Concentration refers to the weight of a species in the population.
Commonly used concentration expression methods are:
Weight percentage concentration: generally used and most commonly used.
Volume percentage concentration: commonly used to represent alcohol.
Volume molar concentration: commonly used in chemistry.
weight-molality
Molar fraction
The broad concept of concentration refers to the amount of solute in a certain amount of solution or solvent; This general concept of concentration, like the concept of "quantity", has no clear meaning; Traditionally, concentration involves measuring the volume of solution, and the quantity of solution often takes the quality, while the quality of solution takes the quantity, quality and volume of substance.
It has been stipulated that the narrow concentration is the abbreviation of the quantity concentration of substances, which was also called the molar concentration before. It refers to the amount of solute B per liter of solution, with the symbol C and the unit as mol/L or mol/dm3, namely:
cB≡nB/V
In view of the fact that the volume of solution changes with temperature, the quantity and concentration of substance also change with temperature. In strict thermodynamic calculation, in order to avoid the influence of temperature on the data, molar concentration is often used to replace the quantity concentration of substances, which is defined as the quantity of solute substances per 1kg solvent, with the symbol of m and the unit of mol/kg, namely:
MB≡nB/wA=nB/ (Ma Na)
Where b is a solute and a is a solvent. For example, m(NaCl)=0. 1mol/kg, which means that every 1kg solution contains 0. 1mol of NaCl.
The concentration expression that does not change with temperature has mass fraction in addition to molar concentration, which used to be called mass percentage concentration, which is the ratio of solute mass to solution mass.
When the influence of temperature is ignored, the molar concentration can be replaced by the amount and concentration of the substance, and the following contents are generally treated approximately in this way.
Finally, it should be mentioned that the concentration of the solution has nothing to do with the amount of the solution. You take a drop from a bottle of NaCl solution with a concentration of 0. 1 mol/L, and the concentration of this drop is still 0. 1mol/L, which seems nonsense, but it is not. Because there are two kinds of physical quantities, the first physical quantity is additive, such as mass, quantity, volume and length of matter. , called breadth quantity; Another physical quantity, which is not additive, is called intensity quantity. Concentration is the quantity of intensity. In addition, pressure (pressure), temperature and density are also intensity quantities.
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