A Chem Exam 1

Aliquot

Precisely measured portion of a larger sample, typically used for analysis/storage/experiments.

Analyte

Substance which is being identified and measured. In a titration, it is the substance that is in the flask on the bottom.

Aqueous

“In water”. A solution of a solute dissolved in water.

Calibration Curve

AKA standard curve, graph of detector response as a function of analyte concentration

Heterogenous

Substance or mixture that does not have a uniform composition and consists of 2+ distinct components

Homogenous

Something with uniform composition and structure throughout

Interference

Any factor that falsely alters result of analytical measurement or experiment, leading to inaccurate data

Qualitative Chemical Analysis

Process of determining the identity of the constituents of a substance

Quantitative Chemical Analysis

Measurement of how much of a chemical substance is present

Species

Any atom/molecule/etc. that can be involved in a chemical process or measurement

Standard Solution

Contains known concentrations of certain components. Prepared with high accuracy using high-purity substances/precision glassware

Anhydrous

Substance with no water. Crucial for compounds where water would interfere with the reaction

Concentration

States how much solute is contained in a given volume of solution

Density

Mass per unit volume (m/V)

Formal Concentration

Description of how solution was made by dissolving F mol/liter, even if substance is converted into other species in soln. Used for molarity of electrolyte

Formula Mass

Sum of the average atomic masses of all atoms represented in chemical formula

Limiting Reagent

Reagent in reaction that is completely consumed first, limiting amount of product that can be formed

Molality

Composition expressed as moles of substance per kilo of solvent (m/kilogram of SOLVENT)

Molarity

Amount of substance per liter of soln. (M/L)

Mole

Unit of measurement for amount of a substance, representing a specific number of particles (avogadro’s number)

Molecular Mass

Total mass of atoms within one molecule

Ppb/Ppm

Parts per billion/million, grams of substance per ___ grams of total solution.

Solute

Minor species

Solvent

Major species

Stoichiometry

Study of quantitative relationships between reactants and products in chemical reaction

Volume Percent

(volume of solute/volume of total soln.) * 100

Weight Percent

(mass of solute/mass of total soln.) * 100

Absorption

Particles penetrate into entire volume of the material

Adsorption

Surface phenomenon, particles adhere to the surface of a material

Buret

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

Calibration

Process of determining the relationship between known amount of substance and the instrumental response it produces

Meniscus

Surface of most liquids form this in a concave manner

Parallax

Error that occurs when your eye is not at the same height as the liquid

Glass Transfer Pipet

Narrow, graduated glass tube, used to transfer small, app

Micropipette

Slender glass capillary filled with an electrolytic solution

Relative Uncertainty

(Uncertainty in quantity/magnitude of quantity) * 100

Serial Dilution

Process of making successive dilutions to obtain a desired concentration of reagant

Tare

Mass of empty vessel

Volumetric Flask

Prepares solutions of precise volume by holding single, specified quantity of liquid up to calibration mark on its narrow neck

Absolute Uncertainty

Measurement of error expressed with the same units as the measured quantity

Accuracy

Measures how close a measurement is to its true value

Matrix

Everything else in sample other than analyte

Precision

Measures how close repeated values are to each other

Random/Indeterminate Error

Standard deviation, arises from uncontrolled variables

Significant Figures

Minimum number of digits needed to write given value in scientific notation

Systematic/Determinate Error

Arises from flaw in equipment or design of experiment

Blank Solution

Solutions containing all reagents and solvents, but deliberately no analyte

Confidence Interval

Range of values calculated from sample data that is likely to contain true value of population parameter

Degrees of Freedom

Quantity n-1

Gaussian Distribution

Normal distribution, ideal bell shaped curve

Intercept

Predicted value where the data’s variable will reach 0

Linear Range

Range of analyte or input concentrations where instrument’s signal is directly proportional to amount of substance present

Linear Response

Response of system to weak external force with dynamics in equilibrium

Method of Least Squares

Used to find best fit line/curve for set of data points by minimizing sum of squares of deviations

Relative Standard Deviation

Standard deviation expressed as a percentage of the mean (=100% * s/x bar)

Slope

Change in y/change in x

Standard Deviation

Statistical measure of data spread, indicating how much individual data points vary from the mean

Standard Uncertainty

u subscript x, expression of any source of measurement uncertainty in a form that can be propagated

Student’s t

Statistical tool used to express confidence intervals and to compare results from different experiments

T test

Determines if there is a significant difference between the two means of populations

Variance

Measures speed or dispersion of numbers in dataset by calculating average of their squared differences from the mean

Quality Assurance

QA, steps and metrics put in place before performing analysis to ensure that we can get the right answer

External Standards

Known solutions of analyte that do not involve the unknown solution

Standard Addition

Known quantities of analyte added to unknown

Dilution Factor

DF, ratio of total final volume of solution to initial volume of stock solution

Beer’s Law

Relationship between the amount of light absorbed by solution and the concentration of the light absorbing substance. A = εbc

Chromophore

Part of molecule responsible for light absorption

Cuvette

Cell that has flat, fused-silica faces

Electromagnetic Spectrum

Entire range of EM waves which are all forms of radiation

Emission Spectrum

Unique pattern of EM radiation emitted by substance when its electrons transition from higher energy state to lower

Excited State

Higher energy state for quantum system

Fluorescence

Physical property of a molecule to absorb photons at one wavelength and quickly re-emit them at a different, lower energy wavelength

Ground State

Configuration of an atom that possesses the lowest possible energy

Irradiance

Amount of EM energy received by a surface per unit area, measured in W/m²

Luminscence

Emission of light by substance that has not been heated

Molar Absorptivity

Measure of chemical’s ability to absorb light at a specific wavelength

Monochromatic Light

Contains only a single frequency or wavelength

Monochromator

Optical device that isolates and selects specific narrow band of wavelengths

Photon

Fundamental particle that carries EM energy, including light, and has no mass or electric charge

Quenching

Process by which emission from an excited state molecule is decreased by energy transfer to another molecule

Reagant Blank

Control sample used in analytical chemistry that contains all reagants, solvents and equipment used in test, but lacks analyte

Spectrophotometry

Measures how material interacts with light by quantifying its light absorption or transmission as function of wavelength

Transmittance

Quantitative measure of fraction of incident light that passes through a sample without being absorbed or scattered

Wavelength

Distance between two consecutive, identical points on the wave

Wavenumber

Number of wavelengths per unit distance

Colorimeter

Compares amount of light getting through a solution with the amount that can get through a sample of pure solvent

Diffraction

Bending and spreading of waves as they pass by an obstacle or through aperture (opening)

Diffraction grating

Optical component with many lines that separates light into its constituent wavelengths through diffraction

Laser

Provide isolated lines of a single wavelength for many applications

Monochromator

Disperses light into its component wavelengths and selects narrow band of wavelengths to pass on to sample/detector

Optical Fiber

Thin strand of highly pure glass/plastic designed to transmit light signals. Carry light by total internal reflection.

Photodiode

Photodetector in which light striking semiconductor generates electrical current

Phodiode Array

PDA, contains 10+ individual photodiodes. Electronic sensor that detects light and converts it into electrical signals.

Photomultiplier tube

PMT, Highly sensitive detector that converts single photon into measurable electrical current by amplifying electron emissions from photocathode.

Phototube

Emits electrons from photosensitive, negatively charged surface (cathode) when struck by visible light/radiation

Photovoltaic Detector

Operates on principle of the photovoltaic effect within photodiode to convert light to electrical current

Polychromatic Light

Light of many wavelengths

Polychromator

Optical instrument that splits broad spectrum of light into multiple narrow spectral channels simultaneously using concave grating/filters.

Calibration Methods

• External Calibration

• Standard Addition

• Matrix

Solutions

• Standard solution

• Serial Dilution

• Concentrations

• Blank Solution