Acids and Bases Section A2.4 Unit A Science 10
Objective Checklist • At the end of this lesson, will be able to: • Identify and classify acids and bases based on their properties • Name acids and bases
Acids and Bases • Important • Control digestion in our bodies (stomach acid and activation and deactivation of enzymes) • Found in foods and used in industry
Acid or a Base? • Taste: • Acids- sour (ex. Lemons- citric acid) • Bases- bitter (ex. Soap) • Touch: • Bases- slippery to the touch and corrosive to the skin • What does corrosive mean? • Acids- not slippery and corrosive to the skin • Reaction with Metal: • Acids- react; forms H2 gas (bubble formation) • Bases- don’t react
Using pH • What is pH used for? • What does the scale look like? • What substance is considered neutral? • Where do the following substances place on the scale? • Acid rain, normal rain, lemon juice, stomach juices • Baking soda, human blood, oven cleaner, window cleaner (ammonia)
Conductivity • Both acids and bases have or form ions in solution • In solution, these ions can conduct electricity, so they are electrolytes • Can you think of any everyday items that contain an acid or a base (alkali) to conduct electricity?
Indicators • To determine pH and whether something is an acid or base, we use indicators • Indicators change color depending on pH • Litmus paper is created through extracting the chemical from lichens • Acid: blue litmus paper turns red (BRA) • Base: red litmus paper turns blue (RBB) • Neutral: paper stays same color ACID RED BASE BLUE
Demonstration • What color should the acid (lemon juice, citric acid) turn the blue litmus paper? Red litmus paper? • What color should the base (bleach) turn the red litmus paper? Blue litmus paper? • How do we test whether the unknown is an acid or base? If blue litmus stays blue, can we conclude that it is a base? Why or why not?
Recognizing Acids • In acids, the formula often has a “H” (hydrogen ion – may be more than one) on the left side of the formula (ex. HCl) • Can also appear on the right side as “-COOH” (organic acid group) (ex. CH3COOH) • They are bonded to an anion (one or more non-metals) • To identify acids from formulas, look for “H” on the left or “-COOH” on the right
Recognizing Acids • Which of the following are acids? HBr(aq) NaCl(aq) H2SO4(aq) HCOOH(l) NaOH(aq) H2O(l) HNO3(aq) C6H5COOH(l) K2SO4(aq)
Naming Acids • IUPAC method: name as an aqueous ionic compound • What would HCl be using these rules? • Another method: • 1) When containing hydrogen and non-metallic element (anion name ends in –ide): • Use prefix “hydro” and suffix “ic” • Ex. HCl becomes hydrochloric acid • What would HF be using this rule?
Naming Acids cont… • 2) When acid contains oxygen (ex. H2SO4(aq)), name based on the anion • What is the anion in H2SO4(aq)? • If anion ends in “ate”, name of acid ends in “ic” • Ex. H2SO4(aq) contains sulfate anion (SO42-) and is then named sulfuric acid • What is the acid name of H3PO4(aq)? How do we approach naming it?
Naming Acids cont… • 3) if anion ends in “ite”, name of acid ends in “ous” • H2SO3 (aq)contains the anion sulfite (SO32-), so the acid is named sulfurous acid • What is the name of the acid HNO2(aq)?
Practice nitric acid H2CrO4(aq) hydroiodic acid HBr(aq) hypochlorous acid
For your reference Back of periodic table sheet
Recognizing Bases • Often, bases are identified by presence of “OH-” (hydroxide ion) with a metal ion or the ammonium ion (NH4+) • It is more complicated than this, but for now: • Any compound with high solubility and an OH on right is a base • Name base as would name an ionic compound • What would NaOH be named using rules we already know?
Practice potassium hydroxide NH4OH(aq) Ca(OH)2 magnesium hydroxide Al(OH)3(s)
Neutralization • Reaction between acid and a base which produces water and a salt • The acidic and basic properties disappear • Why would this be important? Give an example • Ex. A bee’s sting contains methanoic acid which dissolves nerve endings in the skin (lots of pain!). Sting creams containing ammonia limit the pain as the ammonia neutralizes the acid
Neutralization Demo • What pH is water? • Is vinegar an acid or a base? • What color do we observe initially? • If I add alka-seltzer (a base) predict the color change • What do we observe as I add the base? • Explain why this occurred