Lesson 5. Mole and molar mass

Lessons archive › Basic laws of chemistry

In Lesson 5 " Mole and Molar Mass " from the Chemistry for Dummies , we'll look at the mole as a unit of measurement for the amount of a substance; Let's define Avogadro's number, and also learn how to determine molar mass and solve problems involving the amount of a substance. The basis for this lesson will be the basics of chemistry outlined in previous lessons, so if you are learning chemistry from scratch, I recommend looking at them at least briefly.

What is a mole

Before we talk about how to find the molar mass of a substance, let's define the concept of “mole”.
It was introduced as an artificial quantity to simplify calculations. This is the amount of substance that contains the same number of tiny particles as 12 g of one of the carbon isotopes - C12. For all chemicals this amount is the same and is Avogadro's number 6.02 1023. Avogadro's constant is denoted NA and is measured in mol-1.

Avogadro's number is the number of molecules, ions or other small particles in 1 mole of a substance.

NA = 6.02 1023 mol-1.

Historical reference

In 1811, chemist Amedeo Avogadro suggested that if you take two equal volumes of gases under equal significant conditions (at the same temperature and pressure), then the number of molecules in these volumes will also be the same. Based on his hypothesis, he determined the atomic and molecular masses of many substances, and also calculated the number of atoms in molecules of water, nitrogen oxides, etc. However, Avogadro’s hypothesis was not understood for a long time in scientific circles. It became generally accepted only in 1860.

How to prevent moths from entering your home?

Moths can enter any home, no matter how clean and tidy it is. To avoid them, it is necessary to follow certain preventive measures.

By following them, you will minimize the likelihood of moths appearing in your home.

Prevention methods:

All food should be stored in glass or ceramic containers with tight-fitting lids.
Carefully inspect food products and products made from natural fibers and fur when purchasing.
Brush your pet's coat after a walk.
Regularly ventilate closets, wipe down shelves and check your belongings.
In summer, leave your outerwear to dry and expose it to light.
Avoid storing large supplies of groceries in canvas bags.

The pest does not tolerate strong odors. Therefore, lavender, wormwood and citrus fruits can be ideal moth repellents. Sprigs of herbs and fruit peels should be placed in cupboards and renewed monthly.

Place garlic cloves, bay leaves or cloves near produce and nuts to repel food moths.

To prevent the appearance of moths in the house, you can also use various essential oils. These include:

Clove oil;
camphor;
lavender;
orange;
geranium;
cedar;
lemon.

To repel, sprinkle the product onto cotton swabs and place them on cabinet shelves. Update every 2-3 weeks.

You can also find special sections on the market to prevent moths from appearing. To use this product, remove the protective tape from its surface and then place it in a cabinet or drawer.

The sections are based on essential oils, the smell of which is unpleasant for pests. One such disk covers 0.5 square meters of area.

This device is completely safe for human health. Therefore, it can be used to protect fragile items and children's clothing.

What is molar mass

Molar mass is the mass of one mole of a substance and is measured in grams divided by mole (g/mol). This value is the ratio of the mass of a substance to its quantity, which is measured in moles.

How is molar mass indicated: M.

, where is the mass of the substance, and is the amount of the substance.

Unit of molar mass: g/mol.

Let's remember!

It is correct to say molar mass, not molar mass.

Despite the fact that 1 mole of any chemical substance contains the same number of molecules (and it is equal to Avogadro's number), the molar masses of different substances differ. This is because the atoms that make up these molecules are different. In particular, the difference between them is the relative atomic mass (Ar) - for example, Ar(Mg) = 24, and Ar(Hg) = 200. Now it will become clear why this matters.

How to find moths in the house?

The larvae of this pest can be found in dark, secluded places because they do not tolerate sunlight. These places usually include cupboards, kitchen cabinets and bedside tables.

To find moths, check natural fabrics, fur items, rolled and folded carpets, and look for larvae in food containers and bags.

An environment conducive to active reproduction of moths is high humidity. Therefore, storing things and products in the basement increases the likelihood of pest occurrence.

How to determine molar mass

This quantity is closely related to concepts such as relative atomic and molecular masses. Precisely relative, because the absolute mass of a molecule or atom of a substance in chemistry is not used to solve problems - these are too small values.

The relative atomic mass of a substance (Ar) shows how many times its atom is larger than 1/12 of a carbon atom. This value for each chemical element can be seen in the periodic table.

The relative molecular mass (Mr) is the sum of the Ar of each atom in the molecule of a substance, taking into account the indices. It shows how much the mass of a molecule is greater than 1/12 of a carbon atom.

, where is the number of atoms.

Let's look at examples.

In a molecule of sodium chloride NaCl there is 1 sodium atom and 1 chlorine atom, with Ar(Na) = 23, Ar (Cl) = 35.5.

Mr(NaCl) = 23 + 35.5 = 58.5.

A NaNO2 molecule contains 1 sodium atom, 1 nitrogen atom and 2 oxygen atoms.

Ar(Na) = 23, Ar(N) = 14, Ar(O) = 16.

Mr(NaNO2) = 23 + 14 + 16 2 = 69.

Actually, nothing else is required to calculate the molar mass.

Important

The molar mass of a substance is numerically equal to the relative molecular mass. But these two concepts should not be confused - they have different physical meanings. Molar mass characterizes 1 mole, and relative molecular mass characterizes 1 molecule.

Wax moth tincture, extract, beneficial properties and application

Wax moth (bee moth) is a beekeeping pest. Its caterpillars feed on honey, beebread, and wax frames, damaging bee offspring and the hive. If the infection is severe, the bee colony may die completely or leave its home.

But this pest has a number of properties that made it popular in folk medicine. Parasitic larvae produce cerrase, an enzyme that helps in the treatment of many diseases. Experienced beekeepers take advantage of this and even specifically breed the parasite.

Wax moth tincture

The larvae are able to digest wax. This discovery made them a popular remedy in the treatment of tuberculosis: Koch's bacillus (the causative agent of the disease) is covered with a waxy shell. Accordingly, the use of a parasite destroys the protective shell of the wand and makes it susceptible to medications. At the same time, the larvae are used for coughs, strengthen the immune system and have a beneficial effect on the hematopoietic system.

What is treated with wax moth:

bronchopulmonary diseases, even such serious ones as pneumonia and asthma;
oncological pathologies;
heart disease (heart attack, ischemia, anemia, atherosclerosis);
lack of hemoglobin and red blood cells;
normalize blood pressure;
liver diseases.

Bee moth in gynecology: promotes conception, pregnancy, relieves symptoms of toxicosis, fights anemia. For men, it is useful because it prevents impotence, infertility, and increases sperm activity.

How to prepare wax moth tincture:

Young moth larvae and 70% alcohol are required.
The ingredients are combined in a ratio of 1 to 10. For example, 10 g of larvae are required per 100 ml of alcohol.
Parasites that have not yet pupated (without prior preparation) are doused with alcohol. It is better to use dark glass containers.
The mixture is left for 2 weeks, shaking daily.
The end result is a 10% tincture.

In order not to harm the body, you must strictly adhere to the dosage, which is calculated based on weight and age. For children under 14 years of age, the medicine is given at the rate of 1 year - 1 drop, for adults at the rate of 1 kg - 1 drop. But the dosage may vary depending on the purpose of using the product.

Example of 10% tincture dosage:

to strengthen the immune system and to prevent colds - children 2 drops/year, adults - 4 drops/10 kg of weight;
for diseases of the respiratory system - children 2 drops/year of life, adults 5 drops/per 10 kg of weight.

Wax moth tincture is taken shortly before meals in pure form or diluted with water (a third of a glass).

For prevention purposes, the course lasts 3-4 weeks, then take a break for a month. The preventive course for children is 21 days and the same break. Prevention is carried out for 1-3 months.

Wax moth extract

A product with a high concentration of active substances acts in the following directions:

prevention of aging – has a beneficial effect on skin and hair; improves heart function and vascular condition, preventing heart attack, stroke and other diseases;
treatment of female and male sexual disorders (infertility, impotence);
treatment of tuberculosis - destroys the protective shell of the Koch bacillus, making it susceptible to medications;
elimination of scars, scars. The extract contains lysine, a substance that helps dissolve scars;
treatment of bronchitis and asthma;
beneficial effect on the nervous system, brain – relieves fatigue, fights stress;
improves gastrointestinal tract functions.

How to prepare wax moth extract:

Mix the larvae and 70% alcohol in a ratio of 1 to 5. As you can see, the tincture is less concentrated than the extract.
Leave in a dark glass container for 2 weeks at room temperature, shake daily.

After infusion, you can strain the extract and add water to it in the amount of ½ dose of alcohol.

Young larvae are not processed (not washed, not heated). For home medicines, parasites that have not yet pupated are used.

Contraindications and side effects

Products based on bee moth, like other beekeeping products, are prohibited from being used internally or externally if you have hypersensitivity to them. Individual intolerance is a strict contraindication.

Otherwise, as well as in case of overdose, nausea, headache, general weakness, and skin rash may occur. In such a situation, stop taking the drug immediately.

It is recommended to carry out a tolerance test first: apply a little product to delicate skin (eg the inner side of the wrist). If irritation does not appear, use the product. Treatment should also begin with minimal doses.

Wax moth excrement: application

To obtain this raw material, beekeepers place black honeycombs (already treated with moth) in the hive. They are covered with special devices and after a maximum of six months, a black substance appears at the bottom of the hive - excrement itself. Ognevka processes them several times during this time, due to which they are saturated with useful enzymes.

The excrement of this pest is used in folk medicine in the following cases:

bronchial diseases;
adenoma, prostatitis in men;
benign tumors of the mammary glands and uterus in women;
infertility and failure to carry a pregnancy to term;
tuberculosis of the lungs and other organs;
diseases of the heart and blood vessels (heart attack, ischemia, hypertension, angina).

How to prepare a tincture of excrement:

for 25 ml of substance, 220 ml of 70% alcohol is required;
the components are mixed;
Leave the mixture for 2 weeks, shaking regularly.

Application:

Excrement tincture is taken orally. Single dose – 15 drops per 50 ml of liquid (tea, water, juice). Drink it up to 3 times a day, doing this shortly before meals.

For tuberculosis, the single dose is increased - 30 drops.

Duration of the course is 2 months. Between courses, breaks of 3 weeks are indicated.

Conclusion

Both the dead wax moth and the tincture of larvae and excrement are traditional medicines that have been proven for more than one generation. Our ancestors have long used recipes based on them, and they managed to cure many diseases, even serious ones.

Nowadays, beekeeping products are becoming more and more popular. Honey, of course, remains a favorite, but more and more people give preference to others: wax, propolis, bee bread, zabrus and even pests like these.

When choosing treatment, take into account the presence of contraindications and strictly adhere to the dosage. Just because a product is natural does not mean that it is absolutely safe. Even these need to be able to be used correctly.

Quantity of substance

From the previous formulas it is clear that the molar mass and the amount of a substance are closely related. Let's look at this connection in more detail. Let's start with the fact that the amount of a substance can be denoted by either a Latin letter or a Greek letter (nu). The international designation is , but do not be surprised when you encounter any of these letters in formulas.

In the formula for finding the molar mass, we denoted the amount of substance through:

, hence .

Using this, we can find the amount of a substance (in moles) if we know its absolute and molar mass.

Example 1

How to determine what amount of substance is included in 350 g of barium sulfate BaSO4?

Let's use the formula.

We remember that M = Mr (the value of the molar mass is equal to the value of the relative molecular mass).

Mr(BaSO4) = Ar(Ba) + Ar(S) + Ar(O) 4 = 137 + 32 + 16 4 = 233.

M(BaSO4) = Mr(BaSO4) = 233 g/mol.

Let's substitute the molar mass value into the formula:

mole.

There is another formula for the amount of a substance that allows you to find it if the number of molecules or other structural units is known.

, where is the number of structural units, is Avogadro’s number.

Example 2

Let's say a certain volume of CaCO3 contains 3.01 · 1023 molecules. How to find the amount of a substance corresponding to a given volume?

Let's use the formula mole.

Molar volume

Above we found the amount of a substance through molar mass, but for gases this can also be done through molar volume. According to Avogadro's law, an amount of any gas equal to 1 mole will occupy the same volume if the gases are considered at the same temperature and pressure.

Under standard physical conditions - temperature 0°C and pressure 1 atm or 760 mmHg, 1 mole of gas occupies a volume of 22.4 liters.

Molar volume is the volume of gas taken in the amount of 1 mole. It is designated Vm.

Under normal conditions, Vm = 22.4 l/mol.

The values of the molar and actual volume of a gas help to find the amount of a substance.

, where is the actual volume of gas, and is the molar volume.

Example 1

How many moles are contained in 120 liters of gas under normal conditions?

Let's calculate using the formula mole.

Answer: 120 liters of any gas under standard conditions contain 5.36 moles.

Relative density of one gas to another

Sometimes, to solve a problem, you need to know how to find the molar mass of a gas, for which only its density in air or another gas is reported. This is possible if you know the relative density formula, which is denoted by the letter D.

, where and are some gases.