1. Review U2 S3

2. An indicator is a weak acid which changes color in response to specific change in pH. –The pH range at which an indicator molecule changes from the weak acid form to the conjugate base form is a function of the ease with which the proton can be removed from the weak acid form. Indicators

3. Thymol Blue indicator (H 2 Tb) is a diprotic indicator. Thymol blue can transfer two protons and changes from red to yellow at pH 1.2 - 2.8 and yellow to blue at pH 8.0 – 9.6 a.Write the net ionic equations for the reactions between phenol red (HPr) indicator and water. b.Predict the position of the indicator equilibrium when a drop of the indicator is added to a flask containing 50 mL of 0.100 M nitric acid. c. Predict the position of the indicator equilibrium when a drop of the indicator is added to a flask containing 50 mL of 0.100 M sodium hydroxide.

4. A sample of bog water causes is tested for pH. Samples of the bog water are tested; a drop of phenolphthalein is colorless, a drop of methyl red to be red and a drop of methyl orange to be yellow. What is the approximnate pH of the bog water?

5. Which indicator would be most suitable to show the equivalence point of this titration curve? a.Congo red b.Chlorophenol red c.Thymol blue d.1,3,5-trinitrobenzene

6. Which indicator would be most suitable to show the equivalence point of this titration curve? a.Congo red b.Chlorophenol red c.Thymol blue d.1,3,5-trinitrobenzene

7. Titrations Titration is the progressive addition of one reagent to another. –In acid-base chemistry, the reagents are aqueous solutions, one of which is either a strong acid or a strong base. –A typical titration involves progressively adding a solution of known concentration (the titrant) from a buret to a solution of unknown concentration (the sample) situated in a container below the buret

8. The amount of titrant added is just enough to completely neutralize the sample. An indicator is usually added to the sample to detect the equivalence point Equivalence point: The point at which chemically equivalent amounts of titrant and sample have reacted. Endpoint: The point at which the indicator changes color is the indicator endpoint

9. 4.pH tests of water in a holding pond at a potash production plant revealed alkaline conditions. 500.0 mL water samples from the pond were titrated with a standardized 0.0221 M hydrochloric acid solution. (a)Complete the table by calculating the missing values and calculate the average volume of HCl used in the titrations. (b)Write a chemical equation for the reaction between hydrochloric acid and potassium hydroxide. (c)Calculate the hydroxide ion concentration and the pH of the pond water. Trial 1Trial 2Trial 3 initial buret reading (mL)50.0044.7639.68 final buret reading (mL)44.7639.6834.57 volume of titrant added (mL)

10. Standards A standardized solution is one whose concentration is determined from data collected by titration. –HCl has to be standardized because it is a gas at room temperature. It is difficult to dissolve precise amounts of any gas in water. Moreover, once dissolved, tiny amounts of HCl have the tendency to escape from solution thereby reducing the concentration of dissolved HCl. –NaOH is a deliquescent or hygroscopic solid - it absorbs moisture from the air. That is, when you weigh out a sample of NaOH, you are obtaining the mass of NaOH plus the mass of the water it has absorbed from the air. If you prepare a solution using the measured mass of NaOH, its molar concentration will be slightly lower than expected because of the absorbed moisture. A primary standard or a solution that can be prepared from a pure form of the solute to a precise molar concentration. Acids Ie: HCl are standardized using a primary standard such as sodium carbonate (Na 2 CO 3 ) bases like NaOH and KOH are standardized using potassium hydrogen sulfate (KHSO 4 ) or potassium hydrogen phthalate (KHC 8 H 4 O 4 ).

11. Excess reagent Calculate the pH of a mixture formed by the addition of 5.82 mL of 0.105 mol/L HCl to 100.0 mL of 0.00250 mol/L Ca(OH) 2.

12. 5.Which compound is suitable for use as a primary standard in the standardization of a nitric acid solution? A.hydrochloric acid B.potassium hydrogen phthalate C.sodium carbonate D.sodium hydroxide 6.Which term represents the point in a titration where neither the sample nor the titrant is in excess? A.buffering capacity B.endpoint C.equilibrium D.equivalence point 7.Three samples of water from the same bog hole were filtered and tested using indicator solutions. Benzopurpurine-48 was red, methyl red was red, and methyl orange was yellow. What is the approximate pH of the bog water sample? A.4.5 B.6.0 C.greater than 4.8 D.less than 3.2

13. 8.Bromothymol blue is commonly used in acid-base titration experiments. Which term refers to the instance when bromothymol blue changes colour during a titration? A.buffer endpoint B.indicator endpoint C.sample endpoint D.titrant endpoint 9.What indicator form and colour will be visible when thymol blue indicator is added to a 1.00 M H I solution? A.H 2 Tb, red B.HTb -, yellow C.Tb 2-, blue D.Tb 2-, green 10.Which species is classified as dibasic? A.Ca(OCl) 2 B.CH 3 COOH C.H 2 SO 4 D.Na 2 S

14. 11.Which indicator should be used to detect the first equivalence point? A.methyl orange B.phenol red C.phenolphthalein D.thymolphthalein 12.Which interpretation of this titration curve is incorrect? A.the pH at the second equivalence point is 3.6 B.the sample has two ionizable protons C.the sample is dibasic D.the titrant is an acid

15. Sketch the titration curve of Ammonia with hydrochloric acid.

16. Write the neutralization equations for the reaction of sodium phosphate Na 3 PO 4 with hydrochloric acid. Sketch the titration curve. Diprotic/dibasic