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Questions and Answers
What is the spring constant (k) of the spring balance?
What is the spring constant (k) of the spring balance?
What is the approximate mass (m) of the oscillating body calculated from the spring balance?
What is the approximate mass (m) of the oscillating body calculated from the spring balance?
Using the given formulas, what does the period of oscillation (T) depend on?
Using the given formulas, what does the period of oscillation (T) depend on?
What is the calculated weight (W) of the body in Newtons?
What is the calculated weight (W) of the body in Newtons?
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What force (F) is applied to produce maximum extension in the spring balance?
What force (F) is applied to produce maximum extension in the spring balance?
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What role does Hooke's Law play in determining the spring constant?
What role does Hooke's Law play in determining the spring constant?
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What is the primary factor in determining the oscillation period (T) in a spring-mass system?
What is the primary factor in determining the oscillation period (T) in a spring-mass system?
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What would be the effect of increasing the spring constant (k) on the oscillation period (T)?
What would be the effect of increasing the spring constant (k) on the oscillation period (T)?
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What is the final product measured in the Dumas method for nitrogen determination?
What is the final product measured in the Dumas method for nitrogen determination?
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Which reagent is used as an oxidizing agent in the Dumas method?
Which reagent is used as an oxidizing agent in the Dumas method?
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What is the molar volume at STP according to the Dumas method?
What is the molar volume at STP according to the Dumas method?
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In the Kjeldahl method, what natural compound is formed during the digestion process?
In the Kjeldahl method, what natural compound is formed during the digestion process?
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What is the primary application of the Kjeldahl method?
What is the primary application of the Kjeldahl method?
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What is the role of alkali in the Kjeldahl method?
What is the role of alkali in the Kjeldahl method?
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How is nitrogen content calculated in the Dumas method?
How is nitrogen content calculated in the Dumas method?
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In which method is ammonia liberated and then titrated to quantify nitrogen?
In which method is ammonia liberated and then titrated to quantify nitrogen?
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Which of the following statements is true regarding the applicability of the Dumas method?
Which of the following statements is true regarding the applicability of the Dumas method?
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What is the relationship between the normality of the acid and the calculation of nitrogen percentage in Kjeldahl’s method?
What is the relationship between the normality of the acid and the calculation of nitrogen percentage in Kjeldahl’s method?
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Study Notes
Dumas Method
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Purpose: Determines nitrogen content in organic compounds.
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Principle: Converts nitrogen to molecular nitrogen (N2) through strong heating with an oxidizing agent (e.g., excess oxygen or CuO). Carbon and hydrogen are oxidized to CO2 and H2O.
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Reactions:
- Carbon and hydrogen oxidized to CO2 and H2O.
- Nitrogen liberated as N2. Any nitrogen oxides are reduced to N2.
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Procedure:
- Known mass of organic compound mixed with excess CuO.
- Heated in a combustion tube.
- Gases passed through solution to absorb CO2 and H2O.
- Volume of N2 gas collected and measured.
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Calculation:
- Nitrogen content calculated using formula:
%Nitrogen = (Volume of N2 × Molar mass of N × 100) / (Mass of sample × Molar volume at STP)
- Molar volume at STP = 22.4 L/mol.
Kjeldahl's Method
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Purpose: Determines nitrogen content, commonly used in food, fertilizers and soil analysis.
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Principle: Organic compound digested with concentrated sulfuric acid (H2SO4) in the presence of a catalyst, to convert nitrogen to ammonium sulfate ((NH4)2SO4). Ammonium sulfate is then treated with alkali (e.g., NaOH) to liberate ammonia gas (NH3).
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Reactions:
- Nitrogen converted to (NH4)2SO4 through digestion.
- (NH4)2SO4 reacted with alkali (NaOH), liberating NH3.
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Procedure:
- Organic compound digested with concentrated H2SO4 and catalyst (e.g., selenium or copper sulfate).
- Digest neutralized with alkali (e.g., NaOH), liberating NH3.
- NH3 distilled into known volume of standard acid.
- Titrated with standard base.
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Calculation:
- Nitrogen content calculated using formula:
%Nitrogen = (Volume of acid reacted × Normality of acid × 14) / (Mass of sample × 1000)
- 14 is the molar mass of nitrogen.
Differences Between Methods
| Feature | Dumas Method | Kjeldahl's Method |
|---|---|---|
| Principle | Nitrogen converted to N2 | Nitrogen converted to NH3 |
| Oxidation agent | Cupric oxide (CuO) | Sulfuric acid (H2SO4) |
| End product | N2 | NH3 |
| Measurement | Volume of N2 gas | Titration of NH3 |
| Applicability | Limited to organic compounds, doesn't work well for compounds with Halogens or Sulfur | Suitable for wider range of compounds |
| Applications | Organic compounds w/o halogens or sulfur | Agriculture, food, biochemistry for protein analysis |
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Description
This quiz covers the Dumas Method and its principles for determining nitrogen content in organic compounds. Learn about the oxidation processes involved, procedure steps, and calculation methods used in nitrogen analysis. Perfect for students in analytical chemistry courses.
