# How to calculate grams to atoms

## EL-MO elements and molecules, textbook

Exercises 11.1 to 11.3 Substance mass and amount of substance KM-5: Modeling 11 11 The molar mass M and the amount of substance n The amount of substance n cannot be measured directly. For practical work, you therefore need a quantity that links the number of moles with the mass. This quantity is the molar mass M. It indicates the mass of 1 mol of a substance in g / mol. In the case of atoms, the numerical value corresponds to the atomic mass in u / atom, since the Avogadro constant is the conversion factor between unit and gram. The molar mass for atoms is therefore found in the periodic table of the elements. For example, a chlorine atom only has an average mass of 35.5 u / atom - but there is no existing atom with this mass. One mole of chlorine atoms has a mass (molar mass) of 35.5 g / mol - an appropriate value, since one mole contains the chlorine nuclides in the naturally occurring isotope ratio. The molar mass of each compound is the sum of the molar masses of the atoms involved. For example, the molar mass of C 6 H 12 O 6 is calculated by taking 6 x the molar mass of C, 12 x the molar mass of H and 6 x the molar mass of O. The molar mass of grape sugar is M (C 6 H 12 O 6) = 6. M (C) + 12. M (H) + 6. M (O) = 6. 12.01 + 12. 1.01 + 6. 16.00 = 180 g / mol. (Exercise 11.1) From the amount of substance (n) to the mass of substance (m) and back One can therefore calculate the mass of any amount of substance at any time with a simple final calculation or deduce the amount of substance from a mass. This final calculation can of course also be put into a formula - with the corresponding quantities (Fig. 11–1): m = M. n total mass = mass of 1 mol x number of moles Examples 1. What is the mass (in g) of 3.00 mol of ammonia (NH 3)? The first step is always to “translate” the text into the symbols used in chemistry. The units used for the specification must be checked and, if necessary, converted. n (NH 3) = 3.00 mol If you know the formula, then you know the molar mass M (NH 3) = 17.04 g / mol The mass m is the required quantity m (NH 3) =? Then the required size is calculated. It is also advisable to use units for the calculation. m (NH 3) = M (NH 3). n (NH 3) = 17.04 g / mol. 3.00 mol = 51.12 g Indication of the results with the corresponding unit. The number of decimal places in the result is always based on the number of significant places in the data. The mass of 3.00 mol of ammonia is 51.00 g. 2. How many moles of water molecules (H 2 O) does 1.00 kg of water contain? (1.00 kg of water corresponds to 1 L of water due to the density of 1 kg / L.) Information: m (H 2 O) = 1 kg = 1000 g M (H 2 O) = 18.02 g / mol n (H 2 O) =? Calculation and result n (H 2 O) = m / M = 1000 g / 18.02 g / mol = 55.49 mol 1 kg of water contains about 55.5 mol of water molecules. This is a number that you should remember or that you can recalculate at any time. The Avogadro constant can also be used to calculate the total number of water molecules in one liter. Number of water molecules / L = 55.49. 6.02. 10 23 = 3.34. 10 25 molecules / L It is not usual to calculate the number of individual molecules, since the term “mole” covers all requirements for chemical calculations. Fig. 011–1: Basic quantities and their mathematical relationship to one another Molar mass M (molar mass) * It corresponds to the numerical value of the atomic mass * It has the unit g / mol (also kg / kmol or mg / mmol) * It can can be read from the periodic table * It is the tool (proportionality factor) to convert the "pieces" of atoms and molecules that cannot be measured and counted due to the large number of them into measurable masses. Amount of substance n ("countable") * This is the term used to describe the "number of pieces" of atoms and molecules. * It has the unit mol * Every chemist thinks and works in "mol" * Simple! * Not directly measurable! Mass m ("weighable") * It is usually given in chemistry in grams (g) * It can be determined with a balance. 1. Determine the molar masses of the following substances: M (S 8) = M (CH 4) = M (H 2 SO 4) = M (HNO 3) = 2. Calculate the mass of 1.7 mol acetic acid ( CH 3 COOH). 3. How many moles of carbon dioxide are there in a 10 g CO 2 cartridge? n = m M Student experiment 1.1 Mol - Molar mass - Mass VS For testing purposes only - property of the publisher öbv