Common beverages may be either acidic or basic. Fruit juices, for example, get t

Question

Common beverages may be either acidic or basic. Fruit juices, for example, get their sweet taste from sugars and their sour or tart taste from weak organic acids such as citric acid. If the juice contains too much sugar it will taste bland, but too much acid and the juice will taste sour. The concentration of acids in various consumer beverages can be determined by titration with, sodium hydroxide. The main acids present in fruits and fruit juices are citric acid (found in citrus fruits), tartaric acid (found in groups) and malic acid (found in apples). All of these are classified as weak organic acids: Acid-base titrations are an extremely useful technique to determine the concentration of an acid or base in a sample. In titrating beverages such as orange juice, apple juice, and sodas that contain weak acids, the juice is called the analyze and a strong base is used an the titrant. In the titration procedure, a sodium hydroxide solution of known molarity is carefully added using a buret to a measured volume of fruit juice containing an indicator. The exact volume of sodium hydroxide that must be added to reach the indicator end point is measured and then used to calculate the concentration of citric acid in the juice. Since solid NaoH rapidly absorbs both water and carbon dioxide from the air, a solution of exact a solution cannot be prepared by weighing the solid and diluting to a certain volume. Instead, you must prepare acid of approximately the desired concentration and find its exact molarity by titrating it against the weak potassium hydrogen phthalate (KHP). We will be titrating KHP with sodium hydroxide. Look up the chemical formula for KHP and write a balanced equation of the reaction of KHP with sodium hydroxide. A 6.0 M solution of NaOH will be diluted to approximately 0.10M during this lab. Write out the steps needed to produce 1 liter of this solution. Include the calculation and glassware required. A 10.0 mL sample of a weak monoprotic acid required 12.8 mL of NaoH to reach the endpoint. If the weak acid had a concentration of 0.120 M, what was the concentration of NaOH used? Read through and record the lab procedures for part 1 and create a data table. Clean a 1 liter bottle and carefully label with _________ M NaOH and your names. Rinse the bottle with 20-30 mL of distilled water. Use your calculations from pre-lab questions #2 to make your solution of sodium hydroxide.

Explanation / Answer

3. Volume of weak acid taken = 10.0 mL.

Concentration of weak acid = 0.120 M.

Volume of NaOH required = 12.8 mL.

Note down the neutralization reaction as

HA + NaOH -----> NaA + H2O

(HA = weak acid)

At the equivalence point, moles of NaOH added = moles of HA titrated.

Moles of HA titrated = (10.0 mL)*(0.120 mol/L) = 1.2 mmole.

Moles of NaOH added = 1.2 mmole.

Concentration of NaOH added = (1.2 mmole)/(12.8 mL) = 0.09375 M (ans).

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