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Acids and Bases

Acids and Bases. Take 2!. pH. pH depends on the concentration of hydrogen ion (H + )in the solution Lots of hydrogen ion = low pH Very little hydrogen ion = high pH. What’s concentration?. Involves the amount of solute (solute is the dissolved stuff) and the volume of the solution

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Acids and Bases

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  1. Acids and Bases Take 2!

  2. pH • pH depends on the concentration of hydrogen ion (H+)in the solution • Lots of hydrogen ion = low pH • Very little hydrogen ion = high pH

  3. What’s concentration? • Involves the amount of solute (solute is the dissolved stuff) and the volume of the solution • Demo of concentration

  4. Vocabulary • Dilute: • Verb – to make less concentrated, usually by adding solvent (water) • Adjective - of or pertaining to a solution that has a low concentration of solute

  5. Diluting acids • Does the amount of acid change when you add water to it? • What changes? • Will the pH change? • How much?

  6. Molarity (M) • Concentration is usually measured in units of molarity. It is defined as: • Molarity = • Solute could be acid or base moles!

  7. Dilution • When you add water to the acid, you dilute it, but the number of moles of acid DO NOT change. Only the volume of the liquid solution changes.

  8. Molarity Practice • If 3.00 moles of acid are added to enough water to make 3.00 liters of solution, what is the concentration (molarity) of the acid solution?

  9. Molarity Practice • If 1.00 moles of acid are added to enough water to make 4.00 liters of solution, what is the concentration (molarity) of the acid solution?

  10. Molarity Practice • If 4.00 moles of base are added to enough water to make 2.00 liters of solution, what is the concentration (molarity) of the acid solution?

  11. Molarity Practice • In 0.200 L of a 1.00 M acid solution, how many moles of acid are there?

  12. Molarity Practice • In 0.500 L of a 0.200 M acid solution, how many moles of acid are there?

  13. Neutralization • When acid and base are added: • Acid + base  water + a salt • Remember salts include almost all ionic compounds

  14. Neutralization • Example • HCl + NaOH  H2O + NaCl • This one makes water and table salt!

  15. Neutralization • Example • HCH3COO + NaOH  H2O + NaCH3COO • This one makes water and a different salt!

  16. Forming water • Water is made because the H+ from the acid and the hydroxide ion (OH-) from the base get together to form water. • If you don’t add exactly the same moles of acid and base, you will have more than just water and salt!

  17. Did I add too much Base? • How could you know whether you’ve exactly cancelled out the acid? • Ans: TITRATION!!!!!!! • And – use an indicator or check the pH

  18. Titration • Add Base carefully to acid and measure EXACTLY how much was used. • The picture shows a burette tube being used to drop base in acid.

  19. Measuring Volumes • The meniscus is the curve at the top. Measure from the bottom of the meniscus. • Notice that the low numbers are on top!

  20. Measuring Volumes • Notice that you can see if the meniscus is between lines or right on a line. • Your volume measurement should have 2 decimal places.

  21. Measuring Volumes • What volume is this indicating?

  22. Phenolphthalein • It turns pink in base – but is clear in acid. • The range is 8-9 • This needs to be swirled to see if the pink will go away!

  23. ENDPOINT • The titration is done at the ENDPOINT. • That’s where the solution stays pink! (hopefully light pink, otherwise there is too much base!)

  24. Calculations • The whole point is to calculate the concentration of the acid or base. • At the endpoint moles of acid = moles of base

  25. Calculations • And remember • Moles = molarity X volume • so MaVa = MbVb Molarity X volume = molarity X volume

  26. Practice calculations • 10.0 mL of a solution of potassium hydroxide was titrated with a 0.10 M solution of hydrochloric acid. 13.5 mL of the acid was required for neutralization. Calculate the concentration of the potassium hydroxide solution.

  27. Practice Calc. • Write down everything you know.   • ACID BASE • Hydrochloric Acid               Potassium hydroxide • Volume used = 13.5mL      Volume used = 10.0 mL Va Vb  • Conc. = 0.10 M                   Concentration=? Ma  Mb  • Then set up MaVa = MbVb

  28. Answer • 0.1M x 13.5 = Mb x 10.0 • Mb = 0.135 M

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