The molecular weight of Arsenous acid [H_{3}AsO_{3}] is 125.943795.

Arsenous acid [H_{3}AsO_{3}] is an inorganic compound of three elements: Hydrogen (H), Arsenic (As), and Oxygen (O). The molecular weight of Arsenous acid is 125.943795 which can be calculated by adding up the total weight (atomic weight multiplied by their number) of Hydrogen, Arsenic, and Oxygen.

**CALCULATION PROCEDURE: Arsenous acid [H**_{3}AsO_{3}] Molecular Weight Calculation

_{3}AsO

_{3}] Molecular Weight Calculation

**Step 1: Find out the chemical formula and determine constituent atoms and their number in an Arsenous acid molecule.**You will know different atoms and their number in an Arsenous acid molecule from the chemical formula. The chemical formula of Arsenous acid is [H

_{3}AsO

_{3}]. From the chemical formula, you can find that one molecule of Arsenous acid has three 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 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 an Arsenous acid molecule by multiplying its atomic weight by its number.**

Number of Hydrogen atoms in Arsenous acid: 3

Atomic weight of Hydrogen (H): 1.008

Total weight of Hydrogen atoms in Arsenous acid: 1.008 x 3 = 3.024

Number of Arsenic atoms in Arsenous acid: 1

Atomic weight of Arsenic (As): 74.921595

Total weight of Arsenic atoms in Arsenous acid: 74.921595 x 1 = 74.921595

Number of Oxygen atoms in Arsenous acid: 3

Atomic weight of Oxygen (O): 15.9994

Total weight of Oxygen atoms in Arsenous acid: 15.9994 x 3 = 47.9982

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

Molecular weight of Arsenous acid: 3.024 (Hydrogen) + 74.921595 (Arsenic) + 47.9982 (Oxygen) = 125.943795

So the molecular weight of Arsenous acid is 125.943795.

**Arsenous acid [H _{3}AsO_{3}] Molecular Weight Calculation**

Molecular weight of Arsenous acid [H_{3}AsO_{3}] | |||

Constituent atoms | Number of each atom | Atomic weight | Total weight |

Hydrogen (H) | 3 | 1.008 | 3.024 |

Arsenic (As) | 1 | 74.921595 | 74.921595 |

Oxygen (O) | 3 | 15.9994 | 47.9982 |

Molecular weight of Arsenous acid [H_{3}AsO_{3}]: | 125.943795 |

## REFERENCES:

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

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