Transcript 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
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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
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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) ACID
RED
Neutral: paper stays same color
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)
NaOH(aq)
H2O(l)
HNO3(aq)
K2SO4(aq)
HCOOH(l)
C6H5COOH(l)
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
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What would HF be using this rule?
Naming Acids cont…
 2) When acid contains oxygen (ex. H2SO4(aq)), name
based on the anion
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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
Acid Formula
HNO3(aq)
Name
nitric acid
chromic acid
H2CrO4(aq)
HI(aq)
hydroiodic acid
HBr(aq)
hydrobromic acid
HClO(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
Base
KOH(s)
Name
potassium hydroxide
NH4OH(aq)
ammonium hydroxide
Ca(OH)2
calcium hydroxide
Mg(OH)2(s)
Al(OH)3(s)
magnesium hydroxide
aluminium hydroxide
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