Concentration
The concentration of the solution. The physical quantity of the solution composition is expressed by the amount (moles) of the solute substance contained in a unit volume. Which is called the molar concentration of the solute. It is also called the amount of concentration of the solute substance.
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Basic Classification of Concentration
Concentration refers to the amount of a substance in the total.
Commonly used concentration representations are:
Mass percent concentration (mass fraction, m / m): Most commonly used. Refers to the mass (in grams) of solute per 100 grams of solution.
Mass percentage concentration = (mass of solute (g)) / mass of solution (g)) × 100% = mass of solute (g)) / (mass of solute (g) + mass of solvent (g)) × 100%
Volume percent concentration (volume fraction, V / V): commonly used in wine. Refers to the volume (in ml) of solutes per 100 ml of solution.
Volume percent concentration = (solute volume (mL) / solution volume (mL)) × 100% = solute volume (mL) / (solute volume (mL) + solvent volume (mL)) × 100%
Concentrations per million (ppm): Refers to the mass of solutes (in mg) per kilogram of solution.
Parts per million = mass of solute (mg) / mass of solution (kg)
Mass molar concentration: refers to the number of solutes (in moles) per kilogram of solvent.
Mass molar concentration = amount of solute substance (mol) / mass of solvent (kg) 1m = 1 mol / kg
Molar fraction: amount of solute substance (mol) / amount of solution (mol)
Volume molar concentration (molar concentration): The amount of solute (in moles) per liter of solution.
Volume molar concentration = amount of solute (mol) / solution volume (L) 1M = 1 mol / L
Explain
The amount of solute contained in a units solution is called the concentration of the solution
The more solute content, the greater the concentration
Concentration can be calculated by the number of grams of solute, gram molecule or gram equivalent in a certain solution. It is expressed as a percentage of the weight of the solute contained in a unit solution.
Display Method
The symbol is C and the unit is mol/L. The formula is C=n/V. C =1000ρω/M
Concentration refers to the amount of a substance in the total.
- Quality score (%)
- Molar fraction (%)
- Amount of substance (mol / L)
- Mass molar concentration (mol / kg)
- Mass percent concentration: most commonly used in general.
- Volume percent concentration: commonly used in the wine.
- Molar volume concentration: commonly used in chemistry.
- Molar concentration
The broad concept of concentration refers to the amount of solute in a certain amount of solution or solvent; this general concept of concentration has no clear meaning like the concept of “amount”, conventionally, the amount of solution involved in concentration refers to the volume and the amount of solution It often takes mass, and the amount of solute varies from the amount, mass, and volume of the substance.
It has been stipulated that the concentration in the narrow sense is the abbreviation of the amount concentration of a substance. It was also previously called the molarity (molarity), which refers to the amount of the solute B substance per liter of solution, the symbol is c, and the unit is mol / L or mol / dm³. which is:
cB≡nB / V
Given that the volume of a solution changes with temperature, the amount and concentration of a substance also change with temperature.
In scientific calculations, in order to avoid the influence of temperature on the data, the molar concentration of the substance is often used instead of the mass concentration. The latter is defined as the amount of solute substance per 1 kg of solvent, the symbol is m, and the unit is mol/kg, that is:
m B ≡n B / w A = n B / （nA MA）
Where B is the solute and A is the solvent. For example, m (NaCl) = 0.1 mol / kg, which means 0.1 mol of NaCl per 1 kg of solution.
The concentration notation that does not change with temperature has a mass fraction in addition to the molar mass concentration. It was previously called mass percentage concentration, which is the ratio of the mass of the solute to the mass of the solution.
When neglecting the influence of temperature, the mass concentration of the substance can be used instead of the molar concentration. The following content generally makes this approximation.
Finally, it should be mentioned that the concentration of the solution is an amount that has nothing to do with the amount of solution taken. You take a drop from a bottle of 0.1mol / L NaCl solution, and the concentration of this drop is still 0.1mol/L.
This seems nonsense, but it is not. Because there are two types of physical quantities, the first type of physical quantities has additive properties, such as mass, amount of matter, volume, length, etc.
This type of physical quantity is called a broad metric, the other type of physical quantity has no additive nature, such physical quantities called the intensity amount. Concentration is the amount of intensity. In addition, pressure (pressure), temperature, density, etc. are also strength quantities.
Blood concentration
Blood concentration refers to the steady-state concentration of the drug in human blood. Steady-state concentration means that the daily blood drug concentration of the patient is relatively constant and stable in the effective range. Each drug takes a certain amount of time to reach steady-state concentrations. The antiepileptic drug reaches a steady-state concentration.
It takes about 5 half-lives. The half-life of a drug is the time it takes for the blood concentration to reach half of its value after a single dose. Based on the half-life of each drug, it can be calculated how long each drug takes to achieve the best effect.
Such as phenytoin, phenobarbital half-life of 20 hours, then it is necessary to reach a steady-state concentration half-life of 20 hours = 100 × 5 hours that can play the best effect after 5 days, valproate, carbamazepine of The half-life is 10 hours. It takes 10 hours × 5 half-lives = 50 hours to reach steady-state concentration, that is, 2-3 days can play the best therapeutic effect. Some medicines are taken from a small dose and slowly added to the effective amount.
Therefore, the time required to reach the steady-state concentration in the blood is correspondingly prolonged. When taking these medicines, you need to observe at least 7-10 days to determine its effectiveness.
Different patients have certain differences in drug absorption, metabolism, and excretion, especially in children. Taking the same dose of the same weight, some can control the onset, some cannot, some have non-toxic side effects, and some have toxic reactions.
One reason is the same dose and different blood concentrations. Therefore, sometimes it is necessary to measure the blood concentration to achieve the purpose of individualizing the medication.
There are many factors that affect the blood concentration of drugs, such as heredity, taking other drugs at the same time, liver, kidney, and gastrointestinal diseases.
Solution concentration
Solution concentration can be divided into mass concentration (such as mass percentage concentration), volume concentration (such as molar concentration, equivalent concentration) and Mass-volume concentrations.
Mass percent concentration
The concentration of a solution is expressed by the percentage of the mass of the solute as the percentage of the total solution mass.
For example, 25% of glucose injection means 25 grams of glucose in 100 grams of injection.
Mass percent concentration (%) = Solute mass / Solution mass 100%
Volume concentration
(1) the molar solution of a concentration of the number of moles of solute in 1 liter of a solution expressed in molar concentration is called by the symbol mol / L represents, for example, one liter of concentrated sulfuric acid containing 18.4 moles of sulfuric acid, the concentration of 18.4mol.
Molar concentration (mol / L) = moles of solute / solution volume (liter)
(2) Equivalent concentration (N)
The concentration of a solution is called the equivalent concentration expressed by the gram equivalent of the solute contained in a liter of the solution, and it is represented by the symbol N.
For example, if 1 liter of concentrated hydrochloric acid contains 12.0 grams of equivalent hydrochloric acid (HCl), the concentration is 12.0 N.
Equivalent concentration = grams equivalent of solute / solution volume (liter)
Mass-volume concentration
The concentration expressed by the mass of the solute contained in a unit volume (1 cubic meter or 1 liter) of the solution is called mass-volume concentration, which is expressed by the symbol g / m³ or mg / L.
For example, one liter of chromium-containing waste water containing hexavalent chromium mass 2 mg, the hexavalent chromium concentration of 2 mg / liter (mg / L)
Mass-volume concentration = mass of the solute (g or mg) / volume of the solution (cubic meters or liters)
Conversion formula of concentration unit:
- Equivalent concentration = 1000.d. mass percentage concentration / E
- Mass percent concentration = equivalent concentration E / 1000.d
- Molar concentration = 1000.d mass percentage concentration / M
- Mass percent concentration = mass-volume concentration (mg / l) /10.d
- Mass-volume concentration (mg / L) = 10 mass percent concentration
ppm is the percentage of weight, ppm = mg / kg = mg / L
That is: 1ppm = 1ppm = 1000ug / L
1ppb = 1ug / L = 0.001mg / kg
Where: E—gram equivalent of solute, d— specific gravity of solution, M—molar mass of solute
Gas concentration
For atmospheric pollutants, the volume concentration and mass-volume concentration are commonly used to indicate their content in the atmosphere.
Volume concentration
Volume concentration is expressed as the volume of pollutants in the atmosphere per cubic meter (cubic centimeters) or (ml / m³). The commonly used method is ppm, that is, 1 ppm = 1 cubic centimeter / cubic meter = 10⁻⁶. In addition to ppm, there are ppb and ppt, and the relationship between them is:
1ppm = 10⁻⁶ = one millionth, 1ppb = 10⁻⁹ = one billionth,
1ppt = 10⁻¹² = one trillion, 1ppm = 10 3 ppb = 10 6 ppt
Mass-volume concentration
The concentration expressed by the mass of pollutants in the atmosphere per cubic meter is called mass-volume concentration, and the unit is milligram / cubic meter or grams / cubic meter.
Its conversion relationship with ppm is:
X = MC / 22.4
concentration
C = 22.4X / M
In the formula: X—the concentration value of pollutants expressed in milligrams per standard cubic meter;
C—concentration value of pollutant expressed in ppm;
M—the fractional amount of the pollutant.
The following relationship can be obtained from the above formula:
1ppm = M / 22.4 (mg / m³) = 1000.m / 22.4ug / m³
Example 1: Find the ppm concentration of 30 mg / standard cubic meter of hydrogen fluoride under standard conditions.
Solution: The molecular weight of hydrogen fluoride is 20, then:
C = 30.22.4 / 20 = 33.6ppm
Example 2: It is known that the concentration of sulfur dioxide in the atmosphere is 5 ppm. Find the concentration value expressed in mg / Nm³.
concentration Solution: The molecular weight of sulfur dioxide is 64.
X = 5.64 / 22.4mg / m³ = 14.3mg / m³
Conversion of ppm, ppb and mass content in soil, animals and plants, solid waste :
1ppm = 1mg / kg = 1000ug / kg
1ppb = 1ug / kg = 10⁻³mg / kg
1mg / kg = 1ppm = 1000ug / kg
1ug / kg = 1ppb = 10⁻³ppm
Concentration relationship
Volume percentage concentration
The volume (ml) of the solute contained in a 100ml solution, such as 95% ethanol, is to make up 95ml ethanol with water to 100mL (due to the molecular volume, the volume of the solution obtained by adding 95mL ethanol to 5mL water is less than 100mL, so the volume percentage concentration is generally It can only reflect the volume of the solute. Depending on the solution, the volume of the solute solvent cannot be simply added).
If the concentration is very thin, it can also be expressed in ppm and ppb. 1ppm = 1mg ∕ L, 1ppb = 1ng ∕ L.
Mass percentage concentration
The concentration expressed as the percentage of the mass of the solute in the total mass of the solution is called the mass percentage concentration (abbreviated as percentage concentration). Mass percentage concentration is a concentration commonly used in daily life and production, and it has no dimension. It will be legally measured in the future
Unit mass fraction (W) instead. The mass fraction WB of substance B is the ratio of the mass of substance B to the mass of the mixture. For example, 5g of sodium chloride is dissolved in 95g of water to make a 100g solution.
It’s mass percentage concentration is 5%, and its mass fraction is 0.05 or 5 × 10⁻². 0.9% physiological saline is used for medical purposes, 0.9% is the mass-volume percentage concentration. What it means is that 0.9 g of sodium chloride is dissolved in water to make a 100 mL solution.
Baume degree (° Bé) is a way to express the concentration of a solution. When the Baume hydrometer is immersed in the measured solution, the degree obtained is called Baume degree.
Baume is named after French chemist Antoine Baume. Baume was a pharmacy apprentice and was a professor at the Paris Academy of Pharmacy. He created a hydrometer, the Baume Hydrometer.
Baume Hydrometer
There are two types: a weight gauge for measuring liquids heavier than water and a light gauge for measuring liquids lighter than water. When the Baume degree is measured, the concentration percentage of the solution can be conveniently found from the comparison table of the corresponding chemistry manual.
For example, the Baume degree of concentrated sulphuric acid measured at 15 ° C is 66 ° Bé. Checking the table shows that the mass percentage concentration of sulphuric acid is 98%.
The value of Baume degree is large and the reading is convenient, so Baume degree is often used in production to indicate the concentration of a solution (a solution with a certain concentration has a certain density or specific gravity).
The methods for measuring the Baume degree of different solutions are similar. They are all based on the method of measuring specific gravity. According to the measured specific gravity, check the table to convert the concentration. Since 2011, Baume watches for different solutions have been dedicated, such as alcohol Baume watches and saltwater Baume watches. On this Baume watch, the concentration of the solution corresponding to the Baume degree of the solution can be directly read. No need to look up the table.
Baume degree and specific gravity conversion method
Baume degree = 144.3- (144.3 / specific gravity); Specific gravity = 144.3 / (144.3- Baume degree)
For lighter than water: specific gravity = 144.3 / (144.3 + Baume degree)
In general, Baume hydrometers should be measured at a temperature of 15.6 degrees, but the temperature usually does not meet the standard in actual use, so it needs to be calibrated. Generally speaking, every time the temperature differs by 1 degree, the Baume meter differs by 0.054 degrees. Increase when the temperature is higher than the standard, and decrease when the temperature is lower.
