How to find the mass of a substance in physics formula. How to find the volume of a substance
In chemistry, as well as in physics, the concept of volume is very important, since in order to solve problems related to gaseous substances, it is necessary to operate with this very quantity.
a) Avogadro's law, molar volume of gas
Since gases are the most simple object for research, then their properties and reactions between gaseous substances have been studied most fully.
The French scientist J.L. Gay-Lussac established the law of volumetric ratios: the volumes of gases reacting under the same conditions (temperature and pressure) relate to each other as simple integers. For example, when 1 liter of chlorine interacts with 1 liter of hydrogen, 2 liters of hydrogen chloride will be formed, etc.
This law allowed the Italian scientist A. Avogadro to suggest that the molecules simple gases consist of two identical atoms (hydrogen, oxygen, nitrogen, etc.). The study of the properties of gases allowed him to formulate a hypothesis, which later received experimental confirmation and became known as Avogadro's law: equal volumes different gases under the same conditions (temperature and pressure) contain the same number of molecules. Hence , under normal conditions, 1 mole of various gases occupies a volume equal to 22.4 liters... This volume is called the molar volume of the gas:
b) Gas laws gas volume
In addition to the above formula for solving the calculated chemical tasks, it is often necessary to use the gas laws known from the physics course.
- Boyle-Mariotte's law
At a constant temperature, the volume of a given amount of gas is inversely proportional to the pressure under which it is located:
- Gay Lussac's Law
At constant pressure, the change in gas volume is directly proportional to temperature:
- United gas law Boyle-Marriott and Gay-Lussac
In addition, if the mass or amount of the gas is known, its volume can be calculated using the Mendeleev-Clapeyron equation:
where n is the number of moles of the substance, m is the mass (g), b is the molar mass of the gas (g / mol), R is the universal gas constant equal to 8.31 J / (mol × K).
Examples of problem solving
EXAMPLE 1
| Exercise | With complete combustion in air, 7.4 g of oxygenated organic compound formed 6.72 L (n.o.) carbon dioxide and 5.4 ml of water. Output the formula for this compound. |
| Solution | Let's draw up a diagram of the combustion reaction of an organic compound, denoting the number of carbon, hydrogen and oxygen atoms by "x", "y" and "z", respectively: C x H y O z + O z → CO 2 + H 2 O Let us determine the masses of the elements that make up this substance. The values of the relative atomic masses taken from the Periodic Table of D.I. Mendeleev, let's round to whole numbers: Ar (C) = 12 amu, Ar (H) = 1 amu, Ar (O) = 16 amu. m (C) = n (C) x M (C) = n (CO 2) x M (C) = x M (C); m (H) = n (H) × M (H) = 2 × n (H 2 O) × M (H) = × M (H); m (H) = Let's calculate the molar masses of carbon dioxide and water. As you know, the molar mass of a molecule is equal to the sum of the relative atomic masses of the atoms that make up the molecule (M = Mr): M (CO 2) = Ar (C) + 2 × Ar (O) = 12+ 2 × 16 = 12 + 32 = 44 g / mol; M (H 2 O) = 2 × Ar (H) + Ar (O) = 2 × 1 + 16 = 2 + 16 = 18 g / mol m (C) = x 12 = 3.6 g; m (H) = = 0.6 g m (O) = m (C x H y O z) - m (C) - m (H) = 7.4 - 3.6 - 0.6 = 3.2 g We define chemical formula connections: x: y: z = m (C) / Ar (C): m (H) / Ar (H): m (O) / Ar (O); x: y: z = 3.6 / 12: 0.6 / 1: 3.2 / 16; x: y: z = 0.3: 0.6: 0.2 = 1.5: 3: 1 = 3: 6: 2 Hence the simplest formula of the compound is C 3 H 6 O 2 and the molar mass is 64 g / mol. |
| Answer | C 3 H 6 O 2 |
EXAMPLE 2
| Exercise | What is molecular formula alcohol, if the mass ratios m (C): m (H): m (O) = 3: 1: 4 and the relative molecular weight Mr = 32? |
| Solution | In order to find out in what relationship they are chemical elements in the composition of the molecule, it is necessary to find their amount of substance. It is known that to find the amount of a substance, you should use the formula: Let us find the molar masses of carbon, hydrogen and oxygen (the values of the relative atomic masses taken from the Periodic Table of D.I.Mendeleev, rounded to whole numbers). It is known that M = Mr, which means M (C) = 12 g / mol, M (H) = 1 g / mol, and M (O) = 16 g / mol. Then, the amount of substance of these elements is equal to: n (C) = m (C) / M (C); n (C) = 3/12 = 0.25 mol n (H) = m (H) / M (H); n (H) = 1/1 = 1 mol n (O) = m (O) / M (O); n (O) = 4/16 = 0.25 mol Let's find the molar ratio: n (C): n (H): n (O) = 0.25: 1: 0.25 = 1: 4: 1, those. the formula for the alcohol compound is CH 3 OH. This is methanol |
| Answer | CH 3 OH |
The space around us is filled with different physical bodies, which are composed of different substances with different weights. School courses in chemistry and physics, introducing the concept and method of finding the mass of a substance, were listened to and safely forgotten by everyone who attended school. But meanwhile, theoretical knowledge acquired sometime may be needed at the most unexpected moment.
Calculation of the mass of a substance using the specific gravity of a substance. Example - there is a 200 liter barrel. You need to fill the barrel with any liquid, say a light beer. How do you find the mass of a full barrel? Using the formula for the density of a substance p = m / V, where p is the specific density of the substance, m is the mass, V is the occupied volume, it is very simple to find the mass of a full barrel:- Volume measures - cubic centimeters, meters. That is, a 200 liter barrel has a volume of 2 m³.
- A measure of specific gravity is found using tables and is constant for each substance. The density is measured in kg / m³, g / cm³, t / m³. The density of light beer and other alcoholic beverages can be viewed on the website. It is 1025.0 kg / m³.
- From the density formula p = m / V => m = p * V: m = 1025.0 kg / m³ * 2 m³ = 2050 kg.
A barrel with a volume of 200 liters, completely filled with light beer, will have a mass of 2050 kg.
Finding the mass of a substance using molar mass. M (x) = m (x) / v (x) is the ratio of the mass of a substance to its amount, where M (x) is the molar mass of X, m (x) is the mass of X, v (x) is the amount of substance X If only 1 known parameter is prescribed in the problem statement - the molar mass of a given substance, then finding the mass of this substance will not be difficult. For example, you need to find the mass of sodium iodide NaI with an amount of 0.6 mol.- Molar mass is calculated in the SI unified system of measurements and is measured in kg / mol, g / mol. The molar mass of sodium iodide is the sum of the molar masses of each element: M (NaI) = M (Na) + M (I). The value of the molar mass of each element can be calculated from the table, or you can use the online calculator on the website: M (NaI) = M (Na) + M (I) = 23 + 127 = 150 (g / mol).
- From the general formula M (NaI) = m (NaI) / v (NaI) => m (NaI) = v (NaI) * M (NaI) = 0.6 mol * 150 g / mol = 90 grams.
The mass of sodium iodide (NaI) with a mass fraction of a substance of 0.6 mol is 90 grams.
- Dilute the solution with water. The mass of the dissolved substance X does not change m (X) = m '(X). The mass of the solution increases by the mass of added water m '(p) = m (p) + m (H 2 O).
- Evaporation of water from solution. The mass of the solute X does not change m (X) = m '(X). The mass of the solution decreases by the mass of evaporated water m '(p) = m (p) -m (H 2 O).
- Draining two solutions. The masses of the solutions, as well as the masses of the solute X, when mixed, add up: m ’’ (X) = m (X) + m ’(X). m '' (p) = m (p) + m '(p).
- Loss of crystals. The masses of the solute X and the solution decrease by the mass of the precipitated crystals: m '(X) = m (X) -m (sediment), m' (p) = m (p) -m (sediment).
Options for finding the mass of matter - a useful course schooling, but methods that are quite applied in practice. Everyone can easily find the mass of the necessary substance by applying the above formulas and using the proposed tables. To facilitate the task, write down all the reactions, their coefficients.
Different, for example, copper and iron, then their volume will be different, since their densities are not the same.
In chemistry, there is a model of an ideal gas of 1 mol with a constant molar volume V = 22.4 mol / L. This gas has such a volume at constant pressure and. The molar volume is considered mainly from the standpoint of chemistry. from a physical point of view, the volume can vary. Nevertheless, there is a relationship between the molar volume and the volume of a certain portion of the gas: Vm = Vw / nw, where Vm is the molar volume; Vv is the volume of a portion of gas; n in - the amount of substance. The amount of substance is equal to: nw = mw / Mw, where mw is the mass of the substance, Mw is the molar mass of the substance. Accordingly, the volume of a portion of gas is: Vw = Vm * mw / Mw.
Sources:
- how to find volume
- Algorithm 2 Calculation of the volume of a substance by known mass
Body weight is one of the most important physical characteristics, which shows its gravitational properties. Knowing the volume of a substance, as well as its density, one can easily calculate and the mass body, which is based on this substance.
You will need
- The volume of matter V, its density p.
Instructions
Let us be given a heterogeneous one with mass V and mass m. Then it can be calculated using the formula:
p = m / V.
It follows from this that in order to calculate the mass, you can use its consequence:
m = p * V. Consider: Let us be given a platinum bar. Its 6 cubic meters. Find it the mass.
The problem is solved in 2 steps:
1) According to the density table of various, the density of platinum is 21,500 kg / cu. ...
2) Then, knowing the density and volume of this substance, we calculate it the mass:
6 * 21500 = 129000 kg, or 129 tons.
Related Videos
Density is the ratio of mass to the volume occupied by it - for solids, and the ratio of molar mass to molar volume - for gases. In the very general view volume (or molar volume) will be the ratio of mass (or molar mass) to its density. Density known. What to do? First determine the mass, then calculate the volume, then make the necessary corrections.
Instructions
The volume of gas is equal to the ratio of the product multiplied by its - to the already known density. Others, even knowing, need to know the molar mass of the gas and the amount, that is, you have a mole of gas. In principle, knowing how many moles of gas you have, you can calculate its volume without even knowing the density - according to Avogadro's law, one mole of any gas occupies a volume of 22.4 liters. If it is imperative to calculate the volume through density, then you will need to find out the mass of gas in a volume that is still unknown.
The volume of a solid can be determined without even knowing the density, simply by measuring it, and in the case of a complex and very irregular shape the volume is determined, for example, by the volume of the liquid displaced by a solid. However, if it is necessary to calculate the volume precisely through density, then the volume of a solid is the ratio of body mass to its density, and is usually determined by simple weighing. If it is impossible to weigh the body for some reason (for example, it is too large or), then you will have to resort to rather complicated indirect calculations. For example, for a moving body, mass is the ratio of doubled to the square of its speed, or the ratio of the force applied to the body to its acceleration. For a very large body at rest, you will have to resort to calculations in relation to the mass of the Earth, using a constant and a moment of rotation. Or - through the calculation of the specific heat capacity of a substance; in any case, knowing only the density to calculate the volume will not be enough.
By calculating the mass of a solid, you can calculate volume by simply dividing mass by density.
note
1. The above methods are more or less applicable only in the case of homogeneity of the substance of which the solid is composed.
2. The above methods are more or less applicable in a relatively narrow range of temperatures - from minus 25 to plus 25 degrees Celsius. When the state of aggregation of matter changes, the density can change abruptly; in this case, the formulas and calculation methods will be completely different.
Weight substances- this is the measure by which the body acts on its support. It is measured in kilograms (kg), grams (g), tons (t). Find the mass substances, if its volume is known, it is very easy.
You will need
- Know the volume of a given substance, as well as its density.
Instructions
Now, having dealt with the missing data, it is possible for finding the mass substances... This can be done using the formula: m = p * V Example: You need to find the mass gasoline, the volume of which is 50 m³. As you can see from the task. initial volume substances is known, it is required to find the density. According to the table of densities of various substances, the density of gasoline is 730 kg / m³. Now find the mass this gasoline can be as follows: m = 730 * 50 = 36500 kg or 36.5 t Answer: gasoline is 36.5 t
note
In addition to body weight, there is another related quantity - body weight. In no case should they be confused, since body weight is an indicator of the degree of impact on the support, and body weight is the force of impact on the earth's surface. In addition, these two quantities have different units of measurement: body weight is measured in Newtons (like any other force in physics), and mass, as noted earlier, is measured in kilograms (according to the SI system) or grams (according to the CGS system).
In everyday life, the mass of a substance is measured using the simplest and most ancient instrument - a balance, which is made based on the physical law of balances. According to it, the scales will be in a state of equilibrium only if at both ends of the given instrument there are bodies with equal masses. Therefore, to use the scales, a system of weights was introduced - a kind of standards with which the masses of other bodies are compared.
You have a two hundredth barrel. You plan to completely fill it with diesel fuel, which you use to heat your mini-boiler room. And how much will it weigh, filled with solarium? Let's calculate now.
In the nature around us, mass is interconnected with volume (we mean exact sciences). Absolutely any body has both mass and volume. Mass represents the weight of the body, that is, its size, and the volume of the body is its real dimensions. And thanks to these two parameters, we can calculate either mass or volume. So how do you find volume through mass? Read about it below.
The first formula
It is worth noting that the rules below apply to both physics and chemistry.
The most basic way to find the right volume is to use density. That is, we divide our mass by the available volume. Here is the formula: ρ = m / V. It follows from it that the required volume is: V = m / ρ.
Remember that the mass of different substances in the formula can be equal, even if the substances are not the same, but the volume will always be different, as well as their density.
Second formula
The science of chemistry has an example (model) of an ideal gas: one mole with a volume (this molar volume is always constant). The formula looks like this: V = 22.4 mol per liter. The presented gas always has this volume at pressure and temperature (they are constant). If we consider this issue from the side of the science of physics, then it (volume) can change. Here are the suitable formulas: V m - the molar volume is equal to Vw - the volume of a portion of gas divided by n in - the amount of substance. (Vm = Vv / nv). And the very amount of substance is calculated thanks to the formula for dividing the mass the required substance per molar mass (nw = mw / Mw). From this it follows that: Vw = Vm * mw / Mw.
Third formula
When, in the problem given to you, the concept of the substance itself is provided, then the required volume, you can easily express according to the formula: c = n / V = m / M / V. In this formula, M is the mass of the substance (molar).
We hope that we have helped you, dear readers, to understand how to find the volume, knowing the mass of the provided substance. We wish you success in chemistry and physics.
Chemistry and physics always imply the calculation of various quantities, including the volume of matter. The volume of a substance can be calculated using some formulas. The main thing is to know what state a given substance is in. There are four aggregate states in which particles can stay:
- gaseous;
- liquid;
- solid;
- plasma.
There is a specific formula for calculating the volume of each of them. In order to find the volume, you need to have certain data. These include mass, molar mass, and for gases (ideal) - the gas constant.
The process of finding the volume of a substance
Let's look at how to find the volume of a substance if it is, for example, in a gaseous state. To calculate, you need to find out the conditions of the problem: what is known, what parameters are given. The formula by which you can determine what is the volume of a given gas is as follows:
It is necessary to multiply the molar amount of the substance present (called n) by its molar volume (Vm). So you can find out the volume (V). When the gas is in normal conditions - n. y., then its Vm - volume in moles is 22.4 liters / mol. If the condition says how much substance there is in moles (n), then you need to substitute the data into the formula and find out the final result.
If the conditions do not provide for the indication of data on the molar amount (n), it must be found out. There is a formula to help you do the calculation:
It is necessary to divide the mass of the substance (in grams) by its molar mass. Now the calculation can be made and the molar amount can be determined. M is a constant that can be found in the periodic table. Each element has a number underneath that indicates its mass in moles.
Determination of the volume of a substance in milliliters
How to determine the volume of a substance in milliliters? What can be indicated in the conditions of the problem: mass (in grams), consistency in moles, the amount of the substance given to you, as well as its density. There is such a formula by which you can calculate the volume:
The mass in grams should be divided by the density of the specified substance.
If you do not know the mass, then it can be calculated as follows:
The molar amount of a substance must be multiplied by its molar mass. In order to correctly calculate the molar mass (M), you need to know the formula of the substance that is given in the problem statement. Need to fold atomic mass each of the elements of the substance. Also, if you need to find out the density of a substance, you can use the following inverse formula:
If you know the molar amount (n) and concentration (c) of a substance, you can also calculate the volume. The formula will look like this:
You need to divide the molar amount of the substance given in the problem by its molar concentration. From here, you can derive a formula for finding the concentration.
To correctly solve problems in physics and chemistry, you need to know some formulas and have the periodic table at hand, then you are guaranteed success.
