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Several example codes

~1 min read • Updated Sep 16, 2025

Program Overview

This Python program calculates the approximate number of water molecules in a given volume of water (in liters).
It uses the known mass of one liter of water and the estimated mass of a single water molecule to compute the result.

Python Code:


# Approximate mass of one water molecule: 2.99e-23 grams
# Mass of one liter of water: ~1000 grams

mass_per_molecule = 2.99e-23  # grams
mass_per_liter = 1000         # grams

liters = float(input("Please enter the volume of water (in liters): "))

total_mass = liters * mass_per_liter
num_molecules = total_mass / mass_per_molecule

print("The approximate number of water molecules is:", num_molecules)

Sample Output:


Please enter the volume of water (in liters): 2
The approximate number of water molecules is: 6.688963210702342e+25

Explanation:

Here’s how the program works:
- It uses the estimated mass of a single water molecule: 2.99 × 10⁻²³ grams
- Assumes one liter of water weighs approximately 1000 grams
- Multiplies the input volume by the mass per liter to get total mass
- Divides total mass by the mass of one molecule to get the number of molecules
- Displays the result using the print() function


Written & researched by Dr. Shahin Siami