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QOTD 5/14/14

QOTD 5/14/14. Please have out to be checked off: Soap reading/ prelab Qs p . 59 Qs QOTD: Rank the following solutions in order of most acidic to least acidic and explain why. 1 M vinegar (weak acid ) 1 M HCl (strong acid) 0.5 M HCl (strong acid) 1 M NaOH (strong base)

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QOTD 5/14/14

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  1. QOTD 5/14/14 Please have out to be checked off: Soap reading/prelab Qs p. 59 Qs QOTD: Rank the following solutions in order of most acidic to least acidic and explain why. 1 M vinegar (weak acid) 1 M HCl (strong acid) 0.5 M HCl (strong acid) 1 M NaOH (strong base) 1 M NH3 (weak base) Pure water

  2. QOTD Answer QOTD: Rank the following solutions in order of most acidic to least acidic and explain why. 1 M HCl (strong acid) 100% ions (excess H+) 0.5 M HCl (strong acid) 100% ions (excess H+) 1 M vinegar (weak acid) less than 100% ions (~1%) Pure water neutral 1 M NH3 (weak base) less basic than a strong base 1 M NaOH (strong base) strong base = most basic = least acidic

  3. Answers Homework Qs! (p. 59)

  4. Check-in Questions: • 1. You have a 1.0 M solution of a strong acid (HCl) and 1.0 M of a weak acid (acetic acid). Predict which will have a lower pH, and explain why: The 1.0 M HCl because it dissociates completely…more H+ means lower pH

  5. Check-in Questions: • 2. How is the Bronsted-Lowry definition of acid/base theory different from Arrhenius? The Bronsted-Lowry theory says that a base can accept a proton (H+) (in addition to donating a OH-).

  6. Homework Questions: • 1. Label the following substances as acids or bases. In each case, list the ions you would expect to form in solution: • a. HydroiodicAcid, HI • b. Rubidium Hydroxide, RbOH • c. Selenousacid, H2SeO4 • d. Phosphine, PH3 • e. Calcium hydroxide, Ca(OH)2 • f. Perchloricacid, HClO4 Acid, H+, I- Base, Rb+, OH- Acid, 2 H+, SeO42- Base, PH4+, OH- Base, Ca2+, 2 OH- Acid, H+, ClO4-

  7. 2. Consider a solution of hydrobromic acid, HBr. If you drew a particle view of HBr in water that contained 10 H+ ions, how many Br- ions would you need? Explain your thinking: 10 Br- ions (to cancel out the 10 H+ ions) • 3. Consider a solution of mangnesium hydroxide, Mg(OH)2. If you drew a particle view of this substance with 10 Mg2+ ions, how many hydroxide (OH- ) ions would you need to draw? 20 OH- ions • 4. The CO32- ion is a weak base. Explain, using Bronsted-Lowry theory, what makes this substance a base: It can accept a proton (H+)

  8. Challenge: Some solutions conduct electricity better than other solutions. Use your knowledge about the different kinds of acids and bases to explain why a 1.0 M hydrochloric acid solution is a better conductor of electricity than a 1.0 M acetic acid solution. The strong acid dissociates completely, making it easier for electricity to flow through the solution . (more ions = more moving charges)


  10. Arrhenius Theory • Acid: A substance that adds hydrogen ions, H+, to an aqueous solution • Base: A substance that adds hydroxide ions, OH-, to an aqueous solution • Not the best definition…

  11. Bronsted-Lowry Definition • Acid: Any chemical that donates a hydrogen ion, H+ • Base: Any chemical that accepts a hydrogen ion into their structure + Base Acid Proton acceptor Proton donor

  12. BAAD • Bases Accept, Acids Donate Example: HCl + H2O  Cl- + H3O+ NH3 + H2O  NH4+ + OH- Acid Base H+ Acid Base H+

  13. Other terms to know • Hydronium ion: H3O+ • Hydroxide ion: OH- • Amphoteric (or amphiprotic) : Water can act as both an acid and a base in different situations

  14. Your Turn (partner talk) H2O + HBr Br- + H3O+ Which compound is acting as an acid? Which is acting like a base? HBr H2O

  15. Your Turn (Partner talk) H2O + SO42- OH- + HSO4- Which of the compounds is acting as a base? SO42-

  16. Your Turn (partner talk) • Predict the products when phosphoric acid (H3PO4) is added to water: H3PO4 + H2O  H2PO4- + H3O+

  17. Properties of Acids • Corrosive • Sour taste • Contains hydrogen ions (H+) when dissolved in water • pH < 7 • Electrolytes (conduct electricity) • Neutralize bases http://qldscienceteachers.tripod.com/junior/chem/acid.html

  18. Examples of Acids • Hydrochloric acid (HCl) in gastric juice • Sulphuric acid (H2SO4) • Nitric acid (HNO3) • Carbonic acid in soft drinks (H2CO3) • Uric acid in urine • Ascorbic acid (Vitamin C) in fruit • Citric acid in oranges and lemons • Acetic acid in vinegar http://qldscienceteachers.tripod.com/junior/chem/acid.html

  19. Properties of Bases • Taste bitter • Slippery • Electrolytes (conduct electricity) • Base + fat = soap • Neutralize acids • Corrosive http://qldscienceteachers.tripod.com/junior/chem/acid.html

  20. Examples of Bases • Sodium hydroxide (NaOH) • Calcium hydroxide ( Ca(OH)2 ) or limewater • Ammonium hydroxide (NH4OH) or ammonia water • Magnesium hydroxide ( Mg(OH)2 ) or milk of magnesia • Many bleaches, soaps, toothpastes and cleaning agents http://qldscienceteachers.tripod.com/junior/chem/acid.html

  21. Indicators • Substances that change color when exposed to an acid or base • Can be used to identify acids and bases, even their strength • Usually a weak acid or base

  22. Examples of indicators • Litmus paper: Red for acid, blue for base • pH paper: universal indicator, compare colors to known pH • Cabbage juice: color changes in response to concentration of H+ ions • Phenolphthalein: color is clear/cloudy in an acid and pink in a base

  23. Solutions • Acidic solution: the hydronium ion concentration is higher than the hydroxide ion concentration [H+] > [OH-] • Basic solution: hydroxide ion concentration is higher than the hydronium ion concentration [H+] < [OH-]

  24. Neutral solution: concentration of hydronium and hydroxide ions is the same [H+] = [OH-] • Ex. Pure water • Created when equal quantities of an acid and base are combined

  25. pH • pH: Measures the concentration of H3O+ions • pH scale: A numeric scale used to describe the acidity of a solution from 0 to 14 • Draw the scale below 0 7 14 Increasing strength Increasing strength Acids Neutral (water) Bases

  26. pH Scale Acidic Neutral solution Basic http://staff.jccc.net/pdecell/chemistry/phscale.html

  27. Strong vs. Weak Acids and Bases • Strong Acid or Base: all of the molecules dissociate (split apart) into ions • Weak Acid or Base: Only some of the molecules actually dissociate • Not as many H+ or OH-ions in solution

  28. Strong base Weak base

  29. Soap! • Let’s review the soap procedure… • SAFETY! What will you use to protect yourself? GOGGLES FOR EVERYONE! Gloves for the person who pours the NaOH and mixes it. • How hot will you make the NaOH and Oils? 50 degrees! They both need to be around 50 (+ or – a couple degrees)

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