Question

i am lost woth Titration, please help... i was able tondo my virtual lab and get the data needed... but i dont understand what to do on the remaining problems! please help!

Experiment 11 part 2 ACID BASE TITRATIONS OBJECTIVES 1. To learn general titration techniques 2. To generate a standardized titrant. 3. To determine the concentration of various acid samples. PROCEDURES - WORK ALONE INTRODUCTION In part 1 you practiced standardizing a titrant: using KHP is a common procedure for this. In this section, you will use a stardardized solution to test various unknowns. First you will use a base (NaOH) to titrate an unknown acid. Then you will develop your own method, using an acid (HCI) to titrate an unknown base PART 2: TESTING UNKNOWN ACID SOLUTION A Background-review if needed from part 1 1. Watch the video about titrations posted on Moodle 2. Use the link titled "virtual lab demo' to learn how to use the virtual lab workbench Note: we recommend using "precise" mode when entering the volume you wish to transfer. B. Analyzing an unknown acid 1. Open the link in Moodle titled "expt 11 part 2: unknown acids and bases." 2. Add the following to your workbench: the unknown acid and phenolphthalein indicator (under solutions), a 25 mL pipette and a 250 mL Erlenmeyer flask (under "glassware 3. Transfer 25 mL of the unknown acid to the flask using the pipette, and add 0.40 mL of phenolphthalein from the dropper bottle. Rename the flask "unknown acid indicator and make three more duplicates of (right click 4 Remove the solutions (except for the unknown acid indicator) and pipette from your workspace. Add a 50 mL burette and the 0.1 M NaOH (under strong bases" in "solutions) to your workspace. Add 520 mL of 0.1 M NaOH to the burette 5. Drag the burette over the sample flask to set up your titration Record the initial meniscus reading (0.00 ml) in table 2. Enter 0.10 mL in the volume box for the burette. You may want to zoom in the screen to see the endpoint more easily (view zoom in). Click the "pour button until the solution turns pink (dont click too fast, or you will miss when the pink first appears!). Record the final burette reading 6. Repeat this process using two of your duplicate samples. You will need to refill your burette with more NaOH. 7. For the last (fourth) flask of unknown acid, you will use a different titrant concentration. Right click on the burette and choose "remove liquid." Add 1M NaOH solution to your workspace, and use it to fill your burette 8. Record the initial burette reading, then titrate the last acid sample at 0.05 ml per dick Record the final reading when the indicator turns pink Table 2: Titration of Unknown Acid Trial 1 Trial 2 25.4 10.7 Volume of unknown acid 25.4mL Initial burette reading 0.0 Final burette reading 16.7 Volume of base used 10.7 Trial 3 25.4 21.4 3a. 10.7 Trial 4 (1 M NaOH) 25.4 0.0 1.a 21.4 10.7

Answer 1

*CORRECTION: The volume of unknown acid in the table should be 25 mL. The 0.4 mL of the indicator should not be counted as an unknown amount of acid.  

Q1)

Trial 1

The volume of NaOH required for complete titration (V1) = 10.7 mL

Molarity of NaOH (M1) = 0.1 M

Volume of unknown acid(V2) = 25 mL

Molarity of unknown acid (M2) = to be found = x

so, application of dimensional analysis yields the formula

{Where n-factor of diprotic acid is 2}

MV1 -factor x V2 n

Plugging the values

0.1M X 10.7mL C 2 x 25ml

therefore x = unknown concentration = 0.0214 M

Trial 2

The volume of NaOH required for complete titration (V1) = 10.7 mL

Molarity of NaOH (M1) = 0.1 M

Volume of unknown acid(V2) = 25 mL

Molarity of unknown acid (M2) = to be found = x

so, application of dimensional analysis yields the formula

{Where n-factor of diprotic acid is 2}

MV1 -factor x V2 n

Plugging the values

0.1M X 10.7mL C 2 x 25ml

therefore x = unknown concentration = 0.0214 M

Trial 3

The volume of NaOH required for complete titration (V1) = 10.7 mL

Molarity of NaOH (M1) = 0.1 M

Volume of unknown acid(V2) = 25 mL

Molarity of unknown acid (M2) = to be found = x

so, application of dimensional analysis yeilds the formula

{Where n-factor of diprotic acid is 2}

MV1 -factor x V2 n

Plugging the values

0.1M X 10.7mL C 2 x 25ml

therefore x = unknown concentration = 0.0214 M

So molarities for Trial 1 = 0.0214 M , Trial 2 = 0.0214 M , Trial 3 = 0.0214 M & Avg = 0.0214 M

Q 2)

Trial 4

The volume of NaOH required for complete titration (V1) = 10.7 mL

Molarity of NaOH (M1) = 1 M

Volume of unknown acid(V2) = 25 mL

Molarity of unknown acid (M2) = to be found = x

so, application of dimensional analysis yields the formula

{Where n-factor of diprotic acid is 2}

MV1 -factor x V2 n

c = IM x 1.2mL 2 x 25mL

Therefore,for Trial 4, x = 0.024 M = molarity

The molarity determined by Trial 4 for appreciably matches with molarities determined by trials 1 to 3. ( small error of 0.0026 was observed). This suggests that the concentration of an unknown acid can be determined by both a small concentration of base and a high concentration of Base.

Q 3)

The volume required by 1 M NaOH was 1.2 mL whereas volume required by 0.1 M NaOH was 10.7 mL i.e volume of Base required for 1 M NaOH was far less than the volume of base required for 0.1 M NaOH.

The reason is that, no. of moles of the base in 1.2 mL NaOH = no. of moles of base in 10.7 mL 0.1 M NaOH

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