Question

1. Why is it important to monitor the pH of wine?

2. In examining the pH scale, determine which values are acidic, basic, and neutral.

3. Explain in detail and show your calculations as to how you will make 100.0 mL of 0.050 M NaOH from a 1.00 M stock solution.

4. What is the purpose of a “scout” titration?

Answer 1

1.) As the pH of a wine is critical not only to its flavor but to nearly every aspect of the wine. According to wine maker Alison Crowe of Winemaker Magazine “pH is the backbone of a wine”. pH is a numerical measurement of the acidity or alkalinity of a chemical solution. The typical pH range for most wines is between 2.90 and 4.00, with the vast majority of wines ranging between 3.20 and 3.80. Red wines will often have a higher pH, between 3.40-3.80, and whites wines will normally be in the range of 3.20 – 3.50. Some wines will test these limits, but most will conform. Winemakers must intervene, as needed or desired, to bring the wine back into the proper pH range.

Sulfur Dioxide is an important part of winemaking because it protects wine from oxidization and microbial contamination during aging and storing. The amount of SO2 used is closely related to the pH of the wine, as wines with lower pH will need less free SO2 to protect them.

As another example, bacteria used to conduct the malolactic fermentation (MLF) are sensitive to low pH and high SO2 levels. Malolactic bacteria generally need a pH above 3.2 and SO2 levels below 10 mg/L; these characteristics vary by bacterial strain.

Not only that, along with total titratable acidity (TA), pH can confirm high or low acid levels and the gustatory impacts in a wine. Any deficiencies can be addressed by increasing acidity to decrease pH, and vice versa, reducing acidity to increase pH. The real value in monitoring pH here is the possibility of having to deal with the more challenging cases of high-TA/high-pH or low-TA/low-pH wines.

These are the main reasons behind the monitoring of pH of wine for getting the better taste of a wine amongst the other wines.

2.) The pH scale measures how acidic or basic a substance is. The pH scale ranges from 0 to 14. A pH of 7 is neutral. A pH less than 7 is acidic. A pH greater than 7 is basic.​

3.) Here's the calculation:
0.100 L * 0.050 mol NaOH/L = 0.0050 moles NaOH.
1000 mL 1.00 M stock NaOH sol'n contains 1.00 moles NaOH.
0.0050 / 1.00 * 1000 mL = 5 mL so, 5 mL stock is made up to total volume of 100 mL with water.

4.) The purpose of scout titration is to determine the approximate amount of titrant needed.

a. With the help of a pipet which is to deliver a known amount of the analyte to the Erlenmeyer flask which has been cleaned and rinsed with distilled water. Since you are concerned with the number of moles in the volume of analyte dispensed from the pipet, the flask does not need to be completely dry before adding the analyte.

b. If you are going to be using a magnetic stir plate, put a clean, dry stir bar into the flask and place the flask on the stir plate. Adjust the water flow so that the stir bar is spinning but not splashing solution onto the walls of the container.

c. Record the initial buret reading. Add titrant from the buret to the flask while stirring magnetically or swirling the flask with your hand. Close the stopcock when the endpoint is seen. Record the final buret reading again. Calculate the amount of titrant needed to reach the endpoint.