Chapter 7: Solutions

1. Chapter 7: Solutions Air is a Gaseous Solution Sodium Chloride Liquid Solution Section 1: Solutions VS Mixtures

2. What is a mixture? • Mixtures of different substances exist all around us. • Many of these mixtures are invisible, and we never notice them. • However, some mixtures can easily be identified.

3. What is a mixture? • All matter is either a pure substance or a mixture of other substances. • Definition: pure substance – matter that has a fixed chemical composition. • For example: Water is a pure substance. It is ALWAYS H2O. Kool-Aid is a mixture of water and other substances.

4. Types of Mixtures • Mixtures can be categorized into two groups: • Heterogeneous and Homogeneous • Definition: heterogeneous mixture – a mixture made of visibly different substances. • The particles in a het. Mixture are not spread evenly. • Orange juice with pulp is an example of a heterogeneous mixture.

5. Heterogeneous Mixture Clear Orange Juice Orange Juice Pulp

6. Heterogeneous Mixtures Different fragments make up this rock. This rock is a heterogeneous mixture.

7. Homogeneous Mixtures • Homogeneous mixtures look the same all over. • Definition: homogeneous mixture – a mixture in which the particles are spread evenly. • Sweet tea is an example of a homogenous mixture. • There are several different substances (tea, water, and sugar) but you cannot see them. The tea looks uniform (the same) throughout.

8. + + =

9. The tea looks the same throughout the pitcher.

10. Solutions • We can call homogeneous mixtures by another name: solutions. • Definition: solution - a homogenous mixture of 2 or more substances that are evenly dispersed.

11. Solutions • Many solutions are formed by dissolving one substance into another substance. • These tablets are dissolving in the water to form a solution.

12. What is in a Solution? • It is important to know what makes up a solution. • All solutions are made of solutes and solvents. • Definition: solute - a substance that dissolves into another substance. • Definition: solvent - a substance that a solute is dissolved into.

13. Solvents • For example: • When you stir sugar into water, the sugar dissolves. • The water is the solvent. • The sugar is the solute. = + Solvent Solution Solute

14. The Universal Solvent • Water is very good at dissolving things. • Water is known as “The Universal Solvent”

15. Other types of Solutions • Not all solutions contain water! • Other states of matter can be solutions. • Gases & Solids can form solutions also. • Air is an example of a gaseous solution. • Air is composed of lots of different gases that we cannot see.

16. Metal Alloys • 2 or more solids can form solutions also. • Metal alloys are homogenous mixtures that contain a metal mixed with another substance. • Some examples are: • Steel – iron and carbon • Brass – copper and zinc • Bronze – copper and tin

17. Metal Alloys • In order to make an alloy, the metals must be melted. • While melted, the metals are mixed to form a solution. Bronze + Tin Copper

18. Chapter 7: Solutions Section 2: How Substances Dissolve

19. How do things dissolve? • Water can dissolve ionic compounds because of its structure. • The electrons in the hydrogen atoms are pulled toward the oxygen atom. • This gives the oxygen atom a slight negative charge. • The hydrogen atoms gain a slight positive charge.

20. The Water Molecule H H Oxygen

21. Polar Compound • Because water’s + and – charges are not spread out evenly, it becomes “polar”. • Definition: polar compound – a molecule that has a positive side and a negative side. • Because water is a polar compound, it is a good solvent.

22. Like dissolves Like • In chemistry, a rule of thumb is that “like dissolves like.” • Water is a polar compound, so it can dissolve other polar compounds. • If water cannot dissolve a substance, then that substance is “nonpolar”.

23. Nonpolar Compound • Definition: nonpolar compound – a compound that has no charge on its molecules.. • Nonpolar compounds can only dissolve other nonpolar substances. • Example – oil-based paint will not dissolve in water. A nonpolar solvent must be used.

24. Polar vs. Nonpolar Oil is Nonpolar Water is Polar They cannot mix.

25. The Dissolving Process • We have all seen solutes dissolve into solvents before. • And we all *probably* know some ways to speed up the process.

26. The Dissolving Process • Making a solute smaller makes it dissolve faster. • By crushing up a solute, you increase the surface area. Crushed Salt Rock Salt

27. The Dissolving Process • Stirring or shaking will make a solute dissolve faster.

28. The Dissolving Process • Increasing the solvent’s temperature will make the solute dissolve faster. Which one will Dissolve sugar Fastest?

29. The Dissolving Process: Gases • Did you know that liquids can dissolve gases? • Fish and other aquatic life breath oxygen that has dissolved into water. • Liquids dissolve gases best when they are cold.

30. The Dissolving Process: Gases • Don’t believe it? Well, consider this… • Which makes a louder “whoosh” sound when opened… a hot soda or a cold one?

31. Concentration • The amount of solute dissolved in a solvent affects its concentration. • Think of concentration as being how “strong” a solution is. • Definition: concentration – the amount of a substance in a certain amount of solution.

32. Concentration • “Concentrated” substances have lots of solute. • “Diluted” substances only have a little solute.

33. Saturated / Unsaturated • When a solvent can no longer hold any more solute, we called it “saturated”. • Definition: saturated solution – a solution that cannot dissolve any more of a given solute. • Definition: unsaturated – a solution that CAN hold more solute.

34. Super Saturated • Sometimes, a solvent can be made to hold more solute than normal. • The solution is called “supersaturated”. • Definition: supersaturated – a solution that has more solute than normal.

35. Super Saturated • Supersaturated solutions are unstable. • The extra solute can “fall out” at any time.