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Molar Mass, Molecular Weight and Elemental Composition Calculator

Molar mass of C7H7As is 166.0521 g/mol

Convert between C7H7As weight and moles
CompoundMolesWeight, g
C7H7As

Elemental composition of C7H7As
ElementSymbolAtomic weightAtomsMass percent
CarbonC12.0107750.6316
HydrogenH1.0079474.2490
ArsenicAs74.92160145.1193

Computing molar mass step by step

First, compute the number of each atom in C7H7As:
C: 7, H: 7, As: 1

Then, lookup atomic weights for each element in periodic table:
C: 12.0107, H: 1.00794, As: 74.9216

Now, compute the sum of products of number of atoms to the atomic weight:
Molar mass (C7H7As) = ∑ Counti * Weighti =
Count(C) * Weight(C) + Count(H) * Weight(H) + Count(As) * Weight(As) =
7 * 12.0107 + 7 * 1.00794 + 1 * 74.9216 =
166.0521 g/mol


Mass percent compositionAtomic percent composition

Related compounds
FormulaCompound name
C3H9AsTrimethylarsine
C5H5AsArsabenzene
C4H4AsHArsole
C4H12As2Cacodyl
C18H15AsTriphenylarsine
As(CH3)5Pentamethylarsenic
C10As2H161,2-Bis(dimethylarsino)benzene

Formula in Hill system is C7H7As

Computing molar mass (molar weight)

To calculate molar mass of a chemical compound enter its formula and click 'Compute'. In chemical formula you may use:
  • Any chemical element. 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.
  • Functional groups: D, T, Ph, Me, Et, Bu, AcAc, For, Tos, Bz, TMS, tBu, Bzl, Bn, Dmg
  • parenthesis () or brackets [].
  • Common compound names.
Examples of molar mass computations: NaCl, Ca(OH)2, K4[Fe(CN)6], CuSO4*5H2O, nitric acid, potassium permanganate, ethanol, fructose, caffeine, water.

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.

Computing molecular weight (molecular mass)

To calculate molecular weight of a chemical compound enter it's formula, specify its isotope mass number after each element in square brackets.
Examples of molecular weight computations: C[14]O[16]2, S[34]O[16]2.

Definitions

  • Molecular mass (molecular weight) is the mass of one molecule of a substance and is expressed in the unified atomic mass units (u). (1 u is equal to 1/12 the mass of one atom of carbon-12)
  • Molar mass (molar weight) is the mass of one mole of a substance and is expressed in g/mol.
  • Mole is a standard scientific unit for measuring large quantities of very small entities such as atoms and molecules. One mole contains exactly 6.022 ×1023 particles (Avogadro's number)

Steps to calculate molar mass

  1. Identify the compound: write down the chemical formula of the compound. For example, water is H2O, meaning it contains two hydrogen atoms and one oxygen atom.
  2. Find atomic masses: look up the atomic masses of each element present in the compound. The atomic mass is usually found on the periodic table and is given in atomic mass units (amu).
  3. Calculate molar mass of each element: multiply the atomic mass of each element by the number of atoms of that element in the compound.
  4. Add them together: add the results from step 3 to get the total molar mass of the compound.

Example: calculating molar mass

Let's calculate the molar mass of carbon dioxide (CO2):

  • Carbon (C) has an atomic mass of about 12.01 amu.
  • Oxygen (O) has an atomic mass of about 16.00 amu.
  • CO2 has one carbon atom and two oxygen atoms.
  • The molar mass of carbon dioxide is 12.01 + (2 × 16.00) = 44.01 g/mol.

Lesson on computing molar mass

Weights of atoms and isotopes are from NIST article.

Related: Molecular weights of amino acids

molecular weights calculated today
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