Cbio 55 - LEC Chap 1 - Analytical Chemistry
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Questions and Answers

What kind of errors arise from the experimenter's carelessness, inattention, or personal limitations?

  • Universal errors
  • Systematic errors
  • Personal errors (correct)
  • Determinant errors

    • Which of the following personal errors involves a preference for the digits 0 and 5?

  • Prejudice favoring large digits
  • Number bias in favor of odd digits
  • Preference for even numbers
  • Preference for 0s and 5s (correct)

    • What is a common form of personal error encountered in estimating the position of a needle on a scale?

  • Preference for digits 0 and 5 (correct)
  • Bias towards digital readings
  • Preference for digital displays
  • Prejudice favoring large numbers

    • Which type of error causes data to be scattered symmetrically around a mean value?

    <p>Random errors</p> Signup and view all the answers

    What is a universal source of personal error mentioned in the text?

    <p>Prejudice or bias</p> Signup and view all the answers

    How do digital and computer displays on electronic instruments help eliminate number bias?

    <p>By reducing number bias</p> Signup and view all the answers

    What is the minimum mass of a sample considered macro in analytical chemistry?

    <p>&gt; 100 mg</p> Signup and view all the answers

    What is the term for a constituent present in a sample at a concentration of 0.01-1%?

    <p>Minor constituent</p> Signup and view all the answers

    What is the purpose of the flame test in analytical chemistry?

    <p>To observe the color of the flame</p> Signup and view all the answers

    What is the type of reaction involved in the dry method of analytical chemistry?

    <p>Thermal decomposition reaction</p> Signup and view all the answers

    What is the name of the test involving borax bead formation?

    <p>Bead test</p> Signup and view all the answers

    What is the product formed when a sample is heated in a charcoal cavity test?

    <p>Metal oxide</p> Signup and view all the answers

    What is the term used to describe results that appear to differ markedly from all other data in a set of replicate measurements?

    <p>Outliers</p> Signup and view all the answers

    How can personal errors in a laboratory setting be minimized?

    <p>By conducting careful and disciplined laboratory work</p> Signup and view all the answers

    What is the recommended way of estimating bias in an analytical method?

    <p>By analyzing Standard reference materials (SRMs)</p> Signup and view all the answers

    What is the main reason for periodically calibrating equipment in a laboratory?

    <p>To ensure instruments' response accuracy over time</p> Signup and view all the answers

    Which term refers to the average value of two or more measurements in a set of data?

    <p>Mean (x)</p> Signup and view all the answers

    What is the middle value in a set of data that has been arranged in order of size?

    <p>Median</p> Signup and view all the answers

    What term describes the reproducibility of measurements?

    <p>Precision</p> Signup and view all the answers

    What is the formula for Absolute Error?

    <p>Difference between measured value and the true value</p> Signup and view all the answers

    Which term represents the closeness of a measurement to its true or accepted value?

    <p>Accuracy</p> Signup and view all the answers

    In the context of measurements, what does RSD stand for?

    <p>Relative Standard Deviation</p> Signup and view all the answers

    How is Relative Error expressed?

    <p>As the absolute error divided by the measured value</p> Signup and view all the answers

    What formula is used to calculate Standard Deviation?

    <p>𝑎2 + 𝑆𝑏2 + 𝑆𝑐2</p> Signup and view all the answers

    What is the focus of Qualitative Chemistry in analytical chemistry?

    <p>Determining the actual constituent present</p> Signup and view all the answers

    What type of analysis determines the amount of each element in a sample?

    <p>Ultimate Analysis</p> Signup and view all the answers

    Which method of analysis employs instruments different from gravimetric and volumetric methods?

    <p>Instrumental Method</p> Signup and view all the answers

    What does Quantitative Chemistry focus on in analytical chemistry?

    <p>Determining the amount of each element</p> Signup and view all the answers

    In analytical chemistry, which analysis is considered as partial and determined for a certain selected constituent?

    <p>Proximate or Partial Analysis</p> Signup and view all the answers

    What is the primary focus of Gravimetric Method Analysis in analytical chemistry?

    <p>Determining the mass of the sample</p> Signup and view all the answers

    Study Notes

    Sample Analyses

    • Macro sample: > 100 mg, > 100 µL
    • Semi-micro sample: 10-100 mg, 50-100 µL
    • Micro sample: 1-10 mg, < 50 µL
    • Ultra-micro sample: < 1 mg, 1% of the sample
    • Minor constituent: 0.01-1% of the sample
    • Trace constituent: 0.001-0.01% of the sample
    • Ultra-trace constituent: < 0.001% of the sample

    Analytical Reactions

    • Dry method: sample and analytical reagent in solid state, subjected to high temperature heating
    • Wet method: performed in qualitative analysis, involves precipitation, titration, and colorimetric methods
      • Accompanied by external effects:
        • Changing of solution coloration
        • Forming or dissolving precipitation
        • Evolution of gas

    Dry Method Flame Test

    • Involves introducing sample to hot, non-luminous flame and observing the color that appears

    Bead Test

    • Reactions for borax bead formation – sodium tetraborate (Na2B4O7 ∙10H2O)
    • When heated, combines with colored transition metal oxides (e.g., Co, Ni, Cr, Cu, Mn) to form metaborates with characteristic colors

    Charcoal Cavity Test

    • Cations converted to metal carbonate in charcoal cavity, which decomposes on heating to metal oxide or metal

    Errors in Chemical Analysis

    • Gross errors: human errors leading to outliers
    • Systematic (instrumental and personal) errors: minimized by:
      • Periodic calibration of equipment
      • Careful, disciplined laboratory work
      • Checking instrument readings, notebook entries, and calculations
      • Choosing the analytical method or using an automated procedure
    • Systematic (method) errors: difficult to detect, estimated by analyzing Standard Reference Materials (SRMs)

    Errors and Statistics

    • Central tendency:
      • Mean (x): average value of measurements
      • Median: middle value in a set of data
    • Personal errors: result from carelessness, inattention, or personal limitations
    • Number bias: preference for certain digits or numbers
    • Random errors (indeterminate error): cause data to scatter around a mean value
    • Precision: reproducibility of measurements, closeness of data to other data obtained in exactly the same way
    • Accuracy: closeness of a measurement to its true or accepted value

    Analytical Chemistry

    • Definition: science of methods to study material composition
    • Branch of chemistry that deals with the operation and analysis of a chemical substance
    • Divisions:
      • Qualitative chemistry/analysis: determination of actual constituents present
      • Quantitative chemistry/analysis: determination of amount of constituent present
    • Importance:
      • Establishing economic value
      • Determining health hazards
      • Diagnosing disease
      • Controlling quality
      • Relating properties to composition and structure
      • Conducting research
    • Classification of methods of analysis:
      • Gravimetric method: mass of sample or compounds chemically related to it is determined
      • Volumetric method: amount of analyte is determined by measuring volume of solution of known concentration
      • Instrumental method: employs instruments other than those used in gravimetric and volumetric methods
    • Classification of analyses:
      • Complete or exact analysis: amount of each constituent of the sample is determined
      • Ultimate analysis: amount of each element is determined
      • Proximate or partial analysis: amount of a certain selected constituent in a sample is determined

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    Description

    Explore the fundamental concepts of analytical chemistry, including qualitative and quantitative analysis methods. Learn about the nature of analytical chemistry and how it is applied in studying material composition.

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