1. a. De%uFB01ne the analyte in a titration. b. Is the indicator generally added

Question

1. a. De%uFB01ne the analyte in a titration.

b. Is the indicator generally added to the titrant or the analyte in a titration?

2. a. What is the primary standard used in this experiment? De%uFB01ne a primary standard.

b. What is the secondary standard used in this experiment? De%uFB01ne secondary standard.

3. Distinguish between a stoichiometric point and an endpoint in an acid%u2013base titration

4. a. When rinsing a buret after cleaning it with soap and water, should the rinse be dispensed through the buret tip or the

top opening of the buret? Explain.

b. In preparing the buret for titration (Experimental Procedure, Part A.5), the %uFB01nal rinse is with the NaOH titrant rather than with deionized water. Explain.

c. How is a %u201Chalf-drop%u201D of titrant dispensed from a buret?

5. In Part A.1, a 4-g mass of NaOH is dissolved in 5 mL of water. In Part A.3, a 4-mL aliquot of this solution is diluted to

500 mL of solution. What is the approximate molar concentration of NaOH in the diluted solution? Enter this information on your Report Sheet.

6. a. A 0.397-g sample of potassium hydrogen phthalate, KHC8H4O4 (molar mass = 204.44 g/mol) is dissolved with 50

mL of deionized water in a 125-mL Erlenmeyer %uFB02ask. The sample is titrated to the phenolphthalein endpoint with

16.22 mL of a sodium hydroxide solution. What is the molar concentration of the NaOH solution?

b. A 25.00-mL aliquot of a nitric acid solution of unknown concentration is pipetted into a 125-mL Erlenmeyer %uFB02ask

and 2 drops of phenolphthalein are added. The above sodium hydroxide solution (the titrant) is used to titrate the nitric acid solution (the analyte). If 12.75 mL of the titrant is dispensed from a buret in causing a color change of the

phenolphthalein, what is the molar concentration of the nitric acid solution?

Explanation / Answer

1.B. Indicator is genrally added to the analyte in a titration.

3. End point refers to the point at which the indicator changes colour while stoichiometric point reefers to the point at which the amount of titrant added is same as the amount of analyte taken.

4.a. when rinsing a burette with soap and water, after rinsing the rinse should be dispensed slowly through the burette tip so that there is no trace of the titrant(or any chemical) in the burette(towards the tip).

b. The reason behind this is that we want to minimise all contaminants that may stay in the burette and affect the concentration of the titrant. If we rinse the burette with deionized water, water because of it high affinity to glass, a few droplets of water may still stick to the burette. THis might affect the concentration of our titrant( in this case NaOH).

c.Carefully open the stopcock just barely and let a drop grow on the tip without allowing it to get too large. Then, touch the tip of the buret to the side wall of the flask, and wash the drop into the flask with water.

5.

Molarity = No.of moles of NaOH in 1000ml of solution

Molar mass of NaOH= 40g

Mass of NaOH taken =4g

Therefore, no. of moles of NaOH in 5ml of solution=0.1

No.of moles in 1000ml of solution = 0.1/5 * 1000 =20

Molarity=20M

Now this is diluted to 500 ml.

According to molarity equation, M1 * V1 =M2 * V2

Here M1=20

          V1=4ml

         V2=500ml

        M2=??

M2= (20*4)/500 = 0.16M (Ans.)

6.a.

Well you need to know amount of NaOH added to make 22ml of the solution inorder to calculate the molarity. SAy u had added x gm.

In that case, molarity of NaOH = ( x/40)/0.022 =M1(say)

b.

Let M1= Molarity of titrant(NAOH)= 0.16M

      M2= Molarity of NItric acid=??

      V1= Volume of titrant consumed = 12.75ml

      V2= Volume of nitric acid taken = 25ml

M1 * V1 = M2 * V2

M2=(M1 * V1)/V2 = (M1 * 12.75)/25

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