Question

we have 1.5 g final product for following experiment. how can I draw acid- base curve for following experiment?

Experimental procedure Weigh approximately 2.5 gof benzoic acid contaminated withtable salt (NaCl) as precisely as possible (record the exact quantity). Transfer the solid to a 100 mL separatory funnel and add 30 mL of ethyl acetate. In a 50 mL beaker, add 20 mL of water and 1.0 mL of 3 M hydrochloric acid. Transferthe mixtureto the separatory funnel. The solid crystals will dissolve in their suitable solvents: NaCl will dissolve in water and the benzoic acid in the ethyl acetate.Insert the glass stopper of the separatory funnel and holding it tightly in its place with your thumb turn the separatory funnel upside down twice. When the tip of the separatory funnel is pointing up, open the stopcock and release the pressure. Repeat this step several times until there is no more gas escaping (“no hissing” sound).Clamp the separatory funnel from a stand and observe these paration of the two phases.The organic phase is on top and the aqueous phase is at the bottom of the separatory funnel.Carefully drain the lower, water (aqueous) phase into a beaker. Add another10 mL of water to the separatory funnel and repeat the extraction (“wash”) .

Report:At this point, where is our product and in what ionization state is it? Where is the NaCl?

Add 20 mL of 2 N NaOH solution to the separatory funnel and repeat the extraction. Allow the layers to separate and carefully drain the aqueous phase into a clean 100mL beaker. Be careful not to allow any ethyl acetate from the upper organic phase to drip in to the beaker.The NaOH solution neutralises the benzoic acid from the organic phase and converts it into benzoate ion, negatively charged, that issoluble in the aqueous phase.Measure 10 mL of 3 N HCl solution and slowly add it to the aqueous extract while stirring it with a glass rod. The sodium benzoate is converted back into benzoic acid. Check the pH with pH paper to insure that the final solution has a pH of 2.0. If not, add additional hydrochloride solution drop wise until a pH of 2.0is attained

Cool the solution to below 10°C by placing the beaker in a larger vessel containing ice and water. A white solid should precipitate out. Separate the product by vacuum filtration, using pure, ice cold water (no more than 10 mL) to transfer any solid which remains in the beaker and to wash the solid on the filter. Air-dry the solid and then dry it in a drying oven.Once dry, transfer your product to a pre-weighed (tared) vial. Record the weight of the solid.Report:What is the purpose of pH 2.0? What is in each phase produced through the course of the procedure?What is the % yield of the experiment?

Answer 1

• At this point, the Benzoic Acid is absolutely Neutral in Ethyl Acetate, it isn't ionised. NaCl is in the Aqueous layer.
• The purpose of pH=2 is to ensure the Complete precipitation of Benzoic Acid, otherwise some Benzoic Acid still may be present as Sodium Benzoate.
• After addition of NaOH, Benzoic Acid forms the Sodium Benzoate Salt and goes into Water. After seperating the Aqueous layer from ethyl Acetate, Sodium Benzoate is again converted to Benzoic Acid, on attainment of pH 2. This Benzoic Acid is insoluble in Water and thus precipitates out from the Aqueous phase as solid.
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