Ch. 20 Notes -- Acids and Bases What makes something an acid? Acid Properties: (1) tastes _______-- _______________ (2) corrosive to _________ (3) contains.

Ch. 20 Notes -- Acids and Bases What makes something an acid?

Acid Properties:

(1) tastes _______-- _______________

(2) corrosive to _________

(3) contains [ ___ ] (or [ _____ ] = “_______________” ions)

(4) proton ([ ___ ]) __________-- Brønsted-Lowry Theory

Example: HCl + H2O ______ + ______

sour lemons

metals

H+ H3O+ hydronium

H+ donor

Cl− H3O+

Examples of Common Acids:

• Pepsi, _________ juices, ___________, stomach acid, battery acid, _____________, ______

citrus aspirinvinegar DNA

Indicators• An indicator is a chemical that will change ___________ when

placed in an acidic, basic or neutral environment.

Indicator Colors For Acids

• litmus paper = _______

• phenolphthalein = ___________

• red cabbage juice (universal indicator) = ________

• methyl orange = _______

colors

red

clear

red

red

pH Paper : Indicator Colors

Acidic

Basic

Neutral

Properties of BasesWhat make something a base?

Base Properties: (…the opposite of acid properties)

(1) tastes ________ -- ___________ peel , parsley, dark chocolate

(2) feels _____________ -- ________

(3) contains [ _____ ] ions

(4) proton ([H+]) ______________-- Brønsted-Lowry Theory

Example: NH3 + H2O ______ + _______

bitter banana

slippery soap

OH−

acceptor

NH4+ OH−

Indicator Colors for Bases• litmus paper = _______

• methyl orange = ____________

• red cabbage juice (universal indicator) =________

• phenolphthalein = ______

Acid Base

phenolphthalein

blue

yellow

blue

pink

Common Bases• Examples of Common Bases: milk of magnesia, ___________,

drain cleaner, soap, blood, ____________ tablets, ___________ ________.

ammoniaantacid baking

soda

Measuring the Amount of H+ and OH− Ions in a Solution

• _____ Scale- measures the _____________ of [H+] ions in a solution

Formulas

pH = − (log [H+]) [H+] = 10−pH

pH + pOH = 14

• With the pH scale, we have another way to define acids and bases:

Acids have a pH _________7.0

Bases have a pH _________7.0

Neutral pH ___7.0

pH concentration

below

above

=

Practice Problems:

1) a) Calculate the pH of a 0.001 M HCl solution

b) Calculate the pH of rain water with a concentraion of 0.000000015 M

c) What would be the [H+] of a vinegar solution with a pH of 2?

[H+] = 0.001 M So…pH = − (log 0.001 M) pH = 3

[H+] = 0.000000015 M

So…pH = − (log 0.000000015 M) pH = 7.8

pH=2 So…[H+]= 10-2 [H+] = 0.01M

Titration• Mixing an acid with a base to

determine a __________________ is called “titration.”

• An ____________ is used to determine when neutralization has occurred.

• ________________ Solution - the solution of known concentration

• ______ _________ - the point of neutralization when titrating

• At the ______ point, the moles of [H+] ions = moles of [OH−] ions.

concentration

indicator

Standard

End Point

end

(Macid)x(Vacid) = (Mbase)x(Vbase)

Practice Problems:

(1) A 25 mL solution of HNO3 is neutralized by 18 mL of 1.0 M NaOH standard solution using phenolphthalein as an indicator. What is the concentration of the HNO3 solution?

(2) How many mL of 2.0 M KOH will it take to neutralize 55 mL of a 0.76 M HCl standard solution?

Determining the Concentration of an Acid (or Base) by Titration

( ) x ( ) = ( ) x ( )

( ) x ( ) = ( ) x ( )

Macid 25 mL 1.0 M 18 mL

Macid = 0.72 Molar

0.76 M 55 mL 2.0 M Vbase

Vbase = 20.9 mL

Thermochemistry:The heat energy of chemical reactions

• Enthalpy is the amount of ________ transferred during a reaction. The symbol for the change in enthalpy is ∆H.

• An endothermic reaction is one that ___________ heat from the surroundings. (___ ∆ H) An endothermic reaction feels ______.

Example--an “instant” ice pack

• An exothermic process is one that _____________ heat to the surroundings. (___ ∆ H) An exothermic reaction feels _____.

Example--burning paper

heat

gains+ cold

loses– hot

Thermochemical Reactions• A thermochemical reaction is written as follows:

2S + 3O2 2SO3 + 791.4 kJ

• This equation represents an ___________ reaction since the heat is a ________.

H2 + Br2 + 72.80 kJ 2HBr

• This equation represents an ___________ reaction since the heat is a __________.

exothermicproduct

endothermicreactant

Thermochemistry Problems

• Example 1: When Sulfur and Oxygen are combined in the following reaction heat is given off. What kind of reaction is this?

2S + 3O2 2SO3 ∆H = -791.4 kJ

• Example 2: When a instant cold pack is broken,

Ammonium Nitrate is mixed with water. The cold pack feels cold to the touch. What kind of reaction is this?

NH4NO3 + H2O = NO2H + HNO3 ∆H = 1800 kJ

Exothermic

Endothermic

Email from Captain Peepers

• So far Mama Hen has rejected the chick - so we have a house pet. He/she is thriving, much to the delight of my daughter Josie who has claimed the role of surrogate hen. They eat breakfast together, watch TV and play in the yard. The chick is even picking out the bedtime stories now....and requesting rides in the car. :)

Calculations in Thermodynamics• In order to calculate how much heat is transferred by a

thermochemical reaction the equation we use is

q = mc∆T

• q = the ______ lost or gained in the process• m = the _____ of the substance• c = the ________ _____ ________

The Specific heat of water is 4.186 Joules/gram °C • ∆T = ________ Temp. – ________Temp.

heat

massSpecific heat capacity

InitialFinal

Calculations Practice

• If the same amount of heat is applied to 5 grams of the following substances, which substance will increase in temperature the fastest?– Carbon with a specific heat of 0.17 cal/g ° C– Water with a specific heat of 1.00 cal/g ° C– Iron with a specific heat of 0.11 cal/g °C– Titanium with a specific heat of 0.125 cal/g °C

Chemical Equilibrium• Some reactions are reversible, so as products accumulate

they can begin to turn back into reactants.

• When the rate of the forward reaction ____________ the rate of the reverse reaction, it is at equilibrium.

• Here’s an example:

• Each is constantly being formed at the same rate that it is being consumed. It is therefore called a “_____________ equilibrium”.

• Chemical equilibrium is the point at which the concentrations of all species are ________________.

N2O4(g) 2NO2(g)

equals

dynamic

constant

Dynamic Equilibrium

• Le Chatelier’s Principle: If a stress is applied to a system that is already at equilibrium, the equilibrium will shift to reduce the effect of the stress.

• We will now look at changing various things on a system at equilibrium.

• Consider this reaction: A + B C + D

Here are some things that one can change in order to shift the equilibrium:

(1) Changing _______________________ of the Solutions

(2) Changing the _____________________ of the Gases

(3) Changing the _____________________

•

Changes in Equilibrium

Concentration Pressure

Temperature

• Le Chatelier’s Principle:

Consider this reaction: A(aq) + B (g) C(aq) + D(aq) + 92 kJ

Here are some things that one can change in order to shift the equilibrium:

(1) Adding more A shifts the equilibrium to the ________

(2) Removing A shifts the equilibrium to the ________

(3) Adding more gas pressure of B shifts the equilibrium to the ________

(4)Removing gas pressure of B shifts the equilibrium to the ________

(5) Decreasing the temperature shifts the equilibrium to the ________

(6) Increasing the temperature shifts the equilibrium to the ________

Changes in Equilibrium

right

left

right

left

right

left

For the reaction below, predict the direction the equilibrium will shift given the following changes. Temperature and volume are held constant.

Fe3+(aq) + SCN–1

(aq) FeSCN2+(aq)

(colorless) (red)

More Fe3+ is added to the reaction. ____________________- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

NO2 (g) + 7 H2 (g) ↔ 2 NH3 (g) + 4 H2O(g)

Predict the shift in equilibrium given the following changes:a. addition of ammonia ____________________

b. removal of nitrogen dioxide ____________________

c. removal of water vapor ____________________

Changes in Equilibrium

Shifts to the right (…more red)

Shifts to the left

Shifts to the left

Shifts to the right