Before we begin to calculate the molar mass of NaCl or any other compound for that matter, it is important that we know what exactly the molar mass of an element is. We know that all things around us are occupied by matter whose building block is molecules. It becomes essential that we measure these molecules in all the experiments to get accurate results for our products in the experiment. Thus, a change in the molecular mass of a compound can greatly vary the results of any scientific calculations. For all laboratory calculations, a tool called the analytical balance is used to measure the weights in grams. After various calculations and observations, a scientist discovers the number of moles required for a particular experiment based on which we calculate the molar mass. A mole is nothing, but a unit used for measurement which helps in comparing particles and mass of a given compound. Once we are aware of the moles required for a particular experiment, we can easily use the concept and notion of molar mass for determining the grams of substance required for our purpose. The molar mass of a compound is also known as its molecular weight and is the total mass in grams of the atoms that form one mole of a certain molecule. Its unit of measurement is g/mol. That is, the molar mass of a substance= 1 gram/I mole
Calculating the molar mass of NaCl can be extremely simple only if you know the difference between elements and compound and have a knowledge about the molecular weight of the respective elements. Compounds are basically substances that are formed when two or more elements react chemically while elements, on the other hand, are naturally occurring substances found mostly in abundance on Earth or in the atmosphere. Let us take the example of the molar mass of NaCl. The compound NaCl is composed of two elements, sodium (Na) and Chlorine (Cl) and together when they react chemically, they form NaCl as the product. NaCl consists of a lattice of Na+ and Cl- ions which react in the ratio of 1:1 to give us halite or salt. Scientifically known as Sodium Chloride and fondly referred to as common salt, NaCl is a compound responsible for making up the extracellular fluids in most cellular organisms and causing the salinity in seawater. Its many applications include that of a food preservative and for de-icing of pathways and highways. In fact, Sodium Chloride has a lot of industrial applications such as in the soda ash industry or the chlor-alkali process and thus, knowing the molar mass of NaCl is very important.
The very first thing while determining the molar mass of a compound is to look at the molecular weight of individual elements in the periodic table. Sometimes it is very difficult to memorize the atomic mass of the heavy elements and in such cases, it is best to see a periodic table to get accurate results. Now, since the compound NaCl is made of sodium and chlorine, the molar mass of NaCl can be calculated only after its atomic weight is known from the table. Individual atoms of sodium and chlorine have an atomic mass of 22.98976 g/mol and 35.453 g/mol respectively. The next step towards calculating the molar mass of NaCl is determining the number of atoms for each element of the compound. For example in NaCl, there are no subscripts or small numbers present at the bottom of the elements which means that both Na and Cl contribute a single atom to make NaCl together. Had the compound been, say CaCl2, then the number of atoms for Calcium would have been one and that of Chlorine would have been two, based on the subscript represented along with its symbol. After finding out about the atoms, we can easily find out the molar mass of NaCl or any other compound. Molar mass of an element= no of atoms X the atomic weight of each element. And, molar mass of the compound= the sum total of molar mass of all the elements.
That is, Sodium (Na) = 1 X 22.98= 22.98 g/mol
Chlorine (Cl) = 1 X 35.45= 35.45 g/mol
Molar Mass= (22.98 + 35.45) g/mol = 58.44 g/mol
After calculating the atomic mass of each element and its individual atom, the molecular mass is determined which comes out to be around 58.44 after rounding off to the nearest decimal.
Determining the molar mass of a compound is extremely essential in the field of chemistry. It forms the basis for all other calculations. This is because it helps the scientists to know how much mass is occupied by a quantity of matter. For any chemical reaction, it becomes extremely vital to know the exact number of atoms that the scientists will be needing to carry out their research. Even a slight variation in the calculation can lead to drastic changes in the field of chemistry. Moreover, even the tiniest substance is made of a large number of atoms amounting to some billions and thus, to avoid any discrepancies scientists make use of the mole concept as a unit of measurement.
Now, the one mole of substance can be defined as the number of atoms present in 12 grams of a carbon-12 atom. This quantity is scientifically known as the Avogadro’s number and its number comes out to be approximately 6.022 X 10^23. To sum up, a mole is nothing, but the total substance that has the same amount of molecules or atoms as that of a 12 gram of a carbon-12 atom. For example, molar mass of NaCl will also contain a similar number of atoms which means that it would weigh around 58 grams and have 6.022 X 10^23 molecules. Just like each atom or ion of a particular element has some mass, in a similar way each mole of a given substance will also carry some mass. Thus, the atomic mass unit or amu of an element is its atomic weight which is equal and similar in quantity to the mass occupied by one mole of that element.
Just like we calculated the molar mass of NaCl, in a similar manner we can determine the molar mass of any other compound. All we have to do is memorize or look up for the atomic weight of all the elements in the periodic table. It is important that we get familiar with the periodic table in order to determine the position of the exact element with ease. To become more acquainted with the concept, let us calculate the molar mass of a complex compound. Take for example, copper (II) sulphate pentahydrate or CuSO4.5H2O. Here we have to write down the atomic mass of all the elements including those present in water. The atomic mass of Copper was found to be 63.55 g/mol while that of sulphur, hydrogen and oxygen was 32.07, 1.008 and 16 g/mol. The compound consisted of 9 atoms of oxygen (4 in sulphur and 5 from water) while hydrogen had a total of 10 atoms and the rest had one atom each. This was put in its formula and the molar mass came out to be:
CuSO4.5H2O = 63.55 + 32.07 + 4X16 + 5(2 X 1.00 + 16). That is, 249.70 g/mol is the molar mass of the respective compound.
By calculating the molar mass of NaCl, we can easily determine the number of moles of NaCl or any other substance. The number of moles of a substance can be calculated by using the following formula.
N=n/m ; Where, N= no of moles, n= number of grams of the substance and m= its molar mass;
For example, if we want to calculate the number of moles of NaCl in a particular gram we simply need to figure out the molar mass of NaCl and the mass of the substance in grams. Like if someone asks us to determine the number of moles in say, 72.33 grams of NaCl. The molar mass of NaCl is 58.44g and thus, the number of moles can be easily calculated.
That is, N= 72.33/58.44
N= 1.2376 mol
This means you have around 1.23 mol of NaCl in 72.33 grams of it. Thus, the molar mass of NaCl can be used to calculate molarity, normality etc.