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For example, water is H 2O, meaning it contains two hydrogen atoms and one oxygen atom. Identify the compound: write down the chemical formula of the compound.One mole contains exactly 6.022 ×10 23 particles (Avogadro's number) Mole is a standard scientific unit for measuring large quantities of very small entities such as atoms and molecules.Molar mass ( molar weight) is the mass of one mole of a substance and is expressed in g/mol.(1 u is equal to 1/12 the mass of one atom of carbon-12) Molecular mass ( molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u).To calculate molecular weight of a chemical compound enter it's formula, specify its isotope mass number after each element in square brackets.Įxamples of molecular weight computations: Molar mass calculator also displays common compound name, Hill formula, elemental composition, mass percent composition, atomic percent compositions and allows to convert from weight to number of moles and vice versa.Ĭomputing molecular weight (molecular mass) Functional groups: D, Ph, Me, Et, Bu, AcAc, For, Tos, Bz, TMS, tBu, Bzl, Bn, DmgĮxamples of molar mass computations: NaCl, Ca(OH)2, K4, CuSO4*5H2O, nitric acid, potassium permanganate, ethanol, fructose, caffeine, water.Capitalize the first letter in chemical symbol and use lower case for the remaining letters: Ca, Fe, Mg, Mn, S, O, H, C, N, Na, K, Cl, Al. Na 2S + Cu(CH 3COO) 2 = Na(CH 3COO) + CuSĬomputing molar mass (molar weight)To calculate molar mass of a chemical compound enter its formula and click 'Compute'. M = 58.7 + 2 x 35.5 + 6 x 18.0 = 237.7 g/molĬalculating the molar mass is essential as it lays the foundation for most of the calculations in stoichiometry such as the mass, moles, number of particles and etc.Copper(II) acetate appears as a blue-green crystalline solid. He formula of the hydrate is NiCl 2♶H 2O, and therefore, the molar mass would be: To calculate the molar mass of a hydrate, determine the molar mass of the salt and add to the molar mass of the water multiplied by its subscript.įor example, calculate the molar mass of nickel (II) chloride hexahydrate. The formula of nitrate ion is NO 3 –, therefore, the molar mass would be: It is a result of either losing or gaining an electron(s) which has negligible mass compared to atoms and molecules.įor example, what is the molar mass of the nitrate ion? Remember, the number outside of parenthesis applies to all the elements in it. Next, we write the ions next to each other and add the correct subscripts:Īnd now, we multiply the molar mass of each element by its subscript. You need to know the common polyatomic ions from where we find that sulfate is the SO 4 2- ion. M (PCl 5) = 30.1 + 5 x 35.5 = 207.6 g/molĪnother example: what is the molar mass of aluminum sulfate?įirst, we know that the aluminum ion has a 3+ charge. To calculate the molar mass of PCl 5, we multiply the molar mass of each element by its subscript: Go over naming covalent compounds to refresh some of the concepts here. The formula of phosphorous pentachloride is PCl5. If the formula of the molecule is not given, you will need to first determine it.įor example, determine the molar mass of phosphorous pentachloride. To calculate the molar mass of a molecule, we add the molar mass of each constituent atom by the corresponding subscript.įor example, the molar mass of water would be: Usually, we round off the molar mass to 1 or 2 decimal places, so for P, we’d use 123.9 or 123.90 for its molar mass. For example, to find the molar of P 4, we multiply 30.974 g/mol by 4: If there is a subscript in the symbol, then you need to multiply the molar mass by that number.
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And we can do this for all the elements in the periodic table. For potassium then, it is 39.098 g/mol which means one mole of potassium atoms weighs 39.098 g. What’s important for today’s topic is that numerically, the molar mass is equal to the average atomic mass of the given atom, so we can look it up in the periodic table. The smaller one is the atomic number which shows the number of protons, and the larger one is the average atomic mass: So, how do we find the molar mass in the periodic table?įor example, there are two numbers given for potassium in the periodic table: 19 and 39.098. To calculate the molar mass of an atom or a molecule, we are always going to need a periodic table. The mass of one mole of atoms/molecules/ions is called its molar mass ( M) expressed in g/mol.