1. What amount of calcium oxide substance has a mass of 140 g? (CaO)
2. Calculate the mass and volume of carbon dioxide Co2 with an amount of substance of 2.2 mol.
Answer the questions.
3. The position of metals in PSCE, features of their electronic structure. General physical properties of metal. Create electronic formulas for calcium, lithium and aluminum.
Answer the questions. Yes/No
1. The composition of the bases must include a hydroxy group??? Not really
2.Water-soluble hydroxides are called alkalis??? Not really
3. The number of hydroxy groups per one atom of a metal element is twice the valency of this element??? Not really
4. Alkalis are part of almost all minerals on Earth??? Not really
5. In the presence of alkalis, phenolphthalein becomes colorless??? Not really
6. Sodium oxide reacts with water to form an alkali??? Not really
7. Alkalis can be obtained through the interaction of the most active metals with water??? Not really
8. Does cuprum(2) oxide actively interact with water? Not really
9.Aluminum hydroxide is an alkali? Not really
10. Does methyl orange turn red in the presence of alkalis? Not really
11.Zinc hydroxide is an amphoteric hydroxide? Not really
12.Barium hydroxide has the formula Ba(OH)3? Not really
Before answering a question, be sure to write the number of the question you are answering. Thank you very much in advance!
Characterize the chemical element C according to plan:a) position in PSHE - period, group, number of energy levels, number of electrons at the last level;
b) the formula of the higher oxide, its character;
c) the formula of the higher hydroxide, its character;
d) formula and name of a volatile hydrogen compound.
1)NO
2) NaCl
3) H2
4) H2O
In the list of substances, acid oxides include:
1) Na2O, N2O5, CaO
2) N2O5, SO2, SiO2
3) CaO, SiO2, SO3
4) CuO, CO2, MgO
Which of the following substances will nitric oxide (V) interact with?
1) KOH;
2) HCl;
3) NaCl;
4) O2
What chemical properties are characteristic of calcium oxide?
Choose the correct answer.
1) gas under normal conditions;
2) a solid, white substance;
3) black solid;
4) colorless volatile liquid.
A5. What is the name of the substance SO3?
1) sulfur oxide;
2) sulfur oxide (II)
3) sulfur oxide (VI)
4) sulfur oxide (IV).
A6. Oxides are formed:
1) during the combustion of simple and complex substances;
2) during the decomposition of soluble bases;
3) only when burning complex substances;
4) during the decomposition of silicic acid.
Which of the following substances will zinc oxide react with?
1) H2O
2) HCl
3) O2
4) Al2O3
Match the formula with the name of the corresponding oxide:
Formula
Oxide name
A) CuO
B) Na2O
B) Mn2O7
D) SO3
1) copper (II) oxide
2) sodium oxide
3) sulfur oxide (VI)
4) manganese (II) oxide
5) potassium oxide
6) manganese (VII) oxide
Establish a correspondence between the formula of the oxide and the reagents with each of which it can interact.
Formula
Reagents
A) Na2O
B) CO2
B) Al2O3
1) HCl, Na(OH), K2CO3
2) H2O, CaO, Ca(OH)2
3) CO2, H2SO4, H2O
4) CaCl2, SiO2, K2O
Vanadium(V) oxide is produced by burning metal powder in oxygen. Calculate the mass of vanadium required to obtain an oxide weighing 50 g.
Another task number 3 in the test that I don’t understand. The chemical formulas are given: a) MnO c) Fe e) 3SO3 g)I presented small letters as numbers: z - 3; z - 2.
Complete task 1,2,3..., selecting one or more correct answers under the letters a, b, c...
1. What letter represents two chlorine molecules?
2. Which entry reads magnesium-chlorine-two?
3. Choose simple substances.
4. Select formulas of substances only with index "1".
5. Select the formula of complex substances only with coefficient “1”.
6. Find formulas with chemical elements of side subgroups of the Periodic System D.I. Mendeleev.
7. Find formulas with chemical elements of the third period.
8 Identify a complex substance whose relative molecular weight is 170.
And help me solve this extra. exercise:
Using the data from task 3, answer the questions.
Which formulas contain the same number of atoms of the same chemical element?
Chemists around the world reflect the composition of simple and complex substances very beautifully and concisely in the form of chemical formulas. Chemical formulas are analogues of words that are written using letters - symbols of chemical elements.
Let us express, using chemical symbols, the composition of the most common substance on Earth - water. A water molecule contains two hydrogen atoms and one oxygen atom. Now let's translate this sentence into a chemical formula using chemical symbols (hydrogen - H and oxygen - O). We write the number of atoms in the formula using indices - numbers located at the bottom right of the chemical symbol (index 1 is not written for oxygen): H 2 0 (read “ash-two-o”).
The formulas of simple substances hydrogen and oxygen, whose molecules consist of two identical atoms, are written as follows: H 2 (read “ash-two”) and 0 2 (read “o-two”) (Fig. 26).
Rice. 26.
Models of molecules and formulas of oxygen, hydrogen and water
To reflect the number of molecules, coefficients are used that are written before chemical formulas: for example, the entry 2CO 2 (read “two-ce-o-two”) means two molecules of carbon dioxide, each of which consists of one carbon atom and two oxygen atoms.
Coefficients are written similarly when indicating the number of free atoms of a chemical element. For example, we need to write down the expression: five iron atoms and seven oxygen atoms. This is done as follows: 5Fe and 7O.
The sizes of molecules, and even more so of atoms, are so small that they cannot be seen even in the best optical microscopes, which provide a magnification of 5-6 thousand times. They cannot be seen even in electron microscopes, which provide a magnification of 40 thousand times. Naturally, the negligible size of molecules and atoms corresponds to their negligible masses. Scientists have calculated, for example, that the mass of a hydrogen atom is 0.000 000 000 000 000 000 000 001 674 g, which can be represented as 1.674 10 -24 g, the mass of an oxygen atom is 0.000 000 000 000 000 000 000 026 667 g, or 2.6667 10 -23 g, the mass of a carbon atom is 1.993 10 -23 g, and the mass of a water molecule is 3.002 10 -23 g.
Let's calculate how many times the mass of an oxygen atom is greater than the mass of a hydrogen atom, the lightest element:
Similarly, the mass of a carbon atom is 12 times greater than the mass of a hydrogen atom:
Rice. 27. The mass of a carbon atom is equal to the mass of 12 hydrogen atoms
The mass of a water molecule is 18 times greater than the mass of a hydrogen atom (Fig. 28). These values show how many times the mass of an atom of a given chemical element is greater than the mass of a hydrogen atom, i.e. they are relative.
Rice. 27. The mass of a water atom is equal to the mass of 18 hydrogen atoms
Currently, physicists and chemists are of the opinion that the relative atomic mass of an element is a value that shows how many times the mass of its atom is greater than 1/12 the mass of a carbon atom. Relative atomic mass is denoted by Ar, where r is the initial letter of the English word relative, which means “relative”. For example, A r (0) = 16, A r (C) = 12, A r (H) = 1.
Each chemical element has its own relative atomic mass value (Fig. 29). The values of the relative atomic masses of chemical elements are indicated in the corresponding cells of D.I. Mendeleev’s table.
Rice. 29.
Each element has its own relative atomic mass value
Similarly, the relative molecular weight of a substance is denoted by M r, for example M r (H 2 0) = 18.
The relative atomic mass of an element A r and the relative molecular mass of a substance M r are quantities that do not have units of measurement.
To find out the relative molecular mass of a substance, it is not necessary to divide the mass of its molecule by the mass of the hydrogen atom. You just need to add up the relative atomic masses of the elements that form the substance, taking into account the number of atoms, for example:
A chemical formula contains important information about a substance. For example, the formula C0 2 shows the following information:
Let's calculate the mass fractions of the elements carbon and oxygen in carbon dioxide CO 2 .
Key words and phrases
- Chemical formula.
- Indices and coefficients.
- Relative atomic mass (A r).
- Relative molecular weight (Mr).
- Mass fraction of an element in a substance.
Work with computer
- Refer to the electronic application. Study the lesson material and complete the assigned tasks.
- Find email addresses on the Internet that can serve as additional sources that reveal the content of keywords and phrases in the paragraph. Offer your help to the teacher in preparing a new lesson - make a report on the key words and phrases of the next paragraph.
Questions and tasks
- What do the entries mean: 3H; 2H 2 O; 5O2?
- Write down the formula of sucrose if you know that its molecule contains twelve carbon atoms, twenty-two hydrogen atoms and eleven oxygen atoms.
- Using Figure 2, write down the formulas of the substances and calculate their relative molecular weights.
- Which form of existence of the chemical element oxygen corresponds to each of the following entries: 3O; 5O2; 4CO2?
- Why do the relative atomic mass of an element and the relative molecular mass of a substance not have units of measurement?
- Which of the substances whose formulas are SO 2 and SO 3 has a greater mass fraction of sulfur? Confirm your answer with calculations.
- Calculate the mass fractions of elements in nitric acid HNO 3.
- Give a complete description of glucose C 6 H 12 0 6, using the example of describing carbon dioxide C0 2.
Chemical formula is an image using symbols.
Chemical element signs
Chemical sign or chemical element symbol– this is the first or two first letters of the Latin name of this element.
For example: FerrumFe , Cuprum –Cu , OxygeniumO etc.
Table 1: Information provided by a chemical sign
| Intelligence | Using the example of Cl |
| Item name | Chlorine |
| Non-metal, halogen | |
| One element | 1 chlorine atom |
| (Ar) of this element | Ar(Cl) = 35.5 |
| Absolute atomic mass of a chemical element
m = Ar 1.66 10 -24 g = Ar 1.66 10 -27 kg |
M (Cl) = 35.5 1.66 10 -24 = 58.9 10 -24 g |
The name of a chemical symbol in most cases is read as the name of a chemical element. For example, K – potassium, Ca – calcium, Mg – magnesium, Mn – manganese.
Cases when the name of a chemical symbol is read differently are given in Table 2:
| Chemical element name | Chemical sign | Chemical symbol name
(pronunciation) |
| Nitrogen | N | En |
| Hydrogen | H | Ash |
| Iron | Fe | Ferrum |
| Gold | Au | Aurum |
| Oxygen | O | ABOUT |
| Silicon | Si | Silicium |
| Copper | Cu | Cuprum |
| Tin | Sn | Stanum |
| Mercury | Hg | Hydrargium |
| Lead | Pb | Plumbum |
| Sulfur | S | Es |
| Silver | Ag | Argentum |
| Carbon | C | Tse |
| Phosphorus | P | Pe |
Chemical formulas of simple substances
The chemical formulas of most simple substances (all metals and many non-metals) are the signs of the corresponding chemical elements.
So iron substance And chemical element iron are designated the same - Fe .
If it has a molecular structure (exists in the form , then its formula is the chemical sign of the element with index bottom right indicating number of atoms in a molecule: H 2, O2, O 3, N 2, F 2, Cl2, BR 2, P 4, S 8.
Table 3: Information provided by a chemical sign
| Intelligence | Using C as an example |
| Substance name | Carbon (diamond, graphite, graphene, carbyne) |
| Belonging of an element to a given class of chemical elements | Non-metal |
| One atom of an element | 1 carbon atom |
| Relative atomic mass (Ar) element that forms a substance | Ar(C) = 12 |
| Absolute atomic mass | M(C) = 12 1.66 10-24 = 19.93 10 -24 g |
| One substance | 1 mole of carbon, i.e. 6.02 10 23 carbon atoms |
| M (C) = Ar (C) = 12 g/mol |
Chemical formulas of complex substances
The formula of a complex substance is prepared by writing down the signs of the chemical elements of which the substance is composed, indicating the number of atoms of each element in the molecule. In this case, as a rule, chemical elements are written in order of increasing electronegativity in accordance with the following practical series:
Me, Si, B, Te, H, P, As, I, Se, C, S, Br, Cl, N, O, F
For example, H2O , CaSO4 , Al2O3 , CS 2 , OF 2 , NaH.
The exceptions are:
- some compounds of nitrogen with hydrogen (for example, ammonia NH 3 , hydrazine N 2H 4 );
- salts of organic acids (for example, sodium formate HCOONa , calcium acetate (CH 3COO) 2Ca) ;
- hydrocarbons ( CH 4 , C2H4 , C2H2 ).
Chemical formulas of substances existing in the form dimers (NO 2 , P2O 3 , P2O5, salts of monovalent mercury, for example: HgCl , HgNO3 etc.), written in the form N 2 O4,P 4 O6,P 4 O 10Hg 2 Cl2,Hg 2 ( NO 3) 2 .
The number of atoms of a chemical element in a molecule and a complex ion is determined based on the concept valency or oxidation states and is recorded index lower right from the sign of each element (index 1 is omitted). In this case, they proceed from the rule:
the algebraic sum of the oxidation states of all atoms in a molecule must be equal to zero (the molecules are electrically neutral), and in a complex ion - the charge of the ion.
For example:
2Al 3 + +3SO 4 2- =Al 2 (SO 4) 3
The same rule is used when determining the oxidation state of a chemical element using the formula of a substance or complex. It is usually an element that has several oxidation states. The oxidation states of the remaining elements forming the molecule or ion must be known.
The charge of a complex ion is the algebraic sum of the oxidation states of all the atoms that form the ion. Therefore, when determining the oxidation state of a chemical element in a complex ion, the ion itself is placed in brackets, and its charge is taken out of brackets.
When compiling formulas for valency a substance is represented as a compound consisting of two particles of different types, the valencies of which are known. Next they use rule:
in a molecule, the product of valence by the number of particles of one type must be equal to the product of valence by the number of particles of another type.
For example:
The number before the formula in a reaction equation is called coefficient. She indicates either number of molecules, or number of moles of substance.
The coefficient before the chemical symbol, indicates number of atoms of a given chemical element, and in the case when the sign is the formula of a simple substance, the coefficient indicates either number of atoms, or the number of moles of this substance.
For example:
- 3 Fe– three iron atoms, 3 moles of iron atoms,
- 2 H– two hydrogen atoms, 2 moles of hydrogen atoms,
- H 2– one molecule of hydrogen, 1 mole of hydrogen.
The chemical formulas of many substances have been determined experimentally, which is why they are called "empirical".
Table 4: Information provided by the chemical formula of a complex substance
| Intelligence | For example C aCO3 |
| Substance name | Calcium carbonate |
| Belonging of an element to a certain class of substances | Medium (normal) salt |
| One molecule of substance | 1 molecule calcium carbonate |
| One mole of substance | 6.02 10 23 molecules CaCO3 |
| Relative molecular mass of the substance (Mr) | Мr (CaCO3) = Ar (Ca) +Ar (C) +3Ar (O) =100 |
| Molar mass of the substance (M) | M (CaCO3) = 100 g/mol |
| Absolute molecular mass of the substance (m) | M (CaCO3) = Mr (CaCO3) 1.66 10 -24 g = 1.66 10 -22 g |
| Qualitative composition (what chemical elements form the substance) | calcium, carbon, oxygen |
| Quantitative composition of the substance: | |
| The number of atoms of each element in one molecule of a substance: | a calcium carbonate molecule is made up of 1 atom calcium, 1 atom carbon and 3 atoms oxygen. |
| The number of moles of each element in 1 mole of the substance: | In 1 mole CaCO 3(6.02 · 10 23 molecules) contained 1 mole(6.02 · 10 23 atoms) calcium, 1 mole(6.02 10 23 atoms) of carbon and 3 mol(3 6.02 10 23 atoms) of the chemical element oxygen) |
| Mass composition of the substance: | |
| Mass of each element in 1 mole of substance: | 1 mole of calcium carbonate (100g) contains the following chemical elements: 40g calcium, 12g carbon, 48g oxygen. |
| Mass fractions of chemical elements in the substance (composition of the substance as a percentage by weight):
|
Composition of calcium carbonate by weight:
W (Ca) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1·40)/100= 0.4 (40%) W (C) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (1 12)/100 = 0.12 (12%) W (O) = (n (Ca) Ar (Ca))/Mr (CaCO3) = (3 16)/100 = 0.48 (48%) |
| For a substance with an ionic structure (salt, acid, base), the formula of the substance provides information about the number of ions of each type in the molecule, their quantity and the mass of ions per 1 mole of the substance:
|
Molecule CaCO 3 consists of an ion Ca 2+ and ion CO 3 2-
1 mol ( 6.02 10 23 molecules) CaCO 3 contains 1 mol Ca 2+ ions And 1 mole of ions CO 3 2-; 1 mole (100g) of calcium carbonate contains 40g ions Ca 2+ And 60g ions CO 3 2- |
| Molar volume of a substance at standard conditions (for gases only) | |
Graphic formulas
To obtain more complete information about a substance, use graphic formulas , which indicate order of connection of atoms in a molecule And valence of each element.
Graphic formulas of substances consisting of molecules sometimes, to one degree or another, reflect the structure (structure) of these molecules; in these cases they can be called structural .
To compile a graphical (structural) formula of a substance, you must:
- Determine the valence of all chemical elements that form the substance.
- Write down the signs of all chemical elements that form the substance, each in an amount equal to the number of atoms of a given element in the molecule.
- Connect the signs of chemical elements with dashes. Each dash denotes a pair that communicates between chemical elements and therefore belongs equally to both elements.
- The number of lines surrounding the sign of a chemical element must correspond to the valence of this chemical element.
- When formulating oxygen-containing acids and their salts, hydrogen atoms and metal atoms are bonded to the acid-forming element through an oxygen atom.
- Oxygen atoms are combined with each other only when formulating peroxides.
Examples of graphic formulas:
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