Chem 311 - Tools of the Trade

Chemical Experimentation

Process that inherently creates hazards requiring discussion and sensible precautions before proceeding.

Contact Lenses in Lab

Not recommended because chemical vapors can become trapped between the lens and the eye.

Vessel Labeling

Mandatory practice of marking all lab containers to clearly indicate their contents.

Chemical Waste Ethics

The ethical responsibility of every chemist to minimize waste generation, follow disposal protocols properly, and recycle chemicals when possible.

Green Chemistry

Set of principles designed to change behavior, encourage sustainability, prevent waste creation, and protect the planet.

Microscale Experiments

Classroom experimental approach encouraged to reduce the cost of chemical reagents and minimize waste generation.

Lab Notebook Functions

Primary legal and experimental record designed to state what was done, state what was observed, and be understandable to a stranger.

Electronic Balance

Instrument that uses electromagnetic force to compensate for a load placed on the pan to measure mass.

Electronic Balance Operation Mechanism

An object pushes the pan down with force (m x g), generating an electric current in a wire coil within a permanent magnetic field that cancels motion and indicates mass.

Readability

The smallest increment of mass indicated on a balance display.

Microbalance

Analytical balance measuring milligram quantities with a readability of 1 microgram.

Tare

The mass of an empty receiving vessel, which can be zeroed out on a balance using the tare button.

Balance Protection Protocols

Never place chemicals directly on the weighing pan, prevent spills into the lower mechanism, and clean spills immediately.

Hygroscopic Reagents

Substances that rapidly absorb moisture from air and require weighing by difference.

Weighing by Difference

Method where a capped bottle with dry reagent is weighed, a portion is poured into a receiver, and the bottle is reweighed to find the delivered mass via subtraction or negative tare reading.

Sources of Balance Error

Fingerprint oils, draft currents from open doors, static charge, off-center placement, spills, general vibrations, direct sunlight/temperature shifts, moving the balance, incomplete transfer, contamination, and strong magnetic fields.

Buoyancy

Upward force exerted on an object in a fluid due to density differences.

Buoyancy Error

Discrepancy where an object weighed in air appears lighter than its true vacuum mass by an amount equal to the mass of displaced air.

Buoyancy Error Condition

Occurs whenever the density of the object being weighed differs from the density of the balance calibration standard weights (typically 8.0 g/mL).

Buoyancy Correction Formula

m = [m' * (1 - da / dw)] / (1 - da / d), where m is true mass, m' is apparent mass, da is air density, dw is calibration weight density, and d is object density.

Calgary Air Density Calculation

Determined using the ideal gas law (P = 0.88 atm) and average molecular weight of dry air (28.950 g/mol) yielding a density of 0.00106 g/mL (1.06 x 10^-3 g/mL) at 298 K.

Tris Primary Standard

Pure compound (density = 1.33 g/mL) used as a primary standard to standardize acid concentrations.

Buret

Precisely manufactured graduated glass tube used to deliver variable, accurately measured volumes of liquid through a bottom stopcock.

Class A Glassware

High-precision grade glassware manufactured to strict tolerances; preferred over Class B glassware.

Buret Reading Interpolation

Practice of estimating volume readings between graduations to the nearest 0.01 mL (one-tenth of a division).

Parallax Error

Apparent shift in meniscus position caused by observing the liquid level above or below eye level.

Buret Operation Steps

Rinse with titrant, eliminate air bubbles in the stopcock, drain liquid slowly, deliver partial drops near the endpoint by touching the tip to the receiver wall, and read the bottom of the concave meniscus.

Volumetric Flask

Glassware calibrated to contain (TC) a specific volume of solution at 20 °C when filled so the bottom of the meniscus touches the calibration mark line.

TC vs TD Markings

TC means "To Contain" (used on volumetric flasks), whereas TD means "To Deliver" (used on pipets and burets).

Temperature Effect on Glassware

Changes liquid and glass volumes via thermal expansion and contraction, necessitating standard calibration at 20 °C.

Volumetric Flask Preparation Steps

Dissolve reagent in ~10% final volume, add liquid with swirling, fill dropwise near the mark to set the meniscus, cap tightly, and invert ~10 times for homogeneity.

Schlieren

Optical streaks observed in solution resulting from non-homogeneous regions refracting light differently; indicates incomplete mixing.

Pipet

Glassware calibrated to deliver (TD) a specific volume of liquid at 20 °C.

Transfer Pipet vs Measuring Pipet

Volumetric (transfer) pipets deliver a single fixed volume, while Mohr (measuring) pipets feature graduations to deliver variable volumes.

Pipet Retained Volume

Small liquid drop remaining inside the pipet tip by design; must never be blown out.

Pipet Operation Protocol

Use a rubber bulb to fill past the calibration mark without sucking liquid into the bulb, discard two volumes to rinse, refill past the mark, hold with a finger, adjust meniscus to the line, drain, and touch the tip to the vessel wall.

Glassware Tolerances

Permissible error limits defined by standards (e.g., ASTM E-288, ASTM E-969); Class B tolerances are twice as large as Class A tolerances.

Serial Dilution

Process of making successive dilutions from a concentrated stock solution to accurately reach low target concentrations.

Serial Dilution Purpose

Accurately transfers small quantities of solute that are too small to weigh directly on an analytical balance.

Serial Dilution Rule of Thumb

Dilutions by factors of 10, 20, or 50 produce lower overall relative uncertainty than a single large dilution step.

Intermediate Stock Solution

A solution prepared during an intermediate step of a serial dilution sequence.

Gravimetric Analysis

Analytical method based on determining the quantity of an analyte by measuring the mass of a solid precipitate.

Fritted-Glass Funnel (Gooch Filter)

Filter crucible containing a porous glass disk used with vacuum suction to collect precipitates during gravimetric analysis.

Suction Filtration Apparatus Setup

Consists of a Gooch crucible fitted with a rubber adapter onto a suction flask, connected via tubing to a safety trap flask linked to the house vacuum.

Paper Filtration Protocol

Fold filter paper into quarters, tear off an outer corner for a tight seal in a conical funnel, pour slurry down a glass rod to prevent splattering, and ensure liquid fills the funnel stem.

Rubber Policeman

Flexible rubber scraper attached to a glass rod used to dislodge precipitate particles from container walls.

Ignition of Precipitate

High-temperature heating procedure used to convert a collected precipitate into a compound of known, constant chemical composition.

Ashless Filter Paper

Special filter paper used during ignition procedures because it leaves virtually no ash residue upon burning.

Drying Oven

Laboratory oven set to ~110 °C used to dry benign solids (e.g., KBr) or glassware.

Desiccator

Sealed chamber containing a drying agent (desiccant) used to store dried samples in a moisture-free environment.

Desiccator Operation Protocol

Grease the glass flange to ensure an airtight seal, place desiccant beneath the perforated plate, slide the lid horizontally to open, and cool hot reagents inside for 30 minutes before weighing.

Desiccant

Anhydrous chemical compound placed in a desiccator to absorb atmospheric water vapor.

Common Desiccants and Efficiency

Magnesium perchlorate (0.2 µg H2O/L left), Barium oxide (2.8 µg/L), Alumina (2.9 µg/L), Phosphorus pentoxide (3.6 µg/L), Calcium sulfate/Drierite (67 µg/L), Silica gel (70 µg/L).

Desiccant Regeneration

Process of driving absorbed water out of spent desiccant by heating it in an oven to restore its drying capacity.

Buret Calibration Steps

Clean buret, fill with distilled water, remove bubbles, check for drop formation, adjust meniscus to 0-0.3 mL, allow to stand 5 min to test stopcock seal, drain ~10 mL intervals at <20 mL/min into a stoppered flask, weigh water, convert mass to volume using water density tables, and plot correction curves.

Buret Draining Speed Limit

Must be kept below 20 mL/min to allow liquid on inner glass walls time to drain completely.

Water Density Table Correction

Conversion factor (e.g., 1.0037 mL/g at 24 °C corrected to 20 °C) that accounts for water density and thermal expansion of glass when converting water mass to true volume.

Buret Correction Calculation

Buret Correction = (Actual Volume Delivered) - (Indicated Volume Reading).

Excel Column and Row Layout

Columns run vertically (labeled A, B, C...) and rows run horizontally (labeled 1, 2, 3...).

Excel Data Entry Types

Labels (text/headings), Numbers (constant numeric values), and Formulas (equations starting with '=').

Excel Formula Syntax

Equations starting with an equals sign (=) that compute values using cell references, relative positioning, or absolute positioning ($ symbol).

Excel Plotting for Calibration

Creates graphical correction curves plotting indicated volume on the x-axis against volume correction on the y-axis to adjust volumetric readings.