A molecule of a substance is at the same time its minimum possible portion, and therefore it is precisely its properties that are decisive for the substance as a whole. This particle belongs to the microworld, therefore it is not possible to consider, let alone weigh it. But the mass of one molecule can be calculated.
You will need
- - the concept of the structure of a molecule and an atom;
- - calculator.
Instructions
If the chemical formula is known substances, define its molar the mass... To do this, determine the atoms that make up the molecule, and find their relative atomic masses in the periodic table of chemical elements. If one atom occurs n times in a molecule, multiply it the mass by that number. Then add the found values and get the molecular the mass given substances, which is equal to its molar mass in g / mol. Find the mass one molecules by dividing the molar the mass substances M per Avogadro's constant NA = 6.022 10 ^ 23 1 / mol, m0 = M / NA.
Example Find the mass one molecules water. A water molecule (H2O) consists of two hydrogen atoms and one oxygen atom. The relative atomic mass of hydrogen is 1, for two atoms we get the number 2, and the relative atomic mass of oxygen is 16. Then the molar mass of water will be 2 + 16 = 18 g / mol. Define the mass one molecules: m0 = 18 / (6.022 ^ 23) 3 10 ^ (- 23) g.
Mass molecules can be calculated if the number of molecules in a given substance is known. To do this, divide the total the mass substances m by the number of particles N (m0 = m / N). For example, if it is known that in 240 g substances contains 6 10 ^ 24 molecules, then the mass of one molecules will be m0 = 240 / (6 10 ^ 24) = 4 10 ^ (- 23) g.
Define the mass one molecules substances with sufficient accuracy, having learned the number of protons and neutrons that are part of its nuclei of the atoms of which it consists. The mass of the electron shell and the mass defect in this case should be neglected. Take the masses of a proton and a neutron equal to 1.67 10 ^ (- 24) g. For example, if it is known that a molecule consists of two oxygen atoms, what is its mass? The nucleus of the oxygen atom contains 8 protons and 8 neutrons. The total number of nucleons is 8 + 8 = 16. Then the mass of the atom is 16 1.67 10 ^ (- 24) = 2.672 10 ^ (- 23) g. Since the molecule consists of two atoms, its mass is 2 2.672 10 ^ (- 23) = 5.344 10 ^ (- 23 ) G.
Attention, only TODAY!
All interesting
The term "molar mass of a substance" means the mass of one mole, that is, the amount of a substance that contains 6.022x10 ^ 23 atoms, ions or molecules. This mass is measured in grams / mol. Instruction 1 How can you calculate ...
Chemicals can be measured not only in kilograms or milliliters, but also in moles. A mole is a unit of quantity of a substance, which appeared due to the fact that substances are composed of molecules and atoms. What is a mole in chemistry: definition of a mole ...
Relative molecular weight is a dimensionless quantity that shows how many times the mass of a molecule is greater than 1/12 of the mass of a carbon atom. Accordingly, the mass of a carbon atom is 12 units. Determine the relative molecular weight of a chemical ...
A molecule, even though its dimensions are negligible, has a mass that can be determined. You can express the mass of one gas molecule in both relative atomic units and grams. You will need - a pen; - paper for notes; - a calculator; - a table ...
A molecule is an object of the microworld. Therefore, direct measurement of its kinetic energy is impossible. The average kinetic energy is statistical concept... This is the average value of the kinetic energies of all molecules included in ...
The relative molecular weight of a substance shows how many times a molecule of a given substance is heavier than 1/12 of an atom of pure carbon. It can be found if its chemical formula is known using the periodic table of elements ...
Molar mass equivalent shows the mass of one mole of the substance. It is denoted by a capital letter M. 1 mol is the amount of substance that contains the number of particles (atoms, molecules, ions, free electrons) equal to Avogadro's number (constant ...
It is almost impossible to measure the number of molecules in a substance by conventional methods. This is due to the fact that the molecule of the substance is too small to be seen. Therefore, the number of molecules in a given mass of a substance is calculated using ...
The mass of 1 mol of a substance is called its molar mass and is denoted by the letter M. The units for measuring molar mass are g / mol. How this value is calculated depends on the specified conditions. You will need - the periodic table of chemical elements of D.I. ...
Quantity molecules in a substance, it is practically unthinkable to measure by ordinary methods. This is due to the fact that the molecule of the substance is too small to be seen. Consequently, the number of molecules in a given mass of a substance is calculated with the help of special formulas.
You will need
- - periodic table of chemical elements;
- - scales;
- - calculator.
Instructions
1. Knowing such a quantity as the number of matter?, Find the number molecules in him. To do this, multiply the number of substances, measured in moles, by the continuous Avogadro (NA = 6.022 × 10 ^ 23 1 / mol), which is equal to the number molecules in 1 mole of substance N =? / NA. Say, if there is 1.2 mol of sodium chloride, then it contains N = 1.2? 6.022? 10 ^ 23? 7.2? 10 ^ 23 molecules .
2. If the chemical formula of a substance is famous, with the support of the periodic table of elements, find its molar mass. To do this, according to the table, find the relative nuclear masses of the atoms that make up molecules a, and fold them. As a result, you will get the relative molecules the bright mass of a substance, which is numerically equal to its molar mass in grams per mole. After that, on the balance, measure the mass of the test substance in grams. To discover the number molecules in the substance, multiply the mass of the substance m by the continuous Avogadro (NA = 6.022 × 10 ^ 23 1 / mol) and divide the total by the molar mass M (N = m × NA / M).
3. Example Define a number molecules, which is contained in 147 g of sulfuric acid. Find the molar mass of sulfuric acid. Her molecules and consists of 2 hydrogen atoms, one sulfur atom and 4 oxygen atoms. Their nuclear masses are equal to 1, 32 and 16. The relative molecules the bright mass is 2 × 1 + 32 + 4 × 16 = 98. It is equal to the molar mass, therefore M = 98 g / mol. Then the number molecules contained in 147 g of sulfuric acid will be equal to N = 147? 6.022? 10 ^ 23/98? 9? 10 ^ 23 molecules .
4. To discover the number molecules gas under typical conditions at a temperature of 0 ° C and a pressure of 760 mm Hg. pillar, find out its volume. To do this, measure or calculate the volume of the container V, in which it is located in liters. To discover the number molecules of gas, divide this volume by 22.4 liters (the volume of one mole of gas under typical conditions), and multiply by Avogadro's number (NA = 6.022 × 10 ^ 23 1 / mol) N = V? NA / 22.4.
A. Avogadro in 1811, at the very beginning of the formation of nuclear theory, made the assumption that an equal number of flawless gases at an identical pressure and temperature contain an identical number of molecules. Later, this assumption was confirmed and became a necessary consequence for kinetic theory... Now this theory is called Avogadro.
Instructions
1. Avogadro's Law: One mole of ideal gas, if the temperature and pressure are identical, will occupy the same volume of molecules. Under typical conditions, this volume is 22.41383 liters. This value determines the molar volume of the gas.
2. Avogadro's constant shows the number of atoms or molecules that are contained in one mole of a substance. The number of molecules, provided that the system is one-component, and the molecules or atoms of the same type contained in it can be detected by a special formula
Related Videos
A molecule is an electrically neutral particle that possesses all the chemical properties inherent in a given particular substance. Including gases: oxygen, nitrogen, chlorine, etc. How is it allowed to determine the number of gas molecules?
Instructions
1. If you need to calculate how many molecules of oxygen are contained in 320 grams of this gas under typical conditions, before each, determine how many moles of oxygen are contained in this number. According to the periodic table, it is allowed to see that the rounded nuclear mass of oxygen is 16 nuclear units. Since the oxygen molecule is diatomic, the mass of the molecule will be 32 nuclear units. Consequently, the number of moles is 320/32 = 10.
2. Further, the universal Avogadro number, named after the scientist who suggested that equal volumes of perfect gases under continuous conditions, contain identical numbers of molecules, will help you. It is denoted by the symbol N (A) and is hefty huge - approximately 6.022 * 10 (23). Multiply this number by the calculated number of moles of oxygen and you will find out that the desired number of molecules in 320 grams of oxygen is 6.022 * 10 (24).
3. And if you know the pressure of oxygen, as well as the volume occupied by it, and the temperature? How to calculate the number of its molecules with such data? And there is nothing difficult here. You just need to write down the universal Mendeleev-Clapeyron equation for perfect gases: PV = RTM / m Where P is the gas pressure in pascals, V is its volume in cubic meters, R is the universal continuous gas, M is the mass of the gas, and m is its molar mass ...
4. Transforming this equation slightly, you get: M = PVm / RT
5. From the fact that you have all the necessary data (pressure, volume, temperature are initially set, R = 8.31, and the molar mass of oxygen = 32 grams / mol), you can simply find the mass of gas at a given volume, pressure and temperature. And then the problem is solved correctly in the same way as in the above example: N (A) M / m. By doing the calculations, you will find out how many oxygen molecules there are under given conditions.
6. It is allowed to simplify the solution even more, from the fact that in the resulting fraction N (A) PVm / RTm the molar masses are reduced, and it remains: N (A) PV / RT. Substituting the quantities you know into the formula, you get the result.
Related Videos
Useful advice
Not a single real gas (including oxygen), of course, is irreproachable; therefore, the Mendeleev-Clapeyron equation can be used for calculations only under conditions that are not too much different from typical ones.
A molecule is so tiny in size that the number of molecules, even in a tiny grain or drop of any substance, will easily be colossal. It defies measurement with the help of ordinary methods of calculation.
What is a "mole" and how, with its support, to find the number of molecules in a substance
To determine how many molecules are in one or another number of a substance, the "mole" representation is used. A mole is the number of a substance in which there are 6.022 * 10 ^ 23 of its molecules (either atoms or ions). This huge value is called "continuous Avogadro", it is named after the famous Italian scientist. The value is designated NA. With the support of continuous Avogadro, it is possible to determine how many molecules there are in any number of moles of any substance. Let's say 1.5 moles contain 1.5 * NA = 9.033 * 10 ^ 23 molecules. In cases where a hefty high measurement accuracy is required, you need to use the value of Avogadro's number with a huge number of decimal places. Especially its full value is: 6.022 141 29 (27) * 10 ^ 23.
How is it allowed to detect the number of moles of a substance
Determining how many moles are contained in a certain amount of a substance is hefty easy. To do this, you just need to have the exact formula of the substance and the periodic table at hand. Let's say you have 116 grams of regular table salt. If you need to determine how many moles are contained in such a number (and, accordingly, how many molecules there are)? Before each, remember the chemical formula of table salt. It looks further: NaCl. The molecule of this substance consists of 2 atoms (or rather, ions): sodium and chlorine. What is its molecular weight? It is made up of the nuclear masses of the elements. With the support of the periodic table, you know that the nuclear mass of sodium is approximately 23, and the nuclear mass of chlorine is 35. Consequently, the molecular mass of this substance is 23 + 35 = 58. The mass is measured in nuclear mass units, where the lightest atom is taken as the standard - And knowing the molecular weight of a substance, you will also be able to determine its molar mass (that is, the mass of one mole). The fact is that numerically, the molecular and molar mass completely coincide, they only have different units of measurement. If the molecular weight is measured in nuclear units, then molar - in grams. Consequently, 1 mol of table salt weighs approximately 58 grams. And you, according to the conditions of the problem, have 116 grams of table salt, that is, 116/58 = 2 moles. By multiplying 2 by the Avogadro continuous, you find that there are approximately 12.044 * 10 ^ 23 molecules in 116 grams of sodium chloride, or approximately 1.2044 * 10 ^ 24.
A molecule is the smallest unit of a substance that still retains the characteristics of that substance. It is very small and cannot be seen with the naked eye or weighed. How to calculate the mass of a molecule?
Mole and atomic weight of a molecule
To calculate the mass of a molecule, a unit called a mole and a measurement called atomic weight are used. A mole is a quantity equal to the number Avogadro, which is approximately 6.022 x 10 ^ 23. Atomic weight is the weight of one atom of a substance in atomic mass units. The weight of one mole of an element is equal to the atomic weight of the element. Knowing this, it is possible to deduce the mass of each molecule from its chemical formula and the atomic weights of its elements, as described in the Periodic Table.
Set the chemical formula of the molecule
- Find the atomic weight of each atom in a molecule. You can find this information in the Periodic Table; it is usually a decimal number above or below the symbol for the chemical element.
- For example, the atomic mass of hydrogen is 1.0079 and the atomic mass of oxygen is 15.999. One mole of each element weighs the same amount in grams.
- Further, proceeding from the formula already known to us, we calculate the sum of all atoms of the molecule.
- In particular, a water molecule contains two hydrogen atoms and one oxygen atom. In this case, the molar mass of water is 1.0079 + 1.0079 + 15.999, or 18.0148 g per mol (g / mol).
- Divide the sum of molecules by mol or Avogadro's number (6.022 x 10 ^ 23).
- For example, 18.0148 / 6.022 x 10 ^ 23 = 2.991 x 10 ^ 23. Thus, one water molecule weighs 2.991 x 10 ^ 23 g.
As can be seen from the above example, using the Periodic Table of Mendeleev, you can get all the necessary indicators to calculate the mass of molecules of various substances.
Quantity molecules v substance it is almost impossible to measure by conventional methods. This is due to the fact that the molecule of the substance is too small to be seen. Therefore, the number of molecules in a given mass of a substance is calculated using special formulas.
You will need
- - periodic table of chemical elements;
- - scales;
- - calculator.
Instructions
Knowing such a quantity as the amount of substance?, Find the number molecules in him. To do this, the amount of substance, measured in moles, multiply by Avogadro's constant (NA = 6.022 10 ^ 23 1 / mol), which is equal to the number molecules in 1 mole of substance N =? / NA. For example, if there is 1.2 mol of table salt, then it contains N = 1.2 6.022 10 ^ 23? 7.2 10 ^ 23 molecules.
If you know the chemical formula of a substance, use the periodic table of elements to find its molar mass. To do this, use the table to find the relative atomic masses of the atoms that make up molecules a, and fold them. As a result, you will get the relative molecules the bright mass of a substance, which is numerically equal to its molar mass in grams per mole. Then, on the balance, measure the mass of the test substance in grams. To find the quantity molecules v substance, multiply the mass of the substance m by Avogadro's constant (NA = 6.022 10 ^ 23 1 / mol) and divide the result by the molar mass M (N = m NA / M).
Example Determine the quantity molecules, which is contained in 147 g of sulfuric acid. Find the molar mass of sulfuric acid. Her molecules and consists of 2 hydrogen atoms, one sulfur atom and 4 oxygen atoms. Their atomic masses are 1, 32, and 16. The relative molecules the bright mass is 2 1 + 32 + 4 16 = 98. It is equal to the molar mass, therefore M = 98 g / mol. Then the amount molecules contained in 147 g of sulfuric acid will be equal to N = 147 6.022 10 ^ 23/98? 9 10 ^ 23 molecules.
To find the quantity molecules gas under normal conditions at a temperature of 0? C and a pressure of 760 mm Hg. pillar, find its volume. To do this, measure or calculate the volume of the container V, in which it is located in liters. To find the quantity molecules of gas, divide this volume by 22.4 liters (the volume of one mole of gas under normal conditions), and multiply by Avogadro's number (NA = 6.022 10 ^ 23 1 / mol) N = V NA / 22.4.
Attention, only TODAY!
All interesting
A molecule of a substance is at the same time its minimum possible portion, and therefore it is precisely its properties that are decisive for the substance as a whole. This particle belongs to the microworld, therefore, it does not seem to be considered, and even more so to weigh it ...
The molecular formula of a substance shows which chemical elements and in what quantity are included in the composition of this substance. In practice, it is determined in various ways, both experimental, using quantitative and qualitative methods ...
The mass of a substance is found using a device called a balance. You can also calculate body weight if you know the amount of the substance and its molar mass or its density and volume. The amount of a pure substance can be found by its mass or ...
In order to find the molar mass of a substance, determine its chemical formula and use the periodic table to calculate its molecular weight. It is numerically equal to the molar mass of the substance in grams per mole. If the mass of one ...
To find the volume of one mole of a substance in a solid or liquid state, find its molar mass and divide by its density. One mole of any gas under normal conditions has a volume of 22.4 liters. In the event that conditions change, calculate the volume of one ...
Determine its molar the mass... To do this, determine what the molecule consists of and find their relative atomic masses in the periodic table of chemical elements. If one atom occurs n times, multiply it the mass by that number. Then add the found values and get the molecular the mass given substances, which is equal to its molar mass in g / mol. Find the mass one by dividing the molar the mass substances M to Avogadro's constant NA = 6.022 ∙ 10 ^ 23 1 / mol, m0 = M / NA.
Example Find the mass one molecules water. A water molecule (H2O) consists of two hydrogen atoms and one oxygen atom. The relative atomic mass of hydrogen is 1, for two atoms we get the number 2, and the atomic mass of oxygen is 16. Then the molar mass of water will be 2 + 16 = 18 g / mol. Define the mass one molecules: m0 = 18 / (6.022 ^ 23) ≈3 ∙ 10 ^ (- 23) g.
Mass molecules can be calculated if the number of molecules in a given substance is known. To do this, divide the total the mass substances m by the number of particles N (m0 = m / N). For example, if it is known that in 240 g substances contains 6 ∙ 10 ^ 24 molecules, then the mass of one molecules will be m0 = 240 / (6 ∙ 10 ^ 24) = 4 ∙ 10 ^ (- 23) g.
Define the mass one molecules substances with sufficient accuracy, having learned the number and neutrons that enter its nuclei of the atoms of which it consists. The mass of the electron shell and the mass defect in this case should be neglected. And take the mass equal to 1.67 ∙ 10 ^ (- 24) g. For example, if it is known if a molecule consists of two oxygen atoms, what is its mass? The nucleus of the oxygen atom contains 8 protons and 8 neutrons. The total number of nucleons is 8 + 8 = 16. Then the mass of the atom is 16 ∙ 1.67 ∙ 10 ^ (- 24) = 2.672 ∙ 10 ^ (- 23) g. Since the molecule consists of two atoms, its mass is 2 ∙ 2.672 ∙ 10 ^ (- 23) = 5.344 ∙ 10 ^ (- 23) g.
A molecule is the smallest particle of a substance that carries its chemical properties. The molecule is electrically neutral. Chemical properties are determined by the aggregate and configuration chemical bonds between the atoms that make up it. Its size, in the overwhelming majority of cases, is so small that even in a tiny sample of matter, their number is unimaginably huge.
Instructions
Imagine that you have some kind of container, densely filled with small identical balls. You know, for example, that the total mass of these balls is, and their number is 10 thousand pieces. How to find the mass one? Easier than ever: dividing 1000 kg by 10000 pieces, you get: 0.1 kg or 100 grams.
In your case, the role of the number of balls will be played by the so-called "mole". This is the amount of substance, which contains 6.022 * 10 ^ 23 of its elementary -, atoms, ions. In another way, this value is called "Avogadro's number", in honor of the famous Italian scientist. The value of a mole of any substance (molar mass) numerically coincides with its molecular weight, although it is measured in other quantities. That is, summing up the atomic weights of all elements included in molecules of any substance (taking into account the indices, of course), you will determine not only the molecular the mass, but also the numerical value of its molar mass. Here she also plays the role of the mass of those same balls in the previous example.
Consider specific. A widely known substance is slaked lime, Ca (OH) 2 hydroxide. The atomic weight of its elements (rounded, expressed in atomic mass units) is 40 for calcium, 16, 1 for. Taking into account the index 2 for the hydroxyl group, you will get the molecular the mass: 40 + 32 + 2 = 74. Therefore, 1 mole will weigh 74 grams.
Well, then the problem is solved in an elementary way. 74 grams of this substance contains 6.022 * 10 ^ 23 molecules. How much does one molecule weigh? Dividing the molar the mass by Avogadro's number, you get: 12.29 * 10 ^ -23 grams. (Or 12.29 * 10 ^ -26 kg). This is the answer. Of course, the problem of finding the mass molecules any other substance.
Related Videos
Useful advice
The atomic mass of calcium is not exactly 40 amu, but 40.08. But to simplify calculations, it can be rounded.
The vast majority of molecules are so small that they cannot be seen even with the most powerful microscope. Accordingly, the mass of one molecule is unimaginably small. Therefore, for an ignorant person, the very thought that one can weigh a single molecule will seem absurd. However, it is quite possible.
Instructions
It is known that under normal conditions one mole (that is, the amount
Molecular mass is the mass of a molecule, which is the sum of the masses of all the atoms of this molecule. Molar mass is equal to the mass of 1 mole of a substance, measured in g / mol.
Mole and atomic weight of a molecule
Atoms and molecules are extremely small particles, so the portions of substances that are taken for chemical reactions, are characterized by physical quantities corresponding to a large number particles. The amount of a substance is a physical quantity that is directly proportional to the number of particles that make up a given substance and are included in the taken portion of this substance. According to the famous chemical formula a complex substance is determined by the mass fraction of the elements included in this substance. In chemical calculations, the mass of gaseous reagents and products is often replaced by their volumes.
You know that a water molecule contains two hydrogen atoms and one oxygen atom. As you know, Avogadro's law applies only to gaseous substances. The word "mole" comes from the word "molecule".
Friends! I am sure, of course, that you can calculate the relative molecular weight of any compound without the aid of this calculator. Everything is elementary: in the left column, select the symbol of the corresponding element, in the right - the number of atoms of this element in the molecule. We press the button "Calculate" and - before us the result - 100.5. This is the relative molecular weight of perchloric acid.
Therefore, in a laboratory, for example, the molar mass of hydrogen would be recorded as 36.46 g / mol, and glucose 180.14 g / mol.
For example, the atomic mass of hydrogen is 1.0079 and the atomic mass of oxygen is 15.999.
The numbers in front of chemical formulas or chemical signs are called coefficients.
All chemicals have a different composition and molecular size. This is the mass that the portion will have. carbon dioxide consisting of 6.02 ∙ 1023 molecules. The main thing is to understand the essence of basic concepts such as mole, molar mass and relative atomic mass, and then solving problems in chemistry will not cause you any difficulties. Under the line chemical formula of the compound in the drop-down list, select the first chemical element included in the structure formula chemical... If there are brackets in the chemical formula of a substance, then expand them by adding a corresponding index to each element.
Sometimes a person is interested in solving the most impossible tasks. People are driven by the desire to know as much as possible, to penetrate into the very depths of what seems unattainable at first glance. At first it was the discovery of the laws of mechanics, then magnetism and electrostatics. A huge breakthrough was the discovery of atoms and molecules. Until recently, a rather difficult, but solvable problem was how to determine the mass of a molecule.
Nowadays it is not amounts to no labor. The process of calculating the mass of any atom or complex molecule is carried out in several steps and is the same for any substance. The first step is to determine the molecular weight of the substance. That is, you should write down which atoms and in what quantity each is found in a given molecule. This should also be done if the task is to calculate the mass of gas.
Next, you need to resort to using the periodic table. In any cell, there is an element designation in Latin letters, its ordinal number and atomic mass. The latter is most often found in one of the corners and is a number with three to four decimal places. When solving the problem of how to determine the mass of a solution, one should also calculate the atomic mass of each of the components.
Further, in order to avoid confusion, it is better to consider a specific example, namely, to calculate the mass of the sulfuric acid H2SO4 molecule. There are 2 hydrogen atoms, one sulfur and 4 oxygen. The atomic mass of hydrogen is 1 atomic unit (a.u.), sulfur - 32 a. e., Oxygen - 16 a. e. The total mass will be 2 * 1 + 32 + 64 = 98 amu. e. This means that the molar mass of sulfuric acid is 98 grams per mole. The problem of how to find the relative molecular weight is solved, it remains to translate it into ordinary grams or kilograms.
Next, you need Avogadro's constant. This number indicates the number of structural units in one mole of a substance. The constant itself is approximately 6.7 * 10 ^ 23 mol ^ (- 1). This means that 98 grams of sulfuric acid contains Avogadro's number of molecules. All that remains is simply to divide the mass of one mole by the number of molecules it contains. When solving the question of how to find the mass of the mixture, you should also use the Avogadrov constant, because it is universal.
So, 98 / 6.7 * 10 ^ 23 = 6.7 * 10 ^ (- 23) grams. That is, this is a number that represents a zero, a comma, twenty-three more zeros after the decimal point, and then 6.7. This negligible amount of mass, however, takes place. For a more accurate calculation, you can take the complete periodic tables and use more accurate computing tools than a calculator.