Acids and Bases

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Transcript Acids and Bases

Drill #8 5/1 & 2/14

What do you do if you spill acid in the lab?

Do you add acid to water or water to acid?

Drill #8 5/1 & 2/14

How do you clean up an acid spill?

• Tell your instructor immediately • Place baking soda (base) over it to neutralize and clean up with paper towels.

Do you add acid to water or water to acid?

• Acid to water

Objectives

SWBAT: • Define acid rain and it’s effects on our environment • list major differences between acids and bases • list products of neutralization reactions • distinguish between 2 methods of defining acids and bases.

• list properties of a salt

Agenda

• Solutions/Mixture Quiz (15 mins) • Acid Rain Reading (20 mins) • Notes on Acids and Bases (50 mins) • Worksheets

Homework Due

• Naming Acids WS

Acid Rain Reading

• Look at the following pictures on the powerpoint. From the pictures and your own experiences, what are some of the damaging effects of acid rain?

Reading Activity: Acid Rain

Before, During and After Reading (20 minutes)

Acids and Bases

Properties of Acids (in aq solution) 1. Sour taste 2. Low pH 3. Turn blue litmus paper red 4. Conduct electrical current

Properties of Bases (in aq solution) 1. Bitter taste 2. Slippery 3. High pH 4. Turn red litmus paper blue 5. Conduct electrical current

What happens when Mg reacts with HCl??

• Hydrogen gas is produced (popping noise we heard in earlier lab)

Indicators

• Substance that turns 1 color in acidic solutions and another in basic solutions.

• Examples: phenolphthalein (used in bio) and litmus paper (made from a species of lichen)

Acid-Base Reactions

• Known as a

neutralization reaction

. Acids and bases will react with each other to form

salt

and

water

A + B  Salt + H 2 O HCl + NaOH  NaCl + H 2 O

Characteristics of Salts

• Electrolytes • Ionic compounds • High melting points • Products of neutralization

Arrhenius Definition Acid = substance that releases

H +

in aq solution HCl  H + + Cl ions Base ions = substance that releases

OH -

in aq solution NaOH  Na + + OH Neutralize each other: H + + OH  H 2 O

Bronsted-Lowry Definition As more and more substances were determined to have acidic or basic properties, even some without obvious H + or OH , a new definition was needed.

• •

Acid = proton donor Base = proton acceptor

Bronsted-Lowry Definition • Acid = proton donor H 2 O + HCl  H 3 O + + Cl -

Bronsted-Lowry Definition • Base = proton acceptor NH 3 + H 2 O  NH 4 + + OH –

• When water gains a proton it is called HYDRONIUM.

H 3 O +

• When water loses a proton it is called HYDROXIDE .

OH -

Acids & Bases Review • Acid – substance that releases

H +

– Proton donor ions in aq solution • Base – substance that releases

OH -

solution ions in aq – Proton acceptor

H 2 O is both an acid and a base Water is simultaneously donating and accepting protons = amphoteric substance

Assignment

• Bronsted-Lowry Acids & Bases WS • Titration Curve Data Graph

Drill #9 5/5, 5/6/2014

Homework Due

• Bronsted-Lowry Acids & Bases WS • Keep Titration Graph

Homework

• Conjugate Acid-Base Pairs WS • 18-1 Review & Reinforcem

Conjugate Acids & Bases

• Conjugate acid – what is produced when a base gains a H + ion • Conjugate base – what is produced when an acid loses a H + ion • Conjugate base pair – two substances related to each other by the donating and accepting of a single H + ion

Conjugate acid-base pairs

HF + H 2 O H 3 O + F – acid base conjugate conjugate acid base

Objectives

• SWBAT compare the strength of a weak acid with the strength of its conjugate base • SWBAT explain the relationship between acid and base strength and the values of their ionization constants.

Acid Strength

A stronger acid will react completely to form ions (strong electrolytes) and hydronium ions (H 3 O + ) in water.

Hydrochloric acid (all HCL molecules are ionized into hydronium and chloride ions) HCl + H 2 O  H 3 O + + Cl Acetic Acid (not all A.A. molecules are ionized into hydronium and ions) CH 3 COOH + H 2 O  H 3 O + + CH 3 COO -

Examples of Strong & Weak Acids Strong Weak HCl CH 3 COOH HBr H 2 SO 4 H 2 CO HClO 3

Base Strength

• A strong base has the strongest affinity for H + ions and dissociates entirely into metal ions and OH .

• For ex. Calcium oxide (CaO); oxygen strongly attracts H + ions.

• Strong bases: CaO, NaOH, KOH • Weak base: ammonia (NH 3 )

Conjugate Pairs Inverse Relationship

• The stronger the acid, the weaker its conjugate base • The stronger the base, the weaker its conjugate acid HCO 3 + H 2 O  H 3 O + CO 3 weak A strong B weak strong C.A.

C.B.

Sample Problem

• Write an equation to show the dissociation of hydrochloric acid in water.

Answer

HCl + H 2 O → H 3 O + + Cl − • HCl is a STRONG ACID

Sample Problem

• Write an equation to show the dissociation of the hydrogen carbonate ion in water.

Answer

HCO 3 + H 2 O  H 3 O + + CO 3 • The hydrogen carbonate ion (HCO 3 ) is a WEAK ACID

How can the strength of an acid or base be quantified?

Measure the amount of hydronium ions created (acids) or the amount of hydroxide ions created (bases) by calculating dissociation constants.

Acid Dissociation Constant

HA + H 2 O  H 3 O + + A HA = acid (H = hydrogen, A = rest of acid molecule A = rest of acid after H + is removed [ ] = concentration K a = [H 3 O + ] [A ] [HA]

Acid Dissociation Constant

• For HClO 2, show the dissociation Rx and write the expression for it in terms of K a • HClO 2 + H 2 O  ClO 2 + H 3 O + K a = [H 3 O + ] [A ] K a = [H 3 O + ] [ClO 2 ] [HA] [HClO 2 ]

Your Turn

• For HNO 2 show the dissociation Rx and write the expression for it in terms of K a • HNO 2 + H 2 O  NO 2 + H 3 O + K a = [H 3 O + ] [A ] K a = [H 3 O + ] [NO 2 ] [HA] [HNO 2 ]

Acid Dissociation Constant

• The larger the dissociation value, the more the acid reacts with water to produce hydronium ions, therefore the stronger the acid • Weak acids have values less than 1 (only small fraction of acid molecule dissociates in water)

Base Dissociation Constant

B + H 2 O  HB + B = base + OH HB = B after H + is added [ ] = concentration K b = [HB + ] [OH ] [B]

Base Dissociation Constant

• For C 6 H 13 NH 2 , show the dissociation Rx and write the expression for it in terms of K a C 6 H 13 NH 2 + H 2 O  C 6 H 13 NH 3 + + OH K b = [HB + ] [OH ] K b = [C 6 H 13 NH 3 + ][OH ] [B] [C 6 H 13 NH 2 ]

Your Turn

• For HSO 3 , show the dissociation Rx and write the expression for it in terms of K a HSO 3 + H 2 O  + H 2 SO 3 + OH K b = [HB + ] [OH ] K b = [H 2 SO 3 ] [OH ] [B] [HSO 3 ]

Base Dissociation Constant

• The stronger the base, the larger the concentration of OH ions and the larger the K b .

• Weak bases have a K b less than 1.

Acid & Bases Lab: Litmus Test

Predict if substance is acidic, basic or neutral and record in 2 nd column of WS. Show me your predictions before going to lab. Test the 18 substances using red and blue litmus paper. Record your results in columns 3 & 4 of table by placing a  under a category if acidic or basic. If no reaction, no  . Place used litmus papers on paper towel on top of runway.

Show me your work before conducting pH test.

Acid & Bases Lab: pH Test

For each substance, record the color that the pH paper changed to after you dipped it into the solution.

Record the pH value that matches with the color on the pH paper.

Assignment

• 18-2 Review and Reinforcement – due tomorrow.

• Cross out #9.

• Cross out Practice Probs on the back – not required to do these types of problems!

What is concentration?

• Using molarity, it is a measure of moles of solute in liters of solution.

• Concentration is measured in WATER!

Drill #11 5/9, 12/14

Identify the following as acid, base, conjugate acid, and conjugate base: HBr + H 2 0  H 3 0 + + Br Reactions between acids and most metals produce what type of gas?

Write balanced neutralization equations for the following reactants: 1.

HBr and NaOH H 2 SO 4 and NH 4 OH H 2 CO 3 and NaOH

Answers to Drill

• The reaction of an acid and a base results in the formation of a salt and water. The process is known as neutralization.

• HBr + NaOH ------> NaBr + H 2 O • H 2 SO 4 + 2 NH 4 OH -----> (NH4) 2 SO4 + 2H 2 O • H 2 CO 3 + 2 NaOH --> Na 2 CO 3 + 2 H 2 O • Mg + 2HCl  H 2 + MgCl 2

Question

• Who is taking an AP test next week and when?

Homework DUE

• Titration Lab

Announcements

• Review – two worksheets • Test – May 16 (4B) or May 19 (4A)

Agenda

• Review Titration Problems • Finish up Acids and Bases • Titration Problems • Review Sheet 1 • Review Sheet 2

Homework

• Titration Practice – front side only • Review Worksheets

Test Topics • Properties of acids, bases, and salts • Bronsted-Lowry definition of acids/bases • Lewis definition of acids/bases • Amphoteric substance • Neutralization reaction – must be balanced • Naming acids • Calculating pH, pOH, [H + ], and [OH ] • Titration calculations

Lewis Definition of Acids/Bases

• Lewis Acid – something that accepts an electron pair to form a covalent bond • Lewis Base – something that donates an electron pair to form a covalent bond A + :B → A—B

Conjugate Pairs Inverse Relationship

• The stronger the acid, the weaker its conjugate base • The stronger the base, the weaker its conjugate acid HCO 3 + H 2 O  H 3 O + CO 3 weak A strong B weak strong C.A.

C.B.

Naming Acids

1. Binary – contains hydrogen & one other element

– Start with hydro – Then element – End with –ic acid Ex . HCl = hydrochloric acid HBr = hydrobromic acid

Naming Acids

2. Oxyacids – Contains both hydrogen & oxyanion =

polyatomic ion containing one or more oxygen atoms (NO 2 , SO 4 ) • If anion ends in –ate then the acid ends in –ic “I ate something, and now I am s ic k” • If the anion ends in –ite then the acid ends in –ous Ex. HNO 2 = nitrous acid, HNO 3 = nitric acid

Your Turn

• Name the following acids and bases: 1.HClO

3 2.H

2 SO 3 3.NaOH

4.NH

4 OH 5.HI

Your Turn

• Name the following acids and bases: 1.HClO

3 – chloric acid 2.H2SO

3 – sulfurous acid 3.NaOH – sodium hydroxide 4.NH

3 OH – ammonium hydroxide 5.HI – hydroiodic

Nitric acid Hydrochloric Sulfuric acid Sulfurous acid Acetic acid Hydrobromic acid Nitrous acid 8.

Phosphoric acid Hydrosulfuric 10. Carbonic acid

Announcement

• Make up Titration Lab and Help available afterschool today.

Agenda/Announcements

• Acids and Bases Quest postponed until tomorrow.

• Make-up date = Monday, May 21.

• Go over Acids and Bases Review Sheet • Hand in Titration Lab Calculations

Drill #65 5/17/12

• Write the balanced neutralization equations for the following reactions: 1. carbonic acid & calcium hydroxide 2. potassium hydroxide and acetic acid 3. barium hydroxide and hydrochloric acid

What are the ion concentrations in water?

• The concentrations of H 3 O + OH in pure water are each and 1.0

×

10 -7 mol/L at 25 ºC.

• Putting a symbol in brackets is used to signify the concentration.

• [H 3 0 + ] = 1.0

×

10 -7 • [OH ] = 1.0

×

10 -7 M M

Ionization Constant of water, K W • K W • K W = [H 3 0 + ] [OH ] = (1.0

×

10 -7 )(1.0

×

10 -7 ) = 1.0

×

10 -14

• Acids increase the [H 3 0 + ] Whenever [H 3 0 + ] is greater than [OH-], the solution is acidic.

• Bases increase the [OH-] Whenever [OH-] is greater than [H 3 0 + ], the solution is basic.

With an increase in [H 3 0 + ], some of the H 3 0 + ions will react with the OH ions, reducing [OH ] . [H 3 0 + ][OH ] will still = 1.0x10

-14

• Concentration values tend to be small…so we use a more convenient scale. pH!

pH + pOH = 14 •

– A measure of the acidity of a solution. • It is the negative logarithm of the hydronium ion [H 3 0 + ] concentration.

pH = -log [H

0 ]

pH + pOH = 14 •

pOH –

A measure of how basic a solution is. • It is the negative logarithm of the hydroxide [OH ] concentration.

pOH = -log [OH

]

• The logarithm scale is created to make numbers over a large range more manageable.

• The logarithm base 10 of a number x is the power to which 10 must be raised in order to equal x.

• Log 10 • 10 ?

= x x = ?

Log 100 = ?

10 ?

= 100

• Remember, our concentrations are SMALL. So we are going to be dealing with decimals… • Log 10 • 10 ?

= x x = ?

Log .001 = ?

10 ?

= .001

[H + ] = 1 × 10 -3 = 0.001

pH = -log [H + ] pH = -log (1 × 10 -3 ) pH = 3 To determine pH from a concentration where 1 is the only digit, write the concentration in scientific notation. The absolute power of the exponent will be the pH.

• For a base, you do the same thing except remember that you are solving for pOH first…

Ionization Constant of water, K W • K W • K W = [H 3 0 + ] [OH ] = (1.0

×

10 -7 )(1.0

×

10 -7 ) = 1.0

×

10 -14

Solutions

1.0

× 10 -3 M HClO 4 0.010 M HCl

[H + ]

1.0

×10 -3 M 1.0

× 10 -2 M 0.000001 M KOH 6.00

× 10 -4 HBr 0.20 M NaOH 1 × 10 -8 M 6.00

× 10 -4 M 5.0

× 10 -14 M 0.00300 H 2 SO 4 6.00

× 10 -3 M

3.0

2.0

[OH ]

1.0

× 10 -11 M 1.0

× 10 -12 M 1 × 10 -6 M 3.22

1.67

× 10 -11 M

pOH

11 12 6 10.8

13 2.0

× 10 -1 M .70

2.22

1.67

× 10 -12 M 11.8

Drill – 5/12/11 • Calculate the hydronium ion concentration in a 0.000500 M solution of NaOH.

• What is the pH?

Green Workbook • Pg. 262 #2 • Pg. 264 #1 • Pg. 267 #3 • Pg. 269 #1 & #2 • Pg. 270 #7

Equations to Know!!

• [H

0 ] [OH

] = 1.0

×10

-14

M • pH + pOH = 14 • pH = -log [H

0 ] • pOH = -log [OH

] • [H

0 ] = 10

-pH

• [OH

] = 10

-pOH

Drill – 5/9/11 • Write the equation for the neutralization reaction between carbonic acid (H 2 CO 3 ) and calcium hydroxide.

Agenda

• Gallery Walk – record notes from posters on Guided Notes sheet.

Stay out of lab area • Topics include: – Props of acids and bases – Arrhenius definition of an acid and a base – Bronsted-Lowry definition of an acid and base – Determining the strength of acids and bases – Acid dissociation constant – Naming and Identifying acids and bases

Drill 54 – 5/2/2012 • What do you think are properties of acids? Of bases?

Drill #57 5/7/2012

• Do you add acid to water or water to acid?

• AAA • A lways A dd A cid to water • AW

Drill #63 5/15/12

• A solution of KOH is titrated with HCL. The pH is measured as the HCl is added to the flask. The value of the pH will • Please be patient with me today, I barely have a voice!

Drill #63 5/15/12

• A solution of KOH is titrated with HCL. The pH is measured as the HCl is added to the flask. The value of the pH will decrease.