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Chapter 10

Chapter 10. Acids and bases. Identifying features of acid. Sour tastes ( ex. lemon juice, vinegar) Conducts electricity when in liquid (electrolyte) React with a base to form water & a salt (neutralization rxn) A salt is the ionic product of an acid base rxn. Identifying features of acid.

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Chapter 10

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  1. Chapter 10 Acids and bases

  2. Identifying features of acid Sour tastes ( ex. lemon juice, vinegar) • Conducts electricity when in liquid (electrolyte) • React with a base to form water & a salt (neutralization rxn) • A salt is the ionic product of an acid base rxn

  3. Identifying features of acid • Acids react with certain metals to form H2 gas. • Look at table J. • All metals that are above Hydrogen will react with it, but those below wont. • Cause indicators to change colors (more on this later)

  4. Bases • Bitter taste (bleach, ammonia, soap) • Slippery or soapy feeling • Conduct electricity in liquid (electrolyte) • React with acids to form water and a salt • Cause indicators to change colors (more on this later)

  5. What makes an acid an acid • Scientists had known for a long time common features of acids, but they didn’t know why an acid displayed those features • What was it that made an acid an acid.

  6. Arrhenius • Svante Arrhenius proposed that an acid is any substance that when mixed with water will give off a Hydrogen ion. • HCl ---- H+ & Cl- • HNO2-- H+ & NO2- • H2SO4 2H+ & SO42-

  7. Not everything with a hydrogen is an acid • Methane CH4 • & Sugar C6H12O6 are molecules with a hydrogen that are not acids. • Molecules with H are only acids if the molecule is ionic, but if the molecule is covalent the H is not released in liquid.

  8. So what makes a hydrogen acidic? • When a H+ ion is in water it cannot remain there alone. • It will quickly react with water to form H30+ • This new molecule is called a hydronium ion. • So all the acidic substances act the way they do, bc of their Hydronium ions.

  9. Bases • According to the Arrhenius theory a base is any substance that increases the amount of OH- (hydroxide) ions in water. • NaOH  Na+ & OH- • KOH  K+ & OH- • Ca(OH)2  Ca+2 & 2OH- • The properties of a base is because of the OH

  10. Exception • NH3 (ammonia) is classified as a base even though it lacks OH. • But upon closer examination we find NH3 does create OH- ions. • NH3 + H2O  NH4+ & OH-

  11. Table K & L • On your reference table the common acids and bases you need to know for the regents are listed.

  12. Strength of acids and bases • Hydrocloric acid --- very dangerous • Citric acid ----Found in plants • Boric acid--- used in eye washes

  13. Strenghts of acids • A very strong acid will have all of its Hydrogen’s leave the compound and enter the water • A very weak acid will only have a few of its H’s leave the compound and enter the water

  14. Reactions • As we saw on from table J acids react with most metals to release H2 gas. • We also have a Neutralization reaction. This is when an acid and base react to balance each other out.

  15. Neutralization reactions • HCl + NaOH  H2O + NaCl • Acid + Base  Water + salt

  16. Neutralization reaction • The H of acid combines with the OH of base to create H2O • The left over molecules combine to make a salt.

  17. Neutralization reaction • HNO3 + KOH ? • Acid + Base  Water & salt • H & OH combine to make H2O • NO3 & K combine as the salt = KNO3

  18. Neutralization reactions • HNO3 + NaOH • HCl + KOH •  H3PO4 + 3 NaOH

  19. PH Scale • In chemistry we measure the concentration of an acid or base on a scale of 1-14 • This is called the PH scale.

  20. On the PH scale 0-7 is acidic. The lower the number the more acidic. (More H+) 7-14 is basic. The higher the number the more basic (more OH-) 7 is neutral. (Pure water)

  21. PH Scale • If bananas have a PH of about 5 & milk is about 6, which is more acidic? • Ammonia has a PH of 11, soap has a PH of 12. Which has more OH- Ions

  22. Indicator • An indicator is a chemical that will change colors in order when placed in a certain PH. • They are used to indicate what the PH of a liquid is.

  23. PH Scale • Each number moved on the PH scale is increased 10 times more acidic, or basic. • Example if HCl is a ph of 1 • And Acetic acid is a ph of 2 • How much more acidic is HCl then acetic acid?

  24. PH • If 1 number on the scale is 10 times more acidic (or basic) • Then 2 numbers is 100 times more acidic (or basic) • And 3 numbers is 1000 times more

  25. Example • How much more basic is a solution of PH 10 then a solution of PH 8? What about PH 9? PH 7? • How much more acidic is ph 6 then 7?

  26. Example • A truck carrying nitric acid overturns and spills its content in a neerby lake, that had a PH of 8. • After the spill the lake is 1000 times more acidic. • What is the new PH?

  27. Titration • In a neutralization reaction there must be a 1:1 ratio of H+ to OH- • Using this knowledge we can determine the concentration of an acid by only knowing the concentration of the base it reacted with.

  28. Titration • For example • If I have 1 L of 1 molarity acid I will need 1 L of 1 molarity base to cancel it out. • What about if I only had 2 Molarity base, how much would I need to cancel out the acid?

  29. Titration • I would only need half a liter of the 2 Molarity base to cancel out all the acid.

  30. Titration • The formula for titration is found on your reference table. • It is Ma * Va = Mb * Vb • This mean Molarity of acid X volume of acid = Molarity of base X volume of base

  31. Titration • What is the concentration of sulfuric acid if 50 mL of .25 Molarity KOH are needed to neutralize 20 mL of the acid? • Ma * Va = Mb * Vb • X * (20) =(.25) * (50) • X is the Molarity of sulfuric acid

  32. Bronsted Lowry theory • There is another theory of acids & bases besides Arrhenious called the Bronsted Lowry theory. • The regents just calls it the alternative theory.

  33. Bronsted Lowry theory • According to this theory an acid is anything which is a H+ donor • And a base is anything that accepts H+

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