30 Questions
What kind of errors arise from the experimenter's carelessness, inattention, or personal limitations?
Personal errors
Which of the following personal errors involves a preference for the digits 0 and 5?
Preference for 0s and 5s
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
Which type of error causes data to be scattered symmetrically around a mean value?
Random errors
What is a universal source of personal error mentioned in the text?
Prejudice or bias
How do digital and computer displays on electronic instruments help eliminate number bias?
By reducing number bias
What is the minimum mass of a sample considered macro in analytical chemistry?
> 100 mg
What is the term for a constituent present in a sample at a concentration of 0.01-1%?
Minor constituent
What is the purpose of the flame test in analytical chemistry?
To observe the color of the flame
What is the type of reaction involved in the dry method of analytical chemistry?
Thermal decomposition reaction
What is the name of the test involving borax bead formation?
Bead test
What is the product formed when a sample is heated in a charcoal cavity test?
Metal oxide
What is the term used to describe results that appear to differ markedly from all other data in a set of replicate measurements?
Outliers
How can personal errors in a laboratory setting be minimized?
By conducting careful and disciplined laboratory work
What is the recommended way of estimating bias in an analytical method?
By analyzing Standard reference materials (SRMs)
What is the main reason for periodically calibrating equipment in a laboratory?
To ensure instruments' response accuracy over time
Which term refers to the average value of two or more measurements in a set of data?
Mean (x)
What is the middle value in a set of data that has been arranged in order of size?
Median
What term describes the reproducibility of measurements?
Precision
What is the formula for Absolute Error?
Difference between measured value and the true value
Which term represents the closeness of a measurement to its true or accepted value?
Accuracy
In the context of measurements, what does RSD stand for?
Relative Standard Deviation
How is Relative Error expressed?
As the absolute error divided by the measured value
What formula is used to calculate Standard Deviation?
𝑎2 + 𝑆𝑏2 + 𝑆𝑐2
What is the focus of Qualitative Chemistry in analytical chemistry?
Determining the actual constituent present
What type of analysis determines the amount of each element in a sample?
Ultimate Analysis
Which method of analysis employs instruments different from gravimetric and volumetric methods?
Instrumental Method
What does Quantitative Chemistry focus on in analytical chemistry?
Determining the amount of each element
In analytical chemistry, which analysis is considered as partial and determined for a certain selected constituent?
Proximate or Partial Analysis
What is the primary focus of Gravimetric Method Analysis in analytical chemistry?
Determining the mass of the sample
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
- Accompanied by external effects:
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
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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