Notes: Acids and Bases (text Ch. 14 & 15)

NOTE: This set of class notes is not complete. We will be filling in information in class. If you are absent, it is yourresponsibility to get missing information from a fellow classmate or the chemistry website: http://othschem.weeblv. com/

I. Properties of Acids and BasesAcids BasesContain more H+ than OH' ions Contain more OH'than H+ionspH less than 7 (acidic) pH greater than 7 (alkaline)Taste sour Taste bitter, feel slipperyTurn litmus red Turn litmus blueConduct electricity (are electrolytes) Conduct electricity (are electrolytes)React with metals to produce hydrogen gas React with acids to produce a salt and water

Examples of common household acids and bases:• Acids: lemon juice and other citrus juices (citric acid, ascorbic acid), tomato juice (ascorbic acid),

vinegar (acetic acid), carbonated beverages (carbonic acid)• Bases: ammonia (Nhb), drain cleaner (NaOH or lye), antacids (CaCOs), bleach (NaCIO), baking

soda (NaHCOs), and soaps/shampoos

II. Acid-Base TheoriesTheory Acid defined as: Base defined as: ExamplesArrhenius

in f t formv lc

Contains OH-

i tVi bormolcvH NO3 ~ ( Cic\

NfcOJi1 sostBronsted-Lowry*

H+ dono Ht at cpjvr HCl = aci Nttz - B se

*The Bronsted-Lowry theory includes the terminology conjugate acid and conjugate base.• Conjugate acid is the particle formed when a base has accepted a proton (H+).

Every base has a conjugate acid.

• Conjugate base is the particle formed when an acid has donated a proton (H+).Every acid has a conjugate base.

A conjugate acid-base pair are the 2 substances related by loss or gain of a single hydrogen ion.

Reactants Prod cts

Identify the acid, base, conjugate acid, and conjugate base in the following reaction:A 5 co

(hci +&

It O HsO

'Nhb] Hr (bkd)CA

nh4

+

+

©C6

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111. Review: Nomenclature of Acids & Bases

• Writing acid names from formulas:Acids are composed of hydrogen (H+) followed by an anion (negative ion).If the acid formula contains oxygen in the anion, such as in H2SO4, it is known as an oxyacid.3 rules, based on the anion name:

\) H + anion ending in -ide: Acid name is hydro_ake the root from the anion name and fill in the blank.

ic acid

Examples: HCI Cl~ is the anion, its name is chlorideName of acid is: hydrochloric acid

HF F~ is the anion, its name is fluorideName of acid is: h drofluoric acid

2nH + anion ending in -ate: Acid name is ic acid Take the root from the anion name and fill in the blank.What I TE was ICky

Examples: HNOs NO31~ is the anion, its name is nitrateName of acid is: nitric acid

H2CO3 COs2" is the anion, its name is carbonateName of acid is: carbonic acid

Note: when the anion contains sulfur or phosphorus, the roots are sulfur- and phosphor-, respectively, not sulf- andphosph-. So H2SO4 is sulfuric acid, not sulfic acid. And H3PO4 is phosphoric acid, not phosphic acid.

3) H + anion ending in -ite: Acid name is ous acid Take the root from the anion name and fill in the blank.“The snake bITE was poisonOUS

Examples: HNO2 NO21' is the anion, its name is nitriteName of acid is: nitrous acid

HCIO2 CIO21' is the anion, its name is chloriteName of acid is: chlorous acid

• Writing acid formulas from names:Sometimes you may be asked to write the formula for the acid, given the name. In this case youwould just work backwards, using the 3 rules above. Acid formulas must be criss-crossed, as welearned with ionic compounds, so that the charges equal out to zero.

Examples: Hydrobromic acid anion is bromide (Br ) formula is HBr

Acetic acid anion is acetate (C2H3O2') formula is HC2H3O2

Phosphorous acid anion is phosphite (PO33') formula is H3PO3

• Writin base names from formulas:There are many substances that act as bases in chemistry, with various formulas. But we are onlygoing to focus on the hydroxides, and also ammonia.

Hydroxide bases are composed of a cation (positive ion) followed by hydroxide (OH ).Naming bases is much simpler than naming acids. Name the cation and then add hydroxide.

Examples: NaOH name of base: sodium hydroxideMq(OH)2 name of base: magnesium hydroxideLiOH name of base: lithium hydroxide

• Writin base formulas from names:Writing base formulas is straightforward. Find the formula for the cation and then add OH \ You alsoneed to criss-cross the formula so that the charges equal out to zero.

Memorize: NHa = ammonia

Examples: potassium hydroxidecalcium hydroxidealuminum hydroxide

cation is potassium (K+)cation is calcium (Ca2+)cation is aluminum (Al3+)

formula is KOHformula is Ca(OH)2formula is AI(OH)3

IV. Strong/Weak Acids and BasesStrong acids and bases ionize completely in aqueous solution toproduce free H+ or free OH ions. Free H+ and OH' give acids andbases their power.

Any substance that ionizes or dissociates completely or almostcompletely in aqueous solution is known as an electrolyte. Solutionsof electrolytes conduct electricity. Strong electrolytes are strongacids, strong bases, and soluble salts.

Strong acids Strong basesHCI Group I and II soluble hydroxides, such as:HBr NaOHHI Ca(OH)2HIO4HCIO4HCIO3HNOsH2SO4

***Acids and bases not on these lists are weak, meaning they ionizeonly a small amount. They are also weak electrolytes.

Stro g acids c m letely dissociate ta water.

„.. d d acid to water'

f r 'TI |

*0 # I(CN. j

§ (C1-) j"

11 Cl Ur and Cl-mm

Weak ad s DO .NOT completely dissociate in w ter.

Add aci to water* I

Ac lit and Ac a t HAc

¦IcH. partial k iizationHAc = acet c ac d ~ H-CM

• Concentrated and dilute vs. Strong and weakConcentrated solutions have a large amount of dissolved solute and a Molarity > 1.Dilute solutions have a small amount of dissolved solute and a Molarity < 1.This is independent of the extent of ionization which determines if the acid or base is strong or weak.

Examplesj 1 M HCP strong and dilute12 M HCI strong and concentrated

1 M H2CO3 weak and dilute16 M H2CO3 weak and concentrated

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V. The pH ScalepH is a numerical scale, typically ranging from 0-14. pH stands for power of hydrogen ion.Diagram of the pH scale:

4r incn OiilCitVly cidfc.

N.Cvf <x\ i nciTeaji*nojly B&.S»'c

1 |0 1 2 3 4 5 .6 @ 8 9 10 11 12 13 14

A N 6pH gives us a quantitative measure of the acidity or basicity of the aqueous solution.Whether or not a solution is acidic, basic, or neutral depends on the balance of H+ and OH' ions:

Neutral: [H+] = [OH']Acid: (Hj, > O Base: [H+] < [OH ],

The concentrations of these ions are usually very small numbers, like 1.0 x 10~8 M, so the pH scalewas developed to generate numbers that are easier to work with.

VI. pH CalculationspH is the negative base 10 logarithm of the hydrogen ion concentration: pH = - logic [H+]

Review of base 10 lo s:[H+] = 1.0 x 10 "3 What is the base 10 log? -3 What is the ne ative base 10 log (the pH)? 5

[H+] = 1.0 x 10'4 What is the base 10 log?-H What is the ne ative base 10 log (the pH)?

***Notice that if the [H+] decreases by a factor of 10 (1 decimal place to left), the pH goes up by 1.

We can also calculate pOH: pOH = - logic [OH ]. pH is just used more often than pOH.

There is a special relationship between pH and pOH.

Because [H+]x [OH ] = 1.0x10 -14 this means that pH + pOH = 14.

pH pOH Solution type H+ concentration OH" concentration= 7 = 7 Neutral 1.0 x 10 7 1.0 X 10'7< 7 > 7 Acidic > 1.0 x 10 7 < 1.0 x 10'7> 7 < 7 Basic < 1.0 x 10 -7 > 1.0 x 10 7

***For practice, do worksheet on pH calculations***Use Guide to pH Calculations (last page of notes) to help you.

VII. Neutralization Reactions Neutralization reactions are double replacement reactions between an acid and a base:

acid + base - salt (ionic compound) + waterExamples:

1. h|oI (aq) + Naj3H(aq)

2. H;js04(aq) +2Kj3H(aq) ->

3. ! INO.. ,1 + Ca{OH)2(aq)

MaC \ + MiO• r Don'+ For&e-t-

KtSO + 2Mj.O-tt) BAui.Mce)*

Co.((V/03 2 + 2H2.O

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VIII. TitrationsA titration is a laboratory procedure in which an acid of unknown Molarity (concentration) is mixedwith a base of known Molarity (concentration) until neutralization occurs. By measuring the volumesof acid and base necessary for neutralization to occur, the concentration of the unknown can becalculated. This is the purpose of a titration.

Laboratory Setup:A buret is used to dispense the base in a precise manner, in order to combine it with the acid.

An indicator, such as phenolphthalein, bromthymol blue, or methyl red, is achemical that is used to identify (through a color change) when neutralizationhas occurred. Without an indicator, you cannot tell when neutralization occurs.

The point at which the acid and base stoichiometry is equal (there is one mole ofacid for every one mole of base) is the equivalence point.We say that neutralization has occurred here.

buret

The point at which the indicator changes color is called the end point.

We must choose our indicator so that the end point and equivalencepoint coincide as closely as possible. Different combinations of acidand base require different indicators for a successful titration.Discussion of how to choose the indicator is beyond the scope of this course.

acid of u know concentration

Titration calculations: ***First you need a balanced neutralization equation***This formula can be used to solve all titration problems:

rib Ma Va = na Mb Vb

nb = coefficient of base in bal. eqn.Ma = molarity of acidVa = volume of acid

na = coefficient of acid in bal. eqnMb = molarity of baseVb = volume of base

Examples: ? Ma Vc\ V Mb1. What is the molarity of a HCI solution if 55.0 ml neutralized 75.0 ml of 2T) M NaOH?

Equation: ll-ta + IN/aOH -LN/aCI ±AhUQf t

* = riftMb b _

nb Vo,

I x 2.0 x 75.0™l.

I X SS.OrviL2-7 M HCI

? Mb Vb Vfc M<x2. What is the molarit ofa Ca(OH)2 solution if 20.0 ml neutralized 5.0 ml. of 1 0 M HNOs?

Equation: 7HMO3 -b-LCft(0H -1 C .2MzOT t,na. nb

bbM I X I QM X g.OmL

2 20.0 Al0.13 M CaCOH)

HovVb -

GUIDE TO pH CALCULATIONS

1. Given pH, find pOH• Remember that pH + pOH = 14Examples:

a. pH = 7 pOH=b. pH = 3 pOH= II

2. Given pOH, find pH• Remember that pH + pOH = 14Examples:

c. pOH = 10 pH= 4d. pOH = 0 pH=

3. Given [H+], find [OH ]• Remember that [H+] x [OH'] = 1.0x1 O'14Examples:

e. [H+] = 1.0 x 10'9 [OH ] = I 0 X1 f. [H+] = 1.0 x 10 2 [OH ] = I-OXIO'11

4. Given [OH ], find [H+]• Remember that [H+] x [OH ] = 1.0x10 14Examples:

g. [OH-] = 1.0x 10-6 [H+]= I.OXIO 8h. [OH ] = 7.3 x 10 12 [H+] = |.i( |0-3

5. Given [H+], find pH:• Take the negative base 10 logarithm of [H+]• On the calculator press: - Ctrl 10x to put in: -log[H+]Examples:

i. [H+] = 1.0 x 10'7 pH= 7j. [H+] = 3.5 x 10 10 pH= q.5

6. Given [OH ], find pOH:• Take the negative base 10 logarithm of [OH']• On the calculator press: - Ctrl 10X to put in: -log[OH']Examples:

k. [OH'] = 1.0x 10'3 pOH =3-0l. [OH'] = 2.5x1 O'13 pOH = 13

Sv -bra -

D iclc

-lo C )

7. Given pH, find [H+]: I O A • Find 10 A-pH (on the calculator, press 10x and type in - pH)Examples:

m. pH = 3 [H+]= I XIO'5n. pH = 10.5 [H+]= 3.K, xiQ-"

8. Given pOH, find [OH ]:• Find 10 A - pOH (on the calculator, press 10x and type in - pOH)Examples:

o. pOH = 9 [OH-] = I lO'1p. pOH = 5.2 [OH] = (,,.5 XIO'1

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