Molecular Mass Calculator

Learning Objectives

In this challenge you will improve your string manipulation techniques as well as use Python to perform some basic mathematical calculations.

Did you know?

The molecular weight (mass) may be calculated from the molecular formula of the substance; it is the sum of the atomic weights of the atoms making up the molecule. The molecular mass is expressed in atomic mass unit (amu).

For example, water has the molecular formula H₂O, indicating that there are two atoms of hydrogen and one atom of oxygen in a molecule of water.

Atom	Atomic Mass	Quantity	Total Mass
H	1.008	2	2.016
O	15.999	1	15.999
H20			18.015

In the following script we use a Python dictionary called atomicMass to store the atomic mass of some of the main atoms (C, H, O…)

We then work out the molecular mass of water: H₂0.

Your Challenge

Adapt this script to get the program ask the end-user to enter a molecular formula of their choice.
Using string manipulation techniques your Python script will break down the formula entered by the end-user and calculate the total mass of the molecule.

Test your script with the following molecules:

Molecule	Formula
Water	H2O
Carbon Dioxide	CO2
Methane	CH4
Butane	C4H10
Carbonic Acid	H2CO3
Acetone	CH3COCH3
Lactose	C12H22O11

Challenge #2

Add more atoms to the atomMass dictionary as follows:

Atom	Atomic Mass
Fe	53.939
Ag	106.905
Cu	62.929
Na	22.989
Cl	34.968

Adapt your script so that it recognises when these atoms are used by the end-user when entering their molecular formula. This will be based on the use of uppercase & lowercase letters.

Test your script with the following molecules:

Molecule	Formula
Sodium Chloride	NaCl
Iron Oxide	Fe2O3
Copper Chloride Hydroxide	HOCuCl