Chemistry - Mixtures and substances

chemistry

Prof. J. Peña

Complutense University of Madrid

Mixtures & pure substances

mixtures & pure substances

UCM - Faculty of Education

Classification

Mixtures

Substances

Solutions

Others...

Essentials of Chemistry

classification of matter

UCM - Faculty of Education

Essentials of Chemistry

mixtures

UCM - Faculty of Education

In chemistry, when two or more substances mix with each other without participating in a chemical change, the resulting substance is called a Mixture.

Properties

Types

Map

Essentials of Chemistry

pure substances

UCM - Faculty of Education

Essentials of Chemistry

• Elements: Substances made of only one type of atom (e.g., oxygen, O₂).
• Compounds: Substances made of two or more elements chemically combined in fixed proportions (e.g., water, H₂O).

Pure vs mixture

solutions

UCM - Faculty of Education

• A solution is a homogeneous mixture of two or more components. The dissolving agent is the solvent. The substance that is dissolved is the solute.

• According to the amount of solute, we have dilute (contains a small amount of solute) or concentrated solutions (contains a large amount of solute relative to the solvent).

Essentials of Chemistry

other types of mixtures

UCM - Faculty of Education

• Suspensions: The particles in suspensions are larger than those found in solutions. Example: Oil and water
• Colloids: Particles intermediate in size between those found in solutions and suspensions. Example: Milk

Essentials of Chemistry

Suspensions are mixtures where solid particles are dispersed in a liquid but will eventually settle out (e.g., sand in water).

A colloidal dispersion is a heterogeneous system consisting of a continuous phase (the dispersing medium) and a dispersed phase made up of small regions (weakly connected or not connected at all), which are distributed more or less homogeneously

Mayonnaise is a colloidal dispersion, i.e., it is an emulsion, which is a type of colloid where tiny droplets of one liquid (oil) are dispersed in another liquid (water, vinegar, or lemon juice) that they are immiscible with. The emulsifying agent, typically egg yolk, helps to stabilize this dispersion, preventing the oil and water from separating.

Chicken soup is considered a heterogeneous mixture, because it is not particularly well-mixed. Even if you stir the soup for quite some time, it doesn’t have a uniform composition. If I want a bowl of this soup, it makes a difference whether I take from the top of the pot or the bottom of the pot. No two bowls taken from this pot will ever be identical.

A solution or homogeneous mixture is a homogeneous system upon subdivision but heterogeneous upon a change of state. For example, seawater is a homogeneous system upon subdivision; any portion of the system has the same properties.

Matter is defined as anything that has the properties of mass and volume.

Mixtures can be classified into two main categories: homogeneous and heterogeneous. A homogeneous mixture is one in which the composition of its constituents are uniformly mixed throughout.

Elements are substances that are made up of only one type of atom. At this time, there are 118 known elements, most of which are metals. These elements are thought of as the elemental building blocks of matter.

Solvent particle

Solute particle

• Example of an element in the liquid state: Mercury (Hg). This is the only metal that is liquid at room temperature (around 20°C).
• Another element that can be in liquid form under slightly elevated temperatures is bromine (Br), a non-metal that becomes a liquid just above room temperature.

A mixture of sand mixed with salt is an example of a heterogeneous mixture. Heterogeneous mixtures possess different properties and compositions in various parts i.e. the properties are not uniform throughout the mixture.

Sugar mixed with water is the most common example of a homogeneous mixture. Homogeneous mixtures can be defined as the mixtures which possess the same properties and combination throughout their mass.

• The components of a mixture each keep their original properties.
• The separation of components can be easily done.
• The proportion of the components is variable.

Colloids are mixtures where tiny particles are dispersed but do not settle out (e.g., milk, fog).

A pure substance means that the substance is the same no matter where it is found. If you were to find a sample of 100% pure gold, it would only be made up of gold atoms. It wouldn’t matter where you found the pure gold, it would be made up of gold atoms.

Some mixtures are so well blended that they are considered homogeneous mixtures. Homogeneous mixtures have such a consistent composition, that all parts of the sample are the same. If you stir a small amount of salt into a glass of water, the salt will distribute so well that the consistency is considered constant.

Compounds are substances that are made up of more than one type of atom, e.g., water is made up of hydrogen and oxygen atoms. Water is still a substance because it has a consistent composition. Anywhere that you find pure water, it will be made up of molecules consisting of one oxygen atoms bonded to two hydrogen atoms.

A suspension refers to a solid dispersed in a liquid medium. In this case, when at rest, the particles settle and can be separated by filtration, resulting in a turbid preparation. Examples include carbon particles in water or antibiotics in suspension.