1 / 26

Understanding Acids, Bases, and pH Calculations in Chemistry

In this lesson, we explore the properties of acids and bases, focusing on their dissociation reactions and pH calculations. Students will work collaboratively on practice problems, including writing complete dissociation reactions for various acids and bases, such as HNO3 and NaOH, and calculating pH and pOH values. The objective is to understand the principles of weak acids and bases, including Ka and Kb equations. Remember to prepare for the open-note quiz tomorrow and review the concepts covered in previous classes.

yul
Télécharger la présentation

Understanding Acids, Bases, and pH Calculations in Chemistry

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. Unit 12: Acid and Bases Chapter 19

  2. 4th Hour • I am gone today so you will go through this Powerpoint to get the notes for objective 38 and the beginning of 39. • Remember, there is an open-note quiz tomorrow and I expect a good report from the sub.

  3. Before we get to the new material, I want to get an idea of how you are doing on the material from the previous few days. • Work on the following problems with the person sitting next to you. • Record your answers on a separate piece of paper (one per group).

  4. Name the following: • HNO3 • Mn(OH)3 • HBr • CuOH • H3PO3

  5. Write the complete dissociation reaction for the following: • HNO3 + H2O  • H2CO3 + H2O 

  6. Calculate the pH for the following. • [H3O-] = 0.0008 M • HCl + H2O  H3O- + Cl- [HCl] = 0.02 M • NaOH Na+ + OH- [NaOH] = 0.036 M

  7. Turn your answers. • At this point, we will begin objective 38. • This objective deals with weak acids and weak bases.

  8. Writing Kaequations • The same principles that apply to equilibrium equations will also apply to acids and bases. • For example: HBr(aq) + H2O(l) H3O+(aq) + Br-(aq) Ka =

  9. Using K equations • Most commonly, these K equations are used to determine the pH of a substance. • This is done by calculating the concentration of the hydronium ion. Ka= • Once that concentration is known, use the pH equation: -log[H3O+]

  10. Example HF(aq) + H2O(l) H3O+(aq) + F-(aq) • Given the following equation, calculate the pH with the following information. • [HF] = 0.5M • Ka = 7.2 x 10-4

  11. Example HF(aq) + H2O(l) H3O+(aq) + F-(aq) • Given the following equation, calculate the pH with the following information. • [HF] = 0.5M • Ka = 7.2 x 10-4 First, write the Ka equation.

  12. Example HF(aq) + H2O(l) H3O+(aq) + F-(aq) • Given the following equation, calculate the pH with the following information. • [HF] = 0.5M • Ka = 7.2 x 10-4 Second, fill in the numbers. Since every HF breaks into H3O+ and F-, then we can assume that they both have the same concentration.

  13. Example HF(aq) + H2O(l) H3O+(aq) + F-(aq) • Given the following equation, calculate the pH with the following information. • [HF] = 0.5M • Ka = 7.2 x 10-4 X2 = 3.6 x 10-4 X = 0.019 M = [H3O+] Third, solve for X.

  14. Example HF(aq) + H2O(l) H3O+(aq) + F-(aq) • Given the following equation, calculate the pH with the following information. • [HF] = 0.5M X = 0.019 M = [H3O+] • Ka = 7.2 x 10-4 -log [0.019] = pH pH = 1.72 Finally, solve for pH.

  15. Kb • It is simple to calculate the pH for acids using a Ka equation because the hydronium ion (H3O+) concentration can be solved for. • For bases though, it is the hydroxide ion that is solved for: Fe(OH)2(aq) Fe+2(aq) + 2OH-(aq) Thus: Kb =

  16. Kb • Once [OH-] is known, it is possible to calculate pOH • pOH= -log[OH-] • Since most bases are aqueous solutions, we can use the water dissociation to complete the problem. • pKw=pH + pOH

  17. Kb Recap • Write the dissociation equation. • Calculate [OH-] from the Kb equation. • Determine pOH • Use the water dissociation to determine pH: • 14 = pH + pOH

  18. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M • [Ca+2] = 0.0136 M • Kb = 3.7 x 10-3

  19. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M • [Ca+2] = 0.0136 M • Kb = 3.7 x 10-3 First, write the Kb equation.

  20. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M • [Ca+2] = 0.0136 M • Kb = 3.7 x 10-3 Second, fill in the numbers.

  21. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M X2 = 1.36 x 10-2 • [Ca+2] = 0.0136 M • Kb = 3.7 x 10-3 x = 0.12 M = [OH] Third, solve for X.

  22. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M x = 0.12 M = [OH] • [Ca+2] = 0.0136 M -log [0.12] = pOH • Kb = 3.7 x 10-3 0.93 = pOH Fourth, solve for pOH.

  23. Example • Ca(OH)2(aq) Ca+2(aq) + 2OH-(aq) • Calculate the pHgiven the following information: • [Ca(OH)2] = 0.05 M 0.93 = pOH • [Ca+2] = 0.0136 M 14 = pH + pOH • Kb = 3.7 x 10-3 14 = pH + 0.93 pH = 13.07 Fifth, solve for pH.

  24. 39 Neutralization • When acids and bases react, they will create a neutralization reaction. • This is because the pH begins to return to 7 (neutral) • Neutralization reactions are essentially double replacement reactions in which the products are always a salt and water. • A salt does not refer to NaCl but rather the product of an acid/base reaction. Acid + Base  Salt + Water

  25. Two Examples • HCl + NaOH H2O + NaCl • 2HBr + Ca(OH)2 2H2O + CaBr2 Acid Base Water Salt Remember to balance the equations

  26. The rest of class is designated to work on your homework packet. • Remember, we have an open-note quiz tomorrow.

More Related