# Molecular Weight Determination

**Chemistry
Software Download**

### Determination of molecular weight (formula weight)

**Example:** What's the molecular weight of CH_{3}COOH
(acetic
acid) knowing that C=12g/mole,O=16g/mole and H=1g/mole?

Add all elements: 2*C + 2*O + 4*H -->
2*12g/mole +
2*16g/mole + 4*1g/mole = __60 g/mole__

**CHEMIX Molecular Calculator solution:**

Insert CH3COOH in the **formula **text field and **Calculate**

### Determination of Weight % Composition From Formulas

Formulas allow us to determine molecular weight of a compound as well
as
the weight % composition of each element represented in the compound.

The Molecular Weight is determined by taking the subscript for each
element
represented in the formula and multiplying it by the atomic weight of
the
element to get a mathematical product. Then the products are all added
up
for the molecular weight. For example:

**Example 1 **: *Determine the molecular weight of H2O
(water) knowing
that: H=1 g/mole and O=16 g/mole .*

There are 2 H's in the formula so the weight of the hydrogen has to
be 2
grams (or a.m.u). There is only one O in the formula so the weight of O
has
to be 16 grams.

The molecular weight of H2O = 2*1 grams + 16 grams = 18 grams

**Example 1 - The CHEMIX molecular calculator
solution**

Insert H2O in Formula text field and **Calculate**

**Example 2** : *Determine the weight percent of hydrogen and
oxygen
in H2O* knowing* that H2O = 18 gram/mole*

18 grams = 100 % so the

weight % of hydrogen has to be : 18 grams/ 2 grams * 100% =
11.19 %

weight % oxygen = 18 grams / 16 grams * 100% = 88.81 %

**Example 2 - The CHEMIX molecular calculator
solution**

**Solution:** Insert H2O in Formula text field and **Calculate**

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