Topic 2 Notes

What makes Materials Dissolve  Forming a mixture by mixing two or more materials together is called dissolving.  Eg. Salt dissolves in water  Mixing materials together does not always form a solution.  Eg: Orange juice or Milk

What Makes a mixture dissolve or not?  Remember back to the Particle Model:  Particles attract each other  Particles are always moving  Eg: Sugar dissolving in water:  Water attracts sugar particles greater than sugar particles attract one another.  Fig 1.8 pg 17  First the water particles pull the sugar away from other sugar particles  next, the water particles move it away.  This process continues until the sugar has fully dissolved.

Example 2 A water droplet on a table:  Water particles are attracted to one another, however they also are always moving  The particles on the outside of the drop occasionally get pulled away by warm air particle until eventually the drop is gone.

Solvents and Solutes  When sugar dissolves in water we call the water the solvent and the sugar the solute.  Solute: the substance that dissolves in the solvent  Solvent: the substance that dissolves the solute “Sugar dissolves in water” = “sugar is soluble in water”  Soluble: able to be dissolved in a particular solvent  Table 1.1 pg 18

Water: THe universal solvent  2/3s of the earth’s surface is covered in water  water is known as the universal solvent because of its ability to dissolve many materials.  ½ of our blood is made up of water  blood carries vitamins, minerals, and many other essential substances throughout your body  98% of our bodies are water

THe rate of dissolving Definition: the speed of a solvent dissolving a solute in a solvent. What factors might affect the rate of dissolving?

Answers?  Agitation: shaking or stirring  what happens when you add juice crystals to a water bottle and shake it?  when you shake the mixture the water particles move farther away from the juice crystals. As a result, the water particles pull the juice crystals away from the other crystals. Speeding up the rate of dissolving.

How much can be dissolved?  Not all particles dissolve in the same amount or at the same rate. The degree of attraction varies from substance to substance.  Solubility: the mass of a solute that can dissolve in a given amount of solute to form a saturated solution as a given temperature.  A Saturated Solution: a solution where no more solute will dissolve in a specific amount of solvent at a specific temperature.  Unsaturated Solution: a solution where more solute can be dissolved

Example: Scientists have determined that no more than 35.7g of salt will dissolve in 100g of ice-cold water at zero degrees. So the solubility of salt is 35.7g/100g of water. Table 1.2 pg 20

How does a substance become saturated A solution is saturated when the particles of the solvent have attracted all the possible particles of the solute that they can. No more stirring or mixing will help

Supersaturated solutions It is possible to pass the saturation limit in SOME solutions. A solution that contains more solute that would normally dissolve at a certain temperature is called a supersaturated solution. HOW?: saturate a solution, then cool it down WITHOUT stirring. The solute will stay dissolved for a short time. if you add more solute, crystals will form. Pg 1.13 pg 21

Cleaning up with solvents  Sometimes mixing materials together does not always result in a solution.  Some solutes are insoluble, with means, not able to be dissolved in a particular solvent.  Why are some solutes insoluble? Think apart particle attraction.  Cleaning solvents have extremely strong high attraction forces which allows them to dissolve stains and messes.

Topic 2 review page 26