1 / 50

Chapter 14

Chapter 14. Acids and Bases in the Environment. Acids and Bases. Acids and Bases (video) H + ions - ? OH - ions - ? Soapy slippery - ? Taste sour - ? Acids give up H + when added to water forming - ? More Hydronium – pH ___________. Safety.

majed
Download Presentation

Chapter 14

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. Chapter 14 Acids and Bases in the Environment

  2. Acids and Bases • Acids and Bases (video) • H+ ions - ? • OH- ions - ? • Soapy slippery - ? • Taste sour - ? • Acids give up H+ when added to water forming - ? • More Hydronium – pH ___________

  3. Safety • When diluting a concentrated acid, always add acid to water • Weak and strong acids and bases can all be dangerous. Handle with care • Rinse with running water immediately if spilled on skin

  4. Binary AcidsA binary compound consists of two elements. Binary acids have the prefix hydro in front of the full name of the nonmetallic element. They have the ending -ic. Examples include hydrochloric and hydrofluoric acid. Hydrofluoric Acid - HFHydrochloric Acid - HClHydrobromic Acid - HBrHydroiodic Acid - HIHydrosulfuric Acid - H2S Common Acids

  5. Ternary AcidsTernary acids commonly contain hydrogen, a nonmetal, and oxygen. The name of the most common form of the acid consists of the nonmetal root name with the -icending. The acid containing one less oxygen atom than the most common form is designated by the -ous ending. An acid containing one less oxygen atom than the -ous acid has the prefix hypo- and the -ousending. The acid containing one more oxygen than the most common acid has the per- prefix and the -ic ending. Common Acids

  6. Nitric Acid - HNO3Nitrous Acid - HNO2Hypochlorous Acid - HClOChlorous Acid - HClO2 Chloric Acid - HClO3Perchloric Acid - HClO4Sulfuric Acid - H2SO4Sulfurous Acid - H2SO3 Phosphoric Acid - H3PO4Phosphorous Acid - H3PO3Carbonic Acid - H2CO3Acetic Acid - HC2H3O2 Oxalic Acid - H2C2O4Boric Acid - H3BO3Silicic Acid - H2SiO3 Common Acids

  7. Corrosive ('burns' your skin) Sour taste (e.g. lemons, vinegar) Contains hydrogen ions (H+) when dissolved in water Has a pH less than 7 Turns blue litmus paper to a red colour Reacts with bases to form salt and water Reacts with metals to form hydrogen gas Reacts with carbonates to form carbon dioxide, water and a salt PROPERTIES OF ACIDS

  8. General Equations and Review • Note the general equations page 319 • Complete the revision questions 1, 2 page 319

  9. Common Bases • Bases • Sodium Hydroxide - NaOHPotassium Hydroxide - KOHAmmonium Hydroxide - NH4OHCalcium Hydroxide - Ca(OH)2 • Magnesium Hydroxide - Mg(OH)2Barium Hydroxide - Ba(OH)2Aluminum Hydroxide - Al(OH)3Ferrous Hydroxide or Iron (II) Hydroxide - Fe(OH)2 • Ferric Hydroxide or Iron (III) Hydroxide - Fe(OH)3Zinc Hydroxide - Zn(OH)2Lithium Hydroxide - LiOH

  10. PROPERTIES OF BASES AND ALKALIS • Corrosive ('burns' your skin) • Soapy feel • Has a pH more than 7 • Turns red litmus paper to a blue colour • Many alkalis (soluble bases) contain hydroxyl ions (OH-) – A base that is soluble in water is called an alkali • Reacts with acids to form salt and water

  11. Johannes Brønsted Thomas Lowry (1879-1947) (1874-1936) Denmark England

  12. The Lowry-Bronsted theory of acids and bases • An acid is a substance that donates a proton (H+ ion) to another substance • A base is a substance that accepts a proton (H+ ion) from another substance • Since a hydrogen atom is simply a proton and an electron, removing the electron leaves a proton, H+ .

  13. The Lowry-Bronsted theory of acids and bases • Acid– proton donor • Base – proton acceptor • The general reaction for an acid dissolving in water is

  14. A Brønsted-Lowryacidis a proton donor A Brønsted-Lowrybaseis a proton acceptor conjugatebase conjugateacid base acid

  15. The Lowry-Bronsted theory of acids and bases • HNO3 (l) + H2O (l)  H3O+ (aq) + NO3- (aq) • According to Bronsted-Lowry the water in this equation is acting as a base since it accepts a proton H+ Acid loses a proton Base gains a proton

  16. Review • Complete question 3 page 321

  17. Ionisation and the production of the hydronium ion • Ionisation is a reaction in which a molecule reacts with water to produce two or more ions • Water acts as a base accepting a proton from the acid. • Forms hydronium ion (H3O+)

  18. Hydrolysis • When an ionic substance dissolves in water, the resulting solution is often not neutral • This is because the ions can act as acids or bases when reacting with water and produce solutions that are either acidic or basic – known as hydrolysis • Hydrolysis reaction • An anion reacts with water to produce OH- • A cation reacts with water to produce H3O+ • Not all cations and anions hydrolyse egNaCl

  19. Hydrolysis • Ammonium chloride is dissolved in water. Ammonium and chloride ions are produced. The ammonium ions react as follows • NH4+ (aq) + H2O (l)  H3O+ (aq) + NH3 (aq) • Is the resulting solution acidic or basic?

  20. Hydrolysis • Sodium carbonate is dissolved in water, sodium ions and carbonate ions are produced. • The carbonate ion reacts as follows • CO32- (aq) + H2O (l)  HCO3- (aq) + OH- (aq) • Is the resulting solution acidic or basic?

  21. Dissociation of Bases • When ionic bases dissolve in water, they dissociate or separate into their constituent ions. • They do not ionise since they do not actually react with the water to produce ions as acids do. • NaOH (s) ---> Na+ (aq) + OH- (aq) H2O

  22. Dissociation of Bases • Molecular bases such as NH3 cannot dissociate as they do not contain ions • Ammonia ionises • NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

  23. Neutralisation • Neutralization Reaction - a reaction in which an acid and a base react in an aqueous solution to produce a salt and water: • Write the neutralisation equation below as ionic and net ionic equation HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l) • Note – can the H+ ion exist by itself in water? • Therefore the ionic equation of neutralisation is • H3O+ (aq) + OH- (aq)  2H2O (l)

  24. Neutralisation • Neutralisation reactions are one way of producing pure samples of salts. • Hydrochloric acid and calcium hydroxide mixed – an aqueous solution of calcium chloride results • 2HCl (aq) + Ca(OH)2(aq)  CaCl2 (aq) + 2H2O (l) • The water can be removed by evaporation • How do antacid tablets work in our stomach which contains HCl?

  25. Review • Complete the revision question 4 page 323

  26. Acid – Base terms • Conjugate acid-base pairs • In an acid-base reaction, the substance acting as the acid gives away a proton and forms a conjugate base. • The substance acting as a base, after accepting a proton, forms its conjugate acid. • An acid-base reaction will therefore form two conjugate pairs, with the formulas of each pair member differing by the H+ ion that was transferred.

  27. Conjugate Pairs

  28. Learning Check! Label the acid, base, conjugate acid, and conjugate base in each reaction: HCl + OH-   Cl- + H2O H2O + H2SO4   HSO4- + H3O+

  29. Polyprotic Acids • A polyprotic acid can donate more than one proton • Acids can be classified as monoprotic, diprotic or polyprotic depending on the actual number of protons that can be donated • EgHCl – monoprotic (only one to donate) • Eg (Phosphoric acid )H3PO4 – triprotic (3 to donate)

  30. Amphiprotic substances and ampholytes • Amphiprotic substances and ampholytes are substances that can act as either acids or bases. • The way they react depends on the relative strengths of the acids and bases they are being reacted with. • Water is a common example of an amphiprotic substance • Ampholytes are electrolytes of ionic substances such as HSO4- or HPO3-

  31. Review • Complete the revision questions 5 – 9 page 324

  32. Strengths of Acids and Bases • The strength of an acid or base is related to the ease with which it donates or accepts a proton • A strong acid donates protons readily • A strong base accepts protons readily • Weak acids or bases do not donate or accept protons readily

  33. Strengths of Acids and Bases • Conductivity is also related to strength. • A strong acid will react nearly to completion in water and produce many ions, therefore conducting electricity (a good electrolyte) • Write the equation for HCl reacting in water • A weak acid will not react to completion and its solution will be a poor conductor of electricity because not many ions are produced. • Write the equation for acetic acid CH3COOH reacting in water

  34. Strengths of Acids and Bases • The strength of a base also affects its conductivity • A base is strong if it produces many hydroxide ions in solution because the hydroxide ions readily accept protons • Write the equation for NaOH dissociating • Ammonia is a weak base and does not readily dissociate, therefore it is a poor conductor of electricity • NH3 (aq) + H2O (l) NH4+ (aq) + OH- (aq)

  35. Strong and Weak Acids/Bases The strength of an acid (or base) is determined by the amount of IONIZATION. HNO3, HCl, H2SO4 and HClO4 are among the only known strong acids.

  36. Strong and Weak Acids/Bases • Generally divide acids and bases into STRONG or WEAK ones. STRONG ACID:HNO3 (aq) + H2O (l) ---> H3O+ (aq) + NO3- (aq) HNO3 is about 100% dissociated in water.

  37. Strong and Weak Acids/Bases • Weak acids are much less than 100% ionized in water. One of the best known is acetic acid = CH3CO2H

  38. CaO Strong and Weak Acids/Bases • Strong Base:100% dissociated in water. NaOH (aq) ---> Na+ (aq) + OH- (aq) Other common strong bases include KOH andCa(OH)2. CaO (lime) + H2O --> Ca(OH)2 (slaked lime)

  39. Strong and Weak Acids/Bases • Weak base:less than 100% ionized in water One of the best known weak bases is ammonia NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)

  40. Weak Bases

  41. Review • Complete the revision questions 10 – 12 page 327

  42. Strength vs Concentration • The strength of a solution is determined by the number of ions present • Strong acid – many ions in solution • Weak acid – few ions in solution • Concentration refers to the amount of an acid or base that is dissolved in a given volume of water • It is possible to have a weak, concentrated acid or a dilute solution of a strong acid.

  43. The pH Scale • The pH scale is usually applied over a range from 1 to 14 • 7 = _____________ ? • 1 – 6 = ___________ ? • 8 – 14 = ____________ ?

  44. pH testing • 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 acid, >7 base) • Universal indicator (multi-colored) • Indicators like phenolphthalein • Natural indicators like red cabbage, radishes

  45. Paper testing • Paper tests like litmus paper and pH paper • Put a stirring rod into the solution and stir. • Take the stirring rod out, and place a drop of the solution from the end of the stirring rod onto a piece of the paper • Read and record the color change. Note what the color indicates. • You should only use a small portion of the paper. You can use one piece of paper for several tests.

  46. pH paper

  47. pH meter • Tests the voltage of the electrolyte • Converts the voltage to pH • Very cheap, accurate • Must be calibrated with a buffer solution

  48. pH indicators • Indicators are dyes that can be added that will change color in the presence of an acid or base. • Some indicators only work in a specific range of pH • Once the drops are added, the sample is ruined • Some dyes are natural, like radish skin or red cabbage

  49. Review • Read the chapter summary and note the terminology and concepts • Complete the multiple choice questions 1 – 11 page 331, 332 • Complete the review questions 4, 5 (a), (b), (d), 8, 12 (a), (b),(c), 17, 19 (a), 21

  50. Extras • Acid Base review on line • Review Acids, Bases and pH (video)

More Related