Question

CHEM LAB

hello can someone help me come up with a procedure for this lab

it is an standarization of acid and base solution

• Each student will receive approximately 100 mL of an unknown HCl. The approximate concentration of HCl will be 0.1 M or 1.0 M. There will be a common container with NaOH. The approximate concentration of NaOH will be 0.1 M or 1.0 M. You will be given the approximate concentrations of NaOH and HCl on the day of the experiment, but in all cases, the concentration of one reagent will be 10 times that of the other reagent. The Virtual Lab program provides reagents for both scenarios and may be used to devise the experimental procedure ahead of time. Solid KHP will be available, but the calculated amount must be approved by the TA before you will be allowed to proceed. Prepare 100.0 mL of KHP solution. • Each student determines the concentration of both the NaOH and the HCl and records all data on their Experimental Design Form. At least two titrations are required for each reagent; if the titrations for a reagent do not agree within 0.15 ml, a third titration must be performed Discussion with other students is not permitted. You may ask your TA for assistance at any time. Note however, that the TA will not answer any direct questions about the procedure but will help students find their own answers. Marks will be assigned based on the accuracy of each student's result.

Answer 1

This is a double titration experiment meaning that two different sets of titrations need to be performed to standardise NaOH followed by HCl.

PREPARATION OF KHP SOLUTION:

We can prepare 1M KHP solution for the first titration to standardise NaOH using primary standard, KHP. Since the concentration of NaOH is to vary between 0.1 M and 1M, if 1M KHP solution is taken it would lead to consumption of KHP between 2mL to 20mL. (Assuming that 20mL of given concentration of NaOH is taken).

Molar Mass of KHP = 204.22 g mol^{​​​​-1}

To prepare 1M KHP solution in 100 mL, the following calculation is performed.

Since we know that Serce we brons that 1M = 1 mol 1 L 204.2 29 of KHP - 1000 mL of solution = KHP solution. 1M 7 хо КНР 100 mL of solution = 1M KHP solution 2 of KHP X 1M 100 mL 204. 22 g * IM 1000 mL x = 204.229 X1M X 100 mL 1MX 1000 mL >> X = 20.4229 Hence 20.4229 of KHP is required to prepare 1M KHP solution in 100mL.

20.422 g of KHP is dissolved in minimum quantities of warm water and the solution is then made up to 100mL in a standard volumetric flask.

The solution is homogenised and labelled.

TITRATION - 1: Standard KHP vs NaOH

1. The prepared KHP solution is taken in a burette.

2. 20mL of the given NaOH solution is transferred into a conical flask and added with 2 drops of phenolphthalein.

3. This will turn the solution to pink colour.

4. Begin the titration by turning the knob of the burette to release the KHP solution into the conical flask to react with the NaOH solution. Ensure KHP solution is added drop wise and slowly.

5. Swirl the conical flask regularly to ensure the reaction mixture is homogenised as the reaction takes place.

6. At the end point, the reaction mixture will turn colourless.

7. The burette reading at the end point is noted.

8. Concentration of NaOH solution is calculated using the formula.

My = M₂ V2 -> M, - moority of KHP solution = 1M - v, = burette reading of KHP solution - at end point (in mL) M₂ = molarity of given NaOH = 'x' solution V = volume of NaOH taken = 20 mL.

9. The experiment is repeated till concordant readings are obtained.

NOTE: KHP solution is taken in the burette instead of NaOH because NaOH being a base is slippery and may be problematic during wash up. Phenolphthalein gives pink colour in alkaline medium and is colourless in acidic medium. Hence the endpoint is marked by the pink colour disappearing.

TITRATION - 2: Standard NaOH vs HCl

1. The given HCl solution is taken in a burette.

2. 20mL of the standardised NaOH is taken in a conical flask and added with 2 drops of phenolphthalein. The solution becomes pink in colour.

3. Titration is begun by turning the knob of the burette to release the HCl solution dropwise and slowly.

4. The conical flask is continuously swirled to homogenise the reaction mixture.

5. Endpoint is marked by the disappearance of pink colour of the solution.

6. Burette reading is marked at the endpoint.

7. Concentration of unknown HCl solution is calculated as follows.

| MY, = M₂ V2 | = M = molarity of Hel solution = x N = volume of Hal used = burette reading at the end point (in ml) M₂ = molarity of NaOH solution = from previous titration V = volume of NaOH taken = 20mL.

8. The titration is repeated till concordant reading are obtained.

NOTE: HCl is taken in the burette instead of NaOH because NaOH being slippery is problematic during wash up. HCl on the other hand is easier to wash off.