01A_Short Quiz Flashcards
List the 7 steps in a chemical analysis
(1) Formulating the question : Convert a general question into a specific one that can be answered by a chemical measurement.
(2) Selecting Analytical Procedures
(3) Sampling :Obtain a representative sample
(4) Sample Preparation :Convert the representative sample into a sample suitable for analysis. If necessary, concentrate the analyte and remove or mask interfering species.
(5) Analysis :Measure the unknown concentration in replicate analyses.
(6) Reporting and Interpretation :Produce a clear report of results, including estimates of uncertainty.
(7) Drawing conclusions
What is the purpose of a calibration curve?
A calibration curve shows the response of an analyte method as function of the known concentration of analyte in standard solutions. Once the calibration curve is known, the the concentration of an unknown can be deduced from a measured response.
A calibration curve is a graphical representation used to determine the concentration of an unknown substance. It’s created by plotting the measured response of a series of solutions with known concentrations (standards) against their respective concentrations. This curve then acts as a reference to translate the instrument’s response of an unknown sample into its actual concentration.
For example, in a laboratory setting, a chemist might use a calibration curve to determine the concentration of glucose in a blood sample. By measuring the absorbance of light by the blood sample and comparing it to the calibration curve established using glucose solutions of known concentrations, the chemist can accurately determine the blood glucose level.
Another example is in environmental monitoring. Scientists can use calibration curves to analyze the concentration of pollutants in water samples. By measuring the response of a sensor to different concentrations of a pollutant in standard solutions, they can create a calibration curve. Subsequently, they can measure the sensor’s response to the unknown water sample and use the calibration curve to determine the pollutant’s concentration in the sample.
Define standard solutions.
Standard solutions containing known concentrations of pure compounds (e.g. pure theobromine and caffeine), and the resulting peak heights were measured.
What does it mean to mask an interfering species?
Masking converts an interfering species into a noninterfering species
Masking an interfering species in analytical chemistry involves selectively removing or altering the interfering substance without affecting the analyte of interest. This is achieved by adding a masking agent, which reacts specifically with the interfering species to form a complex, precipitate, or other inactive form.
The masked species then no longer interferes with the analytical method being used, such as titration or spectrophotometry. Masking agents are crucial for accurate and precise analysis, especially in complex samples containing multiple components.
For example, in the analysis of iron in a solution containing both iron and copper, copper can interfere with the determination of iron.
To mask copper, a masking agent like cyanide can be added. Cyanide forms a stable complex with copper ions, effectively removing them from the solution and preventing them from interfering with the subsequent analysis of iron.
How would you do sampling from a segregated
heterogeneous material?
A homogeneous material has the same composition everywhere. In a heterogeneous material, the composition is not the same everywhere.
In a segregated heterogeneous material, the composition varies on a large scale. There could be large patches with one composition and large patches with another composition. The differences are segregated into different regions. In a random heterogenous material, the differences occur on a fine scale. If we collect a “reasonable-size” portion, we will capture each of the different compositions that are present.
To sample a segregated heterogenous material, we take representative amounts from each of the obviously different regions. Collect random segments with the help of a table of random numbers.
- Sampling segregated heterogeneous materials requires careful consideration to ensure representativeness.
- Divide the material into distinct segments based on visible differences in composition.
- Collect a representative sample from each segment, ensuring proper proportion to the overall material.
- Combine the samples from each segment to create a composite sample.
- Thoroughly mix the composite sample to achieve homogeneity.
- Finally, take a smaller subsample from the well-mixed composite for analysis.
Transforming a sample into a state that is suitable for
analysis.
Sample preparation is the crucial step of transforming a sample from its original state into a form suitable for analysis by an instrument. This involves various techniques like dissolving, extracting, filtering, and drying, depending on the sample’s nature and the analytical method. Proper preparation ensures accurate and reliable results by making the sample compatible with the instrument and removing any interferences that might hinder the analysis.
What is a chromatogram?
A chromatogram is a visual representation of the results obtained from a chromatography experiment. It’s typically a graph where the x-axis represents time or retention time, and the y-axis represents the signal intensity or concentration of the separated components.
Each peak on the chromatogram corresponds to a different component in the sample mixture.
The retention time, which is the time it takes for a specific component to travel through the chromatographic system, is characteristic for that particular compound under specific conditions.
Chromatograms are essential for qualitative and quantitative analysis, allowing scientists to identify and quantify the components present in a mixture.
What solvent was used in extracting fat from
chocolate?
Petroleum ether : A mixture of hydrocarbons, often the preferred choice for fat extraction due to its high solvency for fats and relatively low boiling point.
