6.5a Strong and Weak Acids and Bases

8/13/2019 6.5a Strong and Weak Acids and Bases

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Section 6.5 pg. 254-259


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ACIDS BASES

Tastes sour

Turn blue litmus red

pH less than 7

Neutralize bases

React w/ active metals to

produce H2(g)

React w/ carbonates to

produce carbon dioxide

Taste bitter

Feel slippery

Turn red litmus blue

pH greater than 7

Neutralize acids

Fill in as many empirical properties for acids and bases as you can ...


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Investigation 6.3:

Comparing the Properties of Acids (pg. 254)

Read over the Design. What are two importantcontrolled variables?


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The evidence from the demonstration clearly shows that acids withthe same initial concentration can have different degrees of acidic

properties.

This difference was shown in the different conductivity

measurements and the different rate of reactions.

What were the two important controlled variables?

concentrationand temperature

Why? A very dilute strong acid could have a higher pH than a more

concentrated weak acid which is incorrect and the conductivity and

rate of reaction measurements would be misleading.


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The concept of strong and weak acids was developed todescribe and explain the differences in properties of acids.

An acid can be described as a weak acid if itscharacteristic properties (under the same conditions) areless than those of a common strong acid

There are relatively few strong acids:

HClO4(aq), HI(aq), HBr(aq), HCl(aq)H2SO4(aq), HNO3(aq)


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Strong Acids: have high conductivity, high rate of reactionw/ metals and carbonates and a relatively low pH

These empirical properties suggest many ions are present(lots of H3O

+ions present); which is consistent with the ideathat strong acids react completely (>99%) with water to

form hydronium ions

HCl(aq) + H2O(l) H3O+

(aq) + Cl-(aq)

>99%


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Weak Acids: have low conductivity, a lower rate of reactionw/ active metals and carbonates and a relatively high pH

These empirical properties suggest fewer hydronium ionsare present

Based on this evidence, a weak acid reacts incompletely(


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Because of this difference, weak acids are much safer tohandle you can even eat and drink many of them.

Lactic acidin many

dairyproductsand builds

up inmuscles

Citrus acid in fruits

Stearic Acid in Animal Fat

Carbonicacid indrinks

Tannic Acid in Tea


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Pg. 255 #1-5


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Strong bases

have a high electricalconductivity, fast reaction rate and a very highpH (>>7)

Weak bases have a low electrical conductivity(if molecular bases), slower reaction rate and a

pH closer to, but greater than, 7

How do we explain the difference?


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Strong Bases

all soluble ionic hydroxides thatdissociate completely (>99%) to releasehydroxide ions

NaOH(s)

Na+

(aq) + OH-

(aq)

Weak Bases an ionic or molecular substancethat reacts partially (


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Explain the weak base properties of baking soda.

NaHCO3 (aq)Na+

(aq) + HCO3-(aq)

HCO3-(aq) + H2O(aq)H2CO3(aq) + OH-(aq)

Explain why sodium acetate has a pH of 8 whendissolved in water.

NaCH3COO(aq) Na+

(aq) + CH3COO-(aq)

CH3COO-(aq)+ H2O(l) CH3COOH(aq) + OH

-(aq)


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Pg. 257 #6, 7, 9


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Strong Acids Weak Acids Strong Bases Weak Bases

Empiricalproperties

(need sameconcentration& temperature)

Very low pH Med to low pH Very high pH Med to high pH

High

conductivity

Low

conductivity

High

conductivity

Low

conductivity*

Fast reactionrate

Slow reactionrate

Fast reactionrate

Slow reactionrate

ModifiedArrhenius

Theory

Completelyreact with

water to formH3O

+(aq) ions

Partially reactwith water to

form H3O+(aq)ions

Completelyreact with

water to formOH-(aq) ions

Partially reactwith water to

form OH-(aq)ions

* Applies only to weak bases that are molecular

6.5a Strong and Weak Acids and Bases

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