# Methylarsonic Acid [CH3AsO(OH)2] Molecular Weight Calculation

The molecular weight of Methylarsonic acid [CH3AsO(OH)2] is 139.970495.

Methylarsonic acid [CH3AsO(OH)2] is an organic compound of four elements: Carbon (C), Hydrogen (H), Arsenic (As), and Oxygen (O). The molecular weight of Methylarsonic acid is 139.970495 which can be calculated by adding up the total weight (atomic weight multiplied by their number) of all its elements.

# CALCULATION PROCEDURE: Methylarsonic acid [CH3AsO(OH)2] Molecular Weight Calculation

Step 1: Find out the chemical formula and determine constituent atoms and their number in a Methylarsonic acid molecule.
You will know different atoms and their number in a Methylarsonic acid molecule from the chemical formula. The chemical formula of Methylarsonic acid is CH3AsO(OH)2 or CH5AsO3. From the chemical formula, you can find that one molecule of Methylarsonic acid has one Carbon (C) atom, five Hydrogen (H) atoms, one Arsenic (As) atom, and three Oxygen (O) atoms.

Step 2: Find out the atomic weights of each atom (from the periodic table).

Atomic weight of Carbon (C): 12.0107 (Ref: Jlab-ele006)
Atomic weight of
Hydrogen (H): 1.008 (Ref: Lanl-1)
Atomic weight of Arsenic (As): 74.921595 (Ref: Jlab-ele033, ciaaw-arsenic)
Atomic weight of Oxygen (O): 15.9994 (Ref: Jlab-ele008)

Step 3: Calculate the total weight of each atom in a Methylarsonic acid molecule by multiplying its atomic weight by its number.

Number of Carbon atoms in Methylarsonic acid: 1
Atomic weight of Carbon (C): 12.0107
Total weight of Carbon atoms in Methylarsonic acid: 12.0107 x 5 = 12.0107

Number of Hydrogen atoms in Methylarsonic acid: 5
Atomic weight of Hydrogen (H): 1.008
Total weight of Hydrogen atoms in Methylarsonic acid: 1.008 x 5 = 5.04

Number of Arsenic atoms in Methylarsonic acid: 1
Atomic weight of Arsenic (As): 74.921595
Total weight of Arsenic atoms in Methylarsonic acid: 74.921595 x 1 = 74.921595

Number of Oxygen atoms in Methylarsonic acid: 3
Atomic weight of Oxygen (O): 15.9994
Total weight of Oxygen atoms in Methylarsonic acid: 15.9994 x 3 = 47.9982

Step 4: Calculate the molecular weight of Methylarsonic acid by adding up the total weight of all atoms.

Molecular weight of Methylarsonic acid: 12.0107 (Carbon) + 5.04 (Hydrogen) + 74.921595 (Arsenic) + 47.9982 (Oxygen) = 139.970495

So the molecular weight of Methylarsonic acid is 139.970495.

Methylarsonic acid [CH3AsO(OH)2] Molecular Weight Calculation

## REFERENCES:

• Lanl-1: https://periodic.lanl.gov/1.shtml
• Jlab-ele006; https://education.jlab.org/itselemental/ele006.html
• Jlab-ele008: https://education.jlab.org/itselemental/ele008.html
• Jlab-ele033: https://education.jlab.org/itselemental/ele033.html
• https://www.ciaaw.org/arsenic.htm

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