Unified State Exam
How to determine mass by volume and density. How to find mass, knowing density and volume. How to find mass knowing speed

How to determine mass by volume and density. How to find mass, knowing density and volume. How to find mass knowing speed

In chemistry you can’t do without a lot of substances. After all, this is one of the most important parameters chemical element. How to find the mass of a substance different ways, we will tell you in this article.

First of all, you need to find required element, using the periodic table, which can be downloaded on the Internet or purchased. The fractional numbers under the sign of an element are its atomic mass. It needs to be multiplied by the index. The index shows how many molecules of an element are contained in a given substance.

When you have compound, then you need to multiply the atomic mass of each element of the substance by its index. Now you need to add up your received atomic masses. This mass is measured in units of gram/mol (g/mol). We will show how to find the molar mass of a substance using the example of calculating the molecular mass of sulfuric acid and water:
H2SO4 = (H)*2 + (S) + (O)*4 = 1*2 + 32 + 16*4 = 98g/mol;

H2O = (H)*2 + (O) = 1*2 + 16 = 18g/mol.

Molar mass simple substances, which consist of one element, are calculated in the same way.
You can calculate molecular weight using an existing table of molecular weights, which can be downloaded online or purchased at a bookstore
You can calculate molar mass using formulas and equate it to molecular mass. In this case, the units of measurement must be changed from “g/mol” to “amu”.
When, for example, you know the volume, pressure, mass and temperature on the Kelvin scale (if Celsius, then you need to convert), then you can find out how to find the molecular mass of a substance using the Mendeleev-Claiperon equation:

M = (m*R*T)/(P*V),

where R is the universal gas constant; M is the molecular (molar mass), a.m.u.
You can calculate the molar mass using the formula:
where n is the amount of substance; m is the mass of a given substance. Here you need to express the amount of substance using volume (n = V/VM) or Avogadro's number (n = N/NA).
If the volume of a gas is given, then its molecular weight can be found by taking a sealed container with a known volume and pumping out the air from it. Now you need to weigh the cylinder on the scales. Next, pump gas into it and weigh it again. The difference in mass of an empty cylinder and a cylinder with gas is the mass of the gas we need.
When you need to carry out the cryoscopy process, you need to calculate the molecular weight using the formula:
M = P1*Ek*(1000/P2*Δtk),

where P1 is the mass of the dissolved substance, g; P2 is the mass of the solvent, g; Ek is the cryoscopic constant of the solvent, which can be found from the corresponding table. This constant is different for different liquids; Δtk is the temperature difference, which is measured using a thermometer.

Now you know how to find the mass of a substance, be it simple or complex, in any state of aggregation.

Class: 7

Lesson objectives.

1. Educational: systematize the knowledge that students have about the concepts: “density”, “mass”, “volume”, expand the scope of knowledge about these concepts, develop the ability to apply the studied material to solve practical problems.

2. Developmental: formation of logical thinking, continue to develop the skill of solving physical problems.

3. Educational: instilling in students friendly communication and mutual assistance.

Lesson type: combined.

Equipment: 15 sets of tables 1 and 2.

During the classes

1. Organizational stage.

2. Updating knowledge.

Teacher activities	Student activities
- What is density?	Physical quantity, which shows how much of a substance is contained in a unit volume.
- What does it mean that the density of iron is 6800 kg/m 3? How can you find the density of a substance? What does body weight depend on?	This means that the mass of 1 m 3 of iron is 6800 kg. To find the density of a substance, you need to divide the mass by the volume.
- How to find body mass?	The mass of a body depends on its volume and the density of the substance of which the body consists.
- How to find the volume of a body if its mass and the substance of which the body consists are known?	To find the mass of a body, gently multiply its density by its volume. To find the volume of a body, you need to divide its mass by its density.

3. Problem solving
1. How will we grade work in class based on the principle of addition or subtraction?	Based on the principle of addition.
2. Table 1(Appendix No. 1). There are loads in the warehouse: chalk, cork, birch, ice, steel. Each cargo is packed in 2 m3 containers.	Five vehicles were called in to transport these goods. Your task is to distribute the cargo among the vehicles.
- What needs to be done to distribute cargo among vehicles?
- How to find the mass of a substance if its density and volume are known?	kg/m 3
- In what units is the density of matter measured?	In kilograms
- In what units will the mass be calculated?	In tons and kilograms
- In what units is the carrying capacity of vehicles expressed?	In tons, and for a Muscovite in kilograms
- In what units should the mass of cargo be obtained? Decide this task and distribute the cargo among the vehicles. The teacher checks the correctness of the completed task with the first student to solve it and appoints him as his assistant. In the cards (Appendix No. 3) of the students, records are made of the number of points scored.	Students solve problems and distribute loads.
3. table 2(Appendix No. 2). There are five different liquids that have the same mass. These liquids need to be poured into five. various vessels	What needs to be done to pour liquids into vessels?
Find the volume of liquids.
- How to find the volume if the mass of the substance and its density are known?	- In what units will the calculated volume be obtained?
in m3.	- In what units is the volume of the vessels given?
In liters and milliliters	- In what units is the volume of the vessels given?
- In what units should the volume of liquids be obtained? Solve this problem and distribute the liquid among the vessels.	The teacher checks the correctness of the completed task with the first student to solve it and appoints him as his assistant. The number of points scored is recorded on student cards.
4. Students solve the problem.
Reflection. - Which physical concepts Did you use it to complete tasks? Compare number of points , which you gave yourself, with the number of points that the inspectors gave you. What conclusion can you draw for yourself? Are you ready for?	test work

Mass, density, volume. Homework:

repeat 18-22.

In chemistry and physics, we often come across problems in which it is necessary to calculate the mass of a substance, knowing its volume. How to find mass through volume. A table of densities will help you with this, since in order to find the mass, you need to know both the density and volume of the substance.

The rule states that the volume of a substance multiplied by its density equals the mass of that substance. From this rule, the formula for mass through volume is derived. It looks like this: m = V*p. Where m is mass, V is volume, and p is density. Knowing the number that is equal to the volume, you can look up the number that will be equal to the density and multiply the data. This way you can get a lot.

Example calculation

For example, a volume of 5 ml is given. The volume of a substance is calculated in units such as liters and milliliters. The substance whose mass needs to be found is gelatin. Looking at the table, you can see that its density is 1.3 g/ml. Now use the formula. Volume V is 5 ml. It is necessary to multiply 5 ml. by 1.3 g/ml. That is: 5 * 1.3 = 6.5 grams. So m - mass is 6.5 grams. Why gram: when multiplying volume by density, we have units such as milligrams. We reduce them, leaving grams, which indicate mass.

You can use another method. It is necessary to know or have at hand the periodic table. This method involves using the molar mass of the substance (in the table). You need to know the formula, which states that the mass of a substance is equal to the product of volume and molar mass. That is, m = V*M, where V is the volume of a given substance, and M is its molar mass.

Many of us at school asked the question: “How to find body mass”? Now we will try to answer this question.

Finding mass through its volume

Let's say you have a two hundred liter barrel at your disposal. You intend to completely fill it with diesel fuel, which you use to heat your small boiler room. How to find the mass of this barrel filled with diesel fuel? Let's try to solve this seemingly simplest problem together with you.

Solving the problem of substances through its volume is quite easy. To do this, apply the formula for the specific density of a substance

where p is the specific density of the substance;

m - its mass;

v - occupied volume.

The values will be grams, kilograms and tons. Volume measures: cubic centimeters, decimeters and meters. Specific density will be calculated in kg/dm³, kg/m³, g/cm³, t/m³.

Thus, in accordance with the conditions of the problem, we have at our disposal a barrel with a volume of two hundred liters. This means that its volume is 2 m³.

But you want mass. From the above formula it is derived as follows:

First we need to find the value of p - specific. You can find this value using a reference book.

In the book we find that p = 860.0 kg/m³.

Then we substitute the obtained values into the formula:

m = 860*2 = 1720.0 (kg)

Thus, the answer to the question of how to find the mass was found. One ton and seven hundred and twenty kilograms is the weight of two hundred liters of summer diesel fuel. Then you can make an approximate calculation of the total weight of the barrel and the capacity of the rack for the barrel of solarium in the same way.

Finding mass through density and volume

Very often in practical tasks in physics you can find quantities such as mass, density and volume. In order to solve the problem of how to find the mass of a body, you need to know its volume and density.

Items you will need:

1) Roulette.

2) Calculator (computer).

3) Capacity for measurement.

4) Ruler.

It is known that objects with the same volume, but made of different materials, will have different masses (for example, metal and wood). The masses of bodies that are made of a certain material (without voids) are directly proportional to the volume of the objects in question. Otherwise, the constant is the ratio of the mass to the volume of an object. This indicator is called “substance density”. We will denote it by the letter d.

Now you need to solve the problem of how to find the mass in accordance with the formula d = m/V, where

m is the mass of the object (in kilograms),

V is its volume (in cubic meters).

Thus, the density of a substance is the mass per unit volume.

If you need to find from which an object is created, you should use the density table, which can be found in a standard physics textbook.

The volume of an object is calculated using the formula V = h * S, where

V - volume (m³),

H - object height (m),

S is the area of the base of the object (m²).

If you cannot clearly measure the geometric parameters of the body, then you should resort to the laws of Archimedes. To do this, you will need a vessel that has a scale used to measure the volume of liquids and lower the object into water, that is, into a vessel that has divisions on it. The volume by which the contents of the vessel will be increased is the volume of the body that is immersed in it.

Knowing the volume V and density d of an object, you can easily find its mass using the formula m = d * V. Before calculating the mass, you need to bring everything measuring units V unified system, for example, into the SI system, which is an international measuring system.

In accordance with the above formulas, the following conclusion can be drawn: to find the required amount of mass with a known volume and known density, it is necessary to multiply the density value of the material from which the body is made by the volume of the body.

Many of us at school asked the question: “How to find body mass”? Now we will try to answer this question.

Finding mass through its volume

Solving the problem of how to find the mass of a substance through its volume is quite easy. To do this, apply the formula for the specific density of a substance

where p is the specific density of the substance;

m - its mass;

v - occupied volume.

The measures of mass will be grams, kilograms and tons. Volume measures: cubic centimeters, decimeters and meters. Specific density will be calculated in kg/dm³, kg/m³, g/cm³, t/m³.

Thus, in accordance with the conditions of the problem, we have at our disposal a barrel with a volume of two hundred liters. This means that its volume is 2 m³.

But you want to know how to find mass. From the above formula it is derived as follows:

First we need to find the value p - the specific density of diesel fuel. You can find this value using the reference book.

In the book we find that p = 860.0 kg/m³.

Then we substitute the obtained values into the formula:

m = 860*2 = 1720.0 (kg)

Finding mass through density and volume

Items you will need:

1) Roulette.

2) Calculator (computer).

3) Capacity for measurement.

4) Ruler.

Now you need to solve the problem of how to find the mass in accordance with the formula d = m/V, where

m is the mass of the object (in kilograms),

V is its volume (in cubic meters).

Thus, the density of a substance is the mass per unit volume.

If you need to find the density of the material from which an object is made, you should use the density table, which can be found in a standard physics textbook.

The volume of an object is calculated using the formula V = h * S, where

V - volume (m³),

H - object height (m),

S is the area of the base of the object (m²).

Knowing the volume V and density d of an object, you can easily find its mass using the formula m = d * V. Before calculating the mass, you need to bring all measurement units into a single system, for example, into the SI system, which is an international measuring system.