General Chemistry

Lab glass materials affect durability, heating, and clarity in chemistry work. Glass is common in the laboratory because it is relatively low cost, extremely durable, and precise for many tasks. Some labware is now replaced by plastic or even everyday kitchen materials, but glass remains the standard material for laboratory work. Good lab technique also depends on best practices for using glassware.

Not all glass used in labs is the same. Standard consumer-grade glass is called soda-lime...

Preparing and measuring solution concentration are key parts of chemistry. A solution is a homogeneous mixture. It contains solutes, which are present in small amounts, and a solvent, which is present in a large amount.

This topic focuses on solid-liquid solutions. In these mixtures, one or more solid solutes dissolve in a liquid solvent. Solutions are used often in chemistry because they help store and handle small amounts of material, support chemical reactions, and make materials with...

Density is the mass of a substance divided by its volume. It is often written in units such as g/mL or kg/m3. Because density does not change with the amount of material present, it is an intensive property.

To find density, both mass and volume must be measured. A balance is used to measure mass for both solids and liquids. The method for volume depends on the type of sample.

Liquids take the shape of their container, so their volume can be measured with glassware such as a graduated...

Analyzing solute content in water solutions is an important analytical and forensic technique. In an aqueous solution, water is the solvent. The solvent is the main component. The dissolved minor component is the solute.

The solute is dissolved in the solvent to make a solution. Water is the most common solvent in everyday life. It is also the main solvent in nearly all biological systems. In chemistry labs, the solvent may be another liquid, such as acetone, ether, or an alcohol.

The solute...

Gravimetric analysis can be used to determine the empirical formula of a compound. The empirical formula gives the smallest whole-number ratio of elements in a molecular compound. In this experiment, that ratio is found for copper chloride hydrate, Cu x Cl y · nH2O.

The method relies on the law of conservation of mass. Because mass is conserved, a reaction can be tracked by measuring changes in mass. This makes gravimetric analysis a simple and accurate way to help determine chemical formulas...

Qualitative analysis can be used to identify the ions in an ionic compound and to infer solubility from the products that form. It is a branch of analytical chemistry that uses chemical properties and reactions to determine whether a cation or an anion is present. The same known solubility rules that guide these tests can also be learned by observing the reaction products.

This approach is not usually used in modern industrial chemistry labs, but it is practical in the field because it does...

Measuring acidic and basic pH helps describe how a solution behaves. Acids donate protons, or H+ ions, and bases donate hydroxide ions, or OH- ions. When acids and bases are mixed, they can neutralize each other. A neutral substance is neither acidic nor basic.

pH is a practical way to compare proton concentration in solutions. The amount of H+ in most solutions is very small, so pH makes the value easier to use. pH was first defined from the reciprocal of proton concentration and was later...

Acid-base titration is a common way to measure the concentration of an unknown solution. It is also called volumetric analysis because careful volume measurement is a key part of the method. In this technique, a standard solution is used to react with an analyte whose concentration is not known.

Titrations can be grouped by the type of reaction they use. The most common examples are acid-base titrations and redox titrations. During a typical titration, the titrant is placed in a burette and...

Gas laws explain how pressure, volume, temperature, and the amount of gas are related. For most common gases near normal conditions, these relationships are a useful model. They also help connect what happens on the microscopic level with what we can measure in a lab, such as pressure and volume.

The history of the ideal gas law began in the 17th century with a key pattern in air. Robert Boyle confirmed that pressure and volume are inversely proportional. This relationship is called Boyle’s...

The equilibrium constant, K, can be measured by tracking color in a chemical equilibrium. For a system with one colored species, spectrophotometry is used to relate absorbance to concentration. The colored component can then be measured directly, while the colorless components are found from the balanced chemical equation.

This lab uses the Fe(SCN)2+ system to build a Beer’s law curve from experimental data. That curve is then applied to find the concentration of the colored ion in the...

Chemical equilibrium shifts are shown with a color test using iron(III) ions and thiocyanate ions. In this reversible reaction, Fe3+ and SCN- combine to form FeSCN2+. The changing color of the solution helps show which side of the equilibrium is favored.

The experiment follows Le Châtelier's principle. This principle says that when temperature, pressure, or concentration changes disturb a system at equilibrium, the system responds by counteracting that change. Here, the focus is on...

Freezing-point depression can help identify an unknown compound. When a solid compound dissolves in a solvent, the freezing point of the solution becomes lower than the freezing point of the pure solvent. This change is linked to the molecular weight of the solute.

In this experiment, the unknown compound is dissolved in cyclohexane. The freezing point of the cyclohexane solution is measured, and the freezing point of pure cyclohexane is measured as well. The difference between the two...

Chemical reaction speed depends on the rate law and the reaction order. These ideas help describe how reactants change into products over time. The rate of a reaction can be affected by temperature, concentration, and the physical properties of the reactants.

The rate law shows the role of each reactant in a reaction. It is written as a rate equation, where A and B are concentrations of different molecular species, m and n are reaction orders, and k is the rate constant. The reaction rate also...

Differential scanning calorimetry, or DSC, is a thermodynamic analysis method that tracks heat flow as temperature changes. It compares a sample material sealed in a pan with an empty reference pan. Both pans are exposed to the same temperature conditions.

The instrument records the energy difference needed to keep the two pans at the same temperature. This difference comes from the different heat capacities of the sample and the reference pan. As the temperature changes, the energy absorbed...

Transition metals form coordination complexes with ligands in many everyday materials. These metals appear in vitamin supplements, electroplating baths, pigments in paints, and minerals. In many cases, they are found as cations because they readily oxidize, or lose electrons.

Ligands are electron donors that surround the metal center. Their bond to the metal is called a coordinate-covalent bond. This bond is not purely ionic or covalent. It is dynamic, so ligands can exchange and re-coordinate...