Guide

1

Consider the following example.Do you have any copper object such as a piece of thick wire or plate.How to determine how many atoms of copper it contains?In order to simplify the solution, assume that it is - pure copper without any impurities and oxides without covering its surface.

2

First of all, consider this item.Best of all - at the laboratory scale.Suppose his weight - 1270 grams.

3

Now look at the periodic table.The atomic mass of copper (rounded) - 63.5 amu(atomic mass units).Consequently, the molar mass of copper - 63.5 g / mol.From this you can easily find that in the sample
contained in 1270 / 63.5 = 20 moles.

4

number of copper atoms in the sample calculated using the formula: m * NA, where m - the number of moles of the substance, and NA - so-called Avogadro's number.It corresponds to the number of the smallest particles of matter - atoms, ions, molecules - in one of his mole and equal 6.022 * 10 ^ 23.In your case it is a question about atoms.Multiplying by Avogadro's number 20, get an answer: 1.204 * 10 ^ 25 - as the copper atoms in the sample.

5

little complicate the task.It is known that copper because of its softness and ductility is often not used in pure form, but as a component of alloys with other metals, to give it the hardness.For example, the famous bronze - an alloy of copper and tin.

6

Do you have a bronze piece, made of alloy, which includes 20% tin and 80% copper.Workpiece weight - 1186 grams.How many atoms it contains?First of all, find the mass of the alloy components:

1186 * 0.2 = 237.2 grams of tin;

1186 * 0.8 = 948.8 grams of copper.

1186 * 0.2 = 237.2 grams of tin;

1186 * 0.8 = 948.8 grams of copper.

7

With Mendelev get the molar mass of tin - 118.6 g / mol.Therefore, the alloy contains 237.2 / 118.6 = 2 mol of tin.Then, 948.8 / 63.5 = 14.94 mol of copper.To simplify the calculations, it is possible to take the number of moles of copper 15, the error is very small.

8

Then make a calculation using the following formula:

(15 + 2) * 6.022 * 10 ^ 23 = 1.02 * 10 ^ 25.

so many atoms contained in the existing pattern of bronze.

(15 + 2) * 6.022 * 10 ^ 23 = 1.02 * 10 ^ 25.

so many atoms contained in the existing pattern of bronze.

Helpful Hint

«atomic mass units" - is 1/12 of the mass of an atom of carbon, adopted as a unit, "moles" - the amount of substance which contains 6.022 * 10 ^ 23the smallest particles of matter, "molar mass" - the mass of one mole of a substance.It should be remembered that although the molar mass equal in magnitude to the atomic mass, it is measured in other terms!