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antiseptic1488 [7]
3 years ago
8

A 0.7834 g sample of a primary standard KHP was titrated with 38.45 mL of NaOH solution to a phenolphthalein end-point. What is

the molarity of the NaOH solution?
Chemistry
1 answer:
Zinaida [17]3 years ago
6 0

Answer:

0.0998 M

Explanation:

KHP is a weak <em>monoprotic</em> acid. This means that t<u>he moles of acid are equal to the moles of OH⁻ that were added in the titration</u>.

KHP Molecular weight = 204.22 g/mol

  • moles KHP = 0.7834 g ÷ 204.22 g/mol = 3.836x10⁻³ mol KHP

So  3.836x10⁻³ moles of OH⁻ were added in the titration. With moles and volume we can <u>calculate the molarity of the NaOH solution</u>:

38.45 mL ⇒ 38.45/1000 = 0.03845 L

  • 3.836x10⁻³ mol OH⁻ / 0.03845 L = 0.0998 M
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Answer:

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Explanation:

The solubility of NaCH₃CO₂ in water is ~1.23 g/mL. This means that at room temperature, we can dissolve 1.23 g of solute in 1 mL of water (solvent).

<em>What would be the best method for preparing a supersaturated NaCH₃CO₂ solution?</em>

<em>a) add 130 g of NaCH₃CO₂ to 100 mL of H₂O at room temperature while stirring until all the solid dissolves.</em> NO. At room temperature, in 100 mL of H₂O can only be dissolved 123 g of solute. If we add 130 g of solute, 123 g will dissolve and the rest (7 g) will precipitate. The resulting solution will be saturated.

<em>b) add 130 g of NaCH₃CO₂ to 100 mL of H₂O at 80 °C while stirring until all the solid dissolves, then let the solution cool to room temperature. </em>YES. The solubility of NaCH₃CO₂ at 80 °C is ~1.50g/mL. If we add 130 g of solute at 80 °C and let it slowly cool (and without any perturbation), the resulting solution at room temperature will be supersaturated.

<em>c) add 1.23 g of NaCH₃CO₂ to 200 mL of H₂O at 80 °C while stirring until all the solid dissolves, then let the solution cool to room temperature.</em> NO. If we add 1.23 g of solute to 200 mL of water, the resulting solution will have a concentration of 1.23 g/200 mL = 0.00615 g/mL, which represents an unsaturated solution.

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