Acids and Bases

Acids – Arrhenius Definition Produce Hydronium ion (H3O+1) in water Hydronium ion is water + a hydrogen cation H O water H O +1 H +1 By this definition, if an acid is to give a H+1 to water, then all acids will have hydrogen as the cation (first element written).

How do Acids produce Hydronium Ions? - water acid Hydrogen cation with some anion

How do Acids produce Hydronium Ions? - +1 H O

How do Acids produce Hydronium Ions? - +1 H O Hydronium ion Anion

Properties of Acids You eat acidic things every day. Acids have a sour taste, like orange juice, lemonade and vinegar (ketchup). Acids are also a main component of soft drinks, like Pepsi and Coke. Your body uses acids to dissolve foods in your stomach.

Properties of acids Acids are used to dissolve metals and turn them from the elemental metal into the ionic cation. When metals are dissolved, hydrogen gas is released. Because they can dissolve and eat through many things, acids are considered corrosive.

Bases Bases are the opposite of acids. Bases are defined as a chemical substance that accepts a proton. Bases have extra electrons that they share with a lone proton that has no electrons. The proton is accepted by the base, and forms a covalent bond.

Bases – Arrhenius Definition Bases produce the hydroxide ion in water H O -1 Hydroxide Ion

Properties of Bases Bases have a bitter taste. Dark chocolate for example, is slightly basic. Bases are commonly used as household cleaning products. Ammonia, dish soap, and detergent are all types of bases that help us clean.

Properties of Bases When food or dirt is stuck to something, it is attached with trillions of hydrogen bonds. Bases have the ability to disrupt the hydrogen bonds, making the food or dirt fall of the surface of whatever you are cleaning. Another example of this, is when we used a tiny amount of dish soap to break the hydrogen bond surface tension in liquid water causing the paperclip to sink.

Identifying acids and bases HCl, H2SO4, HBr, H3PO4, HF These are all acids, what is similar about all of these compounds? If a chemical formula has a Hydrogen as the first element, it can usually be considered an acid.

Identifying acids and bases NaOH, Ba(OH)2, LiOH, KOH What is similar about these compounds? Bases can be identified because they have a hydroxide group (OH) at the end.

Strong Acids The definition Strong Acid means that every molecule of acid will donate the proton if it is mixed into solution. Strong acids are 100% dissociated in water.

Strong Acids The only strong acids are HI – Hydroiodic Acid HBr - Hydrobromic Acid HCl - Hydrochloric Acid H2SO4 - Sulfuric Acid HNO3 – Nitric Acid These acids are all extremely dangerous, even at low concentrations.

Strong Bases The definition Strong Base means that every molecule of base will accept a proton if it is mixed into solution. Strong bases are 100% dissociated in water. All strong bases contain OH in their molecules.

Weak Bases Only partially ionized May or may not contain OH in their molecules. Al(OH)3 is a weak base. Ammonia, NH3, is also a weak base, but does not contain OH.

Strong Bases The only strong bases are NaOH - Sodium Hydroxide KOH - Potassium Hydroxide Ca(OH)2 - Calcium Hydroxide Ba(OH)2 - Barium hydroxide All of these bases are very dangerous, even at low concentrations.

Mixing acids with water When an acid is mixed with water, the proton is donated and a hydronium ion is formed in water. HCl + H2O è H3O+ + Cl-

Mixing acids with water Conjugate Acid - The conjugate acid is the chemical on the product side that receives the donated proton. HCl + H2O -> H3O+ + Cl- The H3O+, the hydronium ion, is the conjugate acid.

Mixing acids with water Conjugate Base- The conjugate base is the chemical on the product side that gave the proton away. HCl + H2O -> H3O+ + Cl- The Cl- is the conjugate base.

Mixing bases with water When a base is mixed with water, the water donates protons to the base, forming more water, but leaving the hydroxide ion behind. NaOH + H2O è Na+ + OH- + H2O

Mixing bases with water NaOH + H2O è Na+ + H2O + OH- NaOH is the base, and in this case, the water acts as an acid, donating a proton. What is the conjugate acid in this case? What is the conjugate base in this case?

Water as a amphoteric molecule Amphoteric – Molecules that are relatively neutral on the pH scale, like water, have the ability to either act as a acid or base, depending on what they are mixed with. If you mix water with an acid, the water will act as a base. If you mix water with a base, the water will act as an acid.

Characteristics of Acids & Bases Produce H3O+1 (hydronium ion) in water Produce OH-1 (hydroxide ion) in water Tastes sour Tastes Bitter React with active metals to form hydrogen gas Feels slippery

Strength versus Concentration

Strong versus Weak Acids How many hydronium ion – anion pairs can you find? - + - 3 + How many intact acid molecules can you find? + - 1 Strong acid Most of the acid molecules have donated the H+1 to water

Strong versus Weak Acids + How many hydronium ion – anion pairs can you find? 1 How many intact acid molecules can you find? - 3 Weak acid Only a few of the acid molecules have donated the H+1 to water

Concentrated versus Dilute solvent solute Lower concentration Not as many solute (what’s being dissolved) particles Higher concentration More solute (what’s being dissolved) particles

Combinations of Concentration & Strength Concentrated Dilute Strong A lot of acid added & most dissociates Not much acid added, but most of what is there dissociates Weak A lot of acid added, but most stays together Not much acid added and most of what is there stays together

pH

pH scale pH is a measure of the concentration of protons in solution. This gives us a relative scale of how acidic the solution is. At home, you use pH indicators to check your pool, hot tub, and fish tanks, to make sure that the water is at the appropriate pH.

pH Scale Is a scale to measure the acidity of a sample 1 14 7 Highly acidic Very basic (not acidic) neutral 7 A solution with a pH less than 7 indicates that the solution is acidic. Water is right in the middle with a pH of 7. Water is considered the neutral mark when it comes to the acid/base scale. A solution with a pH of greater than 7 is considered basic.

pH is a Logarithmic Scale Logarithm –The number of times a base must be multiplied by itself to reach a given number # of multiples Base # you’re trying to reach

Calculating pH pH scale – Logarithmic scale of the acidity of a solution The pH scale uses base “10” [ ] = concentration in Molarity pH has no units

The “-” in the pH equation Because pH is the negative log of concentration of hydronium, as concentration increases, the pH goes down. The lowest pH is the highest concentration of hydronium

What does a “log” scale really mean? Every change of 1 in pH shows a change of 10x in concentration of hydronium pH 4 3 2 1 Level of acidity increases 1000x more acidic 100x more acidic 10x more acidic

An example of calculating pH Find the pH if the concentration of [H3O+1] is 0.25 M

An example of calculating pH Find the pH if the concentration of [H3O+1] is 0.25 M pH = 0.60

An example of calculating hydronium ion concentration Find the [H3O+1] if the pH is 2.7

An example of calculating hydronium Find the [H3O+1] if the pH is 2.7 H3O+1 = 0.0020 M

Ways to measure pH Indicators change color based on pH Liquid indicators – various indicators change colors at different pH’s (phenolphthalein, methyl red) Universal indicator – a combination of liquid indicators to produce a “rainbow” changing colors at several pH’s Paper Indicators Paper with a liquid indicator on it (Litmus paper or pH paper) pH meters or pH probes Electronically determine pH and give a read-out

Common pH indicators This picture © 1998 David Dice

pH of common substances 0.1M HCl 1 Stomach contents 2 Vinegar 2.9 Soda pop 3 Grapes 4 Beer 4.5 Pumpkin pulp 5 Bread 5.5 Intestinal contents 6.5 Milk Urine 6.6 Bile 6.9 Saliva 7 Blood 7.4 Eggs 7.8 0.1M NH3 (aq) 11.1 0.1M NaOH 13

pH These are the pH values for several common substances.

Section 2.4—Defining, Naming & Writing Acids & Bases We need to know what acids we’re talking about when talking about ant-acids!

Naming non-oxygen Acids These compounds: Start with “H” (more than 1 “H” is OK, too). Do not contain oxygen To name these compounds: Use “hydro____ic acid” Fill in the blank with the anion’s name without the last syllable

Example #1 HBr

HBr Example #1 Hydrobromic acid Hydrogen cation Bromine It’s an acid No oxygen Use “hydro___ic”

Naming Oxygen Acids These compounds: To name these compounds: Start with “H” (more than 1 “H” is OK, too). Do contain oxygen To name these compounds: Use “___ic acids” for “-ate” anions Use “___ous acids” for “-ite” anions Do not use “hydro” with these…the word “acid” is how you know it begins with hydrogen, not “hydro-”

Example #2 H2SO3

H2SO3 Example #2 Sulfurous acid Hydrogen cation Sulfite ion It’s an acid Hydrogen cation H2SO3 Sulfite ion “-ite” ion Use “___ous” acid Sulfurous acid

Example #3 H2SO4

H2SO4 Example #3 Sulfuric acid Hydrogen cation Sulfate ion It’s an acid Hydrogen cation H2SO4 Sulfate ion “-ate” ion Use “___ic” Sulfuric acid

Write the name for the following compounds Let’s Practice HCl HNO3 H2S H3PO3 Example: Write the name for the following compounds

Write the name for the following compounds Let’s Practice HCl HNO3 H2S H3PO3 Hydrochloric acid Nitric acid (Hydrosulfuric acid) Hydrogen sulfide Phosphorous acid Example: Write the name for the following compounds

Writing Acid Formulas

“Hydro-” acids To write these formulas: The cation is H+1 Write the anion and charge Balance the charges by adding the appropriate subscript to the hydrogen cation

Example #4 Hydrofluoric acid

Does not contain oxygen Example #4 H+1 Hydrogen cation Hydrofluoric acid Does not contain oxygen F-1

Does not contain oxygen Example #4 H+1 Hydrogen cation Hydrofluoric acid Does not contain oxygen H+1F-1 F-1 +1 + -1 = 0 HF The compound is neutral. Subscripts are not needed

NON “Hydro-” acids Acids with Polyatomic Ions To write these formulas: The cation is H+1 If it is an “-ic” acid, the anion is the “-ate” polyatomic ion If it is an “-ous” acid, the anion is the “-ite” polyatomic ion Add subscript to the hydrogen cation to balance charges

Example #5 Carbonic acid

From the “___ate” anion Example #5 H+1 Hydrogen cation Carbonic acid From the “___ate” anion CO3-2

From the “___ate” anion Example #5 H+1 Hydrogen cation H+CO32- +1 + -2 = -1 Carbonic acid H+H+CO32- +1 + 1 + -2 = 0 From the “___ate” anion CO3-2 H2CO3

Example #6 Nitrous acid

From the “___ite” anion Example #6 H+1 Hydrogen cation Nitrous acid From the “___ite” anion NO3-1

From the “___ite” anion Example #6 H+1 Hydrogen cation Nitrous acid H+NO2- From the “___ite” anion +1 + -1 = 0 NO3-1 HNO2

Write the formula for the following acids Let’s Practice Phosphoric acid Hydroiodic acid Carbonous acid Perchloric acid Example: Write the formula for the following acids

Write the formula for the following acids Let’s Practice Phosphoric acid Hydroiodic acid Carbonous acid Perchloric acid H3PO4 HI H2CO2 HClO4 Example: Write the formula for the following acids

Naming & Writing Bases

Naming Bases Most bases are just ionic compounds with “hydroxide” as their anion The most common exception to this is ammonia NH3 (ammonia) is a base even though it doesn’t contain “-OH” as the anion

Example #7 NaOH

Example #7 Sodium NaOH Sodium Hydroxide Hydroxide

Write the formula or name for each Let’s Practice Ca(OH)2 KOH Sr(OH)2 Copper (II) hydroxide Magnesium hydroxide Example: Write the formula or name for each

Write the formula or name for each Let’s Practice Ca(OH)2 KOH Sr(OH)2 Copper (II) hydroxide Magnesium hydroxide Calcium hydroxide Potassium hydroxide Strontium hydroxide Cu(OH)2 Mg(OH)2 Example: Write the formula or name for each