Mixture

Key takeaways

Mixture belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Mixture to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Mixture from memory before moving on to harder problems.

Reference excerpt

In chemistry, a mixture is a material made up of two or more different chemical substances which can be separated by physical method. It is an impure substance made up of two or more elements or compounds mechanically mixed together in any proportion. A mixture is the physical combination of two or more substances in which the identities are retained and are mixed in the form of solutions, suspensions or colloids. Mixtures are one product of mechanically blending or mixing chemical substances such as elements and compounds, without chemical bonding or other chemical change, so that each ingredient substance retains its own chemical properties and makeup. Despite the fact that there are no chemical changes to its constituents, the physical properties of a mixture, such as its melting point, may differ from those of the components. Some mixtures can be separated into their components by using physical (mechanical or thermal) means. Azeotropes are one kind of mixture that usually poses considerable difficulties regarding the separation processes required to obtain their constituents (physical or chemical processes or, even a blend of them).

Characteristics of mixtures All mixtures can be characterized as being separable by mechanical means (e.g. purification, distillation, electrolysis, chromatography, heat, filtration, gravitational sorting, centrifugation). Mixtures differ from chemical compounds in the following ways:

The substances in a mixture can be separated using physical methods such as filtration, freezing, and distillation. There is little or no energy change when a mixture forms (see Enthalpy of mixing). The substances in a mixture keep their separate properties. In the example of sand and water, neither one of the two substances changed in any way when they are mixed. Although the sand is in the water it still keeps the same properties that it had when it was outside the water.

mixtures have variable compositions, while compounds have a fixed, definite formula. when mixed, individual substances keep their properties in a mixture, while if they form a compound their properties can change. The following table shows the main properties and examples for all possible phase combinations of the three "families" of mixtures :

Homogeneous and heterogeneous mixtures

Mixtures can be either homogeneous or heterogeneous: a mixture of uniform composition and in which all components are in the same phase, such as salt in water, is called homogeneous, whereas a mixture of non-uniform composition and of which the components can be easily identified, such as sand in water, it is called heterogeneous. In addition, "uniform mixture" is another term for homogeneous mixture and "non-uniform mixture" is another term for heterogeneous mixture. These terms are derived from the idea that a homogeneous mixture has a uniform appearance, or only one phase, because the particles are evenly distributed. However, a heterogeneous mixture has constituent substances that are in different phases and easily distinguishable from one another. In addition, a heterogeneous mixture may have a uniform (e.g. a colloid) or non-uniform (e.g. a pencil) composition. Several solid substances, such as salt and sugar, dissolve in water to form homogeneous mixtures or "solutions", in which there are both a solute (dissolved substance) and a solvent (dissolving medium) present. Air is an example of a solution as well: a homogeneous mixture of gaseous nitrogen solvent, in which oxygen and smaller amounts of other gaseous solutes are dissolved. Mixtures are not limited in either their number of substances or the amounts of those substances, though in most solutions, the solute-to-solvent proportion can only reach a certain point before the mixture separates and becomes heterogeneous. A homogeneous mixture is characterized by uniform dispersion of its constituent substances throughout; the substances exist in equal proportion everywhere within the mixture. Differently put, a homogeneous mixture will be the same no matter from where in the mixture it is sampled. For example, if a solid-liquid solution is divided into two halves of equal volume, the halves will contain equal amounts of both the liquid medium and dissolved solid (solvent and solute)

Homogeneous mixtures

Solutions

A solution is equivalent to a "homogeneous mixture". In solutions, solutes will not settle out after any period of time and they cannot be removed by physical methods, such as a filter or centrifuge. As a homogeneous mixture, a solution has one phase (solid, liquid, or gas), although the phase of the solute and solvent may initially have been different (e.g., salt water).

Gases Gases exhibit by far the greatest space (and, consequently, the weakest intermolecular forces) between their atoms or molecules; since intermolecular interactions are minuscule in comparison to those in liquids and solids, dilute gases very easily form solutions with one another. Air is one such example: it can be more specifically described as a gaseous solution of oxygen and other gases dissolved in nitrogen (its major component).

… excerpt ends here. Continue reading the full article.

Illustrations

Mixture: Making an heterogeneous mixture of water and oil — Making an heterogeneous mixture of water and oil

Worked examples

Example 1 — a first encounter with Mixture

Start with the simplest possible case. Write down what Mixture claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Mixture before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Mixture ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Mixture

In research: Mixture appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Mixture in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Mixture is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical mixtures, Chemistry, Physical chemistry, so understanding it makes those chapters shorter.
In everyday life: Look for Mixture outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Mixture in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Mixture means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Mixture out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Mixture in simple terms?

In chemistry, a mixture is a material made up of two or more different chemical substances which can be separated by physical method. It is an impure substance made up of two or more elements or compounds mechanically mixed together in any proportion.

Why does Mixture matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Mixture?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Mixture.