Chemistry

Measurement Accuracy The ability to repeat an experiment and get the same results, or reproducibility, is essential in scientific research. However, it’s impossible to repeat an experiment if you don’t know how you did it. Thus, scientists keep detailed records of their experiments in lab notebooks. These records include important information like the amount of each material used and descriptions of each step of the procedure. Equipment, like balances and volumetric or graduated glassware, is...

Two-Dimensional Graphs Some chemistry experiments take the form of directly changing one property of the system that you are studying otherwise known as the independent variable, like temperature, and measuring the effects on another property, otherwise known as the dependent variable, like volume. Once the data have been collected, the interaction between the two parameters must be quantified — or converted into a form that can be evaluated — and compared to other relationships.

Chemical equations represent how a chemical reaction proceeds from reactants to products through physical or chemical change using chemical formulas. Stoichiometry is a term that describes the relative quantities of reactants and products in a chemical reaction. It is based on the Law of Conservation of Mass, which is a fundamental law that states that matter is neither created nor destroyed. Quite simply, the number and identity of reactant atoms must equal the number and identity of product...

Oxidation and Reduction Some chemical reactions can be classified as reduction-oxidation reactions, or redox reactions. Oxidation is the process of matter, like an atom or ionic molecule, losing one or more electrons, and reduction is the process of the matter gaining one or more electrons. Oxidation States Each atom in a molecule has its own oxidation state or oxidation number. The oxidation state describes how oxidized a molecule is relative to its free elemental form. The oxidation state is...

Derivation of the Ideal Gas Law Gases are a fundamental state of matter. A gas is a collection of molecules that have a significant distance between their molecules. Due to this distance, colorless gases are invisible to the human eye and are studied using four measurable parameters: pressure (P), volume (V), number of moles (n), and temperature (T). The ideal gas law is a mathematical equation that relates all of these parameters. It is a combination of several different laws that describe the...

Acids and Bases An Arrhenius acid produces hydrogen ions when it is dissolved in water: HA + H2O → H+(aq) + A-(aq) Here, HA is the non-dissociated acid, H+ is the hydrogen cation, and A- is the solvated anion — called the conjugate base. An Arrhenius base produces hydroxide ions when dissolved in water: BOH + H2O → B+(aq) + OH-(aq) Here, BOH is the non-dissociated base, OH- is the hydroxide ion, and B+ is the solvated cation — called the conjugate acid. A conjugate base is formed when an acid...

Buffers When an Arrhenius acid (HA) is added to water, it dissociates into its conjugate base (A-) and a hydrogen cation (H+). HA + H2O → H+(aq) + A-(aq) The amount of hydrogen ions present in the solution determines the acidity of the solution, where more hydrogen ions indicate a lower or more acidic pH. Similarly, when a strong Arrhenius base (BOH) is added to water, it dissociates into its conjugate acid (B+) and a hydroxide ion (OH-). BOH + H2O → B+(aq) + OH-(aq) Generally, the addition of...

Enthalpy of Reaction Thermodynamics is the study of heat energy and other types of energy, such as work. The laws of thermodynamics are used across all known science fields and have applications ranging from biology to physics. Three Laws of Thermodynamics There are three principle laws of thermodynamics that describe the interactions occurring within the universe, regardless of scale. The first is the law of conservation of energy, which describes that the total energy of an isolated system is...

Solubility Solubility describes how much of a solute can dissolve in a given volume of a specific solvent. Solubility is usually reported in terms of solute mass per solvent volume or solute mass per solvent mass. For example, the solubility of sodium chloride in water at room temperature is reported as 36 g per 100 mL of water. If solubility is reported in solute mass per solvent mass, the solvent mass will need to be converted to volume for further calculations. Solubility changes with...

Metal Flame Emission Flame testing is an analytical technique where a sample is placed in a flame, and the characteristic flame color is used to identify the substance. Each element has a characteristic light emission when placed into a flame, meaning each element produces a unique color. This phenomenon is used in fireworks displays, where the color of the fireworks corresponds to a specific characteristic of a metal. The emission of colored light from a burning sample is the direct result of...

The Bohr Model Niels Bohr proposed a model for the hydrogen atom in 1913 that described discrete energy states are associated with a fixed electron orbit around the nucleus. Importantly, an atom cannot discharge energy while its electrons are in stationary states. An electron can only emit energy by changing energy states. To change energy states, an electron must move from one orbit to another by either absorbing or emitting energy. This change can only occur if the absorbed or emitted energy...

Absorbance and Fluorescence When light hits a substance, it is either absorbed, transmitted, or reflected. Typically, a substance interacts with a range of wavelengths of light, each one interacting with the molecules or atoms differently. A substance may absorb a specific range of wavelengths, reflect another range of wavelengths, and transmit the other wavelengths of light. When a molecule absorbs light, the energy is used in four different ways: (1) translation, which causes the molecule to...

Chemical Kinetics and the Reaction Rate Law Chemical kinetics refers to the rate or speed of a chemical reaction. The rate depends on the mechanism, complexity, and number of reactants in the reaction. Reactant concentration also plays a significant role in the rate of a reaction. The rate law quantifies this relationship through experimentation. Each reactant contributes to the speed of the reaction by a factor known as the reaction order. This factor can range from zero to two, and it depends...

Chemical Kinetics The reaction rate is the speed at which a chemical reaction occurs. The reaction rate is defined as the change in concentration of a component in the reaction with time. The speed of a reaction depends on several factors, including the concentration of reactants and the temperature at which the reaction is performed. Each reactant contributes to the speed of the reaction by a specific factor. This relationship is defined by the reaction rate law. Rate Law The rate law is an...

Electrochemistry Electrochemistry is a branch of chemistry that studies the relationship between electrical energy and a chemical change. These chemical reactions involve the movement of electrons from one species to another. This movement either generates current, or it is driven by applied current. The key reaction in electrochemistry is the oxidation-reduction, or redox, reaction. The redox reaction is composed of two half-reactions; the oxidation reaction, where a substance loses electrons,...

Electrochemistry Electrochemistry is a branch of chemistry that describes and measures the relationship between electrical energy and a chemical change. Electrochemical reactions involve the movement of electrons from one species to another. If the reaction is spontaneous, it can result in a generated current. If the reaction is not spontaneous, it can be driven by the application of current. In electrochemistry, the key reaction is the oxidation-reduction reaction, called a redox reaction. The...

Organic Lab Notebook Keeping Record keeping is a vital skill in science and organic chemistry labs. Without proper notes, descriptions, quantities, or observations, an experiment conducted in the lab cannot be replicated or reproduced. Therefore, keeping an accurate and up-to-date notebook is necessary to achieve reproducibility in science. A laboratory notebook is a powerful tool in both academic and industrial settings. It becomes especially important when a discovery is patented and...

Glassware in Organic Chemistry There are standard pieces of glassware that are used in the organic chemistry lab. Beakers and Erlenmeyer flasks are typically used for simple mixing or to hold solvents but they should not be used to measure volume, unless only an approximate volume is needed. Glassware can be divided into the following categories: Volumetric Glassware – This includes glassware such as graduated cylinders, volumetric glass pipettes, and volumetric flasks. The purpose of these...

Melting Points in Organic Chemistry The melting point of a compound is the temperature at which the solid phase transitions into the liquid phase at a standard pressure of 1 atmosphere. The melting point of a compound is a physical property, like solubility, density, color, and electronegativity that can be used to identify a compound. Determining the exact temperature at which a compound begins to melt is a challenging task; because of this, the melting point of compounds is reported as a...

Boiling Point Determination Similar to the melting point, the boiling point is a physical property. If the sample is a pure compound, then the boiling point can be used to determine the identity of the compound. Ultimately, experimentally determining the exact boiling point is challenging. Like melting points, experimental boiling points are given as a range and vary by a few degrees from the actual literature value. Vapor Pressure To understand why a solvent boils, which is characterized by...

Recrystallization Often, the desired product of a chemical reaction is part of a more complex reaction mixture, which can be composed of the solvent, starting materials, and impurities. Learning how to purify organic compounds properly is a valuable technique in organic chemistry. Recrystallization harnesses the differences in solubility of the desired compound and the impurity in the solvent to purify the desired product as a solid. There are three standard methods of purification:...

Extraction Extraction is a common technique used in organic chemistry to isolate a target compound. In the extraction process, a solute is transferred from one phase to another to separate it from unreacted starting materials or impurities. Extraction is also used to facilitate the isolation of a solute from a reaction solvent that is difficult to remove by evaporation, such as a solvent with a high boiling point. Generally, there are three types of extractions. First, in solid-liquid...

Distillation of a Miscible Mixture Some liquids will evaporate entirely over time if left in an open container at room temperature. However, this evaporation process can be significantly accelerated if the liquid is heated. As the liquid is heated, the molecules within it gain the energy to escape the liquid phase and transition into the gas phase in the form of bubbles. This phenomenon is called boiling. Vapor Pressure Consider a closed container of liquid. Initially, some of this liquid...

Steam Distillation Steam distillation is a separation technique that harnesses the low boiling point property of immiscible mixtures. It is predominately used to separate temperature-sensitive organic molecules from a non-volatile contaminant. The organic molecule must be immiscible in water. In steam distillation, the immiscible mixture is heated to boiling, causing the distillation of both water and the volatile organic compounds. This means that the gaseous mixture travels upwards to a...

Chromatography Chromatography is a technique used in organic chemistry to separate compounds in a mixture based on their differences in solubility between two different phases. The concept is similar to liquid-liquid extraction, except in chromatography, the two phases consist of the stationary phase and the mobile phase. The stationary phase is a solid — typically a microscale hydrogel bead — while the mobile phase is a carrier solvent. In traditional chromatography, the stationary phase is...

Column Chromatography Multiple techniques exist to purify and separate compounds in an organic chemistry laboratory. One of the most reliable separation techniques for microscale separations, where less than 10 grams of the compound is available for analysis, is column chromatography. This technique separates compounds in a mixture based on their physical properties, such as their solubility, polarity, hydrophobicity, size, and charge. Chromatography Basics The main components of any...

Triglycerides Triglycerides are triester molecules composed of a glycerol backbone that is bound to 3 fatty acids. These form the basis of many biological lipids that are found in vegetable oils and fats. Lipids that are isolated from plant material are the basis of vegetable oils, whereas lipids extracted from animals are used as lard or general sources of fats. A fatty acid molecule has a long carbon chain — between 12 and 20 carbons — with a weak organic acid at one end. Some fatty acids...

Chemical reactions can be classified as endothermic or exothermic depending on whether the reactions absorb or release heat when they change to products. The difference in energy between reactants and products is known as the enthalpy of the reaction. This is found by calculating the difference in energies between the products and the reactants, or ΔH. If ΔH is positive, the reaction is endothermic; if it is negative, the reaction is exothermic. While chemical reactions are traditionally...

Esters The structure of an ester is a carbonyl with an alkyl or aryl group (R) on one side, and an oxygen bound to another alkyl or aryl group (R’) on the other side, represented by the general formula: RCOOR’. Esters can be commonly derived by an esterification reaction between a carboxylic acid and an alcohol. The hydroxyl group of the carboxylic acid is replaced by an alkyl or aryl group. Simple esters, which have low molecular weight and small R and R’ functional groups, have smells and...

Aldehydes and Ketones Aldehydes and ketones have a carbonyl group (C=O) as a functional group. A ketone has two alkyl or aryl groups attached to the carbonyl carbon (RCOR’). The simplest ketone is acetone, which has two methyl groups attached to the carbonyl carbon (CH3COCH3). An aldehyde is similar to a ketone, except that instead of two side groups connected to the carbonyl carbon, they have at least one hydrogen (RCOH). The simplest aldehyde is formaldehyde (HCOH), as it has two hydrogens...

Absorbance When light interacts with a substance, a portion of the light is absorbed while the rest is either reflected or transmitted through it. Substances that we perceive as having a color reflect light in the visible range. The color of the substance that we are able to see depends on which wavelength of light is reflected. A substance that we perceive as blue reflects light in the blue range (430 – 480 nm) of the visible spectrum. According to the color wheel, the same substance absorbs...

Alcohols Alcohols are organic compounds that are amongst the most recognizable and familiar, as they have wide-ranging applications and uses in everyday life. Alcohols are organic molecules containing a hydroxyl functional group connected to an alkyl or aryl group (ROH). If the hydroxyl carbon only has a single R group, it is known as primary alcohol. If it has two R groups, it is a secondary alcohol, and if it has three R groups, it is a tertiary alcohol. Like many other organic compounds,...