The molecular weight of Sodium arsenite (NaAsO₂) is 129.91016428.

Sodium arsenite (NaAsO₂) is an inorganic compound of three elements: Sodium (Na), Arsenic (As), and Oxygen (O). The molecular weight of Sodium arsenite is 129.91016428 which can be calculated by adding up the total weight (atomic weight multiplied by their number) of all its elements.

CALCULATION PROCEDURE: Sodium arsenite [NaAsO₂] Molecular Weight Calculation

Step 1: Find out the chemical formula and determine constituent atoms and their number in a Sodium arsenite molecule.
You will know different atoms and their number in a Sodium arsenite molecule from the chemical formula. The chemical formula of Sodium arsenite is NaAsO₂. From the chemical formula, you can find that one molecule of Sodium arsenite has one Sodium (Na) atom, one Arsenic (As) atom, and two Oxygen (O) atoms.

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

Atomic weight of Sodium (Na): 22.98976928 (Ref: Ciaaw-sodium)
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 molecular weight of Sodium arsenite by adding the total weight of all atoms.

Number of Sodium (Na) atoms in Sodium arsenite: 1
Atomic weight of Sodium: 22.98976928
Total weight of Sodium atoms in Sodium arsenite: 22.98976928 x 1 = 22.98976928

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

Number of Oxygen (O) atoms in Sodium arsenite: 2
Atomic weight of Oxygen: 15.9994
Total weight of Oxygen atoms in Sodium arsenite: 15.9994 x 2 = 31.9988

Step 4: Calculate the molecular weight of Sodium arsenite by adding up the total weight of all atoms.

Molecular weight of Sodium arsenite : 22.98976928 (Sodium) + 74.921595 (Arsenic) + 31.9988 (Oxygen) = 129.91016428

So the molecular weight of Sodium arsenite is 129.91016428.

Sodium arsenite [NaAsO₂] Molecular Weight Calculation

REFERENCES:

• Ciaaw-sodium : https://www.ciaaw.org/sodium.htm
• Jlab-ele033: https://education.jlab.org/itselemental/ele033.html
  
• ciaaw-arsenic: https://www.ciaaw.org/arsenic.htm
  
• Jlab-ele008: https://education.jlab.org/itselemental/ele008.html

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