Reference no: EM133249922

Preparing Stock Solutions and Standardizing the Base

Hydrochloric acid and sodium hydroxide are the most common strong acids and bases used in the laboratory. Both reagents need to be standardized to learn their exact concentrations. Section 11-7 in the textbook provides background information for the procedures described below. Unknown samples of sodium carbonate or potassium hydrogen phthalate can be analyzed by the procedures described in this section.

NaOH + KHP→ NaKP + H2O

Equipment Needed	Reagents Needed
50 mL buret 10 mL beaker   4-125 mL Erlenmeyer flask  2L Erlenmeyer Flask or beaker 500 mL beaker	50% (w/w) NaOH Concentrated  37 % (w/w) HCl  Phenolphthalein indicator   Potassium hydrogen phthalate dried before lab, and stored in a desiccator.

Go to Canvas for your full prelab instructions and videos.
1. Prepare your lab notebook with procedure and expected lab data table.
2. Then, in your lab notebook, Calculate the volume of 50% NaOH that will be needed to prepare 1L of 0.1M NaOH. Show your work!
4. Calculate the volume of 12M HCl that will be needed to make 500 mL of 0.1M HCl Show your work.
5. The reaction between KHP and NaOH is: KHP + NaOH --> H2O+ NaKP. KHP has a (MM 204.22 g/mol) Calculate the mass of KHP that can be neutralized by 25 mL of 0.1M NaOH. Show this in your lab notebook

Preparing Stock Solutions of HCl and NaOH for future labs

1) Obtain approximately 1.5 L of deionized water in a 2L beaker or Erlenmeyer flask. Bring it to a boil. Boil 10 minutes, then cool to room temperature. This will be used in the preparation of your NaOH stock solution. Note that you are boiling more water than is needed!!!!! (Why would we want to start with more water than we will need, if we are boiling the water?)
2) While the water is cooling, obtain a 500 mL beaker and partially fill it with deionized water. In the hood, use a graduated cylinder to measure the approximate volume of concentrated HCl that you calculated in your pre-lab. Slowly, add the HCl to the water in the beaker, allowing it to cool if needed.
3) Obtain a 500 mL Volumetric flask. Rinse it three times with a few mL of deionized water and discard the rinse water. Add a few mL of deionized water to the flask and then transfer the diluted HCl to the volumetric flask. Fill the flask to the mark with DI water. (Note: Since this is not yet standardized, if you miss the mark a little bit, it doesn't matter. This is just a convenient
means to making approximately 500 mL of the stock solution, and will likely be a little bit more accurate.
4) Transfer the HCl solution that you have just prepared into a 1 L glass storage bottle. Label the bottle with the contents (0.1M stock HCl, your initials and date). This solution will be combined with other solutions and used in L04.
5) Now, back to the NaOH prep. Use a graduated cylinder to transfer the calculated volume of 50% NaOH from your pre-lab to the bottle of pre-boiled and cooled water. (CAUTION: 50% (w/w) NaOH is corrosive. Flood any spills on your skin with water.) Mix well and cool the solution to room temperature (preferably overnight). We are trying to make approximately 1 L of solution, total. Do your initial dilution of the base in a beaker to allow for heat dissipation, add water until you have prepared a total volume of 1L. It needn't be exact because we will standardize the solution in the next step.

Standardizing NaOH solution with KHP

1. Obtain dried primary standard grade potassium hydrogen phthalate (heated for 1 h at 105°C and stored it in a capped bottle in a desiccator).
2. Rinse a clean 50 mL buret with a few mL of DI water. If the water drains and shows no "fingers", it is clean enough to use. If needed, rinse with a few mL of EOSULF, and then rinse 7 times with a small volume of deionized water. Drain it into sink, but do NOT run the buret dry. This prevents air bubbles from lodging in the stopcock assembly.
3. Use about 2 mL of the prepared NaOH stock to rinse the inside of the buret. Drain it into sink, but do NOT run the buret dry.
4. Fill the buret with about 40 mL of your NaOH stock solution for titration. Note the Vi on the buret in your lab manual. Note the Vi is NOT 40! Vi is read from the buret. The buret notes the amount that is dispensed, not the volume contained!!! The buret should have a loosely fitted cap to minimize entry of CO2 from the air. We will use an upturned 10 mL beaker or loose flap of Parafilm to serve this purpose.
5. Based on your pre-lab calculation, weigh four samples of solid potassium hydrogen phthalate. Be sure to note the masses in your lab notebook. Transfer each to a 125 mL Erlenmeyer flask. Using a wash bottle, rinse the weighing paper into the flask so that no KHP sample is lost. Add approximately 25 mL of distilled water to the flask and swirl it to dissolve the KHP. Label each flask with the trial number and your initials. Add 3 drops of phenolphthalein to each flask and titrate one rapidly to find the end point. The end point is the first appearance of faint pink color that persists for 15 s. (The color will slowly fade as CO2 from the air dissolves in the solution.)
6. In the image below, the 2nd image is the endpoint after 15 s. The third is likely the initial color. The 4th has been overshot, and the trial should be discarded. Since the color is very pale, it is common to use a white reader card behind the flask to verify that the solution is not colorless.

7. Calculate the titer for this experiment: The titer is the mL of titrant (here, the NaOH) / g of the titrand (here the KHP). The titer is used to predict the amount of titrant needed for the remaining samples: It will allow you to obtain better results, faster.

	Mass KHP	Vi NaOH (±0.01 mL)	Projected Vf	Vf NaOH (±0.01 mL)	Volume NaOH dispensed (mL)	Titer (mL NaOH/g KHP
Trial 1 (rough)			N/A
Trial 2			Vi2 + T1*m2=
Trial 3			Vi3+T2*m3=
Trial 4			Vi4 + T3*m4=
Trial 5

8. Use the titer to calculate the volume of NaOH required for each of the other three samples and titrate them carefully. Refill the buret to about 40 mL before each trial. During each titration, periodically tilt and rotate the flask to wash all liquid from the walls into the bulk solution. Near the end, deliver less than 1 drop of titrant at a time. To do so, carefully suspend a fraction of a drop from the buret tip, touch it to the inside wall of the flask, wash it into the bulk solution by careful tilting, and swirl the solution.

9. Based on the amount of KHP used, stoichiometry, and the volume of NaOH used, calculate the standardized concentration of the NaOH that you have prepared.

10. Transfer the remaining NaOH that has now been standardized into a clean, dry Polyethylene (Nalgene) Bottle. Label the bottle (x. xxxx M NaOH standard, name, date). This solution will be used in lab 05. (Acid Titration using a pH meter)

Before you leave the lab, show a sample of the following in your lab notebook

1. Calculate the titer for each titration. This is the ratio of volume titrant vs mass of dissolved standard. Using the statistical function in your calculator, report the Mean, Std Dev'n. and %RSD for each solution. If they are within 3% of each other, you needn't do another trial. If not, you will need to do another trial.

2. Calculate the molar concentration of NaOH in one of your trials, based on the mass of KHP used and the volume of NaOH needed for the titration.

Processing the Data After Class

Report the mean molarity, Std Deviation, and %RSD for the concentration of your standard NaOH solution.

There is no formal writeup for this. Your lab report will consist of three parts, but check your rubric to make sure that you have a complete submission.

1. Raw Data table

2. The sample calculations needed to determine the concentrations and relevant statistics
(even though you have this in your notebook, record these in your report as well)

3. Discuss the types of standards, primary and secondary. Which applies to KHP? Which is your standardized solution? What are the characteristics of each type?

Attachment:- Standardizing the Base.rar