Chemistry Unit 7 Acids and Bases

Acids An acid is a substance that produces positive hydrogen ions when placed in water. (H + ) The strength of an acid depends on how completely the substance ionizes. Strong acids completely ionize in water. Weak acids ionize only slightly.

Base A base is a substance that produces negative hydroxide ions when placed in water. (OH - ) The strength of a base depends on how completely the substance dissociates into metal ions and hydroxide ions in water. Strong bases dissociate completely. Weak bases do not.

BasicAcidicNeutral H+ OH- Solution Which solution is Acidic? Basic? Neutral???

Acids and Bases Produce H+ ions in water Have a sour taste Break down metals Formula starts with H Poisonous and corrosive to skin pH less than 7 Produce OH- ions in water Have a bitter taste and a slippery feel Break down fats and oils Formula ends with OH Poisonous and corrosive to skin pH greater than 7

Acids and Bases ACIDS Examples: vinegar, lemon juice, aspirin, stomach acid, battery acid, cola, milk BASES Examples: soap, shampoo, ammonia, drain cleaner, antacids

Neutral Substances pH = 7 Safe to ingest and leave on skin Concentrations of H + ions and OH - ions are equal Examples: dH2O, salts, most cosmetics, lotions, eye drops, etc.

Naming Acids (This should be review!) Every acid formula starts with H, a cation. To name an acid, look at the anion the hydrogen is bonded to. H 2 S anion = chloride ion H 2 SO 3 anion = sulfite ion H 2 SO 4 anion = sulfate ion

Naming Acids 1) If the name of the anion ends in –ide, the acid name begins with the prefix hydro- The stem of the anion is given then the suffix -ic is added and is followed by the word acid. H 2 S (anion sulfur)  hydro + stem + ic + acid Hydrosulfuric Acid

Naming Acids 2) If the name of the anion ends in –ite, the acid name is the stem of the anion with the suffix –ous and is followed by the word acid. H 2 SO 3 (anion Sulfite)  stem + ous + acid Sulfurous Acid

Naming Acids 3) If the name of the anion ends in –ate, the acid name is the stem of the anion with the suffix –ic and is followed by the word acid. H 2 SO 4 (anion Sulfate)  stem + ic + acid) Sulfuric Acid

Does the formula contain Oxygen? Hydro “stem”ic acid Anion end in __ ? NoYes “stem”ous acid “stem”ic acid “ate”“ite” Naming Acids

Writing Formulas for Acids If the name starts with “hydro” Hydrosulfuric Acid Write the hydrogen ion with charge. H +1 Write the anion with the proper charge. S -2 Balance the charges using subscripts. H 2 S

Writing Formulas for Acids If the name contains the suffix –ous Sulfurous Acid Write the hydrogen ion with charge. H +1 Look up the polyatomic ion (sulfite) and write it with the correct charge. SO 3 -2 Balance the charges using subscripts. H 2 SO 3

Writing Formulas for Acids If the name contains the suffix –ic without the prefix hydro Sulfuric Acid Write the hydrogen ion with charge. H +1 Look up the polyatomic ion (sulfate) and write it with the correct charge. SO 4 -2 Balance the charges using subscripts. H 2 SO 4

Writing Formulas/Naming Acids Remember the following statements… “I ate it and it was icky.” -ate becomes -ic “Rite ous” -ite becomes -ous (Righteous)

Naming Bases Bases are named using the traditional ionic naming system. Metal name + polyatomic ion name Examples: Ca(OH) 2 = calcium hydroxide NaOH= sodium hydroxide Al(OH) 3 = aluminum hydroxide

Writing Base Formulas Base formulas are written using the traditional ionic system. Look up the metal ion. Write the symbol with the proper charge. Ca +2 Look up the polyatomic ion. With bases, this will always be hydroxide, OH -1. Balance the charges using subscripts. Ca(OH) 2

Neutralization Reactions When an acid is added to a base, the end products are always salt and water. (neutral) A salt is defined as the neutral end product of an acid/base reaction. ACID + BASE  SALT + WATER H 2 S + Ca(OH) 2  CaS + H 2 O What is wrong with this equation???

Balance the final equation! H 2 S + Ca(OH) 2  CaS + H 2 O 1Ca1 1S11S1 4H24H2 2O12O1 H 2 S + Ca(OH) 2  CaS + 2 H 2 O

Neutralization Reactions Try another example: Acid + Base  Salt + Water H 2 SO 4 + NaOH  Na 2 SO 4 + H 2 O 1Na2 1SO 4 1 3H23H2 1O11O1 H 2 SO NaOH  Na 2 SO H 2 O

Take it one step further… Sulfurous acid and sodium hydroxide yields sodium sulfite and water. H 2 SO 3 + NaOH  Na 2 SO 3 + H 2 O 1Na2 1SO 3 1 3H23H2 1O11O1 H 2 SO 3 + 2NaOH  Na 2 SO 3 + 2H 2 O

One Last Step Hydrosulfuric acid and calcium hydroxide yields what??? H 2 S + Ca(OH) 2  1) One product will always be water. H 2 S + Ca(OH) 2  H 2 O + 2) The other product will be the + ion of the base bonded with the – ion of the acid. H 2 S + Ca(OH) 2  2H 2 O + CaS

pH Scale pH – a number used to denote the hydrogen ion concentration, or acididty, of a solution pH Scale Typically runs from 0 – Acidic Basic Neutral

pH Indicators A chemical substance that changes color in the presence of an acid and/or a base. 1) pH paper – Dip the paper, match color to scale on vial to determine numeric pH. pH 7 = base, pH = 7 neutral 2) Litmus – Dip one red and one blue paper. Red stays red, blue turns red  Acid Blue stays blue, red turns blue  Base Red stays red, blue stays blue  Neutral

pH Indicators 3) Bromthymol Blue – Add a few drops of bromthymol blue to the substance. If the blue color turns to yellow  Acid If the blue color stays blue  Base 4) Phenolphthalein – Add a few drops of phenolphthalein to the substance. If the clear liquid turns to pink  Base If the clear liquid remains clear  Acid

Concentration Strength of an acid or base is determined by the amount of ionization. Concentration is determined by the amount of water added to the substance. Molarity (M) The number of moles of solute dissolved in each liter of solution. Molarity = moles of solute liters of solution

Example Problem #1 If 1.00 liter of sugar water contains exactly 1.00 mole of sugar, what is its molarity? Molarity = 1.00 mol 1.00 L Molarity = 1.00 M

Example Problem #2 If 1.00 liter of sugar water contains exactly 2.00 mole of sugar, what is its molarity? Molarity = 2.00 mol 1.00 L Molarity = 2.00 M or 2.00 mol/L (Twice as concentrated…)

Example Problem #3 What is the molarity when 0.75 mol is dissolved in 2.50 L of solution? Molarity = 0.75 mol = 0.30 mol/L or 0.30M 2.50 L

In Lab, grams are typically used in place of moles. If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? First, calculate the molar mass of the acid. H 1 x = Cl 1 x = =

If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? First, calculate the molar mass of the acid. HCl contains g/mol It would take g of HCl to make 1 liter of a 1M HCl solution. How many grams would it take to make 2L of a 1M solution? 2 x g = g

If you wanted to make 2.00L of a 6M HCl solution, how much HCl would you need? It takes g of HCl to make 2 liters of a 1M solution. How much would it take to make 2 liters of a 6M solution? 6 x g = g

Try One More Suppose you wanted to make 2 liters of a 0.5 M solution of HCl. How much HCl would you need? Each mole of HCl is equal to g For a 0.5 M solution, you would need half that much x 0.5 = g. However, you want to make 2 liters, so double that amount x 2 = g.