Ch.4 - Reactions in Aqueous Solution

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.4 - Reactions in Aqueous Solution

Problem 84

Chapter 4, Problem 84

The distinctive odor of vinegar is due to acetic acid, CH3COOH, which reacts with sodium hydroxide according to: CH3COOH1aq2 + NaOH1aq2¡ H2O1l2 + NaCH3COO1aq2 If 3.45 mL of vinegar needs 42.5 mL of 0.115 M NaOH to reach the equivalence point in a titration, how many grams of acetic acid are in a 1.00-qt sample of this vinegar?

Verified step by step guidance

Step 1: First, we need to convert the volume of NaOH from mL to L. We know that 1 L = 1000 mL. So, 42.5 mL = 42.5/1000 = 0.0425 L.

Step 2: Next, we can calculate the moles of NaOH using the molarity formula. Molarity (M) = moles/volume(L). So, moles of NaOH = Molarity * Volume = 0.115 M * 0.0425 L.

Step 3: From the balanced chemical equation, we can see that the reaction between acetic acid and sodium hydroxide is a 1:1 ratio. Therefore, the moles of acetic acid will be equal to the moles of NaOH.

Step 4: Now, we can calculate the mass of acetic acid using the formula: mass = moles * molar mass. The molar mass of acetic acid (CH3COOH) is approximately 60.052 g/mol.

Step 5: Finally, we need to find out how many grams of acetic acid are in a 1.00-qt sample of vinegar. We know that 1 qt = 946.353 mL. So, if 3.45 mL of vinegar contains the mass of acetic acid we calculated, then 1.00 qt of vinegar will contain = (mass of acetic acid in 3.45 mL) * (946.353/3.45).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Titration

Titration is a quantitative analytical technique used to determine the concentration of a solute in a solution. It involves the gradual addition of a titrant, a solution of known concentration, to a sample until the reaction reaches the equivalence point, where the amount of titrant equals the amount of substance in the sample. This method is commonly used in acid-base reactions to find the concentration of acids or bases.

Molarity

Molarity is a measure of concentration defined as the number of moles of solute per liter of solution. It is expressed in moles per liter (M) and is crucial for calculations in titration, as it allows for the determination of how much of a reactant is needed to react with a given amount of another substance. Understanding molarity is essential for converting volumes and concentrations during titration calculations.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the relationships between the quantities of reactants and products in a chemical reaction. It is based on the balanced chemical equation, which provides the mole ratios needed to calculate the amounts of substances involved. In the context of the titration question, stoichiometry is used to relate the volume and concentration of sodium hydroxide to the amount of acetic acid present in the vinegar.

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