Post on 18-Dec-2021
transcript
I. DEFINING ACIDS AND BASESAcids and bases are just a specific type of solution in water. There are two main theories that explain
acids and bases.
1. Arrhenius Theory
Acids
• An _____ is a substance which dissociates (breaks up) in water and
_____________________
*Note – an ion is just an atom with a charge (+ or -)
Example: HCl H+ + Cl –
or
HCl (g) + H2O (l) H3O + (aq) + Cl - (aq)
*Note - _____is called a ____________. It forms when the H+ that is released
from the acid bonds to the H2O molecules. So H+ and H3O + both mean the
solution is acidic.
• For ___________, see _______in your reference tables
Dissociation of acids in water animation
acid
releases hydrogen ions (H+)
H3O + hydronium ion
common acids Table K
Bases
• A _____ is a substance which dissociates in water and
_____________________
Example: NaOH Na+ + OH-
• For ___________, see ______ in your reference tables
Arrhenius’s theory was the first to define acids and bases and it is simple and useful;
however, there were some flaws. Look at Table L. Do you see a common base that does not
fit the Arrhenius definition?
Ammonia (NH3) was a substance that acted like a base but did not have any OH- molecules
to release . As a result, the next, more advanced acid-base theory was proposed.
base
releases hydroxide ions (OH-)
common bases Table L
NH3
2. Bronsted-Lowry Theory
• Acid = substance that ____________
Example: HCl (g) + H2O (l) H3O + (aq) + Cl - (aq)
(the HCl is “donating” its H+ to the water)
• Base = substance that _____________
Example: NH3 + H2O NH4+ + OH-
(the NH3 is “accepting” a H+ from the water)
• _______Theory – _____________________
• This theory doesn’t go against the Arrhenius theory, it just adds to it.
donates H+ ions
accepts H+ ions
“BA-AD” Bases accept, acids donate
PRACTICE
1. Hydrogen chloride, HCl, is classified as an Arrhenius acid because it releases
(1) H+ ions in aqueous solution
(2) Cl– ions in aqueous solution
(3) OH– ions in aqueous solution
(4) NH4+ ions in aqueous solution
2. Which ion is released in an aqueous solution of an Arrhenius base?
(1) H- (3) H+
(2) O2 (4) OH-
3. Which compound is an Arrhenius acid?
(1) CaO (3) K2O
(2) HCl (4) NH3
*Hint – look for one that has an ___ and use Table ___ to check!
4. Which compound when dissolved in water is an Arrhenius base?
(1) CH4 (3) NaCl
(2) HCl (4) NaOH
*Hint – look for one that has an ___ and use Table __ to check!
H K
OH L
II. PROPERTIES OF ACIDS AND BASESAcids
• Acids ________or eat away (oxidize) certain ______ to produce hydrogen gas
• Acids have a ___________
• Acids are ________, meaning they _____________________________
• Acids _________, like lemons (but DO NOT TASTE unknown substances)
• Acids “sting”
• Acids have a more “sharp” odor
react with metals
pH less than 7
electrolytes conduct electricity when dissolved in water
taste sour
Bases
• Bases ____________to __________(process called saponification)
• Bases have a ______________
• Bases are also ________, meaning they__________________________
• Bases _________ like ___________ (but DO NOT TASTE unknown substances)
• Bases are _______
• Bases are odorless
*Note – another way to say something is basic is ______
react with fats make soap
pH greater than 7
electrolytes conduct electricity when dissolved in water
taste bitter soap/medicine
slippery
alkaline
WATER IS NEUTRAL, IT HAS A ______;
HOWEVER, IT CAN ACT AS BOTH AN ACID OR
BASE, DEPENDING ON WHAT SUBSTANCE IS
DISSOLVED IN IT.
Example:
Substances that can act as an acid or base are called ___________amphoteric
pH of 7
pH
• The way to measure if a solution is acidic or basic is by ___________
• The pH scale is easiest method to use for comparing the strengths of acids
and bases. We test our fish tanks (fish pee out ammonia, which is a base,
and brings the pH up), our pools, and even food is pH tested as it is being
made to make sure that it falls within the right range. So just what is pH?
• pH stands for the _____________(remember, hydronium is H3O + ) or
the _______________
III. HOW TO KNOW IF A SOLUTION IS ACIDIC OR BASIC
testing its pH
power of hydronium
potential of hydrogen
A pH of 0-7 is __________
A pH of 7 is ____________
A pH of 7-14 is _____________
acidic
neutral
basic
• pH is measured on a scale from ______0 to 14
PRACTICE1. The pH of various aqueous solutions are shown in the table below.
List the substances from most acidic to most basic:
Most Acidic Most Basic
2. Which solution is neutral?
HCl HC2H3O2 NaCl NaOH
NaCl because it’s pH is 7
Testing pH
• A way to test pH is through the use of ________
• Indicator – a substance that __________if an acid or base is present
Examples:
o pH paper—dip the pH paper into the solution and match up the color to
see what the pH is
o Liquid Acid-Base Indicators (Found on ______)
Remember: An acid has a pH less ______and a base has a pH ______
indicators
changes color
than 7 above 7
Table M
Tips on Using Table M
1. Low pH numbers are on the left and high pH
numbers are on the right. They match up.
2. Look at Methyl Orange, red is on the left, 3.2
is on the left. To the left (or below) a pH of
3.2 the color is red. To the right (above) a pH
of 4.4 the color is yellow.
3. Between the 2 numbers will never be asked
on a test. This is where the indicator
changes color.
1. A solution has a pH of 5.5. What color changes will happen to following indicators:
a) Methyl orange __________ c) Bromscresol green____________
b) Bromthylmol blue ________ d) Thymol blue ______________
yellow
yellow
blue
yellow
PRACTICE
*The best way to get an accurate reading is to use multiple indicators*
2. You’re trying to decide if an unknown solution is acidic or basic. It
yields the following results when tested with various indicators:
Methyl Orange = yellow
Phenolphthalein = clear
Bromcresol Green = blue
Thymol Blue = yellow
What can the pH be?
a) 2.8 b) 6.5 c) 8.5 d) 4.8
pH above 4.4
XXXX
pH below 8.0
XXXX
pH above 5.4
XXXX
pH below 8
IV. NEUTRALIZATION
• Neutralization- The process of mixing an ____ and a _____ to form _____ and
____
Example: HCl + NaOH H2O + NaCl
• The H+ from the acid and the OH- from the base combine to make water. The remaining
ions (elements with charges) combine to make the salt. Both products, the water and
salt, are neutral.
• _____________are an everyday example of a neutralization reaction. When you
experience heartburn or indigestion it because of a buildup of acid in your stomach.
_______ are made up of _____ that ____________ in your stomach to
_______________.
Acid + Base Water + Salt
https://www.youtube.com/watch?v=8IRI5gPR5EY&feature=player_embedded&safety_mode=true&p
ersist_safety_mode=1&safe=active
acid base water
salt
Antacids like tums
Antacids bases release OH- ions neutralize the acids