What's the difference between molarity and molality?

Molarity (M) = moles per liter of SOLUTION. Molality (m) = moles per kg of SOLVENT. Molarity changes with temperature (volume changes). Molality is temperature-independent (mass doesn't change). Use molality for colligative properties; molarity for most reactions.

How do I convert between percent and ppm?

Multiply percent by 10,000 to get ppm (both same basis w/w or v/v). 1% = 10,000 ppm. 0.05% = 500 ppm. 50 ppm = 0.005%. Percent is parts per hundred; ppm is parts per million.

Why are there different types of percent concentration?

Different fields have conventions: w/w (industrial, food) is mass-based and additive. v/v (beverages, perfumery) is practical for liquids. w/v (pharmacy) gives convenient dose calculations. Always check which is meant—they give different values for the same solution.

溶液浓度 Converter

About Solution Concentration Conversion

Solution concentration can be expressed in many fundamentally different ways: mass-based expressions (percent w/w, ppm), volume-based (percent v/v), mole-based (molarity, mole fraction, molality), or hybrid forms (percent w/v). Each method has specific advantages—and using the wrong type leads to significant errors. A "5% solution" could mean very different things depending on whether it's w/w, v/v, or w/v, and these are NOT interchangeable.

Common units include percent by weight (% w/w) for industrial chemicals, percent by volume (% v/v) for alcohol content, percent weight/volume (% w/v) for pharmacy, parts per million (ppm) for trace analysis, mole fraction for thermodynamic calculations, and molality for colligative properties. Understanding the distinctions between these expressions is essential for correctly interpreting specifications, preparing solutions, and converting between systems used in different industries and countries.

Our converter helps translate between common solution concentration expressions used across chemistry, pharmacy, food science, and industrial applications.

Common Concentration Relationships

Expression	Definition	Typical Use
% w/w	g solute / g solution × 100	Industrial chemicals
% v/v	mL solute / mL solution × 100	Alcohol content
% w/v	g solute / 100 mL solution	Pharmacy
ppm	mg/kg or mg/L	Trace analysis
ppb	μg/kg or μg/L	Ultra-trace
Mole fraction	moles solute / total moles	Physical chemistry
Molality	moles solute / kg solvent	Colligative properties
Molarity	moles solute / L solution	Laboratory chemistry
Normality	equivalents / L solution	Acid-base titration
ppt	ng/kg or ng/L	Ultrapure materials

Solution Concentration Unit Reference

Percent (% w/w, % v/v, % w/v) – Parts per hundred, the most intuitive concentration expression but dangerously ambiguous—always specify which type. % w/w (weight/weight) means grams solute per 100 grams solution, standard in industrial chemistry; % v/v means mL solute per 100 mL solution, standard for alcohol; % w/v means grams per 100 mL, common in pharmacy. 5% NaCl w/w means 5g salt per 100g total solution mass.

Parts per million (ppm) – Parts per million by mass (mg/kg) or by volume for gases. For dilute aqueous solutions, 1 ppm ≈ 1 mg/L because water density ≈ 1 kg/L. Universal for trace components, pollutants, and specifications. 1% = 10,000 ppm; 0.1% = 1,000 ppm. Always clarify mass vs volume basis, especially for gases.

Mole fraction (χ) – Dimensionless ratio of moles: χ_solute = n_solute / (n_solute + n_solvent). Essential for vapor pressure calculations (Raoult's law), chemical potential, and thermodynamic activity. Mole fractions of all components must sum to 1. Temperature-independent since it's based on mole counts.

Molality (m) – Moles of solute per kilogram of solvent (not solution). Unlike molarity, molality is temperature-independent because mass doesn't change with temperature while volume does. Essential for colligative properties: freezing point depression (ΔT_f = K_f × m), boiling point elevation (ΔT_b = K_b × m), and osmotic pressure. 1 m means 1 mole solute dissolved in 1 kg solvent.