroxide is 0.0019 moles and the volume is 35.73 ml. Thus, the molar concentration of sodium hydroxide is given by:

\(\begin{array}{l}{\rm{Concentration = }}\frac{{{\rm{Moles}}}}{{{\rm{Volume}}}}\\{\rm{Concentration = }}\frac{{0.0019}}{{35.73}}{\rm{ = 5}}{\rm{.3 }} \times {\rm{ 1}}{{\rm{0}}^{ - 3}}\;{\rm{M}}\end{array}\)

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Most popular questions from this chapter

A novel process for obtaining magnesium from sea water involves several reactions. Write a balanced chemical equation for each step of the process.

(a)The first step is the decomposition of solid calcium carbonate from seashells to form solid calcium oxide and gaseous carbon dioxide.

(b)The second step is the formation of solid calcium hydroxide as the only product from the reaction of the solid calcium oxide with liquid water.

(c)Solid calcium hydroxide is the added to the sea water, reacting with dissolved magnesium chloride to yield solid magnesium hydroxide and aqueous calcium chloride

(d)The solid magnesium hydroxide is added to a hydrochloric acid solution, producing dissolved magnesium chloride and liquid water.

(e)Finally, the magnesium chloride is melted and electrolyzed to yield liquid magnesium metal and diatomic chlorine gas.

Classify the following as acid-base reaction or oxidation-reduction reactions.

(a)\(N{a_2}S\left( {aq} \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}S\left( g \right)\)

(b)\(2Na\left( s \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}\left( g \right)\)

(c)\(Mg\left( s \right) + C{l_2}\left( g \right) \to MgC{l_2}\left( s \right)\)

(d)\(MgO\left( s \right) + 2HCl\left( {aq} \right) \to MgC{l_2}\left( {aq} \right) + {H_2}O\left( l \right)\)

(e)\({K_3}P\left( s \right) + 2{O_2}\left( g \right) \to {K_3}P{O_4}\left( s \right)\)

(f)\(3KOH\left( {aq} \right) + {H_3}P{O_4}\left( {aq} \right) \to {K_3}P{O_4}\left( {aq} \right) + 3{H_2}O\left( l \right)\)

Colourful fireworks often involve the decomposition of barium nitrate and potassium chlorate and the reaction of metals magnesium, aluminium, and iron with oxygen.

(a)Write the formulae of barium nitrate and potassium chlorate.

(b)The decomposition of solid potassium chlorate leads to the formation of solid potassium chloride and diatomic oxygen gas. Write an equation for the reaction.

(c) The decomposition of solid barium nitrate leads to the formation of solid barium oxide, diatomic nitrogen gas and diatomic oxygen gas. Write an equation for the reaction.

(d)Write separate equations for the reactions of the solid metals magnesium, aluminium and iron and oxygen gas to yield the corresponding metal oxides.(Assume the iron oxide contains \(F{e^{3 + }}\)ions.)

Titration of a 20.0-mL sample of acid rain required 1.7 mL of 0.0811MNaOH to reach the end point. If we assume that the acidity of the rain is due to the presence of sulfuric acid, what was the concentration of sulfuric acid in this sample of rain?

Uranium can be isolated from its ores by dissolving it as UO2(NO3)2, then separating it as solid UO2(C2O4). Addition of 0.4031 g of sodium oxalate, NaC2O4, to a solution containing 1.481 g of uranyl nitrate, UO2(NO3)2, yields 1.073 g of solid

\(Na{C_2}{O_4} + U{O_2}{\left( {N{O_3}} \right)_2} + 3{H_2}O \to U{O_2}\left( {{C_2}{O_4}} \right) \cdot 3{H_2}O + 2NaN{O_3}\)
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