Mixtures Most forms of matter occur as mixtures A mixture is a combination of 2 or more substances that come in contact with each other but keep their basic identity. This means physical properties can change but chemical properties will not. 2 kinds of mixtures: homogeneous (the same throughout, known as solutions) and heterogeneous (not evenly mixed, either a colloid or suspension).

Solutions Homogeneous Clear (may have color) No settling / can’t be filtered Do NOT exhibit the Tyndall effect Contain very small solute particles (less than 1 nm) – atomic size Examples: salt water, Kool Aid, soda

Colloids Heterogeneous Cloudy appearance No settling / can’t filter Do exhibit the Tyndall effect Contain particles between 1 nm–1000 nm – much larger than atoms Contain particles and a dispersion medium which may both be the same phase or not (see chart on pg. 477) Examples: milk, mayonnaise, motor oil

Suspensions Heterogeneous Cloudy Settles / separates into 2 or more layers Can be filtered Does exhibit the Tyndall effect Contains very large particles compared to dissolved solutes – larger than 1000 nm Ex: muddy water, orange juice, aerosals

Thixotropic A suspension that flows like a liquid when stirred, but quickly settles into a solid layer and a liquid layer when not stirred. Ex: cornstarch in water (Oobleck) house paint

Brownian motion Particles in a colloid have random motion that can be seen under a microscope Caused by collisions with the molecules in the dispersing medium (which can’t be seen with a microscope)

Tyndall Effect The scattering of light Caused by particles suspended in a colloid or suspension due to their size Solutions do not exhibit the Tyndall effect because the dissolved particles are too small to scatter light Examples: laser light show, driving in fog