Discussion on various units used to measure concentration of solutions.
Learning objectives include defining concentration units and performing computations with them.
Learning Objectives
Define the concentration units:
Mass percentage
Volume percentage
Mass/Volume percentage
Parts per million (ppm)
Parts per billion (ppb)
Perform computations relating to solutions' concentration, components, volume, and mass.
Importance of Different Units
Chemists commonly use molarity but other fields use different units:
Mass percent: Common in consumer products (e.g., grocery, hardware store items).
Volume percent: Used in various applications.
Mass/Volume percent: Common in medicine.
Parts per million/billion: Used for measuring toxins in the environment.
Mass Percentage
Defined as the ratio of a component's mass to the solution's mass, expressed as a percentage.
Formula: (Mass of solute / Mass of solution) x 100
Used to describe solute concentrations; can also describe solvent concentrations.
Example: Liquid bleach has 7.4% sodium hypochlorite by mass.
Volume Percentage
Ratio of solute volume to solution volume, expressed as a percentage.
Formula: (Volume of solute / Volume of solution) x 100
Mass/Volume Percentage
Ratio of solute's mass to solution's volume, expressed as a percentage.
Common in saline solutions used in hospitals (e.g., 0.9% mass/volume sodium chloride solution).
Convenient for water solutions due to water's density being close to 1 g/mL.
Parts Per Million (ppm) and Parts Per Billion (ppb)
Used for very low solute concentrations.
ppm: (Mass of solute / Mass of solution) x 10^6
ppb: (Mass of solute / Mass of solution) x 10^9
Example: Trenton Waterworks report showed lead levels exceeding safe limits using ppb.
Action limit for lead: 15 ppb.
Lead is a cumulative toxin with no safe maximum level.
Source often from corrosion of household plumbing.
Example of application: Newark replaced plumbing lines due to similar issues.
Conclusion
Understanding different concentration units is crucial for various applications across fields such as consumer products, medicine, and environmental safety.