Density Formula in Chemistry: Applications, Molar Mass & Solutions

Why Density Matters in Chemistry

Density is a crucial property in chemistry because:

Identifies substances: Each pure chemical has a unique density
Predicts behavior: Determines if substances will float or sink
Quality control: Verifies purity of chemical samples
Concentration measurement: Used to determine solution strength
Molar mass calculation: Can be used to find molecular weight of gases

Density of Common Chemical Substances

Chemical	Formula	Density	State
Water	H₂O	1.0 g/mL (at 4°C)	Liquid
Acetone	C₃H₆O	0.78 g/mL	Liquid
Ethanol	C₂H₅OH	0.79 g/mL	Liquid
Mercury	Hg	13.6 g/mL	Liquid
Sulfuric acid	H₂SO₄	1.84 g/mL	Liquid
Carbon dioxide (gas)	CO₂	1.98 g/L (at STP)	Gas
Oxygen (gas)	O₂	1.43 g/L (at STP)	Gas

Finding Molar Mass from Gas Density

The Relationship

At standard temperature and pressure (STP), the density of a gas is directly related to its molar mass:

Molar Mass = Density (g/L) × 22.4 L/mol

Why this works: At STP, 1 mole of any ideal gas occupies 22.4 liters

Step-by-Step Process

Measure or identify the gas density at STP (in g/L)
Multiply by 22.4 L/mol
The result is the molar mass in g/mol

Example: Finding Molar Mass of CO₂

Given: CO₂ has a density of 1.98 g/L at STP

Formula: M = D × 22.4

Calculation: M = 1.98 g/L × 22.4 L/mol = 44.4 g/mol

Actual molar mass of CO₂: 44.01 g/mol (very close!)

Example: Finding Molar Mass of Unknown Gas

Given: Unknown gas has density of 2.0 g/L at STP

Calculation: M = 2.0 × 22.4 = 44.8 g/mol

Possible identity: Likely CO₂ or N₂O (both ~44 g/mol)

Density of Chemical Solutions

Solution Density Basics

The density of a solution depends on:

The solvent: Usually water (1.0 g/mL as baseline)
The solute: The dissolved substance
Concentration: Higher concentration = higher density (usually)
Temperature: Most solutions become less dense when heated

Common Solution Densities

Solution	Concentration	Density
Sulfuric acid	100% (concentrated)	1.84 g/mL
Sulfuric acid	50% (dilute)	1.40 g/mL
Hydrochloric acid	37% (concentrated)	1.19 g/mL
Ethanol	100% (pure)	0.79 g/mL
Ethanol/Water	50% mixture	0.93 g/mL
Sodium chloride (NaCl)	10% solution	1.07 g/mL

Using Density to Find Solution Concentration

Example: Calculating Solution Concentration

Problem: A sulfuric acid solution has a density of 1.50 g/mL. Is it 50% or concentrated (100%)?

Solution: Compare to known densities:

Concentrated H₂SO₄ (100%): 1.84 g/mL
Dilute H₂SO₄ (50%): 1.40 g/mL
Our sample (1.50 g/mL): Approximately 60% concentration

Calculating Mass of Solute from Solution Density

Real-World Scenario

You need 100 grams of salt solution. A 10% NaCl solution has a density of 1.07 g/mL. How much volume do you need?

Step-by-Step Solution

Use D = M ÷ V to find volume: V = M ÷ D
V = 100 g ÷ 1.07 g/mL = 93.5 mL
You need 93.5 mL of 10% NaCl solution

Example: Preparing a Solution

Given: Need 50 mL of 37% HCl (density 1.19 g/mL)

Find: How many grams of HCl solution needed?

Solution: M = D × V = 1.19 g/mL × 50 mL = 59.5 grams

Note: Of this 59.5 g, 37% (22 g) is HCl, and 63% (37.5 g) is water

Temperature Effects on Density

Why Temperature Matters

Most substances have lower density at higher temperatures because:

Particles move faster and spread out
Same mass occupies larger volume
Lower density = substance rises

Water: The Exception

Water is unusual! It has maximum density at 4°C, not at freezing point:

At 0°C (ice): 0.92 g/cm³ (solid, less dense)
At 4°C (water): 1.00 g/cm³ (maximum density)
At 20°C (water): 0.998 g/cm³
At 100°C (water): 0.958 g/cm³

This is why ice floats! Solid ice is less dense than liquid water.

Chemistry Calculators

Solution Concentration Calculator

Calculate solution concentration or prepare solutions:

Practical Chemistry Applications

Quality Control in Manufacturing

Pharmaceutical companies measure solution density to verify that medications contain the correct concentration of active ingredients.

Identifying Unknown Liquids

Lab technicians use density measurements to identify unknown chemical liquids by comparing to known densities in reference tables.

Determining Gas Molecular Weight

Analytical chemists use gas density at STP to determine molar mass of unknown gaseous compounds.

Environmental Monitoring

Water quality specialists measure solution density to detect contaminants and dissolved substances in water samples.

Key Takeaways

Density is an intensive property—unique to each pure substance
Each chemical has a characteristic density used for identification
Gas density at STP can be used to find molar mass
Solution density depends on solute concentration
Temperature affects density for most substances
Density measurements are crucial for quality control in chemistry
Use the density formula (D = M/V) for all calculations

Density in Chemistry: Applications & Calculations

Molar Mass Calculator