Quantitative Chemistry Definitions On Exams

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Autoprotolysis

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the reaction of a neutral solvent, in which two molecules of the same species transfer a proton from one to the other thereby producing ions

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Buoyancy

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apparent mass of a weighed object is less than the true mass because of the air displaced by the object

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Buret

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precisely manufactured glass tube with graduations enabling you to measure the volume of liquid delivered through the stopcock at the bottom

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Common Ion Effect

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a salt will be less soluble if one of its constituent ions is already present in solution

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Confidence Intervals

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an expression stating that the true mean is likely to lie within a certain distance from the measured mean

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Density

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mass per unit volume

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Detection Limit

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the smallest quantity of analyte that is "significantly different" from the blank Signal DL = Ydl = Yblank + 3s DL (conc) = 3s/m

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Electrolyte

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a substance that dissociates into ions in a solution

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Emission Spectrum

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graph of luminescence intensity versus luminescence wavelength obtained with a fixed excitation wavelength

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F test

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used to compare the standard deviations of two sets of measurements Fcalc = S1^2/S2^2

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Frequency

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number of waves per second that pass a given point in space (1/s, Hz)

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Gibbs Free Energy

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(ΔG) determines if there is a net driving force for reactants or products to be formed ΔG = ΔH - TΔS (-) : spontaneous (+) : nonspontaneous

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Heterogeneous

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Composition differs from one region to another

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Homogeneous

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Composition is the same throughout

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Hygroscopic Reagents

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chemicals that rapidly absorb moisture from the air

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Interference

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the presence of one substance changes the signal in the analysis of another substance

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Internal Standards

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a known amount of a compound, different from analyte, that is added to the unknown

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Le Chatlelier's Principle

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when a system at equilibrium is disturbed, the system will react to get back to equilibrium

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Lewis Acid

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electron pair acceptor

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Lewis Base

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electron pair donor

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Matrix Effect

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a change in the analytical signal caused by anything in the sample other that the analyte

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Method Validation

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the process of proving that an analytical process is acceptable for its intended purpose

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Molality

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(m) moles solute/ kg solvent

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Molarity

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(M) moles solute/ L solution

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ppb

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(g substance/ g sample) *10^9 ng substance/ g sample

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ppm

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(g substance/ g sample) *10^6 μg substance/ g sample

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Q test

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for bad data, to decide whether to retain or discard a questionable data point Qcalc = gap/range

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Quantitative Transfer

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to transfer the entire contents from one container to another

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Self-Absorption

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in luminescence measurement, a high concentration of analyte molecules can absorb excitation energy from excited analyte

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Significant Figures

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the minimum number of digits needed to write a given value in scientific notation without loss of accuracy

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Singlet State

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electronic spins are paired

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Standard Deviation

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measure of how closely the data are clustered to the mean

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Student's t

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a statistical tool used to express confidence intervals and to compare results from different experiments.

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Titration

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a procedure in which one substance (titrant) is carefully added to another (analyte) until complete reaction has occurred. The quantity of titrant required for complete reaction tells how much analyte is present.

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Titration Error

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the difference between the end point and the equivalence point