edph
TRANSCRIPT
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Acid and Bases
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Acid and Bases
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Acid and Bases
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Acids
Have a sour taste. Vinegar is a solution of acetic acid. CitrusHave a sour taste. Vinegar is a solution of acetic acid. Citrusfruits contain citric acid.fruits contain citric acid.
React with certain metals to produce hydrogen gasReact with certain metals to produce hydrogen gas ..
React with carbonates and bicarbonates to produce carbonReact with carbonates and bicarbonates to produce carbondioxide gasdioxide gas
Have a bitter taste.Have a bitter taste.
Feel slippery. Many soaps contain bases.Feel slippery. Many soaps contain bases.
Bases
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S ome Properties of Acids
Produce H + (as H 3O +) ions in water (the
hydronium ion is a hydrogen ion attached to
a water molecule)
Taste sour
Corrode metals
Electrolytes
React with bases to form a salt and water
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Acid Nomenclature
Flowchart
hydro- prefix-ic ending
2 elements
-ate endingbecomes-ic ending
-ite endingbecomes
-ous ending
no hydro- prefix
3 elements
A CIDSstart with 'H'
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HBr (aq)
H2CO 3
H2SO 3
hydro bromic acid
carbon ic acid
sulfur ous acid
Acid Nomenclature Review
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S ome Properties of Bases
Produce OH - ions in water
Taste bitter, chalky
A re electrolytes
Feel soapy, slippery
React with acids to form salts and water
pH greater than 7
Turns red litmus paper to blue ³ Basic
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S ome Common Bases
N aOH sodium hydroxide
KOH potassium hydroxide liquid soap
Ba(OH) 2 barium hydroxide stabilizer for plastics
Mg(OH) 2 magnesium hydroxide ³MOM´ Milk of
magnesia
A l(OH) 3 aluminum hydroxide Maalox (antacid)
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pH of CommonS ubstances
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T he pH scale is a way of expressing the strength of acids and bases. Instead of using very small numbers,
we just use the NEGA T IVEpower of 10 on the Molarityof the H + (or O H-) ion.
Under 7 = acid7 = neutral
O ver 7 = base
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pHpH [H +][H+] [OH -][OH -] pOHpOH
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pH testingT here are several ways to test pH ± Blue litmus paper (red = acid) ± Red litmus paper (blue = basic)
± pH paper (multi-colored) ± pH meter (7 is neutral, <7 acid, >7
base)
± Universal indicator (multi-colored) ± Indicators like phenolphthalein ± Natural indicators like red
cabbage, radishes
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Paper testingPaper tests like litmus paper and pHpaper ± Put a stirring rod into the solution
and stir.
±T
ake the stirring rod out, and placea drop of the solution from the endof the stirring rod onto a piece of thepaper
± Read and record the color change.Note what the color indicates.
± You should only use a small portionof the paper. You can use onepiece of paper for several tests.
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pH meter
T ests the voltage of the electrolyteConverts the voltageto pH
Very cheap, accurateMust be calibratedwith a buffer solution
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pH indicatorsIndicators are dyes that can be added thatwill change color in the presence of an acidor base.
S ome indicators only work in a specificrange of pH
O nce the drops are added, the sample isruined
S ome dyes are natural, like radish skin or red cabbage
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ACID-BAS E REACTIONS
Titrations
ACID-BAS E REACTIONS
TitrationsH2C2O 4 (aq) + 2 Na O H(aq) --->
acid base
Na 2C 2O 4 (aq) + 2 H 2O (liq)Carry out this reaction using a TITR A TION .
Oxalic acid,Oxalic acid,
HH22CC 22OO 44
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S etup for titrating an acid with a baseS etup for titrating an acid with a base
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TitrationTitration1. Add solution from the
buret.2. Reagent (base) reacts
with compound (acid) insolution in the flask.
3. Indicator shows whenexact stoichiometricreaction has occurred.
(Acid = Base)T his is called
NEU T RALIZAT IO N.
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PROBLEM: You have 50.0 mL of 3.0M NaOH and you want 0.50 MNaOH. What do you do?
PROBLEM: You have 50.0 mL of 3.0M NaOH and you want 0.50 MNaOH. What do you do?
3 .0 M N aOH 0.50 M N aOH
H2
O
Concentrated Dilute
But how much water But how much water
do we add?do we add?
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PROBLEM: You have 50.0 mL of 3.0M NaOH and you want 0.50 MNaOH. What do you do ?
PROBLEM: You have 50.0 mL of 3.0M NaOH and you want 0.50 MNaOH. What do you do ?
How much water is added ?
T he important point is that --->
moles of NaOH in ORIGINAL solution =moles of NaOH in ORIGINAL solution =
moles of NaOH in FINAL solutionmoles of NaOH in FINAL solution
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PROBLEM: You have 50.0 mL of 3.0 M NaOHand you want 0.50 M NaOH. What do you do?PROBLEM: You have 50.0 mL of 3.0 M NaOHand you want 0.50 M NaOH. What do you do?
Amount of Na O H in original solution =
M V =
(3.0 mol/L)(0.050 L) = 0.15 mol Na O H
Amount of Na O H in final solution must also= 0.15 mol Na O H
Volume of final solution =
(0.15 mol Na O H) / (0.50 M) = 0.30 L
or 300 mL
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PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What
do you do?
PROBLEM: You have 50.0 mL of 3.0 MNaOH and you want 0.50 M NaOH. What
do you do?Conclusion:
add 2 50 mL of
water to 50.0mL of 3.0 MNa O H tomake 300mL of 0.50 MNa O H.3 .0 M N aOH 0.50 M N aOH
H2 O
Concentrated Dilute
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A shortcut
M1 V1 = M 2 V2
Preparing S olutions by
Dilution
Preparing S olutions by
Dilution
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You try this dilution
problemYou have a stock bottle of hydrochloric acid, which is 12.1 M.
You need4
00 mL of 0.10 M HCl.How much of the acid and howmuch water will you need ?
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Acid/Base definitions D efinition #1: Arrhenius (traditional)
Acids ± produce H+
ions (or hydroniumions H 3O +)
Bases ± produce O H-
ions
(problem: some bases don¶t have
hydroxide ions!)
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Arrhenius acid is a substance that produces H + (H3O +) in water
Arrhenius base is a substance that produces O H- in water
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HN O 3, HCl, H 2SO 4 and HClO 4 are among theonly known strong acids .
S trong and Weak Acids/BasesS trong and Weak Acids/Bases
The strength of an acid (or base) isdetermined by the amount of ION IZATIO N .
The strength of an acid (or base) isdetermined by the amount of ION IZATIO N .
HO N ORS O N LY!HO N ORS O N LY!
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S trong and Weak Acids/BasesS trong and Weak Acids/BasesGenerally divide acids and bases into S T RO NG or Generally divide acids and bases into S T RO NG or WEAK ones.WEAK ones.
S T RO NG ACI D : HN OS T RO NG ACI D : HN O 33 (aq) + H(aq) + H 22O (l)O (l) ------>>HH33OO ++ (aq) + N O(aq) + N O 33
-- (aq)(aq)
HNOHNO 33 is about 100% dissociated in water.is about 100% dissociated in water.
HO N ORS O N LY!HO N ORS O N LY!
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Weak acidsWeak acids are much less than 100% ionized inare much less than 100% ionized inwater.water.
O ne of the best known is acetic acid = CHO ne of the best known is acetic acid = CH 33COCO 22HH
S trong and Weak Acids/BasesS trong and Weak Acids/BasesS trong and Weak Acids/BasesS trong and Weak Acids/BasesHO N ORS O N LY!HO N ORS O N LY!
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S trong Base:S trong Base: 100% dissociated in water.100% dissociated in water.Na O H (aq)Na O H (aq) ------> Na> Na ++ (aq) + O H(aq) + O H-- (aq)(aq)
S trong and Weak Acids/BasesS trong and Weak Acids/Bases
Other common strongOther common strongbases include KOH andbases include KOH andCa(OH)Ca(OH)
22..
CaO (lime) + HCaO (lime) + H 22OO ---->>
Ca(OH)Ca(OH) 22 (slaked lime)(slaked lime)CaOCaO
HO N ORS O N LY!HO N ORS O N LY!
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Weak base: less than 100% ionized in water Weak base: less than 100% ionized in water O ne of the best known weak bases is ammoniaO ne of the best known weak bases is ammoniaNHNH33 (aq) + H(aq) + H 22O (l)O (l) NHNH 44
++ (aq) + O H(aq) + O H-- (aq)(aq)
S trong and Weak Acids/BasesS trong and Weak Acids/BasesS trong and Weak Acids/BasesS trong and Weak Acids/BasesHO N ORS O N LY!HO N ORS O N LY!
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Weak BasesWeak BasesHO N ORS O N LY!HO N ORS O N LY!
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Acid/Base Definitions
D efinition #2: Brønsted ± Lowry
Acids ± proton donor
Bases ± proton acceptor
A ³proton´ is really just ahydrogen atom that has lost it¶selectron!
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A Brønsted-Lowry acid is a proton donor A Brønsted-Lowry base is a proton acceptor
acid conjugatebase
base conjugateacid
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ACID-BAS E THEORIESACID-BAS E THEORIES
T he Brønsted definition means NH 3 is aBAS E in water ² and water is itself an
ACI D
BaseAcidAcidBase
NH 4+ + OH -NH 3 + H 2 O
BaseAcidAcidBase
NH 4+ + OH -NH 3 + H 2 O
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Conjugate Pairs
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Acids & Base Definitions
Lewis acid - a substancethat accepts an
electron pair
Lewis baseLewis base - - aasubstance thatsubstance thatdonates an electrondonates an electronpair pair
Definition #3 ± LewisDefinition #3 ± Lewis
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Formation of hydronium ion is alsoan excellent example .
Lewis Acids & Bases
Electron pair of the new OElectron pair of the new O- -H bondH bondoriginates on the Lewis base .originates on the Lewis base .
HH
H
B A S E
O ³ H
O ³ H
H +
A C I D
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Lewis Acid/Base Reaction
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Lewis Acid-Base Interactions
in BiologyT he heme group inhemoglobin caninteract with O 2 and
CO .T he Fe ion inhemoglobin is aLewis acid
O 2 and C O can act asLewis bases
Heme group
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Calculating the pH
pH = - log [H+](Remember that the [ ] mean Molarity)
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 .7 4 )pH = 4 .7 4
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Try These!
Find the pH of these:1) A 0.15 M solution
of Hydrochloricacid
2) A 3.00 X 10 -7 M
solution of Nitricacid
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pH calculations ² S olving for
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pH calculations ² S olving forH+
A solution has a pH of 8.5.What is the Molarity of hydrogenions in the solution ?
pH =pH = -- log [Hlog [H ++]]8 .5 =8 .5 = -- log [Hlog [H ++]]
--8 .5 = log [H8 .5 = log [H ++]]
A ntilogA ntilog - -8 .5 = antilog (log [H8 .5 = antilog (log [H ++])])1010 --8 .58 .5 = [H= [H ++]]
3 .16 X 1 03 .16 X 1 0 --99 = [H= [H ++]]
pH =pH = -- log [Hlog [H ++]]8 .5 =8 .5 = -- log [Hlog [H ++]]
--8 .5 = log [H8 .5 = log [H ++]]
A ntilogA ntilog - -8 .5 = antilog (log [H8 .5 = antilog (log [H ++])])1010 --8 .58 .5 = [H= [H ++]]
3 .16 X 1 03 .16 X 1 0 --99 = [H= [H ++]]
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pOH S ince acids and bases are
opposites, pH and p O H areopposites!pO H does not really exist, but it isuseful for changing bases to pH.pO H looks at the perspective of abase
pO H = - log [ O H-]
S ince pH and p O H are on oppositeends,pH + p O H = 1 4
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SIPENM ARU 1988
11. S uatu larutan mempunyai pH 1. berapagaram N aOH padat ( M r = 40) harusditambahkan pada satu liter larutan ini, untukmenaikkan pHnya menjadi 3?...gram
A.0,04 C. 0,4 E . 3,96
B. 4,0 D. 7,96
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PEM BAHAS AN
J AWAB : E
Reaksi asam dan basa dapat diseerhnakan sebagai :
H+ + OH - H2O
pH awal 1, berarti H + awal = 0 ,1M
pH akhir 3, berarti H + akhir = 0 ,00 1M
[H+] yang bereaksi = 0 ,1 ± 0 ,00 1 = 0 ,0 99M
[OH -] yang diperlukan = 0 ,0 99M( koefisien sama)
N aOH yang harus ditambahkan 0 ,0 99mol (dalam volum1liter)
Maka; 0 ,0 99 x 4 0 = 3,96 gram
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SIPENM ARU 1987
13. Kedalam 1 liter larutan asam asetat 0,2 M dimasukkan beberapa gram N aOH padat,hingga pH lartan menjadi 4. bila perubahanvolum larutan diabaikan, serta menggunakantetapan ionisasi asam asetat Ka = 2x 10 -5.
M aka jumlah N aOH yang dimasukkanadalah««gram( N a = 23, O = 16, H = 1)
A. 1,33 C. 2,33 E . 3,33B. 2,0 D. 3,0
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PEM BAHAS AN
J AWAB : A
CH3COOH + N aOH CH3COON a + H 2OM : 0,2 X - -
R : X X X XS : 0,2-x - X X
[H+] =Ka x mol asam
mol garam
10 -4 = 2x10 -5 x 0,2-X
X
X = 0,033 mol
Garam N aOH = 0,033 x 40 = 1,33
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SPM B 2005 Regional I , II , III
17. Berapakah pH larutan yang diperoleh dengan
mencampurkan 50ml H N O3 0,2 M dan 50 ml KOH 0,4M ?
A.2 C.. 7 E . 13
B. 5 D. 10
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PEM BAHAS AN
J AWAB : E
HN O3 = 50 x 0,2 = 10 mmol
KOH = 50 x 0,4 = 20 mmolS isa KOh = 20 ² 10 = 10 mmol
[OH- ] = b x M b = 1 x 10 = 10 -1
100
pOH = 1
pH = 13
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PP 1981
19. J ika dari zat-zat dibawah ini dibuat larutan (dalam
air) dengan konsentrasi 1 molar, larutan manakah yangmempunyai pH paling tinggi?
A. N aHS O4 C. HCl E .CH4COON a
B. N aF D. N H4Cl
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PEM BAHAS AN
J AWAB : B dan E
N aHS O4 adalah garam asam, dalam air langsungmenghasilkan ion H +
N aF adalah garam yang bersifat basa, berasal dariasam lemah HF dan basa kuat N aOH.
HCl adalah asam kuatN H4Cl adalah garam yang bersifat basa, berasal dari
asam kuat HCl dan N H4OH
CH3COON a adalah garam yang bersifat basa,bersasal dari asam lemah CH 3COOH dan basa kuatN aOH
Larutan dengan pH tinggi adalah larutan basa
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SIPENM ARU 1981
20. S atu ml larutan N aOH 1 M ditambahkan ke dalam 1
liter air, maka larutan ini akan mempunyai pH kira-kira«
A.3
B.5
C.7
D.9E .11
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PEM BAHAS AN
J AWAB : E
Proses ini adalah proses pengenceran, volum N aOH dari1ml berubah menjadi 1001 ml.
V1 x M 1 = V2 x M 21 x 1 = 1001 x X
X = 1
1001X = ~ 10 -3
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SIPENM ARU 1980
21. Tetapan hasil kali kelarutan magnesium
hidroksida dalah 2 x10-11
. J ika pH dari suatu M gCl2dengan konsentrasi 0,002 molar dinaikkan maka akanmulai trejadi endapan pada pH«.
A.8B.9
C.10
D.11E . 12
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