1 / 18

Acids

Acids. A Swedish chemist, named Arrhenius in 1890 proposed that an acid be defined as any substance that, when added to water, increases the hydronium ion concentration. Hydronium is defined as H 3 O +. Water will attract a H + ion to produce a hydronium ion. H 2 O + H +  H 3 O +.

irene-dalton
Télécharger la présentation

Acids

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acids A Swedish chemist, named Arrhenius in 1890 proposed that an acid be defined as any substance that, when added to water, increases the hydronium ion concentration. Hydronium is defined as H3O+. Water will attract a H+ ion to produce a hydronium ion. H2O + H+H3O+ Many times we will only write the H+ to represent the hydronium ion. For example if HCl(s) is added to water the following will occur. HCl(g) H+(aq) + Cl-(aq) H2O(l) + H+(aq) H3O+(aq) Adding the two reactions together HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)

  2. Strong Acids vs. Weak Acids Strong acids will tend to go to completion when dissolved in water, weak acids do not. HOCl(l) + H2O(l)  H3O+(aq) + ClO−(aq) Weak Acid HNO3(l) + H2O(l)  H3O+(aq) + NO3−(aq) Strong Acid

  3. Bases Arrhenius defined bases as any substance when dissolved in water will produce hydroxide ions. (OH-) KOH(s)  K+(aq) + OH-(aq) If they go to completion when dissolved in water they are said to be strong bases, if they do not dissolve well and produce few hydroxide ions they are called weak bases. Another term used to describe basic solutions is alkaline. An alkaline solution is very basic. This term comes from group 1 of the periodic table which always makes strong basic solution.

  4. The definitions of Arrhenius acid and Arrhenius base given earlier in this book are variants of the definitions of acid and base originally proposed by Arrhenius in the late 19th century. One drawback that the Arrhenius definitions have is that they are limited to aqueous solutions: HCl, for instance, should be considered an acid whether it is in the form of a pure gas or in aqueous solution. Another limitation is that the Arrhenius definition cannot classify substances that sometimes act as acids and sometimes act as bases. Brønsted-Lowry Acids In 1923, the Danish chemist Johannes Brønsted proposed a broader definition of acid. Surprisingly, the same year, the British scientist Thomas Lowry happened to make exactly the same proposal independently. Their idea was to apply the name acid to any species that can donate a proton. Recall that a proton is a hydrogen atom that has lost its electron; it is a hydrogen ion and can be represented as H+. Such molecules or ions are now called Brønsted-Lowry Acids. Proton acceptors are called Brønsted-Lowry Bases.

  5. H2S + H2O → H3O+ + HS− Lost a proton, H+, therefore is the acid. Gained a proton, H+, therefore is the base.

  6. Properties of Acids and Bases Bases Acids Are excellent electrolytes Are excellent electrolytes Have a pH below 7 Have a pH above 7 Will react with many metals to produce hydrogen gas Are said to be basic or alkaline Are said to be acidic

  7. Acids will react with metal to produce hydrogen gas The proton, H+, will react with many metals to produce hydrogen gas using a single displacement reaction. Any metal located above the H2 on table J will react with an acid to produce hydrogen gas.

  8. Write out the chemical react that will occur between the listed acid and metal Mg + HCl  Na + HCl  Cu + HCl  Zn + HCl 

  9. Neutralization Neutralization reaction the reaction of the ions that characterize acids (hydronium ions) and the ions that characterize bases (hydroxide ions) to form water molecules and a salt (ionic compound). HCl(aq) + KOH(aq)  Acid Base H+(aq) + Cl-(aq) + K+(aq) + OH-(aq)  H2O(l) + KCl(aq) Water Salt

  10. pH A value used to express the acidity or alkalinity of a solution; a pH of 7 is neutral, a pH of less than 7 is acidic, and a pH of greater than 7 is basic pH = 7 pH > 7 pH < 7 Water is neutral because it is made up of one acid (H+), and one base (OH-).

  11. pH factors of 10 Each pH number indicated a change of concentration of hydronium ion concentration by a factor of 10. For example: If a sample of pool water has a pH of 8 and after adding chlorine for cleaning the pH changes to 5 how much has the hydronium ion concentration changed? pH 8  7  6  5 x x 10 10 10 10 x 10 x10 = 1000 The hydronium ion concentration changes by a factor of 1000 Because pH is dropping into the acid range, this indicated an increase in hydronium ion concentration.

  12. Indicators Certain dyes, known as indicators turn different colors in solutions of different pH. Dozens of indicator dyes are available. Some indicators, such as litmus, are natural products, but most are synthetic. Each indicator has its own colors and its individual range of pH over which it changes shade. By suitably blending several indicators, chemists have prepared “universal indicators,” which turn different colors throughout the entire pH range.

  13. Titrations The gradual addition of one solution to another to reach an equivalence point is called a titration. The purpose of a titration is to determine the concentration of an acid or a base. In addition to the two solutions, the equipment needed to carry out a titration usually includes two burets, a titration flask, and a suitable indicator. The formula used for titrations is from your reference tables.

  14. A solution of a base differs from a solution of an acid in that the solution of a base 1. is able to conduct electricity 2. is able to cause an indicator color change 3. has a greater [H3O+] 4. has a greater [OH-] Which pH value indicates the most basic solution? 1. 7 2. 8 3. 3 4. 11 A 3.0-milliliter sample of HNO3 solution is exactly neutralized by 6.0 milliliters of 0.50 M KOH. What is the molarity of the HNO3 sample? 1. 1.0 M 2. 0.50 M 3. 3.0 M 4. 1.5 M

  15. Which solution will turn litmus from red to blue? 1. H2S(aq) 2. NH3(aq) 3. SO2(aq) 4. CO2(aq) Which substance is always produced in the reaction between hydrochloric acid and sodium hydroxide? 1. water 2. hydrogen gas 3. oxygen gas 4. a precipitate Equal volumes of 0.1 M NaOH and 0.1 M HCl are thoroughly mixed. The resulting solution has a pH closest to  1. 5  2. 7  3. 3  4. 9

  16. As an aqueous solution becomes more acidic, the hydroxide ion concentration 1. decreases 2. increases 3. remains the same What produces hydrogen ions as the only positive ions in aqueous solution? 1. KOH 2. HBr 3. NH3 4. NaCl When the pH of a solution changes from a pH of 5 to a pH of 3, the hydronium ion concentration is 1. 0.01 of the original content 2. 0.1 of the original content 3. 10 times the original content 4. 100 times the original content

More Related