General Chemistry Laboratory: Measurement, Density, Hydrates, and Stoichiometry

Vocabulary practice flashcards covering laboratory measurements, precision, accuracy, density determination, properties of hydrates, and reaction stoichiometry.

Significant Digits (Significant Figures)

All the digits of an experimental measurement that are known exactly, plus the first digit that is uncertain.

Liquid Meniscus

The curved surface of a liquid in a container, which must be read at its lowest point when determining liquid volume on a graduated scale.

Accuracy

A measure of how close an experimental measurement is to the true, accepted value.

Precision

The degree of uncertainty or reproducibility in a measurement; measuring devices providing more decimal places produce more precise measurements.

Percent Error

A quantitative evaluation of the accuracy of an experimental value ($\text{EV}$) compared to a true value ($\text{TV}$), calculated using the formula: $\text{Percent Error} = \frac{|\text{EV} - \text{TV}|}{\text{TV}} \times 100$.

Melting Point

A physical property defined as the temperature at which liquid first appears when a solid substance is heated continuously.

Melting Point Determination Setup

An apparatus consisting of a capillary tube containing the sample attached to a thermometer via latex tubing, suspended in a heated water bath using a clamp and stand.

Weighing by Difference

A laboratory method used to determine the mass of a substance (such as a powder) by measuring the mass of the empty container, adding the substance, and subtracting the initial container mass from the total combined mass.

Density

An intensive physical property defined as the mass per unit volume of a substance: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$.

Intensive Property

A property of matter that is independent of the quantity of matter present, such as density or melting point.

Extensive Property

A property of matter that depends directly on the quantity of matter present, such as mass or volume.

Water Displacement (Archimedes' Principle)

An indirect method for determining the volume of an irregularly shaped solid by immersing it in liquid, where $\text{Volume of solid} = \text{Final volume} - \text{Initial volume}$.

Best-Fit Line

A single straight line drawn on a scatter plot that comes as close as possible to all data points, expressed by the equation $y = mx + b$.

Slope ($m$)

The ratio of vertical change to horizontal change ($\frac{\Delta y}{\Delta x}$) along a line; on a graph of mass versus volume, the slope represents the density of the substance.

y-Intercept ($b$)

The point on the y-axis where a line crosses; on a mass versus volume plot, its theoretical value is zero because zero volume must have zero mass.

Water of Hydration (Water of Crystallization)

Water molecules that are chemically incorporated in stoichiometric amounts into the crystal structure of an ionic complex, typically bonded to the cation.

Hydrate

A chemical compound containing water molecules in a definite stoichiometric ratio bonded within its solid structure, named using Greek prefixes for the water ratio.

Anhydrous Compound

The solid residue remaining after the water of hydration has been removed from a hydrate through endothermic dehydration.

Efflorescent Substance

A hydrate that spontaneously loses water of hydration to the atmosphere upon standing at room temperature, defined by a mass decrease of $0.005\,\text{g}$ or more.

Hygroscopic Substance

A compound that spontaneously absorbs water vapor from the surrounding atmosphere, defined by a mass increase of $0.005\,\text{g}$ or more.

Desiccant

A hygroscopic material (such as $P_2O_5$ or anhydrous $CaCl_2$) widely used to dry liquids and gases by absorbing moisture.

Deliquescent Substance

A strongly hygroscopic compound (such as solid $NaOH$) that absorbs enough water from the atmosphere to dissolve completely and form an aqueous solution.

True Hydrate

A compound exhibiting all three characteristic hydrate behaviors: release of water upon heating, complete solubility of its anhydrous residue in water, and reversible color return upon rehydration.

Theoretical Yield

The maximum calculated mass of product that could be produced in a chemical reaction assuming complete conversion with zero errors, determined using stoichiometric calculations.

Experimental Yield

The actual mass of product retrieved, dried, and weighed after performing a chemical reaction in the laboratory.

Percent Yield

The ratio of the actual yield obtained experimentally to the theoretical stoichiometric yield, calculated as: $\text{Percent Yield} = \frac{\text{Experimental Yield}}{\text{Theoretical Yield}} \times 100$.

Mole-to-Mole Ratio

The stoichiometric proportion between moles of reactants and products, derived either theoretically from balanced reaction coefficients or experimentally by dividing mole values by the lowest mole quantity.