Advice 1: How to calculate equivalent weight of the oxide and metal

Equivalent that amount of a chemical element, which either binds or replaces one mole of hydrogen atoms. Accordingly, the mass of one equivalent is called the equivalent mass (Me), and is expressed in g/mol. To students in chemistry often aim to determine the equivalent mass of a substance (compound). For example, metal and formed them oxide.
How to calculate equivalent weight of the oxide and metal
Instruction
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First and foremost, you should remember a few simple rules. If we are talking about the metal, its equivalent mass is calculated by the formula: Me=M/V, where M is the atomic mass of the metal, and In his valence. Consider this rule with specific examples.
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Calcium (CA). Its atomic weight 40,08. Rounded take it over 40. Valency equal to 2. Consequently, DOE(Sa) = 40/2 = 20 g/mol. Aluminium (Al). Its atomic weight 26,98. (Rounded 27). Valence equal to 3. Thus, Mae(Al) = 27/3 = 9 g/mol.
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These methods are applicable if we are talking about pure metalX. But if they are part of a connection, for example, the same oxides? Here we must remember another rule: equivalent mass of the oxide is calculated by the formula: Me + Mo, where Mo is the equivalent mass of oxygen. It is, accordingly, calculated according to the formula already considered, that is, 16/2 = 8.
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Suppose you have a primary aluminium oxide, Al2O3. How to calculate equivalent weight? Very simple: 27/3 + 16/2 = 17 g/mol.
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Is there another way to determine the equivalent mass of the metal and its oxide? Yes, and very effective. It is based on the so-called law of equivalents, according to which all substances react with each other in equivalent quantities. For example: metal weight 33.4 grams entered into reaction of oxidation with oxygen. The result is an oxide with a total mass of 43 grams. You want to determine the equivalent mass of the metal and its oxide.
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First, calculate how much oxygen combines with the metal in the course of this reaction: 43 – 33,4 = 9.6 grams. According to the law of equivalents, this mass is as much larger than the equivalent mass of oxygen (which, recall, is equal to 8), many times the equivalent mass of the metal is less than its original amount. That is 33,4/DOE(IU) = 9,6/8. Consequently, Me(me) = 33,4*8/9,6 = 27,833 g/mol, or about 27.8 g/mol. This is the equivalent mass of the metal.
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Equivalent weight of oxide find the following: 27,8 + 8 = 35,8 g/mol.

Advice 2: How to find the equivalent mass of

The chemical elements are connected to each other in strictly defined proportions. That is why there was such a thing as equivalent and equivalent weight. ("Equivalent" literally means "equal", "equivalent"). What is the equivalent in the chemical sense of the word? How to calculate the equivalent (or equivalent mass?
How to find the equivalent mass of
Instruction
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Equivalents and equivalent mass are usually determined either according to the analysis of compounds or on the basis of the results of the substitution of one element with another. It is easy to understand that to determine equivalent (or equivalent mass) of an element does not necessarily come from its compounds with hydrogen. The equivalent (equivalent mass) can similarly compute the compound of this element with any other, equivalent (equivalent mass) is known.
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Example. When connecting 1.50 grams of sodium with excess chlorine formed 3.81 grams of sodium chloride. You need to find the equivalent mass of sodium and its equivalent, if it is known that the equivalent weight of chlorine is equal to 35,45 g/mol.Solution. Subtract from the total mass of the formed product of the original mass of sodium.
Thus, 3, 81 – 1, 50 = 2, 31
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That is, in the formed product (in your case sodium chloride) 1.50 grams of sodium accounts for 2.31 grams of chlorine. From this it follows that knowing the equivalent weight of chlorine (35, 45 gram/mol), you can easily find the equivalent mass of sodium by the following formula:
35, 45 x 1, 50 / 2, 31 is the Equivalent mass of sodium is equal to 23,0 g/mol.
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Molar mass of sodium will also be equal to 23,0 g/mol. From this it follows that the equivalent of sodium is equal to one pray (as the molar equivalent weight of sodium is the same).
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The concept of equivalents and equivalent masses also apply to complex substances. The equivalent complex substance called this number that communicates without residue with one equivalent of hydrogen.
Useful advice
Currently under the equivalent item made to understand this quantity, which is connected with one mole of hydrogen atoms or replaces the same number of hydrogen atoms in chemical reactions. The mass of one equivalent of an element is called its equivalent weight.

Advice 3: How to calculate valence

Valence – the most important concept in chemistry. The physical meaning of this concept became clear through the development of the theory of the chemical bond. The valence of an atom is determined by the number of covalent bonds that it is connected with other atoms.
How to calculate valence
Instruction
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The main role in the formation of chemical linkages valence electrons, which are least strongly associated with the nucleus. The so-called unpaired electrons located on the outer shell of the atom. It is therefore important to imagine the electronic configuration of the considered element.
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Electronic configuration of noble gases have the most resistance. For this reason, noble gases under normal conditions are chemically inert and do not react with other elements. Atoms of other elements tend to acquire the same stable shell with the formation of ties.
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So, the valence is the ability of an atom to form a certain number of covalent bonds with other atoms. It is expressed as a small integer. The number of chemical bonds – a measure of valence.
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To determine valence, we need to understand what is the outer electron shell of the atom how many unpaired electrons it has. In the ground and excited state of the atom the valence may be different.
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In most cases, the higher the valence of the element is equal to the group number in the periodic table in which the element is located. But this rule has exceptions. For example, he did not obey the elements of the second period, nitrogen, oxygen and fluorine.
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So, the higher the valence of phosphorus is +5. Nitrogen is in the same group, but he cannot be a valence greater 4. The outer electron shell of nitrogen has three unpaired electrons, so the compounds with hydrogen nitrogen is trivalent: thus, there is ammonia NH3. Thus between nitrogen and hydrogen may form a fourth covalent bond, but at the donor-acceptor mechanism and not at the exchange. This forms the ammonium ion, NH4+.
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Atoms of beryllium, boron and carbon have a variable valence. This is because electrons are able to steam within the same energy level. The energy spent on steaming electrons, more than kompensiruet energy of formation of additional bonds.
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C, if you look at its electronic configuration that is bivalent. But the true valence of carbon is +4. One electron from 2s orbital jumps to the 2p free-cell, and now the carbon is able to form not two, but four. Tetravalent carbon is the basis of organic chemistry.
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