Substances, Mixtures, and Solubility

1. Substances, Mixtures, and Solubility Chapter 8

2. Substances • A substance is matter that has the same fixed composition and properties. • A substance cannot be broken down into simpler parts by ordinary physical processes (boiling, grinding, filtering). • Only a chemical process can change a substance into one or more new substances. • An element is an example of a pure substance.

3. Compounds • A compound is made of two or more elements that are chemically combined. • Compounds have a fixed composition. • The ratio of atoms in a compound is always the same.

4. Compounds • Water is a substance because it stays the same chemically when frozen or boiled. • Water is also a compound.

5. Mixtures • Mixtures are combinations of substances that are not bonded together. • The substances can be separated by physical processes. • Mixtures do not always contain the same proportions of the substances.

6. Types of mixtures • In a heterogeneous mixture the substances are not mixed evenly. • Different areas of the mixture have different compositions.

7. Types of mixtures • A homogeneous mixture contains two or more substances that are evenly mixed on a molecular level but the substances are not bonded together. • A homogeneous mixtures can also be called a solution.

8. How do solutions form? • The formation of a solution requires that a solute be dissolved in a solvent. • A solute is the substance that disappears when added to another substance. • The solvent is the substance that dissolves the solute.

9. How can a solid form from a solution? • Sometimes a solid can come back out of its solution and form a solid. • Crystallization occurs when the solvent evaporates, leaving a solid. This is the results of a physical change.

10. Forming solids from a solution • Sometimes a solid is formed due to a chemical reaction that occurs when solutions are mixed together. • The solid is called a precipitate. • A precipitate is the results of a chemical change.

11. Types of solutions • Solutions can be made up of different combinations of solids, liquids, and gases. • Examples (see table 2, pg. 221)

12. Examples of common solutions

13. Liquid solutions • Liquid solutions can be either liquid, solid, or even a gas. • Liquid-gas solutions • A gaseous solution and a liquid solvent • Carbonated beverages • Liquid-liquid solutions • Both the solute and solvent are liquid • Vinegar : water (solvent) and acetic acid (solute)

14. Gaseous solutions • Both the solvent and solute are gases. • The air we breath • 78 % nitrogen • 21% oxygen • 1% other gases

15. Solid solutions • The solvent is a solid. • The solute can be a solid, liquid, or gas. • The most common solid solutions are solid-solid solutions • Solid-solid solutions made from two or more metals are called alloys • Steel (iron and carbon atoms) • Brass (zinc and copper atoms)

16. Solubility • Water is often the solvent for many solutions. • A solution in which water is the solvent is called an aqueous solution. • Water is often referred to as the universal solvent.

17. Molecular compounds • The sharing of electrons is called covalent bonding. • Compounds that have covalent bonds are called molecular compounds (molecules).

18. Non-polar covalent compounds • There is an even distribution of electrons in a non-polar covalent molecule. • The atoms share electrons. • The bonds between atoms are called non-polar covalent bonds.

19. Polar covalent compounds • There is an uneven distribution of electrons in a polar molecule • Atoms share electrons. • The bonds between atoms are called polar covalent bonds. • Water is a molecule with polar covalent bonds.

20. Ionic bonds • In some atoms the electrons are not shared. • The atoms will either gain or lose electrons. • The number of protons and electrons in the atoms becomes unequal. • The atom takes on a positive or negative charge. • Atoms with a charge are called ions.

21. Ionic bonds • Bonds between ions that are formed by the transfer of electrons are called ionic bonds.

22. How does water dissolve ionic compounds? • Remember, water has positive and negative charges parts. • Positive part will attract negative ions. • Negative part will attract positive ions. • When an ionic compound is mixed with water, the different ions are pulled apart by the water molecule.

23. How does water dissolve molecular compounds? • Water can dissolve molecular compounds. • However, the water does not break the molecule apart, but moves between the molecules. • The water separates the molecules of the compound.

24. Likes dissolve likes • This means that polar solvents dissolve polar solutes and non-polar solvents dissolve non-polar solutes. • Sugar and water: both are made up of polar molecules • Salt and water: Na and Cl ion pair is similar to the water molecule, both having + and - charges • If a solvent and solute are not similar, the solute will not dissolve . Non-polar molecules will not dissolve polar molecules. • Oil and water

25. How much will dissolve? • Solubility is a measurement that describes how much solute dissolves in a given amount of solvent at a given temperature. • Substances that have extremely low solubility are usually considered insoluble.

26. Solubility of liquid-solid solutions • Temperature is included as an explanation for how much solute will dissolve in a given amount of solvent. • The solubility of many solutes changes as temperature changes. • Increasing the temperature of the solute will often times increase the amount of solute that will dissolve.

27. Solubility in liquid-gas solutions • In these solutions, an increase in temperature decreases the solubility of the gas. • Gases are often less soluble in a warm solution.

28. Saturated solutions • A solution that contains all the solute that it can hold under the given conditions is called a saturated solution. • In a liquid-solid solution, any extra solute that is added will only settle to the bottom of the container. • Some solutions can become supersaturated, meaning it contains more than the normal amount of solute.

29. Rate of dissolving • Several factors, including time, motion, temperature, and contact area, affect the rate of dissolving. • Temperature • Stirring or shaking

30. Concentration • The concentration of a solution is how much solute is present compared to the amount of solvent. • Concentrated solutions have more solute per given amount of solvent than dilute solutions. • Concentrations can be stated as a percentage of the volume of solution that is solute.

31. Acid solutions • Acids are substances that dissolve in water and release positively charged hydrogen ions. • When an acid mixes with water, the acid dissolves, releasing the hydrogen ion. • The hydrogen ion combines with water molecules to form positively charged hydroniumions (H3O+).

32. Properties of Acid solutions • Acids taste sour, conduct electricity, are corrosive, and reactive with certain metals. • Acids have a pH between 0 and 7.

33. What does pH mean? • pH is a measure of how acidic or basic a solution is and relates to the concentration of hydronium ions and hydroxide ions.

34. What is the pH scale? • The pH scale ranges from 0 to 14. • Acidic solutions have pH values below 7. • A solution with a pH of 0 is very acidic . • Hydrochloric acid has a pH of 0. • A solution with a pH of 7 is neutral, meaning it is neither acidic or basic. • Pure water is neutral. • Basic solutions have pH values above 7. • A solution with a pH of 14 is very basic. • Sodium hydroxide can have a pH of 14.

35. What does a change in pH mean? • A change in pH represents a 10 fold change in the acidity of the solution. • Example - if one solution has a pH of 1 and a second solution has a pH of 2, the first solution is not twice as acidic as the second, but 10 times more acidic than the second solution.

36. Calculating change in pH • Use the following calculation to determine the difference in pH strength - 10n, where n = the difference between pHs. • Example - pH3 - pH1 = 2, 102 = 100 time more acidic.

37. How is the strength of an acid determined? • The strength of an acid is related to how easily the acid separates into ions, or how easily a hydrogen ion is released when the acid dissolves in water. • More hydronium ions means the strong-acid solution has a lower pH than the weak-acid solution. • The pH of a solution is more acidic when greater amounts of hydronium ions are present.

38. How us is the strength of a base determined? • The strength of a base is related to how easily the base separates into ions, or how easily a hydroxide ion is released when the base dissolves in water.

39. Strength of acids and bases • An acid containing more hydrogen atoms is not necessarily stronger than an acid containing fewer hydrogen atoms. • An acid’s strength is related to how easily a hydrogen ion separates, not how many hydrogen atoms it has. • Example - nitric acid (HNO3) is stronger than carbonic acid (H2CO3)

40. Examples of acid solutions • Vinegar (made from acetic acid) is used in salad dressings. • Vitamin C (ascorbic acid) comes from lemons, limes, and oranges. • Ants inject formic acid into their victims. • Sulfuric acid is used in fertilizers, steel, paints, and plastics. • Hydrochloric acid (commercially called muriatic acid) is used in pickling (process that removes impurities from the surface of metals). • Nitric acid is used in the production of fertilizers, dyes, and plastics.

41. Acid solutions • Acids are found in foods such as lemons and oranges that contain ascorbic acid and are used in many products such as batteries and plastics. • Sulfuric acids is used in fertilizers, steel, paints, plastics. • Hydrochloric acid (muriatic acid) used in process called pickling. • Nitric acid is used in the production of fertilizers, dyes, and plastics.

42. Acids • Stalactites and stalagmites areformed when carbon dioxide in soil dissolves in water, helps form caves, stalagmites, and stalactites.

43. Base solutions • When bases dissolve in water, some hydrogen atoms from the water molecule are attracted to the base. • A hydrogen atom in the water molecule leaves behind the other hydrogen atom and oxygen atom. • This pair of atoms is a negatively charged ion called a hydroxide ion. • A hydroxide ion has a formula of OH-. • Most bases contain a hydroxide ion which is released when the base dissolves in water.

44. Bases • Bases are substances that accept hydrogen ions; when dissolved in water, a hydroxide ion forms. • Bases taste bitter,feel slippery, are corrosive, and conduct electricity. • Soaps,cleaning products and bloodin the human body are basic.

45. What is an indicator? • Indicators are compounds that react with acidic and basic solutions and produce certain colors, depending on the solution’s pH. • Because there are different colors at different pHs, indicators can help determine the pH of a solution. • Litmus is a indicator that is soaked onto paper. • When litmus paper is placed in an acidic solution, it turns red. • When the litmus paper is placed in a basic solution, it turns blue.

46. What is neutralization? • Neutralization is the reaction of an acid with a base. • When acidic and basic solutions react, hydronium and hydroxide ions react to form water. • Through neutralization the properties of both the acid and base are diminished, or neutralized. • When one hydronium ion reacts with one hydroxide ion, the product is two water molecules.