18 Questions
What type of change occurs at the phenolphthalein end point during titration in the double-indicator method?
Pinkish to colorless
In the double-indicator method for compatible base mixtures analysis, which indicator is added first?
Phenolphthalein
In the given sample problem involving Na2CO3 and NaOH, which indicates the presence of NaOH during titration?
Volume required for methyl orange end point
What type of change occurs at the methyl orange end point during titration in the double-indicator method?
Colorless to pinkish
Which step of the two-step neutralization reaction corresponds to the phenolphthalein end point in the titration process?
Step 1
In a titration with phenolphthalein as the indicator, what indicates the completion of the reaction?
Colorless to pinkish change
Which type of analysis would be most suitable when the analyte in the sample can readily react with the standard solution?
Direct analysis with titration using phenolphthalein
What indicator is commonly used in direct analysis when titrating with a standard base against an acid analyte like acetic acid?
Phenolphthalein
Which method involves the use of two indicators, with one being used first and then the second, to reach the endpoint of the titration?
Double-indicator method
In which scenario would the double-indicator method be particularly useful?
When analyzing mixtures of compatible bases like NaOH, Na2CO3, and Inerts
What is a common application of direct analysis with titration using methyl orange as an indicator?
Analyzing % Na2CO3 in soda ash sample
Why are OH- and HCO3- considered incompatible mixtures in the context of the double-indicator method?
Because they will react with each other
What is the pH range at the equivalence point for titration with phenolphthalein?
8.0 - 9.8
Which indicator is suitable for titration of weak base with strong acid?
Methyl Orange
In a double-indicator method, which indicators are typically used for titration?
Methyl Red and Methyl Orange
What is the appropriate indicator when titrating a weak acid with a strong base?
Phenolphthalein
Which type of titration analysis involves the direct titration of analyte with a standard solution?
Neutralization analysis
What happens to the pH at the equivalence point when titrating a weak base with a strong acid?
pH is less than 7.0
Study Notes
Neutralization Reactions
- Neutralization reaction involved in titration with OH- (like NaOH) with f=1, changes during the reaction, occurring at the phenolphthalein end point.
- Neutralization reaction involved in titration with HCO3- (like NaHCO3) with f=1, changes during the reaction, occurring at the methyl orange end point.
- Neutralization reaction involved in titration with CO32- (like Na2CO3) with f=2, two-step neutralization reaction, occurring in two steps: step 1 at pH end point, step 2 at methyl orange end point.
Titration Analysis using Double-Indicator Method
- Procedure involves dissolving the sample in water, adding phenolphthalein as the first indicator, titrating with standard acid to reach the pH endpoint, then adding methyl orange as the second indicator, and continuing titration to reach its endpoint.
- The procedure is used for the analysis of compatible base mixtures.
Sample Problems
- A 5.0 g mixture of Na2CO3 and NaOH required 28.8 mL of 0.5000N HCl to reach a phenolphthalein endpoint and an additional 14.4 mL to reach a methyl orange endpoint, and the percentages of Na2CO3 and NaOH can be calculated.
- A 1.2034 g sample was titrated with 0.5324 M HCl, with phenolphthalein as the indicator, and the solution turned colorless after adding 25.6 mL of the acid, and methyl orange was then added, requiring 0.3 mL more of the acid, and the identity of the sample and its percent purity can be determined.
pH Range and Indicators
- pH range at equivalence point: 3.5 to 10.5
- Appropriate indicators: Methyl Red (pH: 4.2-6.2), Methyl Orange (pH: 3.1-4.4), and Phenolphthalein (pH 8.0-9.8)
Strong Base with Weak Acid and Weak Base with Strong Acid
- pH range at equivalence point for weak base with strong acid: less than 7.0
- Appropriate indicators: Methyl Red (pH: 4.2-6.2) and Methyl Orange (pH: 3.1-4.4)
- pH range at equivalence point for weak acid with strong base: greater than 7.0
- Appropriate indicator: Phenolphthalein (pH 8-9.8)
Weak Acid with Weak Base
- Not feasible, as the titration curve has no inflection region at the equivalence point, and no sudden changes in pH, resulting in no abrupt color change of the indicator.
Titer-Value
- Grams of analyte equivalent to 1mL of titrant or standard solution.
- Computed from the available accurate normality of the titrant/standard solution.
- Common unit of Titer-Value: g analyte/mL std.
Kinds of Titration Analysis
- Direct Analysis: Analyte in the sample is titrated directly with the standard solution using an appropriate indicator.
- Double-Indicator Method: Titration of analytes in the sample uses two indicators, where one indicator is used first and titration is performed to reach its endpoint, and then the second indicator is added next and titration is further continued to reach the endpoint of the second indicator.
Applications of Double-Indicator Method
- Analysis of compatible mixtures of bases containing OH-, HCO3-, and CO32-.
- Example: Analysis of NaOH-Na2CO3-Inerts mixture, and NaHCO3-Na2CO3-Inerts mixture.
Explore the neutralization reactions involved in titration analysis using a double-indicator method for the analysis of compatible base mixtures. Learn about the changes during titration reactions occurring at different end points like phenolphthalein and methyl orange.
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