1. What is a diprotic acid? Give an example not found in the below text for this investigation. 2. Give the balanced chemical reaction for the titration of the above diprotic acid with potassium hydroxide to the first equivalence point. Give the balanced chemical reaction for the titration of the above diprotic acid with potassium hydroxide to the second equivalence point. A diprotic acid is an acid that can yield two H* ions per acid molecule. Examples of diprotic acids are sulfuric acid, H2SO4, and carbonic acid, H2CO3. A diprotic acid ionizes in water in two stages: H2X(aq) HX (aq) H(aq) + HX¯(aq) H(aq) + x²¯(aq) Equation 1 Equation 2 Because of the successive ionizations, titration curves of diprotic acids can have two equivalence points, as shown in Figure 1. The equations for the acid-base reactions occurring between a diprotic acid, H₂X, and sodium hydroxide base, NaOH, are from the beginning to the first equivalence point: H2X+ NaOH > NaHX + H₂O PH Equation 3 from the first to the second equivalence point: NaHX + NaOH > Na₂X + H₂O Equation 4 The net of equations 3 and 4 show the complete neutralization of a diprotic acid: 1st Equivalence Point 2nd Equivalence Point Volume NaOH H₂X + 2 NaOH Na₂X +2 H₂O Equation 5 At the first equivalence point, all H+ ions from the first dissociation (Equation 1) have reacted with the base. At Figure 1. Titration curve of a diprotic acid the second equivalence point, all H+ ions from both ionization reactions have reacted (twice as many as at the first equivalence point). Therefore, the volume of NaOH added at the second equivalence point is exactly twice that of the first equivalence point (see Equations 3 and 5). The primary purpose of this experiment is to identify an unknown diprotic acid by finding its molecular weight. Further confirmation will be had by comparing the identified acids Ka values to the accepted values.

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Chapter14: Acids And Bases
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1. What is a diprotic acid? Give an example not found in the below text for this investigation.
2. Give the balanced chemical reaction for the titration of the above diprotic acid with potassium
hydroxide to the first equivalence point. Give the balanced chemical reaction for the titration of
the above diprotic acid with potassium hydroxide to the second equivalence point.
Transcribed Image Text:1. What is a diprotic acid? Give an example not found in the below text for this investigation. 2. Give the balanced chemical reaction for the titration of the above diprotic acid with potassium hydroxide to the first equivalence point. Give the balanced chemical reaction for the titration of the above diprotic acid with potassium hydroxide to the second equivalence point.
A diprotic acid is an acid that can yield two H* ions per acid molecule. Examples of diprotic acids are
sulfuric acid, H2SO4, and carbonic acid, H2CO3. A diprotic acid ionizes in water in two stages:
H2X(aq)
HX (aq)
H(aq) + HX¯(aq)
H(aq) + x²¯(aq)
Equation 1
Equation 2
Because of the successive ionizations, titration curves of diprotic acids can have two equivalence points,
as shown in Figure 1. The equations for the acid-base
reactions occurring between a diprotic acid, H₂X, and
sodium hydroxide base, NaOH, are from the beginning to
the first equivalence point:
H2X+ NaOH > NaHX + H₂O
PH
Equation 3
from the first to the second equivalence
point:
NaHX + NaOH > Na₂X + H₂O
Equation 4
The net of equations 3 and 4 show the complete
neutralization of a diprotic acid:
1st Equivalence Point 2nd Equivalence Point
Volume NaOH
H₂X + 2 NaOH
Na₂X +2 H₂O
Equation 5
At the first equivalence point, all H+ ions from the first
dissociation (Equation 1) have reacted with the base. At
Figure 1. Titration curve of a diprotic acid
the second equivalence point, all H+ ions from both ionization reactions have reacted (twice as many as
at the first equivalence point). Therefore, the volume of NaOH added at the second equivalence point is
exactly twice that of the first equivalence point (see Equations 3 and 5).
The primary purpose of this experiment is to identify an unknown diprotic acid by finding its molecular
weight. Further confirmation will be had by comparing the identified acids Ka values to the accepted
values.
Transcribed Image Text:A diprotic acid is an acid that can yield two H* ions per acid molecule. Examples of diprotic acids are sulfuric acid, H2SO4, and carbonic acid, H2CO3. A diprotic acid ionizes in water in two stages: H2X(aq) HX (aq) H(aq) + HX¯(aq) H(aq) + x²¯(aq) Equation 1 Equation 2 Because of the successive ionizations, titration curves of diprotic acids can have two equivalence points, as shown in Figure 1. The equations for the acid-base reactions occurring between a diprotic acid, H₂X, and sodium hydroxide base, NaOH, are from the beginning to the first equivalence point: H2X+ NaOH > NaHX + H₂O PH Equation 3 from the first to the second equivalence point: NaHX + NaOH > Na₂X + H₂O Equation 4 The net of equations 3 and 4 show the complete neutralization of a diprotic acid: 1st Equivalence Point 2nd Equivalence Point Volume NaOH H₂X + 2 NaOH Na₂X +2 H₂O Equation 5 At the first equivalence point, all H+ ions from the first dissociation (Equation 1) have reacted with the base. At Figure 1. Titration curve of a diprotic acid the second equivalence point, all H+ ions from both ionization reactions have reacted (twice as many as at the first equivalence point). Therefore, the volume of NaOH added at the second equivalence point is exactly twice that of the first equivalence point (see Equations 3 and 5). The primary purpose of this experiment is to identify an unknown diprotic acid by finding its molecular weight. Further confirmation will be had by comparing the identified acids Ka values to the accepted values.
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