Aim AB 1aWhat are the properties of Acids and Bases?

Question: What is an electrolyte?

• Electrolytes – think Gatorade!

– As substances dissolve, ionic substances release free ions

– Ions carry a charge

– Electrolytes can therefore carry electricity

– How do we test for electrolyte solutions?

Properties of Acids• Examples to the right; what do they

have in common?• They are all electrolytes

– conduct electricity when aqueous• They taste sour – think lemons• They are corrosive - break down materials• React with active metals to release hydrogen gas

Ex: HCl(aq) + Mg(s) MgCl(aq) + H2(g)

• Neutralize bases to form a salt and water in a double replacement reaction

Ex: HCl(aq) + NaOH(s) NaCl(aq) + HOH(l)

ACID base salt water

Properties of Acids• Cause color changes in indicators

(A chemical that reacts with an acid or base and shows a color change)– blue litmus paper

• changes to red • (aciD = reD)

– phenolphthalein solution • changes to clear

• pH scale – indicates level of acidity or basicity of a solution

• pH of 1 – 6 indicates an acid• pH of 7 is neutral• pH of 8 – 14 indicates a base

Commonly used Acids Regents Chemistry

Table K Common Acids• Monoprotic acid

– only one H+ released

– HCl, HNO3

• Diprotic acid

– Two H+ ions released

– H2CO3, H2SO4

• Triprotic acid

– Three H+ ions released

– H3PO4

Properties of Bases• Examples to the right; what

do they have in common?• They are all electrolytes

– conduct electricity when aqueous

• They taste bitter – what does that tell you about coffee, especially Starbucks?

• They are caustic – break down skin tissue• Feel slippery to the touch – many soaps have this

characteristic• Neutralize bases to form a salt and water in a double

replacement reaction

Ex: HCl(aq) + NaOH(s) NaCl(aq) + HOH(l)

acid BASE salt water

Properties of Bases • Cause color changes in indicators

– red litmus paper • changes to blue color • (Blue = Base)

– Phenolphthalein solution• changes to pink color

• pH scale – indicates level of acidity or basicity of a solution

• pH of 1 – 6 indicates an acid• pH of 7 is neutral• pH of 8 – 14 indicates a base

Commonly used Bases Regents Chemistry

• Monohydroxy base - only one OH- released

– NaOH, KOH

• Dihydroxy base - two OH- ions released

– Ca(OH)2

• Ammonia – special case (more later)

Table K Common Bases

Real World Acid/Base Applications

• Acid Rain– Forms from the reactions

of sulfur and nitrogen oxides reacting with moisture in the air

– Increases the acidity of rainwater– Falls into lakes and ponds– Eats at metals in the lakebeds, ionizing them

and polluting the lakes and ponds– Remediation – add lime (base material) to

neutralize the acid in the lake – expensive!

Uses of Acids• CH3COOH - Acetic acid

– Vinegar in very dilute solution form (3% solution) • HCl – hydrochloric acid

– pH control for swimming pools– Cleaning material for tiles "muriatic acid“

• H2SO4 - sulfuric acid– battery acid in your car

• HNO3 – nitric acid – Reaction with ammonia to make fertilizers– Reaction with glycerol and toluene to make TNT

• H3PO4 – phosphoric acid– can be used to remove rust

Uses of Bases• NaOH – sodium hydroxide

– one of the most used bases in industrial processes, also called "lye" and is in some soaps

– can be used as a drain cleaner • NH3 – ammonia

– most common use as a home cleaner • Used in the production of fertilizers• NaHCO3 - sodium bicarbonate

– is present in most baking powder • CaO – calcium oxide – when mixed with water,

creates Ca(OH)2 – calcium hydroxide– used in plaster, called quicklime

Aim AB 2b How do we explain the difference between Acids and Bases on a molecular level?

Acid/Base Theories• There are two theories that describe the difference

between acids and bases on the atomic level• Arrhenius Theory compares acids and bases in

terms of two ions– Arrhenius Acids – release hydrogen ions (H+)

when dissolved in solution– Arrhenius Bases – release hydroxide ions (OH-)

when dissolved in solution• Bronsted Lowry Theory (also known as the “other”

theory in Regents Chemistry) describes acids and bases in terms of being able to donate or accept a proton

Arrhenius Theory of Acids and Bases

• An Arrhenius Acid is:

– A substance that ionizes in water to produce hydrogen ions (H+)

– Since H+ ions can’t exist alone in solution, they combine with water to form hydronium ions (H3O+)

HCl(g) H+(aq) + Cl–(aq)

or

H2O(l) + HCl(g) H3O+(aq) + Cl–(aq)

Arrhenius Theory of Acids and Bases

• An Arrhenius Base is:

– A substance that ionizes in water to produce hydroxide ions (OH-)

NaOH(s) Na+(aq) + OH–

(aq)

• Note!!! Carbon compounds with hydroxide ions (OH-) are NOT bases – they are alcohols and are neither acid nor base!

• Examples: • CH4OH (methanol) and C2H5OH (ethanol)

Other Theories: • Bronsted-Lowry Theory of Acids

– any substance that can donate or give up a proton (proton = H+ ion)

– Example: NH4+ (ammonium) can donate a proton

H20(l) + NH4+ NH3(aq) + H2O

+(aq)

• Bronsted Lowry Theory of Bases– any substance that can accept a proton– Usually have a free, unshared pair of electrons

that the proton (H+) can attach to

– NH3 (ammonia) has an unshared pair of electrons

H2O(l) + NH3 NH4+

(aq) + OH -(aq)

Other Theories

• Bronsted-Lowry Theory describes how some molecules can act as either an acid or a base

• These are Amphiprotic or Amphoteric substances– They have hydrogen ions to give up like an

acid– They have unshared electrons to absorb

hydrogen ions like a base– Depending on what molecules they hook

up with, they can act as either an acid or base

Other Theories• Examples of Amphiprotic or Amphoteric

substances– Water can donate or accept a H+ ion

H2O(l) + H2O(l) H3O+(aq) + OH-(aq)

Base Acid Acid Base– Ammonia can donate a H+ ion like an acid

NH3(g) + H2O(g) NH2-(aq) + H3O+

(aq) Acid Base Base Acid

– or accept a H+ ion like a base

NH3(g) + H2O(g) NH4+

(aq) + OH-(aq) Base Acid Acid Base

Aim AB 3c

- Why does lemon juice sting when I get it in my eye?

How does acid cause ulcers and heartburn?

• A property of acids is their corrosiveness

• This includes your stomach lining when you are stressed or eat overly spicey food

• Why do acids have this characteristic?

• Its all in their pH

http://www.google.com/url?sa=i&rct=j&q=ph+scale&source=images&cd=&cad=rja&docid=paPicfpSyr92PM&tbnid=9XnJrUxbibX4OM:&ved=0CAUQjRw&url=http%3A%2F%2Fwww.elmhurst.edu%2F~chm%2Fvchembook%2F184ph.html&ei=qDdHUa6YJ6iy0AG8voHIDw&bvm=bv.43828540,d.dmg&psig=AFQjCNH_8cDmBGyXz6EEVniPzjEEgxkMag&ust=1363708198607374

pH – how acidic or basic a substance is

• REMEMBER = Water is polar

• Slightly (+) hydrogens of one water molecule

• Are attracted to (-) oxygens of another

• Because of this, water ionizes (forms (+) and (-) ions) to a very small extent:

H2O + H2O H3O+ + OH–

Acid part Base part

of water of water

Symbol for concentration [ ][X] = Concentration of X

pH – how acidic or basic a substance is

• For every water molecule that becomes an acid ion, one becomes a base ion

• This evens out– for every H3O+ ion there is an OH– ion – When they combine, they make 2 water

molecules • The concentration of the ions in pure water is

measured in moles/liter (molarity)

[H3O+] = 10–7 M or 0.0000001 M[OH–] = 10–7 M or 0.0000001 M

Symbol for concentration [ ][X] = Concentration of X

pH – how acidic or basic a substance is

• The acid and base concentrations, when multiplied together, equals a constant value:

[H3O+] = 10–7 M

[OH–] = 10–7 M

[H3O+] x [OH–] = 10–14 M

[Acid] x [Base] = constant

• In any solution, including acids or bases

• The concentration constant

of [H3O+] x [OH–] is equal to 10-14 M

Symbol for concentration [ ][X] = Concentration of X

pH – how acidic or basic a substance is

• In acids, there are more H3O+ ions (acid ions) than OH– ions (base ions)

• Example: HCl is added to water. The H+ concentration rises to 10-4 M. What would the OH- concentration be?

[H3O+ ] x [OH-] = 10-14 M 10-4 x [OH-] = 10-14 M [OH-] = 10-10 M

• Note – the bigger the negative exponent, the smaller the amount you are dealing with– [H3O+ ] = 10-4 M = 0.0001 M– [OH-] = 10-10 M = 0.0000000001 M

Symbol for concentration [ ][X] = Concentration of X

pH – how acidic or basic a substance is

• In bases, there are more OH– ions (base ions) than H3O+ ions (acid ions)

• Example: NaOH is added to water. The OH- concentration rises to 10-3 M. What would the H3O+ concentration be?

[H3O+ ] x [OH-] = 10-14 M

[H3O+ ] x 10-3 = 10-14 M

[H3O+ ] = 10-11 M

Symbol for concentration [ ][X] = Concentration of X

So where does pH come from???• We said in the previous slides the following:• For water,

– The [H3O+ ] was 10-7 and the [OH- ] was 10-7

– Its pH is 7, or NEUTRAL

• For an acid,– The [H3O+ ] was 10-4 and the [OH- ] was 10-10

– Its pH is 4, or ACIDIC

• For a base, – The [H3O+ ] was 10-11 and the [OH- ] was 10-3

– Its pH is 11, or Basic

• So, to calculate pH, we look at the exponent of the acid part to get the pH

So, to calculate pH, what do we look at?

• Example 1: a solution has a hydronium [H3O+ ] concentration 10-4 M.

– What is the hydroxide [OH- ] concentration?

• [H3O+ ] x [OH- ] = 10-14 (a constant)

• 10-4 M x [OH- ] = 10-14

• [OH- ] = 10-10

– What is the pH of the solution?

• Look at the exponent of the [H3O+ ]

• [H3O+ ] = 10-4 = pH of 4 , acidic

So, to calculate pH, what do we look at?

• Example 2: a floor cleaning solution has a hydroxide [OH- ] concentration 10-6 M.

– What is the hydronium [H3O+ ] concentration?

• Remember:

–[H3O+ ] x [OH- ] = 10-14 (a constant)

–[H3O+ ] x 10-6 M x = 10-14

–[H3O+ ] = 10-8

– What is the pH of the solution?

• Look at the exponent of the [H3O+ ]

• [H3O+ ] = 10-8 = pH of 8 , basic

Aim AB 4d

Oh no! How do I clean up the Liquid Plumber on my kitchen floor safely?

A student spills a container

of acid on the floor. What

does the student need to

add to the acid to get rid of

it?

• Wipe it up?

• Water it down?

• What else could be done?

• More than anything else - the acid needs to be neutralized

Neutralization is a special DOUBLE REPLACEMENT reaction

• It reacts an acid with a base to form a salt and water

• Acid + Base Water + Salt

• General formula

• HA + BOH HOH + BA

• Examples

• HCl + NaOH H2O + NaCl

• H2SO4 + 2 NaOH 2 H2O + Na2SO4

Neutralization / double replacement - determine the

products of each of the following neutralization

reactions:

1. KOH + HBr H2O + KBr

2. H2SO4 + Ca(OH)2 2 H2O + CaSO4

• Spectator ions – ions that stay dissolved in the water of a

solution, do not react– the ions that make up the soluble salts

tend to be spectator ions

Acid Base Indicators tell us how acid or basic a substance is

• See Table M for examples of various indicators

• The pH range on the chart represents the point that a color change will occur

– Values to the left represent more acidic pHs– Values to the right represent more basic pHs

Acid Base Indicator Examples1. A solution leaves thymol blue a blue color and

litmus paper changes to blue; is the solution basic or acidic?

– Thymol is blue above the 8.0 – 9.6 range– Litmus changes blue above the 5.5 – 8.2 range– Both show the solution above 8– Solution is most likely basic

2. A solution changes methyl orange and litmus red and has no effect on phenolphthalein. Is it basic or acidic?

– Methyl orange changes red below 3.2 – 4.4 – Litmus changes red below 5.5 - 8.2– Both show the solution below 7 – Solution is most likely acidic

Aim AB 5e– How strong is my vinegar?

Acid Base Titration• A method for determining the concentration

or molarity of an unknown acid or base, based on

– the molarity of a known acid or base– The volume of acid used– The volume of base used

• Uses the process of neutralization and the concept of endpoint

– Endpoint: the point when the last of the acid and base are completely neutralized

– Determined using an indicator to show the final neutralization point

• To determine the molarity of an unknown acid solution

1 - you choose a good indicator

2 - you choose a known base molarity

3 - you add the base to the acid till it changes color

4 – you calculate

Calculating the molarity of an acid using the titration method and formula

• By using the titration technique and the endpoint of the neutralization reaction

• We can find out three things

1 - the molarity of the known base ( Mb )

2 - The volume of the base used ( Vb)

3 - The volume of the acid sample (Va)

• We can now use the last of our calculations in CRT T to calculate the

Ma x Va = Mb x Vb

Example 1 – a 2.00 M acid solution is used to

titrate an unknown base solution. If 40.00 mL of

acid are used and 20.0 mL of base are used,

what is the molarity of the base?

Remember: M is molarity or concentration

V is measured in mL or liters

Ma x Va = Mb x Vb

2.00 M x 40.0 mL = Mb x 20.0 mL

4.00 M = Mb

Example 2: Tropicana is having an issue with the citric acid levels in its new Tropicana Grapefruit Infused Fresh juice. A quality control chemist determines that 22 mL of an 1.0 M NaOH solution is used to neutralize 4400 mL of acidic TGIF juice. What is the molarity of the juice?

Ma x Va = Mb x Vb

Ma x 4400.0 mL = 1.00 M x 22.0 mL

0.005 M = Ma

What is the pH of the Tropicana? .0050 M = 5.0 x 10-3 = pH of 3

Example 3: A student performs a titration with a known base. She collects the data shown below. If the base has a molarity of 0.120 M, what is the molarity of the acid?

How much acid How much base

was used? was used?

42.4 mL – 22.4 mL 18.4 mL – 13.4 mL

= 20.0 mL = 5.0 mL

Ma x 20.0 mL = 0.120 M x 5.0 mL

Ma = 0.030 M

Acid Volume Base Volume

Starting Burette Measure 42.4 mL 18.4 mL

Ending Burette Measure 22.4 mL 13.4 mL

Acid / Base Strengths

• HCl and H2SO4 release different numbers of H+ ions!– In the neutralization of NaOH,

H2SO4 + 2NaOH 2H2O + Na2SO4

• NaOH and Ba(OH)2 also release different numbers of OH- ions!– In the neutralization of Ba(OH)2Note:

2HCl + Ba(OH)2 2H2O + BaCl2