Fill in as many empirical properties for acids and bases as you can... Tastes sour Turn blue litmus red ph less than 7 Neutralize bases React w/ active metals to produce H 2(g) React w/ carbonates to produce carbon dioxide Taste bitter Feel slippery Turn red litmus blue ph greater than 7 Neutralize acids
Investigation 6.3: Comparing the Properties of Acids (pg. 254) Read over the Design. What are two important controlled variables?
The evidence from the demonstration clearly shows that acids with the same initial concentration can have different degrees of acidic properties. This difference was shown in the different conductivity measurements and the different rate of reactions. What were the two important controlled variables? concentration and temperature Why? A very dilute strong acid could have a higher ph than a more concentrated weak acid which is incorrect and the conductivity and rate of reaction measurements would be misleading.
The concept of strong and weak acids was developed to describe and explain the differences in properties of acids. An acid can be described as a weak acid if its characteristic properties (under the same conditions) are less than those of a common strong acid There are relatively few strong acids: HClO 4(aq), HI (aq), HBr (aq), HCl (aq) H 2 SO 4(aq), HNO 3(aq)
Strong Acids: have high conductivity, high rate of reaction w/ metals and carbonates and a relatively low ph These empirical properties suggest many ions are present (lots of H 3 O + ions present); which is consistent with the idea that strong acids react completely (>99%) with water to form hydronium ions >99% HCl (aq) + H 2 O (l) H 3 O + (aq) + Cl (aq)
Weak Acids: have low conductivity, a lower rate of reaction w/ active metals and carbonates and a relatively high ph These empirical properties suggest fewer hydronium ions are present Based on this evidence, a weak acid reacts incompletely (<50%) with water to form relatively few hydronium ions <50% CH 3 COOH (aq) + H 2 O (l) H 3 O + (aq) + CH 3 COO (aq)
Because of this difference, weak acids are much safer to handle you can even eat and drink many of them. Lactic acid in many dairy products and builds up in muscles Stearic Acid in Animal Fat Citrus acid in fruits Tannic Acid in Tea Carbonic acid in drinks
Pg. 255 #1 5
Strong bases have a high electrical conductivity, fast reaction rate and a very high ph (>>7) Weak bases have a low electrical conductivity (if molecular bases), slower reaction rate and a ph closer to, but greater than, 7 How do we explain the difference?
Strong Bases all soluble ionic hydroxides that dissociate completely (>99%) to release hydroxide ions NaOH (s) Na + (aq) + OH (aq) Weak Bases an ionic or molecular substance that reacts partially (<50%) with water to produce relatively few hydroxide ions <50% NH 3 (aq) + H 2 O (aq) OH (aq) + NH 4 + (aq)
Explain the weak base properties of baking soda. NaHCO 3 (aq) Na + (aq) + HCO 3 (aq) <50% HCO 3 (aq) + H 2 O (aq) H 2 CO 3(aq) + OH (aq) Explain why sodium acetate has a ph of 8 when dissolved in water. NaCH 3 COO (aq) Na + (aq) + CH 3 COO (aq) <50% CH 3 COO (aq) + H 2 O (l) CH 3 COOH (aq) + OH (aq)
Pg. 257 #6, 7, 9
Empirical properties (need same concentration & temperature) Modified Arrhenius Theory Strong Acids Weak Acids Strong Bases Weak Bases Very low ph Med to low ph Very high ph Med to high ph High conductivity Fast reaction rate Completely react with water to form H 3 O + (aq) ions Low conductivity Slow reaction rate Partially react with water to form H 3 O + (aq) ions High conductivity Fast reaction rate Completely react with water to form OH (aq) ions Low conductivity* Slow reaction rate Partially react with water to form OH (aq) ions * Applies only to weak bases that are molecular