Grade 7 Science Solutions
Solutions… a review A homogeneous mixture ie. they appear as ONE substance Examples: tap water, vinegar, gold jewelry, etc.
Solutions have 2 parts: Solute Solvent The substance that dissolves (found in less amounts) Solvent The substance in which the solute dissolves (found in the greatest amounts)
Dissolving... To mix completely ie. the solute dissolves into the solvent. Some substances are able to dissolve better than others.
The Particle Theory of Matter states that “there are attractive forces between the particles”.
In order to dissolve, the particles must be more strongly attracted to the particles of the solvent than to themselves. This means that the solute is soluble in that solvent.
If the particles of the solute are more attracted to their own particles than the solvent particles, dissolving does NOT occur. The solute is said to be insoluble in that solvent. (ie. Mechanical)
Soluble or Insoluble? soluble insoluble
Solvent or Not? Some materials are good solvents for some solutes but not others. For example, oil is insoluble in water but soluble in gasoline.
States of Solutes and Solvents Air Solute: oxygen, carbon dioxide, other gases Solvent: nitrogen Gas Gas
Soda Solute: carbon dioxide Solvent: water Gas Liquid
Vinegar Solute: acetic acid Solvent: water Liquid Liquid
Filtered Sea Water Solute: Salt and other minerals Solvent: Water Solid Liquid
Brass Solute: zinc Solvent: copper Solid Solid **Alloy: Solutions made from two or more metals.
Rate of Dissolving… Factors that affect the rate of dissolving include: Size of the solute Temperature Pressure
Size of Solute The smaller the solute particles, the quicker they will dissolve faster
Temperature The higher the temperature, the more solute and the faster the solute will dissolve faster
Pressure Gases are more soluble in liquids under higher pressure (see page 267) Opened bottle decreases pressure and “bubbles” come out of solution
Separation Techniques Mechanical Sorting: Used to separate the parts of a mixture based on properties such as particle size. Examples: floatation & magnetism
magnetism floatation
Filtration: A common way to separate solid particles from a mixture The filters can have holes of varying sizes… small to microscopic.
Oil filter Coffee filter Colander Furnace filter
Evaporation: Change of state from a liquid to a gas. Used to recover a solid solute from a solution.
Distillation: Uses two changes of state: evaporation and condensation. It allows you to recover BOTH the solute and solvent from a solution.
Condensation Evaporation
Paper Chromatography: Used to separate the colored substances in a mixture such as ink. Used to separate the solvents in a mixture.
Separation Techniques in the Home: Colanders Clothes dryers Window screens Coffee percolators Salad spinners Any others?
Distillation: A Review A method of separation that allows you to recover a single solute and a single solvent. The mixture must boil so that the solvent can evaporate and then cooled so that it can condense back into a liquid.
Distillation Apparatus Evaporation Condensation Boil
Types of Distillations: Simple Distillation Separates a single solute from its solvent.
Fractional Distillation Separates a mixture of liquids based on their varying boiling points.