Water is a compound that has many properties It is necessary to sustain life

1. water • Water is a compound that has many properties • It is necessary to sustain life • Is the most abundant compound in the cells of living things • Plays a major role in maintaining temperature • Also important in making solutions….

2. Solutions

3. What it a solution? A solution is a homogeneous mixture meaning that it is uniform throughout and we cannot see the different components. This means that a sample from one part of the solution is exactly the same as a sample from any other part of the solution.

4. Describing the Parts of a Solution Solute: the component of lesser quantity (the stuff that is dissolved) Solvent: the component of greater quantity which usually defines the physical state of the resulting solution (the stuff that does the dissolving)

5. Using Water in Solutions There are numerous compounds that will dissolve in water – Therefore water is known as the Universal Solvent Water Molecule = H20 -The H side has a positive character -The 0 side has a negative character

6. How do we know if something will dissolve in water? • The rule is “like dissolves like” • Depends on whether the substance is polar or nonpolar.

7. What is “polar” and “nonpolar”? • Polar molecules posititve and negative charges in a molecule Ex: water

8. What is “polar” and “nonpolar”? • Non – polar molecules are those that do not have the different positive and negative sides. • EX – oil • Made up of non – metals (hydrogen and carbon)

9. How Solids Dissolve • Water breaks the + and - charged pieces apart and surround them. • EX : Salt = NaCl is an “ionic compound” so we know it will dissolve in water. We know it’s ionic because its made up of metal and non-metal elements. It has a polar character and will dissolve in water

10. H H H H O O O H H H H O O H H O O H H H H H H O H O H How Solids Dissolve When mixing salt with water the salt dissolves in the water producing a homogenous mixture.

12. How much will dissolve? • For most solutes there is a limit to how much will dissolve in a given amount of water. • This is called solubility • Saturated solution – once the maximum amount of solute is dissolved (no more will dissolve)

13. Types of SolutionsNot every solutions is made up using water! Gaseous solutions gases in gases air is a homogeneous mixture of many gases humid air is a result of water vapor in the air.

14. Types of Solutions: Liquid solutions gases in liquids: carbonated drinks are CO2 in water liquids in liquids: vinegar is acetic acid in water solids in liquids: salt water is NaCl in water

15. Types of Solutions: Solid solutions liquids in solids: dental fillings are a mercury-silver amalgam (Hg is a liquid and Ag is a solid) solids in solids: sterling silver is a mixture of copper and silver brass is a solid solution of zinc and copper

16. Rate of Dissolving The rate at which a given solute will dissolve in a given solvent is dependent upon three factors: • Temperature of the solution • Agitation of the solution • Size of the solute particles.

17. Rate of Dissolving • Temperature of the solution • Heating the solution increases the kinetic energy of the solvent molecules so the solvent molecules move faster. • With the solvent molecules moving faster, they attack the solute particles more frequently. • The solute particles are pulled into the solution faster increasing the rate that they dissolve.

18. Rate of Dissolving 2. Agitation of the solution • Stirring the solution increases the interaction between solvent molecules and the solute. • The greater the interaction between solvent and solute, the more rapid the rate of dissolution.

19. Rate of Dissolving 3. Particle size and the rate of dissolution • The smaller the particle size, the greater the total surface area of the solute. • Since the solvent attacks the solute particles along the surface and edges, the greater the surface area, the more the solute is exposed to attack by solvent. • The more frequently the solvent molecules and attack the solute particles, the more rapid the rate of dissolution.

20. Concentrations & Making Solutions • Concentration = how much solute is dissolved in the solution • Dilute = having a small amt. of solute dissolved in the solution • Concentrated = to having large amts. of solute dissolved in the solution • Need to express the concentration based on percent

21. Percent by Mass(solvent expressed as mass also) Mass Percent: % m/m = X 100% % m/m = x100% Mass of solute (g) Mass of solution (g) grams of solute (grams of solvent) +(grams of solute)

22. Percent by Mass(solution expressed as mass also) Mass Percent: % m/m = X 100% % m/m = x100% (61.5 grams of solution) Mass of solute (g) Mass of solution (g) 12.3 grams of sugar = 0.2074198 X 100% = 20.74198 = 20.7% m/m

23. Preparing % m/v – solute is solid, solvent is liquid

24. To determine the mass of solute needed to prepare a solution the formula can be rearranged. Example – what is the mass of a solute needed to prepare 250 g of a 5.0% m/m glucose solution?

25. Preparing %v/v – both are liquids • EX – 25.0 mL of alcohol are added to water to a final volume of 100.0 mL = 25.0 %v/v Always add the solvent “to a final volume of” and not just combine the volumes of solute and solvent.

26. Acids and Bases Property of some aqueous solutions is their ability to act as an acid or base

27. Originally a chemical or solution was classified as an acid if it had the following 3 properties: • It has a sour taste • It turns a plant dye called litmus red • It eats away at more active metals like zinc to produce a hydrogen gas.

28. Acids

29. Properties of Bases • Bases also have a bitter taste. The bitter taste of milk of magnesia • They turn the plant dye called litmus blue. • Bases are also recognized because they feel slippery or soapy.

30. Bases

31. A scale was developed to relate the acidity or basicity of a soltuion • The scale related the available hydrogen ions in a solution to a numerical value. • It is based on on 0 14 • It’s called the pH scale • The closer the pH value is to 0, the stronger the acid. • The closer the pH value is to 14, the stronger the base. • If the pH value is in the middle, or 7, the pH is neutral

32. Solutions may be: strongly acidic (0 - 2), weakly acidic (2 - 7), neutral (pH=7), weakly basic (7 - 12), strongly basic (12 - 14).

33. More about “litmus” Litmus paper can be used to indicate if a solution is acidic or basic. However, it does not indicate “how acidic” or “how basic”.

34. What is litmus? • Litmus is one of a large number of organic compounds (it is actually extracted from certain mosses) that change colors when a solution changes acidity at a particular point. • Litmus is the oldest known pH indicator. • It is red in acid and blue in base. • Litmus is often impregnated onto paper to make 'litmus paper.'

35. Properties of Acids An acid can be identified in the laboratory because it turns a plant pigment called litmus red. A base can be identified in the laboratory because it turns a plant pigment called litmus blue.

36. Measuring pH pH indicators can also be impregnated onto paper and used to determine pH. Paper, called pHydrion paper, is impregnated with a universal indicator. It can be used to determine the approximate pH over a full range.

37. More about “litmus” Litmus paper can be used to indicate if a solution is acidic or basic. However, it does not indicate “how acidic” or “how basic”.

38. What is litmus? • Litmus is one of a large number of organic compounds (it is actually extracted from certain mosses) that change colors when a solution changes acidity at a particular point. • Litmus is the oldest known pH indicator. • It is red in acid and blue in base. • Litmus is often impregnated onto paper to make 'litmus paper.'

39. Properties of Acids An acid can be identified in the laboratory because it turns a plant pigment called litmus red. A base can be identified in the laboratory because it turns a plant pigment called litmus blue.

40. Measuring pH pH indicators can also be impregnated onto paper and used to determine pH. Paper, called pHydrion paper, is impregnated with a universal indicator. It can be used to determine the approximate pH over a full range.

41. Kinds of pH paper

42. pH Color Chart

43. pH & Buffers • A buffer keeps something where it should be. • It buffers adverse swings. It shields, cushions and protects. • Is necessary to control any change in pH in some systems • Especially in biological systems which need to control pH • Living systems have buffering systems in place In order to maintain pH at a constant requires buffering of the system in a pond

44. Buffers • Buffers tie up foreign acid and base • There is a limit as to how much acid or base a buffer can absorb • This is called buffer capacity • A buffer would be used to maintain the pH of a product within a narrow range. • Buffers reduce the variation in the pH of a product, as shown on the graph