Bases

Properties of acids and basesProperties of acids and bases

• Get a spot plate. Rinse well with water. Add acid to 6 wells, base to the other four.

• Add litmus papers to 2 base wells and pH paper to another (for pH paper use a colour key to find a number). Record results. Repeat for acid.

• Into the four base tubes add: a) two drops (or one strip) of phenolphthalein b) 2 drops of bromothymol c) a piece of Mg d) a small scoop of baking soda. Record results.

Repeat for acid.• Clean up (wash tubes, pH/litmus paper in trash).

BubblesNRBaking soda

BubblesNRMagnesium

*Yellow*BlueBromothymol

*Cloudy/ white

*PinkPhenolphthalein

RedBlueLitmus (blue or red)

114pH (# from the key)

Not slipperySlipperyFeel (choose slippery

or not slippery)

SourBitterTaste

HCl(aq)NaOH(aq)ObservationsObservations

*Usually, but not always

Historical views on Historical views on acids and basesacids and bases

Arrhenius’ theory• Acid gives out H+ when in water

(H3O+)

• Base gives out OH- in water

Ionization

+Cl HH

HO

+H

HH O Cl+

Ionization?

More theories

• Bronsted-Lowry concept

Acid donates protons

Base accepts protons

• Lewis theory

Acid accepts electron pair

Base donates electron pair

Strong vs. weak

• Strong: completely ionized (~99%)• Weak: not completely ionized (<50%)

• Strong acids: Produce many H+ ionsKnow: HCl, H2SO4, HNO3, HBr, HI, HClO4

• Weak acids: Produce few H+ ions (ex: HC2H3O2)

• Strong bases: Produce many OH- ions Know: Strong bases are all Group I and II oxides and

hydroxides (ex: LiOH, Ba(OH)2, MgO)• Weak bases: Produce few OH- ions (ex: NH3)

Conjugate acids/basesConjugate acids/bases• Bronsted Acids and bases are identified based on

whether they donate or accept H+.

• “Conjugate” acids and bases are found on the products side of the equation.

+Cl HH

HO

+H

HH O Cl+

acid base conjugate acid conjugate base

conjugate acid-base pairs

99

The Brønsted definition means NHThe Brønsted definition means NH33 is is a a BASEBASE in water — and water is in water — and water is itself an itself an ACIDACID

BaseAcidAcidBaseNH4

+ + OH-NH3 + H2OBaseAcidAcidBase

NH4+ + OH-NH3 + H2O

1010

Conjugate PairsConjugate Pairs

1111

Learning Check!

Label the acid, base, conjugate acid, and conjugate base in each reaction:

HCl + OH- Cl- + H2O HCl + OH- Cl- + H2O

H2O + H2SO4 HSO4- + H3O

+ H2O + H2SO4 HSO4- + H3O

+

Practice problemsPractice problemsIdentify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:

• Reference: pg. 386 – 387• Try Q18 (p389), Q 8 & 11 (p392): do as above

acid base conjugate acidconjugate baseHC2H3O2(aq) + H2O(l) C2H3O2

–(aq) + H3O+(aq)


acidbase conjugate acidconjugate baseOH

–(aq) + HCO3–(aq) CO3

2–(aq) + H2O(l)


acid base conjugate acidconjugate baseHF(aq) + SO3

2–(aq) F–(aq) + HSO3–(aq)


acidbase conjugate acidconjugate baseCO3

2–(aq) + HC2H3O2(aq) C2H3O2–(aq) + HCO3

–(aq)


acid base conjugate acidconjugate baseH3PO4(aq) + OCl

–(aq) H2PO4–(aq) + HOCl(aq)


Answers: question 18Answers: question 18(a)

(b)

(c)

acid base conjugate baseconjugate acidHCO3

–(aq) + S2–(aq) HS–(aq) + CO32–(aq)


baseacid conjugate acidconjugate baseH2CO3(aq) + OH

–(aq) HCO3–(aq) + H2O(l)


acid base conjugate acidconjugate baseH3O+(aq) + HSO3

–(aq) H2O(l) + H2SO3(aq)


8a)

8b)

11a)

base acid conjugate baseconjugate acidOH

–(aq) + HSO3–(aq) H2O(l) + SO3

2–(aq)


11b)

1515

The pH scale is a way of expressing the strength of acids and bases. (pH = power of Hydrogen

pH = -log[H+]

Under 7 = acid 7 = neutral

Over 7 = base

1616

pH of Common pH of Common SubstancesSubstances

1717Calculating the pH

pH = - log [H+]Example: If [H+] = 1 X 10-10

pH = - log 1 X 10-10

pH = - (- 10)

pH = 10

Example: If [H+] = 1.8 X 10-5

pH = - log 1.8 X 10-5

pH = - (- 4.74)

pH = 4.74

1818

Try These!

Find the pH of these:

1) A 0.15 M solution of Hydrochloric acid

pH = 0.82

2) A 3.00 X 10-7 M solution of Nitric acid

pH = 6.52

1919pH calculations – Solving for pH calculations – Solving for H+H+pH calculations – Solving for pH calculations – Solving for H+H+

If the pH of Coke is 3.12, [H+] = ???

Because pH = - log [H+] then

- pH = log [H+]

Take antilog (10x) of both sides and get

1010-pH -pH == [H[H++]][H+] = 10-3.12 = 7.6 x 10-4 M *** to find antilog on your calculator, look for “Shift” or “2*** to find antilog on your calculator, look for “Shift” or “2nd nd

function” and then the log buttonfunction” and then the log button

2020

Try this

• A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?A solution has a pH of 8.5. What is the Molarity of hydrogen ions in the solution?

3.16 X 10-9 = [H+]

• The pH of rainwater collected in a certain region of Toronto on a particular day was The pH of rainwater collected in a certain region of Toronto on a particular day was 4.82. What is the H+ ion concentration of the rainwater?4.82. What is the H+ ion concentration of the rainwater?

[H+] = 1.51 x 10-5

Bases

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