Quantitative Analysis Exam 1

Quantitative analysis

Determines how much of a substance is present in a sample.

Qualitative analysis

Determines what substances are present in a sample.

Analyte

The substance in a sample that is being measured or analyzed.

Sample

The material being analyzed.

Matrix

Everything in a sample other than the analyte of interest.

Analytical procedure

A series of steps used to analyze a sample and obtain analytical information.

Titrant

A solution of known concentration that is added during a titration.

Titration

A method in which a solution of known concentration is added to determine the amount or concentration of an analyte.

Endpoint

The experimentally observed point indicating that a titration reaction is complete.

Equivalence point

The point where reactants have been combined in exactly the stoichiometric amounts required.

Molarity

Moles of solute per liter of solution.

Molality

Moles of solute per kilogram of solvent.

Formal concentration

The concentration calculated from the amount of a compound initially dissolved, regardless of the chemical species formed.

Percent w/w

Mass of solute divided by mass of solution multiplied by 100.

Percent v/v

Volume of solute divided by volume of solution multiplied by 100.

Percent w/v

Mass of solute divided by volume of solution multiplied by 100.

PPM

Parts per million; a concentration unit used for very dilute solutions.

PPB

Parts per billion; a concentration unit used for extremely dilute solutions.

Stock solution

A concentrated solution used to prepare a more dilute solution.

Dilution

The process of decreasing concentration by adding solvent.

M1V1=M2V2

The equation used to calculate concentrations or volumes during dilution.

Stoichiometry

Using a balanced chemical equation to calculate quantitative relationships between substances.

Limiting reagent

The reactant that is consumed first and limits the amount of product formed.

Excess reagent

A reactant present in more than the amount required to completely react.

Analytical balance

A highly precise instrument used to measure mass.

Buoyancy

The upward force exerted by air or another fluid on an object.

Buoyancy correction

A correction accounting for the effect of air buoyancy on a measured mass.

Buret

Graduated glassware used to accurately deliver variable volumes of liquid.

Pipet

Glassware used to accurately transfer a measured volume of liquid.

Volumetric flask

Glassware designed to contain a very precise volume of solution.

Meniscus

The curved surface of a liquid in glassware.

Calibration

The process of establishing the relationship between an instrument's response and a known quantity.

Calibrated glassware

Glassware whose volume has been established against a standard.

Uncalibrated glassware

Glassware not designed to provide highly accurate volume measurements.

Absolute uncertainty

Uncertainty expressed in the same units as the measured quantity.

Relative uncertainty

Absolute uncertainty divided by the measured value.

Percent relative uncertainty

Relative uncertainty expressed as a percentage.

Random error

Error that varies unpredictably from measurement to measurement.

Systematic error

Error that produces a consistent bias in measurements.

Accuracy

How close a measurement is to the true or accepted value.

Precision

How closely repeated measurements agree with one another.

Bias

A consistent difference between a measured value and the true or accepted value.

Significant figures

Digits that communicate the precision of a measurement.

Propagation of uncertainty

Determining how uncertainties in measurements affect the uncertainty of a calculated result.

Mean

The arithmetic average of a set of measurements.

Standard deviation

A measure of how spread out measurements are around the mean.

Coefficient of variation

The standard deviation divided by the mean and multiplied by 100.

Gaussian distribution

A bell-shaped distribution in which measurements are distributed around a mean.

F test

A statistical test used to compare variances or precision between data sets.

t test

A statistical test used to compare means or determine whether a measured mean differs significantly from a reference value.

G test

A statistical test used to evaluate whether a measurement may be an outlier.

Outlier

A measurement that differs substantially from the other measurements.

Confidence interval

A range of values used to estimate a population parameter from sample data.

Confidence level

The percentage associated with a confidence interval, such as 90%, 95%, or 99%.

Least-squares method

A mathematical method used to find the line that best fits experimental data.

Regression line

The best-fit line representing the relationship between variables.

Calibration standard

A solution containing a known concentration used to construct a calibration curve.

Calibration curve

A graph showing instrument response versus known analyte concentration.

Blank solution

A solution containing everything needed for the measurement except the analyte of interest.

Instrument response

The signal produced by an instrument in response to the analyte.

Linear range

The concentration range where instrument response is proportional or approximately proportional to analyte concentration.

Dynamic range

The range of analyte concentrations over which an analytical method provides a useful measurable response.

Slope

The change in instrument response per change in analyte concentration.

Intercept

The predicted instrument response when analyte concentration is zero.

Unknown

A sample whose analyte concentration must be determined.

Accuracy vs. precision

Accuracy describes closeness to the true value; precision describes agreement between repeated measurements.

Random vs. systematic error

Random error varies unpredictably; systematic error produces a consistent bias.

Analyte vs. titrant

The analyte is what you are measuring; the titrant is the known solution you add to measure it.

Buret vs. pipet

A buret accurately delivers variable volumes; a pipet accurately transfers a measured volume.

Linear range vs. dynamic range

Linear range is where response is proportional to concentration; dynamic range is the overall useful concentration range.

Calibration standard vs. blank

A calibration standard contains a known analyte concentration; a blank contains everything except the analyte.