6th Grade Life Science Miss Sauer SOLUTIONS 6th Grade Life Science Miss Sauer

Chapter 14, Lesson 3: What Properties Do Solutions Have? Main Idea: Mixtures are made up of two or more pure substances that are NOT chemically combined. Mixtures can be heterogeneous or homogeneous. Solutions are a type of homogeneous mixture.

MIXTURE: Mixture: made up of 2 or more substances that are NOT chemically combined. Each substance keeps its original properties (whether we are adding them or taking them out).

Example of a Mixture: Example: Vegetable soup; the carrots in the soup will have the same properties whether they are in the soup or removed from the soup. The soup is an unevenly mixed mixture; the ingredients may be present in variable amounts.

Compounds Have A Chemical Formula: Recall, in a compound, the elements are chemically bound together. The relative amounts of each element are always the same in a given compound. That is why a compound can be represented by a chemical formula.

Mixtures Do Not Have A Chemical Formula: A mixture does NOT have a definite composition and CANNOT be represented by a chemical formula.

Classifying Mixtures Mixtures can be classified as: Heterogeneous Homogeneous

Classifying Mixtures (continued) Heterogeneous: Unevenly mixed (made up of different components). Example: trail mix Homogeneous: Evenly mixed (made up of mostly the same components). Example: sea water; air

By looking at it to see if it is evenly mixed or unevenly mixed. Question? How do you decide whether a mixture is heterogeneous or homogeneous? By looking at it to see if it is evenly mixed or unevenly mixed.

Solution: mixture that is evenly mixed at the molecular level. You cannot see the particles that make up the solution. Many homogeneous mixtures are solutions. Example: Add sugar to a glass of water & stir. The sugar will seem to disappear, meaning it dissolves in the water.

A solution has two parts: Solute Solvent

Solute: substance that is present in the lesser amount. Solvent: substance that is present in the greater amount. (Example: sugar water; sugar is solute & water is solvent)

Tricks for remembering the difference between Solute & Solvent: Solvent has more letters than solute (solvent is the substance that is present in the greater amount). SOLVENT: you can form an arrow from the “V” (if you have more NesQuik powder than milk, it will fall to the bottom of the glass).

Because the solution is a mixture, the substances that make up the mixture keep their properties. And You can separate your sugar-water solution by letting the water evaporate. The sugar will be left behind.

As in a mixture, the ratios of the ingredients may vary in a solution. Add more sugar to your sugar-water solution and it will still be a solution, but the ratio of sugar to water will have changed.

Concentration: the ratio of solute to solvent.

Rate of Dissolving: Rate of Dissolving: Dissolving takes place only at the surface of the solute, where the solvent molecules come in contact with the solute particles.

For Lab: In the case of sugar, loose sugar dissolves much more quickly than sugar cubes. This is because loose sugar has a greater surface area. Since dissolving takes place only at the surface of the sugar, increasing the surface area of the sugar will make it dissolve faster.

For Lab: Less Surface Area More Surface Area

How Can I Increase the Rate of Dissolving?: When you stir or shake a solution, you help the solute particles mix more quickly with the solvent molecules. Increasing the temperature of the solvent also increases the rate of dissolving. Dissolving increases in this case because the molecules of hot water move faster and have higher energy than molecules of cold water. Faster moving solvent molecules will hit the solute crystals with more energy and more frequently, dislodging the solute particles more quickly.

If you continue to add solute to a solution, eventually, the solution will become saturated, meaning, no more solute can be dissolved. This happens because all the solvent molecules have been “used up.”

Alloy: a solution of one or more metals or other solids Alloy: a solution of one or more metals or other solids. (Examples: brass, bronze, stainless steel, and sterling silver)

To make an alloy, the component substances are melted and mixed. Alloys usually have different physical properties than the substances they are made of.

The relative amounts of each substance in an alloy can affect its properties. Example: Steel is an alloy of iron and carbon. The amount of carbon in the mixture determines the hardness; more carbon – it’s harder; less carbon – it’s softer.

Closure Questions What is a mixture? How are mixtures classified? What is the difference between heterogeneous and homogeneous? What is a solution? What are the two parts of a solution? What is a concentration? What is rate of dissolving? How could you increase the rate of dissolving? What is an alloy?