Acids, Bases & pH

WATERBefore understanding Acids and Bases,

you must understand water.1. It is a polar covalent molecule.

Like a magnet.

+ +- -

WATER1. It is a polar covalent molecule.

WHY???Oxygen pulls on the electrons more than

Hydrogen does.

+ +- -

WATERBecause water is POLAR (negative side

and positive side), what types of compounds will it DISSOLVE easily?

Covalent or Ionic?

+ +- -

Ionic Compounds: Ionic Compounds: AcidsAcids

Ionic compounds that break apart (dissolve) in water to form a hydronium ion, H3O+ (hydrogen ion, H+).

The more H+ ions released in water = STRONGER ACID

Or written as HCl H3O+ + Cl-

AcidsAcids

When HCl is put in water, a Hydronium ion, H3O+ (hydrogen ion, H+) is formed.

Or written as HCl H3O+ + Cl-

Acids, Bases and pHAcids, Bases and pHWhy do we need to know?

The pH of a substance determines its physical and chemical properties .

Characteristics of Acids1. Taste Sour2. React Strongly with Metals and

Carbonates (in soil and rocks) 3. Can burn your skin4. Conduct electricity in water5. Turn indicator red

AcidsAcids

Examples of Acids1. Vinegar2. Citrus fruits3. Stomach Acid (HCl)

Ionic Compounds: Ionic Compounds: BasesBases

Ionic compounds that break apart (dissolve) in water to form a negatively charged hydroxide ion (OH-).

More OH- ions released in water = STRONGER BASE

NaOH Na+ + OH-

Acids, Bases and pHAcids, Bases and pHWhy do we need to know?

The pH of a substance determines its physical and chemical properties .

BasesBasesCharacteristics of Bases1. Taste bitter2. Feel Slippery 3. Can burn your Skin4. Turn indicator blue5. Conduct electricity in water

Examples of Bases1. Lye (Sodium Hydroxide)2. Ammonia3. Bleach

pHWhat does it mean?

pH – potential of Hydrogen – the ability to release H+

The more H+ released in water, the HIGHER the pH.

Which one below releases more H+?1.1. HHBr Br HH33OO++ + Br + Br--

or written as or written as HHBr Br HH++ + Br + Br--

2.2. KKOHOH K K++ + + OHOH--

pHpHWhich has a greater ability to release H+ in Which has a greater ability to release H+ in

water? Which has HIGHER pH?water? Which has HIGHER pH?

HHBr Br HH++ + Br + Br-- YES! And therefore this shows aYES! And therefore this shows a higher pH higher pH

(potential of Hydrogen)(potential of Hydrogen)

KKOHOH K K++ + + OHOH-- NO! And therefore this shows aNO! And therefore this shows a lower pH lower pH

(potential of Hydrogen)(potential of Hydrogen)

pHpHCOMPARE: WHAT ARE THEIR pH COMPARE: WHAT ARE THEIR pH

VALUES?????VALUES?????

HHBr Br HH++ + Br + Br-- About 1 to 2About 1 to 2

KKOHOH K K++ + + OHOH-- About 13 to 14About 13 to 14

pHpHpHpH – – ppotential of otential of HHydrogen – the ability to release H+ydrogen – the ability to release H+

WHAT ABOUT NEUTRAL WATER? WHAT ABOUT NEUTRAL WATER?

HH22O O HH++ + + OHOH--

What is the pH for this?What is the pH for this?

pHpHpH – potential of Hydrogen – the ability to release H+pH – potential of Hydrogen – the ability to release H+

NEUTRAL WATER: NEUTRAL WATER: HH22O O HH++ + + OHOH--

NEUTRAL = pH 7NEUTRAL = pH 7

HOW DOES THIS HAPPEN?HOW DOES THIS HAPPEN?

pHpH HH22O O HH33OO++ + + OHOH--

pH 7pH 7Dissociation – the breaking apart of water into Dissociation – the breaking apart of water into

ions. ions. HH33OO++ = = OHOH--

The pH ScaleTells the concentration of (how many) hydrogen (H+)

ions in solution.Hydrogen Ion Concentration in Moles/Liter at 25° C

pH H+ conc.0 1.01 0.12 0.013 0.0014 0.00015 0.000016 0.0000017 0.00000018 0.000000019 0.000000001

10 0.0000000001 11 0.0000000000112 0.00000000000113 0.000000000000114 0.00000000000001

The pH ScaleThe pH ScaleTells the concentration of (or how many) hydrogen (H+) ions in a water solution.

Each move up the scale is a jump of 10 TIMES.Each move up the scale is a jump of 10 TIMES.

HOW MANY TIMES? How many times stronger is pH 3, than pH 4? pH3 is 10 times stronger than pH4 Or another way, 1 jump up the scale equals 10 times

more H+ ions! How many times stronger is pH 5, than pH 8? 3 jumps up the scale? 10 x 10 x 10 1,000 times more H+ ions! 1,000 times stronger! How about pH 1 than pH 7? 6 jumps 10 x 10 x 10 x 10 x 10 x 10 1,000,000 times! 1,000,000 times MORE H+ ions!

The 0 – 14 pH scale was created to show amount of H+ ions in a water solution.

pH of a neutral solution = 7H+ concentration = OH- concentration

Acidic pH values: 0 – 6, MAXIMUM = 0 Basic pH values: 8 – 14, MAXIMUM = 14

The pH ScaleThe pH Scale

IndicatorIndicator – changes color as the pH changes, and Indicator – changes color as the pH changes, and

thus tells us the pH of a solution.thus tells us the pH of a solution.

NEUTRALIZATIONNEUTRALIZATION What happens when an ACID is added

to a BASE ???? They react to form a salt and water

Hydrochloric Acid + Sodium Hydroxide Water + Table Salt

HCl + NaOH H2O + NaCl

Acids and Bases and Neutralization

One of the most important aspects of a living system is the amount of acidity or alkalinity

NEUTRALIZATIONNEUTRALIZATION:Why do we need to know?

Control of pH is very important

Control is accomplished with buffers

Buffers neutralize small amounts of either an acid or base.

pHpHWhy do we need to know?

pHpHWhy do we need to know?

Alkalinity – the ability of a stream to neutralize acids.

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