Solute concentration is the amount of a solute dissolved in a solvent, measured by weight, volume, or molecular mass. Different methods are used depending on the needs, such as weight percent blend, weight per volume, percent by volume, and molar concentration. Molar concentration is often used in laboratories to accurately determine the amount of material available for chemical reactions.
Solute concentration is a term used to describe mixtures and defines the amount of one substance, called a solute, dissolved in another, called a solvent. There are several ways to describe concentration, depending on your needs, and they can involve weight, volume, or molecular mass. The concentration of the mixtures is important because many chemical reactions depend on having the right amount of reactants to complete the reaction.
Perhaps the simplest way to describe solute concentration is by weight. A person wishing to make a consistent mixture of salt in water could weigh both materials and record the results. Repeatedly weighing the same amounts can then reproduce the concentration of salt water, which will give equivalent mixtures. A blend made using this method is usually called a weight percent blend, which defines that weights were used instead of volume.
Weight per volume is also a common measure of solute concentration. An amount of solute is first weighed using a measuring scale, then added to a container. The solvent is then added to a volume mark on the container, resulting in a known volume of mixture. The resulting mixture is defined as weight per volume, such as pounds per gallon or grams per liter.
Volumetric solute concentration is possible if both materials are liquids, but is not used for solids dissolved in liquids. A marked container is used to measure the volume of the solute and solvent, then they are mixed. The concentration is given as a percent by volume to identify that both materials are present by volume, rather than by weight.
For laboratory use, molar or molar concentrations are often used to accurately determine the amount of material available for chemical reactions. Moles of a solute are equal to the weight of the material divided by the molar mass, which is determined mathematically from the periodic table of elements. For example, a water molecule contains two atoms of hydrogen and one of oxygen. The molar mass of hydrogen and oxygen can be found on any published periodic table.
Once found, the molar mass of the molecule is determined by adding the molar mass of oxygen to two masses of hydrogen, which equal the atoms present in a water molecule. Molar mass has no units, but is often published as grams per mole; this can be pounds per mole if the molar masses are pounds. The number of moles is often determined by the chemical reaction itself, as the products react according to their molar masses as the molecules combine.
To determine the amount of solute to add in a molar mixture, the number of moles needed is multiplied by the molar mass to get a weight. This weight is added to a container and a known amount of solvent volume, typically a liter or a gallon, is added to achieve a consistent concentration. The result is a moles per volume ratio, which is called the molar concentration of solute. Adding the same weight to a known weight of solvent gives the molar concentration.
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