A suspension is a type of heterogeneous mixture in which solid particles are dispersed throughout a liquid or gas but do not dissolve. These particles are typically large enough to be seen with the naked eye and will settle over time if the mixture is left undisturbed. This tendency to settle under gravity distinguishes suspensions from colloids and solutions, where the particles either remain suspended indefinitely or are fully dissolved. ^[1–4]

Examples ^[1-6]

• Muddy water: Soil or mud particles are dispersed in water but eventually settle due to gravity.
• Sand in water: Sand grains remain suspended briefly but quickly settle to the bottom without dissolving.
• Flour in water: Forms a thick, cloudy mixture where the flour particles settle over time if not stirred.
• Chalk powder in water: Creates a white, opaque suspension with visibly suspended particles that settle upon standing.
• Medicinal suspensions: Products like antacids or calamine lotion contain undissolved particles that require shaking to evenly redistribute before use.

Characteristics ^[3]

• Heterogeneous composition: The components are not uniformly distributed.
• Lack of a uniform phase: The solid and liquid (or gas) phases remain physically distinct.
• No solute dissolution: The distributed particles in the medium do not dissolve.
• Sedimentation over time: Solid particles settle due to gravity when the mixture is left undisturbed.
• Re-dispersibility: The particles can be mixed back into the medium by stirring or shaking.
• Physically separable: The components can be separated by physical methods such as filtration or decantation.

Suspensions may exhibit poor light scattering, which can result in a weak Tyndall effect that depends on the size of the particles.

Applications ^[3,5]

• Pharmaceuticals: Many medicines, such as oral antacids and antibiotic syrups, are formulated as suspensions to deliver insoluble drugs. These products must be shaken before use to ensure uniform dosing.
• Paints and coatings: Paints are suspensions of pigment particles in a liquid medium, allowing for even color application and surface coverage.
• Construction materials: Cement and lime slurries are suspensions used in construction for tasks such as plastering, grouting, and concrete setting.
• Environmental science: Suspended solids such as silt and pollutants in water are monitored to assess water quality and wastewater treatment efficiency.
• Food and beverage industry: Products like fruit juices with pulp, protein drinks, and salad dressings are suspensions that often require shaking before consumption.

Because the particles in a suspension do not dissolve and can be separated easily, they are used in many areas of everyday life, such as in medicines, paints, building materials, and even food products. Studying suspensions helps us understand mixtures better and shows how chemistry is closely linked to the real world in useful and meaningful ways.