Chemistry Notes: Acids and Bases Chemistry

Properties of Acids and Bases Acids  taste sour (vinegar, lemons)  aqueous solutions of acids are electrolytes  cause indicators to change colors  many metals react with acids to produce H 2 gas  react with bases to form a salt and water  most formulas begin with H Bases  bitter taste (soap, unsweetened chocolate)  bases are electrolytes in aqueous solution  cause indicators to change colors  feel slippery  react with acids to form a salt and water  often contain OH -, or ammonia NH 3

Examples The bolded formulas below to STRONG acids and bases Common acids  HCl  HNO 3  H 2 SO 4  H 3 PO 4  HC 2 H 3 O 2  H 2 CO 3 Common bases  NaOH  KOH  Ca(OH) 2  LiOH  NH 3

 Aqua regia is a concentrated mixture of hydrochloric and nitric acid. It creates toxic fumes of chlorine gas and is capable of dissolving gold. It is represented by a fire-breathing dragon in old alchemy works. Trivia: Aqua Regia

 The pH of a substance can tell us if it’s an acid, a base, or neutral. pH is a measurement of the concentration of hydrogen ions (H + ) in a solution. The more hydrogen ions present, the more acidic a substance is.  Acids have large amounts of hydrogen ions, and low pH (pH < 7).  Bases have small amounts of hydrogen ions, and high pH (pH > 7). Measuring pH

 Another measurement, pOH, tells use the concentration of hydroxide (OH - ) ions in a solution. The more hydroxide ions present, the more basic a substance is.  Acids have small amounts of hydroxide ions, and high pOH (pOH > 7).  Bases have large amounts of hydroxide ions, and low pOH (pOH < 7).  Neutral substances have equal amounts of hydrogen and hydrogen ions (pH = 7, pOH = 7).  The pH and pOH of a substance always add up to 14.

pH = 5.6NH 3 Large concentration of OH - ions Small concentration of H + ions pOH = 3.2pH = pOH H 2 SO 4 NaOH Large concentration of H + ionsHCl Practice: Are these solutions acidic, basic, or neutral?

If the pH of a solution is 6, what is its pOH? Is it an acid or base? If the pH of a solution is 4, what is its pOH? Is it an acid or base? If the pOH of a solution is 3, what is its pH? Is it an acid or base? Practice: Are these solutions acidic, basic, or neutral?

 Indicators are substances that change color in solutions of different pH  Help determine approximate pH Indicators

 Colorless in acid  Pink in base Phenolphthalein

 Mixture of indicators  Changes into different colors at each pH (rainbow)  Red/orange in acid, blue/purple in base, green around pH = 7 Universal indicator

Blue litmus turns red in acid Red litmus turns blue in base Litmus paper

Well, what is H 2 SO 4 ? Why is Johnny no more?

 Acids generally begin with H, so their formulas are easy to recognize. The name of an acid depends on everything after the H in the formula (the anion). Writing Names and Formulas for Acids and Bases—Acids Common acids  HCl hydrochloric acid  HNO 3 nitric acid  H 2 SO 4 sulfuric acid  H 3 PO 4 phosphoric acid  HC 2 H 3 O 2 acetic acid  H 2 CO 3 carbonic acid

 Determine the name of the anion in the acid. For example, HI contains iodide, I -. H 2 SO 3 contains sulfite, SO H 2 Cr 2 O 7 contains dichromate, Cr 2 O  The last three letters of the anion determine the rules you will use to name the acid. You will take the root of the acid’s name from the anion it contains.  -ide  hydro ________ ic acid  -ite  ____________ ous acid (no prefix)  -ate  ___________ ic acid (no prefix) Writing Names and Formulas for Acids and Bases—Acids

 Therefore, HI is hydroiodic acid, H 2 SO 3 is sulfurous acid, and H 2 Cr 2 O 7 is dichromic acid. Note that acid names do not contain the word “hydrogen”.  To determine the name of an acid from its formula, you need to swap and drop the anion with hydrogen ions. For example, nitric acid must contain nitrate, NO 3 -. If you swap and drop hydrogen (H + ) with NO 3 -, you get HNO 3. Writing Names and Formulas for Acids and Bases—Acids

 Bases are relatively easy to name, since many contain the hydroxide ion, OH -. Ex. Ba(OH) 2 is barium hydroxide, NaOH is sodium hydroxide, Al(OH) 3 is aluminum hydroxide, Fe(OH) 2 is iron (II) hyroxide.  One exception to the rule above is the weak base NH 3, ammonia.  Except for ammonia (NH 3, a formula you “just need to know”), you usually need to swap and drop to determine the formula of a base. Most will contain hydroxide. Writing Names and Formulas for Acids and Bases—Bases

Write the names for the following acids and bases. LiOHH 2 SO 4 NH 3 Names and Formulas Practice

Write the names for the following acids and bases. Mg(OH) 2 HNO 2 HCN Names and Formulas Practice

Write the names for the following acids and bases. HBrSr(OH) 2 HClO 4 Names and Formulas Practice

Write the formulas for the following acids and bases. AmmoniaNitric acidHydrochloric acid

Write the formulas for the following acids and bases. Calcium hydroxideChromic acidChlorous acid