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Acids and Bases

Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

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Page 1: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Acids and Bases

Page 2: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• In this chapter, you will learn about the properties of acids and bases.

• You will learn how these properties change when acids and bases react together.

• You will also have a chance to estimate and measure the acidity of aqueous solutions.

Page 3: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• Acids and bases are common products in the home.

• Sometimes it is easy to identify some products as acids. Often the word “acid” appears in the list of ingredients.

• Identifying bases is a bit more difficult.

• Acids and bases have different properties that enable you to distinguish between them.

Page 4: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

AcidsProduct Acids in the Product

Citrus fruits (lemons, limes, oranges, tomatoes)

Citric acid, ascorbic acid

Dairy products (cheese, milk, yogurt)

Lactic acid

Vinegar Acetic acid

Soft drinks Carbonic acid, and sometimes phosphoric and citric acids

Page 5: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Bases

Product Bases in the Product

Oven cleaner Sodium hydroxide

Baking soda Sodium hydrogen carbonate (sodium bicarbonate)

Washing soda Sodium carbonate

Glass cleaner ammonia

Page 6: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Properties of Acids and Bases

• Acids• Taste sour• No characteristic feel• Conducts electricity• Reacts with metals to

produce hydrogen gas• Reacts with carbonated

compounds to produce carbon dioxide gas

• Change color when mixed with colored dyes called indicators (turns blue litmus paper red)

• Bases• Taste bitter• Feel slippery• Conducts electricity• Does not react with metals• Does not react with

carbonated compounds• Also change color when

mixed with indicators (turns red litmus paper blue)

You should never taste or touch acids, bases or any other chemical. Early chemists used their senses of taste and touch to observe the properties of many chemicals. This dangerous practice often lead to serious injury, and sometimes death.

Page 7: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

The Arrhenius Theory• In 1887, Arrhenius published a theory to

explain the nature of acids and bases.• In the theory of acids and bases, he states

that• An acid is a substance that dissociates in water to

produce one or more hydrogen ions (H+)» HCl (aq) H+

(aq) + Cl-(aq)

» HClO4 (aq) H+(aq) + ClO4

-(aq)

• A base is a substance that dissociates in water to form one or more hydroxide ions (OH-)

» LiOH (aq) Li+(aq) + OH-(aq)

» Ba(OH)2 (aq) Ba2+(aq) + 2 OH-

(aq)

Page 8: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• According to the Arrhenius theory, acids increase the concentration of H+ ions in aqueous solutions. An Arrhenius acid must contain hydrogen.

• Bases, on the other hand, increase the concentration of OH- in aqueous solutions. An Arrhenius base must contain the hydroxide ion.

Page 9: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• The Arrhenius theory is useful if you are interested in the ions that result when and acid or a base dissociate in water.

• It also helps explain what happens when an acid and a base undergo a neutralization reaction.

• HCl(aq) + NaOH_(aq) NaCl(aq) + H2O(l)

• In a neutralization reaction, an acid combines with a base to form an ionic compound and water.

• The net ionic reaction is• H+

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

Page 10: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Limitations to the Arrhenius Theory

• There are problems with the theory. One problem involves the ion that is responsible for acidity (H+).

• Look at the dissociation of HCl.• HCl(aq) H+

(aq) + Cl-(aq)

• The dissociation happens in an aqueous solution, but chemists often leave out the H2O component of the reaction. They simply assume it is there. But what is you put it in?

• HCl(aq) + H2O(l) H+(aq) + Cl-(aq) + H2O(l)

Page 11: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• The water is unchanged when the reaction is represented this way, but you know that water is a polar molecule.

• The O atom has a partial negative charge and the H atoms have a partial positive charge.

• The H2O interacts some way with the ion H+ and Cl- ions.

• Chemists realized that protons do not exist in isolation in aqueous solution (the hydrogen ion is simply a proton, a positively charged nuclear particle).

• Instead protons are always hydrates (attached to water) and the result is a hydronium ion, H3O(aq).

Page 12: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases
Page 13: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Another Problem with Arrhenius’ Theory

• Consider the reaction of ammonia with water.• NH3 (g) + H2O(l) NH4

+(aq) + OH-

(aq)

• Ammonia is one of several substances that produce basic solutions in water.

• Ammonia does not contain the hydroxide ion, however it does produce these ions when it reacts with water.

• Arrhenius’ theory does not explain the basic properties of ammonia.

Page 14: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• Arrhenius’ Theory only explains acid-base reactions in water. Many acid-base reactions take place in other solvent.

Page 15: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Brønsted-Lowry Theory

• In 1923, two chemists proposed a new theory of acids and bases. This theory overcame the problems related to the Arrhenius theory.

• A B-L acid is a substance from which a protons (H+) can be removed.

• A B-L base is a substance that can remove a proton from an acid.

Page 16: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• Like the Arrhenius theory, a Brønsted-Lowry acid must contain H in its formula. So basically all Arrhenius acids are B-L acids.

• However, any negative ion (not just OH-) can be a B-L base.

• Also note that water is not the only solvent that can be used.

• According to B-L, there is only one requirement for an acid-base reaction. One substance must provide a proton and the other substance must receive the same proton. Basically, it is a transfer of a proton.

Page 17: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• According to B-L, any substance can behave as an acid, but only if another substance behaves as a base at the same time. The same is true of the reverse, any substance can behave as a base, but only if another substance behaves as an acid at the same time.

• Look at the following reaction:proton transfer

• HCl(aq) + H2O(l) H3O(aq) + Cl-(aq)

acid base

HCl is an acid because it provides a proton. The water is the base because it receives the proton.

Page 18: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• Two molecules or ions that are related by the transfer of a proton are called a conjugate acid-base pair. Conjugate means that they are linked together.

• The conjugate base of an acid is the particle that remains when a protons is removed from the acid.

• The conjugate acid of a base is the particle that results when the base receives the proton.

Page 19: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• HCl(aq) + H2O(l) H3O(aq) + Cl-(aq)

conjugate acid conjugate base

• Every acid has a conjugate base and every base has a conjugate acid.

• The conjugate base of an acid-base pair has one less hydrogen than the acid

• The conjugate acid of an acid-base pair has one more hydrogen than the base.

Page 20: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Conjugate Acid-Base Pair Example

• Hydrogen Bromide is a gas at room temperature. It is soluble in water, forming hydrobromic acid (HBr). Write the equation, determine the products, and then identify the acid, base, as well as the conjugate acid and conjugate base.

• HBr(g) + H2O(l) H3O(aq) + Br-(aq)

Acid BaseConjugate Conjugate acid base

Page 21: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Another Example• Ammonia is a pungent gas at room

temperature. Its main use is in the production of fertilizers and explosives. It is very soluble is water. It forms a basic solution that is used in common products, such as glass cleaners. Identify the acid, the base, the conjugate acid, the conjugate base, and the conjugate acid base pairs in the following reaction.

• NH3 (g) + H2O(l) NH4+

(aq) + OH-(aq)

Page 22: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• NH3 (g) + H2O(l) NH4+

(aq) + OH-(aq)

Base Acid Conjugate Conjugate

acid base

Page 23: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Practice

• The following are considered bases. Write the formula’s for their conjugate acids

a) F_ b) NH3 c) HSO4- d) CrO4

2-

Answers:

a) HF b) NH4+ c) H2SO4 d)

HCrO4-

Page 24: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Practice

• The following are considered acids. Write the formula’s for their conjugate bases

a) HClO3 b) HSO3 c) H2O d) HCO3

2-

Answers:

a) ClO3- b) SO3

- c) OH- d) CO33-

Page 25: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Practice

• Identify the conjugate acid-base pairs in the following reactions:

a)NH4+ (aq) + CO3

2- (aq) NH3 (aq) +

HCO3- (aq)

b) H2O(l) + HS- (aq) H3O+ (aq) +

S2- (aq)

Acid

Acid

Base

Base

C. base

C. base

C. acid

C. acid

Page 26: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• REMEMBER! – Water has the ability to act as both an acid an a base, depending on what it reacts with

– Substance with this ability are considered to be amphiprotic

Page 27: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

Lewis Theory

• A substance that is capable of accepting electrons and are considered to be electron deficient– ie. Positive ions,

substances with less than a full octet, those with expandable valence shells

• A substance that is capable of donating electrons and are considered electron rich– ie. Negative ions,

substances with unshared electron pairs, substances with double bonds.

Lewis Acid Lewis Base

Page 28: Acids and Bases. In this chapter, you will learn about the properties of acids and bases. You will learn how these properties change when acids and bases

• Lewis theory is ‘all-embracing’, so the term Lewis acid usually is reserved for substances that are not also Bronsted-Lowry acids. Many of these do not even contain hydrogen. – BF3 + F− → BF4

– Al2Cl6 + 2Cl− → 2AlCl4−

– AlF3 + 3F− → AlF63−

– The lewis theory also covers substances like transition metals which do not contain protons, yet are capable of accepting electron pairs from ligands (neutral molecules with non-bonding pairs of electons ‘electron rich’)