What is an Acid? Target 7-1

What we know so far Carbon dioxide is produced by pollution Carbon dioxide is absorbed into the ocean from the atmosphere and it becomes an acid The acid is bad for the ocean: It changes the pH It dissolves sea shells It hurts coral reefs But… what is an acid, anyway? What’s really happening here?

What is an Acid? Acid: a chemical that increases the amount of H3O+ ions present in a system They do this by releasing H+ ions into water The H+ ions then react with the water molecules to form hydronium ions (H3O+) ex) HCl + H2O  H+ + Cl- + H2O  H3O+ + Cl- The more H+ ions are in a system, the more acidic it is.

Properties of Acids H+ ions are able to react with almost anything, so acids will react with almost anything Acids are corrosive – they damage items by “eating” them as the H+ reacts with them Acids are acrid – they have a sharp, sour smell/taste caused by the H+ ions reacting with the air

Measuring Acids Strong Acids dissociate completely in water All the H+ ions are released from the acid molecules One-way reaction ex) HCl + H2O  H3O+ + Cl- Formula will start with H Weak Acids dissociate partially in water Some (but not all) H+ ions are released Equilibrium is reached ex) C2H5COOH + H2O <-> H3O+ + C2H5COO- Formula will end with COOH

Measuring Acids pH Scale – a system for measuring how acidic a sample of water is 0-14 7 = neutral 0-6.9 = acidic Lower number = more acidic ex) Vinegar has a pH of 2. Soda has a pH of 4. Which is more acidic?

What is a Base? Base: a chemical that decreases the amount of H3O+ ions in a system Most bases release OH- ions that react with H+ ions to form water ex) NaOH + H3O+  Na+ + OH- + H+ + H2O  Na+ + 2 H2O Some bases react with H3O+ in other ways The more OH- ions are in a system, the more basic it is

Properties of Bases OH- ions are able to react with almost anything, so bases will react with almost anything Bases are corrosive – they damage items by “eating” them as the OH- reacts with them Bases are slippery – they break down fats and oils in a system, so they spread out Also great for cleaning

Measuring Bases Strong Bases dissociate completely in water All the OH- ions are released from the base molecules One-way reaction ex) NaOH  Na+ + OH- Formula will end with OH Weak Bases do not produce OH, but react with H+ in other ways They pull an H+ out of a water molecule, leaving OH- behind Equilibrium is reached ex) NH3 + H2O <-> NH4+ + OH- Formula will vary

Measuring Bases pH Scale – a system for measuring how acidic a sample of water is 0-14 7 = neutral 0-6.9 = acidic 7.1-14 = basic Higher number = more basic ex) Soap has a pH of 10. Bleach has a pH of 12. Which is more basic?

Exit Ticket Label each as an ACID or a BASE: a) pH of 5.5 e) HBr b) KOH f) pH of 9.3 c) CH2COOH g) pH of 7.4 d) C3H8COOH h) pH of 2.9 Which of these is MOST ACIDIC? a) pH 1.1 b) pH 6.2 c) pH 10.1 Which of these is MOST BASIC? a) pH 9.1 b) pH 7.4 c) pH 5.3

Indicators Indicators are chemicals we can use to determine the pH of a substance They will change color based on the pH in the solution

Litmus Paper Litmus paper comes in 2 colors – red and blue Red litmus paper will turn BLUE in a BASE Blue litmus paper will turn RED in an ACID

Phenolphthalein Phenolphthalein tests for strong bases It is CLEAR in pH below 9 It is PINK in pH above 9

Bromthymol Blue Bromthymol Blue tests for weak bases It is YELLOW in pH below 7.6 It is BLUE in pH above 7.6

Methyl Orange Methyl orange tests for strong acids It is RED in pH below 3.1 It is ORANGE in pH between 3.1-4.4 It is YELLOW in pH above 4.4

Universal Indicator Universal Indicator will change a different color for each pH value (like a rainbow)