(Chapter 23)

What is a solution?

·       it is a homogeneous solution (everything is evenly mixed)—it has the same composition, color, density and taste throughout

·       For example, if you add sugar crystals to water and stir, they disappear; the sugar molecules become evenly mixed in the water

All solutions are made up of 2 things: a solvent and a solute. 

·       Solute: the substance being dissolved (ex. sugar that’s put in water)

·       Solvent: the substance doing the dissolving (ex. the water)

·       Solutes and solvents can be liquids, gases, or even solids!

o     Air: a solution of nitrogen, oxygen, and other gases

o     Brass: a solid solution of copper and zinc

o     Beer: a solution of water, ethanol, and carbon dioxide

How do things dissolve?  Example: dissolving sugar in water

·       Remember that the water molecules are moving around constantly, and that water molecules are polar.  Sugar molecules are also polar. 

o     Rule of thumb: LIKE DISSOLVES LIKE  

·       Step 1: Water molecules bump into sugar crystals.  The negative (-) ends of the water molecules are attracted to the positive (+) ends of sugar molecules. 

·       Step 2: the water molecules pull the sugar molecules out of the crystals and into solution, surrounding them

·       Step 3: the dissolved sugar molecules spread evenly through the water

How can you make things dissolve faster?

·       Make the crystals smaller.  Smaller particles dissolve faster, because they have more surface area for the water molecules to find

·       Stir it.  This makes the particles move faster and come into contact with more water molecules

·       Heat it up.  This also causes the water molecules to move faster

·       For gases only: Increase the pressure.  Increased pressure forces more gas molecules into the liquid.  Also: Decrease Temperature