Methods of Qualitative Analysis

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Questions and Answers

What is the basis of identification in simple qualitative analysis?

  • Differences in colour and odour
  • Differences in texture and atomic structure
  • Differences in colour, odour, melting point, boiling point, texture, and atomic structure (correct)
  • Differences in melting point, boiling point, and texture

What is the purpose of adding a series of chemical reagents to the sample in qualitative analysis?

  • To detect and identify the target analyte (correct)
  • To destroy the analyte
  • To separate the analyte from other substances
  • To measure the concentration of the analyte

What is the result of the reaction between copper (II) and ammonia in qualitative analysis?

  • A precipitate
  • A gas
  • A copper-ammonia complex with a deep blue colour (correct)
  • A colourless complex

What is the limitation of classical qualitative analysis?

<p>It provides a partial identification of the molecule (B)</p> Signup and view all the answers

What is the purpose of the urine test in qualitative analysis?

<p>To detect the presence of glucose in the urine sample (C)</p> Signup and view all the answers

What is the characteristic of the product formed in a qualitative analysis reaction?

<p>It is either a coloured complex or a precipitate (A)</p> Signup and view all the answers

What is the next step when a high glucose concentration is detected in a urine test?

<p>To perform a blood glucose test (A)</p> Signup and view all the answers

What is the difference between qualitative and quantitative analysis?

<p>Qualitative analysis identifies the analyte, while quantitative analysis measures concentration (B)</p> Signup and view all the answers

What is the purpose of adding an excess of reagent in gravimetric analysis?

<p>To ensure complete precipitation of the analyte (B)</p> Signup and view all the answers

What is the product formed in the reaction between Silver Nitrate (AgNO3) and chloride ions in water?

<p>Silver Chloride (AgCl) (B)</p> Signup and view all the answers

What is the term used to describe the process of adding a reagent of known concentration to the analyte in volumetric analysis?

<p>Titration process (B)</p> Signup and view all the answers

What is the purpose of using a primary standard solution in volumetric analysis?

<p>To serve as a reference material (D)</p> Signup and view all the answers

What is the requirement for a primary standard solution to have a reasonable large molar mass?

<p>To minimize the relative error associated with weighing the standard (B)</p> Signup and view all the answers

What is the term used to describe the set of methods used in analytical chemistry for the quantitative determination of an analyte based on its mass?

<p>Gravimetric analysis (C)</p> Signup and view all the answers

What is the purpose of washing the precipitate in gravimetric analysis?

<p>To remove impurities from the precipitate (B)</p> Signup and view all the answers

What is the term used to describe the analysis method that involves the gradual addition of a reagent of known concentration to the analyte?

<p>Titrimetric analysis (D)</p> Signup and view all the answers

What is the purpose of adding an indicator in a titration?

<p>To undergo a colour change when the reaction approaches completion (B)</p> Signup and view all the answers

What is the key to performing a successful titrimetric analysis?

<p>Recognizing the equivalence point of the titration (C)</p> Signup and view all the answers

What is the term for the volume of added titrant corresponding to the indicator colour change?

<p>Endpoint (A)</p> Signup and view all the answers

What is the result of serial dilutions in biological titration?

<p>Titer of the virus (B)</p> Signup and view all the answers

Why is sodium hydroxide an example of a secondary standard solution?

<p>Because it contains impurities like NaCl and Na2CO3 (D)</p> Signup and view all the answers

What is the purpose of titration in virus quantification?

<p>To monitor the process and optimize production yields (B)</p> Signup and view all the answers

What is a solution in the context of volumetric analysis?

<p>A homogeneous mixture of two or more substances (B)</p> Signup and view all the answers

What is the term for the process of counting the number of viruses in a specific volume?

<p>Virus quantification (B)</p> Signup and view all the answers

What is the unit of weight in the formula F = wt / (V x mol)?

<p>gm (B)</p> Signup and view all the answers

What is the term sometimes used in place of gram formula weight?

<p>Molecular weight (C), Molar mass (D)</p> Signup and view all the answers

What is the unit of volume in the formula N = No. of equivalent / (V x 1000)?

<p>L (B)</p> Signup and view all the answers

What is the formula weight divided by in order to get the equivalent weight?

<p>Number of reacting units (B)</p> Signup and view all the answers

What is the number of reacting units for acid-base reaction?

<p>Number of H+ or OH- (D)</p> Signup and view all the answers

What is the formula for normality?

<p>N = No. of equivalent / (V x 1000) (D)</p> Signup and view all the answers

What is the equivalent weight for oxidation-reduction reaction?

<p>Formula weight divided by number of electrons (C)</p> Signup and view all the answers

What is the unit of normality?

<p>eq/L (B)</p> Signup and view all the answers

What is the normality of a 5.300gm/L Na2CO3 solution when the CO3-2 reacts with two protons?

<p>0.10 Eq/L (A)</p> Signup and view all the answers

How many millilitres of a 0.25M solution of H2SO4 will react with 10mL of a 0.25M solution of NaOH?

<p>5.0 mL (C)</p> Signup and view all the answers

What is the equivalent weight of Na2CO3 when it reacts with two protons?

<p>105.99 (B)</p> Signup and view all the answers

What is the oxidation state of Cr in the reaction: Cr2O7 2- + 14H+ + 6e- → 2Cr3+ + 7H2O?

<p>3+ (B)</p> Signup and view all the answers

What is the normality of a 5.267 gm/L K2Cr2O7 solution?

<p>0.1074 Eq/L (C)</p> Signup and view all the answers

What is the equivalent weight of K2Cr2O7 when it reacts with 6 electrons?

<p>294.19 (D)</p> Signup and view all the answers

What is the normality of a solution prepared by dissolving 0.212 gm Na2CO3 and diluting to 100mL if it is used as a monoacidic base?

<p>0.020 meq/mL (D)</p> Signup and view all the answers

What is the equivalent weight of Na2CO3 when it reacts with one proton?

<p>105.99 (B)</p> Signup and view all the answers

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Study Notes

Methods and Tools

  • Simple qualitative analysis can be performed without using expensive and complex tools or reagents.
  • Identification may be based on differences in:
    • Colour
    • Odour
    • Melting point
    • Boiling point
    • Texture
    • Atomic structure
    • Ability to conduct electricity
  • Chemical reagents can be added to the sample to detect and identify the target analyte.
  • The reagents are usually chosen to react selectively with one or a single chemical compound to form the desired product.
  • The resulted product is either a coloured complex or a precipitate.

Gravimetric Analysis

  • The principles behind gravimetric analysis involve adding an excess of reagent to the aqueous solution containing the analyte, forming a precipitate.
  • The precipitate is then filtered, washed, dried, and weighed.
  • The resulted mass is used to calculate the concentration or amount of the analyte using appropriate stoichiometric ratios.
  • Gravimetric analysis is used for quantitative determination of an analyte based on its mass.

Volumetric Analysis (Titrimetric Analysis)

  • Volumetric analysis is a method used to determine the concentration of an analyte by reacting it with a reagent of known concentration.
  • The reagent is added gradually or stepwise to the analyte from a burette.
  • The process is called the titration process.
  • A primary standard solution is a highly purified compound that serves as a reference material in all volumetric analyses.
  • Important requirements for a primary standard solution include:
    • High purity
    • Stability towards air
    • Absence of hydrate water
    • Ready availability and inexpensive
    • Reasonable solubility in the titration medium
    • Reasonable large molar mass
  • A secondary standard solution is prepared in the laboratory for a specific analysis and standardized against a primary standard.
  • The key to perform a successful titrimetric analysis is to recognize the equivalence point of the titration.
  • The equivalence point is typically observed as a colour change.
  • If no spontaneous colour change occurs, a small amount of a chemical indicator is added to the analyte before the titration.

Biological Titration

  • Biological titration involves counting the number of viruses in a specific volume to determine the virus concentration in an assay.
  • Serial dilutions are performed on a sample in a fixed ratio until the last dilution does not give a positive test for the presence of the virus.
  • The value is known as the titer.

Expressions and Formulas

  • Solution: a homogenous mixture of two or more substances.
  • Formality (F): the sum of the atomic weights of the atoms that make up an ionic formula.
  • Normality (N): the concentration of a solution that produces one equivalent of solute in one liter of solution.
  • Equivalent weight (Eq.wt): the formula weight divided by the number of reacting units.
  • Formula weight (F.wt): the sum of the atomic weights of the atoms that make up a molecule.
  • Eq.wt for acid-base reaction: formula weight divided by the number of H+ or OH-.
  • Eq.wt for oxidation-reduction reaction: formula weight divided by the number of electrons.

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