KemRisk^®

Calculation of Molecular Weights

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Instructions

In this form you can calculate the molecular weight of two different molecules and their quotient by writing the chemical formulas.

There are two input fields, one for Molecule 1 and one for Molecule 2. The calculation is executed on clic of the button [Calculate]. The molecular weights are then indicated in the fields to the right and the quotient (Molecule 2 / Molecule 1) in the bottom field. If radioactive elements are included this fact is indicated in the lower right field.

Example 1

You want to know the molecular weight of sodium dihydrogen phosphate dihydrate.
Clic on the upper left field and type:
NA H2 P O4 H4 O2
Clic on [Calculate]. The molecular weight (156,008 Da) appears to the right.

Note:

• You must type at least one space character between each element
• The input is case insensitive, i.e. you need not to use upper and lower case letters according to current chemical nomenclature. "NA" is equivalent to "Na" or "nA" or "na" etc
• The same element can occur several times in the formula
• Parentheses are not allowed in the formula
• The number of atoms shall be indicated directly after the element. If no number is indicated the program assume the number to be one.

Example 2

You want to know the weight fraction of mercury in mercury orange (CAS # 3076-91-3).
Clic on the upper left field and write the formula of mercury orange:
C16 H11 CL HG N2 O
Clic on the middle left field and type:
HG
Clic on [Calculate]

The molecular weight of mercury orange (481.321 Da) appears in the upper right field and the atomic weitht of mercury (200.59 Da) in the middle right field.
The fraction of mercury in mercury orange (0.415024 or 41.5%) appears in the lower left field.

Example 3

You want to know the chlorine content in tetrachlorophenol (e.g. 2,3,4,6-tetrachlorophenol).
Clic on the upper left field and write the formula of tetrachlorophenol:
C6 H2 CL4 O
Clic on the middle left field and type:
CL4
Clic on [Calculate]

The molecular weight of tetrachlorophenol (231.094 Da) appears in the upper right field and that of four chlorine atoms (141.812 Da) in the middle right field.
The weight fraction of chlorine (0.611538 or 61.2%) in tetrachlorophenol appears in the lower left field.

Example 3

You want to know the molecular weight of the pertechnietate ion.
Clic on the upper left field and type:
TC O4
Clic on [Calculate]

The molecular weight of the pertechnietate ion (162.998 Da) appears in the upper right field and a warning "RADIOACTIVE" appears in the lower right field.

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