This color change will signify the endpoint, which is assumed to be close to the

Question

This color change will signify the endpoint, which is assumed to be close to the equivalence point (when the stoichiometric ratio of reactants has been reached). The titrant will only react with the indicator after the entire analyte sample has reacted with the titrant. After the NaOH has been standardized with KHP, a sample of wine (the analyte) will be titrated with a strong base (the titrant) to determine the concentration of tartaric acid in a wine sample (equation 4.2). 0 ml buret Buret clamp cd CaHsO (aq)2NaOH (aq) Erlenmeyer ask 2 H O(U)2Na (aq) GH O (aq) (4.2) Tartaric acid is assumed to be the only acid present in the wine. A quantitative amount of analyte will be placed in an Erlenmeyer flask with a few drops of indicator (Figure 3). The titrant will be placed in a buret and slowly delivered to the analyte until a permanent pale pink color is obtained. Ring stand Figure 3. Set-up for titration. Note the relative positions of the buret and flask enmeyer flask Safety Sodium hydroxide is corrosive, if you come in contact with this strong base, wash immediately with water for 15 minutes. Waste All waste produced in this experiment should be placed in the appropriately labeled waste container Materials 50 mL buret wine ring stand buret clamp KHP phenolphthalein 100 mL volumetric flask 25 ml volumetric pipet 5 ml volumetric pipet 0.1 M NaOH pipet bulbs 10 ml weighing bottles 125 mL Erlenmeyer flask Pre Laboratory Assignment After reading the procedure, answer the following on a separate sheet of paper. 1. Use a reliable source to define the following terms: analyte, titrant, endpoint, equivalence point, 2. If 18.14 mL of NaOH is required to neutralize 0.443 grams of KHP, what is the concentration of 3. How will you determine the density of your wine sample using the materials provided? Write a and buret. NaOH? step-by-step protocol identifying the appropriate glassware to be used. Verify this is a reasonable method before performing this protocol. 38

Explanation / Answer

(1)

Analyte is the compound whose concentration is to be determined.

Titrant is the compound which helps in the quantitative determination of the analyte by reacting with it.

Equivalence point is that exact point when all the analyte has reacted completely with the titrant.

End point is that when we are visually able to see some change in the solution which indicates that the recation has completed. End point comes after equivalence point.

Buret is the galssware in which the titrant is stored to add it dropwise to the analyte solution.

(2)

Moles of KHP taken = Mass/MW = 0.443/204.2 = 0.00217

Since 1 mole of KHP reacts with 1 mole of NaOH, so this means that moles of NaOH present initially must be equal to 0.00217

Using the relation:

Moles = Conc*Volume

Put the values:

0.00217 = Conc*0.01814

So,

Conc = 0.119 M

(3)

First we assume that the wine contains only tartaric acid as the sole ingredient.

Next we take 50 mL wine and pour it into a 100 mL volumetric flask.

After this we take 50 mL of the 0.1 M NaOH solution in the buret and fix it on the ring stand using the buret clamp.

Then we add a few drops of indicator phenolpthalein.

Next we keep adding the NaOH solution from the buret into the flask dropwise by continuous stirring of the flask until we see a slight pink color which is permanent and does not disappear on stirring.

At this point we stop the titration and note the volume of the base used.

Since tartaric acid is diprotic, so we use the following equation:

2*Moles of base used = Moles of acid present

2*0.1*(Volume of base used in liters) = Moles of acid present

Put the value of the volume of base consumed by subtracting the final volume from the initial volume.

This will give us the moles of acid present.

MW of tartaric acid = 150 g

So,

Mass of tartaric acid = Moles*MW = Moles*150

This will give us the mass of acid present.

Next, total mass of 50 mL wine = Mass of 50 mL water + Mass of acid present

Assuming density of water as 1 g/mL, we have:

Total mass of 100 mL wine = (50 grams + Mass of acid)

So,

Density of wine = Mass of wine / volume = (50 grams + Mass of acid)/50 = (1+0.02*Mass of acid present) g/mL

This is the protocol to be followed to determine the density of wine.

(4)

In order to prepare a 1:4 dilution of the wine sample, we take 25 mL of wine using a pipette into a volumetric flask, and then add 75 mL distilled water into it.

This makes solution of final volume 100 mL, and the wine gets diluted by a factor of 4.

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