USES OF ACIDS Citric acid and ascorbic acid (Vitamin C) are found in orange juice Carbonic acid and phosphoric acid give a “bite” to soft drinks Acids in your stomach aid in digestion Sulfuric acid is the most widely used industrial acid in the world. It is used in making metals, paper, paints, and fertilizers.
Some Properties of Acids þ Produce H + (as H 3 O + ) ions in water (the hydronium ion is a hydrogen ion attached to a water molecule) þ Taste sour þ Corrode metals þ Electrolytes þ React with bases to form a salt and water (neutralization reaction) þ pH is less than 7 þ Turns blue litmus paper to red “Blue to Red A-CID”
Acids Ionize when dissolved in water (they dissociate (break apart) into their ions; +, -). – This allows the water to conduct electricity (which means they are electrolytes). – Ex- HCl is an acid…when placed in water, it becomes H+ and Cl-
Do you remember what an ion is? An ion is an atom that has lost or gained an electron giving it a positive (+) or negative (-) charge.
Acids – Acids produce Hydrogen Cations Therefore, the formula for an acid must have H in it (usually it will be at the beginning of the chemical formula only) – Ex. HCl, H 2 SO 4
Acids The H + will attach to H 2 O to form Hydronium ions (H 3 O+) – Acids produce H 3 O + in water Most acids produce H + (H 3 O + ) in water
Strong vs. Weak Acids See Table on p. 258 Strong Acid Ionize completely HNO 3 + H 2 O H 3 O + + NO 3 - strong electrolytes – (can conduct electricity well) Weak Acid Don’t ionize completely (don’t produce as many ions) CH 3 COOH + H 2 O H 3 O + + CH 3 COO - weak electrolytes
Some bases contain hydroxide ions, OH -, in their formulas, others don’t. NaOHsodium hydroxidelye KOH potassium hydroxideliquid soap Ba(OH) 2 barium hydroxidestabilizer for plastics Mg(OH) 2 magnesium hydroxide“MOM” Milk of magnesia Al(OH) 3 aluminum hydroxideMaalox (antacid) Al(OH) 3 aluminum hydroxideMaalox (antacid)
Bases – Those that don’t have OH in the formula will react with water to produce OH - ions. Base Waterammonium hydroxide All produce hydroxide ions, OH -, in water & conduct electricity (electrolytes).
Strong vs. Weak Bases Strong Bases Have OH and a metal atom in their formula – (ex-NaOH) Dissociate (break apart) in water to give: OH - & metal ion ex. NaOH OH - + Na + Strong electrolyte Weak Bases Don’t have OH in their formula (ex-NH3) ionize in water to produce OH - (water gives up an H), but doesn’t ionize completely ex. NH 3 + H 2 O NH 4 + + OH - Weak electrolyte
Some Properties of Bases Produce OH - ions in water Taste bitter, chalky Are electrolytes Feel soapy, slippery React with acids to form salts and water (neutralization reactions) pH greater than 7 Turns red litmus paper to blue “Basic Blue”
Uses of Bases Bases are used in soaps (remember, bases are slippery) Bases are used to make paper, in oven cleaners, and to unclog drains Ammonia is a base and is used in many household cleaners
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 A CID B ASE NEUTRALNEUTRAL The pH Scale Acid and Base strength is measured on a scale that ranges from 0 to 14. *TO BE NEUTRAL THE SUBSTANCE MUST HAVE EQUAL AMOUNTS OF H 3 O + AND OH - IONS!! Acid and Base strength is measured on a scale that ranges from 0 to 14. *TO BE NEUTRAL THE SUBSTANCE MUST HAVE EQUAL AMOUNTS OF H 3 O + AND OH - IONS!! Let’s get pHunky!
The pH scale is a way of expressing the strength of acids and bases. Under 7 = acid 7 = neutral Over 7 = base Note: Stronger acids have lower numbers & stronger bases have higher numbers
What does “pH” mean? pH stands for “power of hydronium ion” A strong acid (low pH..2 or 3) has a high amount of Hydronium ions (H 3 O + ) A weak acid (higher pH…5 or 6) has a low amount of Hydronium ions (H 3 O + )
Detecting Acids and Bases You can detect an acid using an indicator. INDICATOR - A substance that changes color in the presence of an acid or a base.
INDICATORS Litmus paper is an indicator An acid turns blue litmus paper red A base turns red litmus paper blue
pH testing There are several ways to test pH There are several ways to test pH – Blue litmus paper (red = acid) – Red litmus paper (blue = basic) – pH paper (multi-colored) – pH meter (7 is neutral, 7 base) – Universal indicator (multi-colored) – Indicators like phenolphthalein – Natural indicators like red cabbage, radishes
Neutralization Reaction When an acid and a base are combined a salt and water are formed. Ex. HCl + NaOH → NaCl + H 2 O (acid) (base)(salt) (water) The pH of the salt should be close to neutral (pH 7)