Properties of Liquids, Suspensions and Colloidal Dispersions

Three States of Matter Solids contain particles that are extremely close together Gases contain particles that are extremely far apart Liquids lie in between the extremes of solids and gases

General Properties of Liquids

Incompressible and have a definite volume Under normal conditions a liquid maintains its volume under pressure an example of this property is the application of liquids in hydraulic systems: braking system of a motor vehicle garage hoist

Viscosity A liquid’s resistance to its flow caused by an internal frictional force between adjacent layers of the flowing liquid

Surface Tension Surface tension, a force, is a resistance of a liquid to an increase in its surface area Arises from the attractive forces between the liquid’s molecules on and below the surface of the liquid Causes water to form spherical droplets Spheres minimize the ratio of surface area to volume Allows some insects to “walk” on water Surface tension of the water’s surface is greater than the weight of the insect Can float a paper clip on water’s surface also As with the insect mg < Fst

surface tension

Capillary Action Capillary action is the spontaneous rising of of a liquid in a narrow tube Capillary action of a liquid is due to the interaction between the cohesive forces within the liquid and the adhesive forces between the liquid and the walls of the tube The narrower the tube, the higher the liquid will rise See the next slide

Capillary Action and the Meniscus The meniscus is the shape of the surface of the liquid when in a tube or cylinder. It can be concave or convex, depending on the liquid. Water Forms a concave meniscus The adhesive forces between the water and the surface are greater than the cohesive forces within the water

Capillary Action and the Meniscus Mercury Forms a convex meniscus The cohesive forces within mercury are greater that the adhesive forces between the mercury and the surface See the next slide of water and mercury in separate graduated cylinders

water forms a concave meniscus mercury forms a convex meniscus

Physical and Thermal Properties of Water Property Value Density 1000 kg/m3 mass of one cubic metre of water at 277 K Boiling Point 373 K Transition temperature between liquid and gas Freezing Point 273 K Transition temperature between liquid and solid Heat Capacity 75.2 kJ/mol/K Heat required to raise one mole of water one Kelvin Heat of Fusion 5.98 kJ/mol Heat absorbed or given off in the solid phase/liquid phase transition Heat of Vaporization 40.5 kJ/mol Heat absorbed or given off in the gas phase/liquid phase transition Thermal Conductivity 0.58 J/(s.m.K) Rate of heat flow through water at 293 K

Physical and Thermal Properties of Water Property Value Compressibility 4.9×10−10/Pa Rate of change of volume per change in pressure. Surface Tension 72.8 mN/m This is the force/metre required to overcome the surface tension of water at 293 K. Note: Surface tension of water decreases as temperature increases. Viscosity 1.13 cSt (at 289 K) The viscosity of a fluid is measured as (force × distance)÷(area × velocity) This value is centipoise, the most common measure for viscosity. Note: Viscosity decreases as temperature increases

Various Mixtures: Solutions, Suspensions, and Colloids

Mixtures in General Mixtures are matter containing two or more substances Mixtures can be homogeneous (uniform throughout) Solutions are homogeneous Mixtures can be heterogeneous (without uniform composition) Suspensions and colloids are heterogeneous

Solutions: Some Definitions and Concepts Solutions are made up of a solute and a solvent the solute – least abundant compound in the solution the solvent – most abundant compound in the solution The solute and solvent can be in relative variable amounts Any acid solutions can be highly concentrated or quite dilute The solute and solvent may be in the same phase or different phases soft drinks are a mixture of a gas (solute) and liquid (solvent)

Solutions and their Properties Homogeneous mixture Dissolved solute is ionic or molecular in size (0.1 to 1.0 nm) Transparent and can be clear or coloured Solute does not settle out with time Solute passes through all filters Solute and solvent can be separated by physical means such as evaporation Light passes through the solution with no scattering

Examples of Solutions, Liquid or Otherwise Ionic solutions (solid solute in water) such as acids: HCl, H2SO4, CH3COOH bases: NaOH, Mg(OH)2 aqueous salts: NaCl, AgNO3, Ca3(PO4)2 ionic solutions are examples of a solid solute in a liquid solvent antifreeze (liquid solute in liquid solvent) soft drinks (gas solute in a liquid solvent) metal alloys (solid solute in a solid solvent)

Suspensions and their Properties Heterogeneous mixture of solid particles in either a liquid or gas Dissolved solute particles are greater than 100 nm The mixture is cloudy The solute settles out with time Solute can be filtered with filter paper Particles are large enough to block light rays impinging on the mixture

Examples of Suspensions Oil and vinegar Muddy water Dust in air

Colloids and their Properties Heterogeneous mixture of solid particles in either a liquid or gas Dissolved solute particles are between 1 nm and 100 nm Mixture is cloudy Particles do not separate out with time Solute can be filtered with a micro-filter Particles are large enough to scatter light passing through the mixture but not block it completely

Types of Colloids and Examples of Each Aerosols (solids in a gas): fog, clouds, smoke Foams (gas in a solid): styrofoam, whipped cream Sol (solid in a liquid): shampoo, ink, paint Emulsion (liquid in a liquid): milk, lotion