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Howard University General Chemistry Lab. I spring 2021- Quiz 7 (Vinegar analysis) Name:

Bryce Augustine

ID: 02987204

Q1.In determining the percent acetic acid in vinegar, the mass of each vinegar sample is measured rather than the volume. Explain. Vinegar is an aqueous solution of acetic acid. When a liquid is mixed their total volume may change because of the dependency of the density of the solution on its concentration.

Q2. The vinegar were measured volumetrically (e.g. a pipet), what additional piece of data would be needed to complete the calculations for the experiment? The density would be needed because it allows us to convert from grams to mLs in an accurate way.

Q3. In the standardization of NaOH using potassium hydrogen phthalate, the procedure states that the weighed phthalate sample should be dissolved in 20 mL of distilled water and then titrated with the NaOH. A student added 40 mL of water instead of the stated amount. The effect of this deviation from procedure on the ultimate molarity of the NaOH will be:

a. b. c. d.

The resulting molarity will be too low because of this change in procedure. The resulting molarity will be unaffected by this change in procedure. The resulting molarity will be too high because of this procedure. It is impossible to predict the effect of this change in procedure

Q4. When 90 mL of water is added to 10 mL of 0.1 M sodium hydroxide, NaOH, the pH. a. b. c. d.

increases by 1. changes to 3. is unchanged because the number of mole of base has not changed. decreases by 1.

Q5. A pipette is used to transfer a base into a flask sitting under a burette filled with acid. The pipette, the flask and the burette should, respectively, be rinsed with a. b. c. d.

distilled water in all cases. base, distilled water and base. base, distilled water and acid. distilled water, base and acid.

Q6. Write a chemical equation for the dissociation of ethanoic acid (vinegar) in water

CH3COOH + H2O H3O+ + CH3COOQ7. Vinegar is an aqueous solution of acetic acid that is produced by fermentation. A 25.00-ml aliquot of a vinegar sample was taken, diluted, and titrated with 31.75 ml of 0.2550 F NaOH to the phenolphthalein end point. Calculate the g of acetic acid per 100 ml of vinegar. CH3COOH + NaOH  NaC2H3O2 + H2) 25.00 ml* X = 31.75 ml * .2550 CH3COOH = .3239 mmol/ml .3239 mmol/ml * .06005 g/mmol = .01949 g/ml .01949 g/ml * 100 = 1.945g CH3COOH per 100 ml...