How would you prepare 250 mL of a 0.100 M solution of fluoride ions from solid CaF2? Specify the glassware that should be used.

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insert step 1> Determine the molar mass of CaF_2 by adding the atomic masses of calcium (Ca) and two fluorine (F) atoms.

insert step 2> Calculate the moles of fluoride ions needed using the formula: moles = molarity \(\times\) volume (in liters).

insert step 3> Since each mole of CaF_2 produces two moles of fluoride ions, divide the moles of fluoride ions by 2 to find the moles of CaF_2 required.

insert step 4> Convert the moles of CaF_2 to grams using the molar mass calculated in step 1.

insert step 5> Use a balance to weigh the calculated mass of CaF_2, dissolve it in a small amount of distilled water in a beaker, transfer the solution to a 250 mL volumetric flask, and fill to the mark with distilled water.

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주요 개념

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Molarity

Molarity (M) is a measure of concentration defined as the number of moles of solute per liter of solution. To prepare a specific molarity, one must calculate the required amount of solute based on the desired volume and concentration. In this case, a 0.100 M solution means that for every liter of solution, there are 0.100 moles of fluoride ions.

Stoichiometry of Calcium Fluoride

Calcium fluoride (CaF2) dissociates in water to produce calcium ions (Ca²⁺) and fluoride ions (F⁻). Each mole of CaF2 yields two moles of fluoride ions. Therefore, to prepare a solution with a specific concentration of fluoride ions, one must account for this stoichiometric relationship when calculating the mass of CaF2 needed.

Glassware for Solution Preparation

The appropriate glassware for preparing a solution includes a volumetric flask and a balance. A volumetric flask allows for precise measurement of the desired volume (250 mL in this case), while a balance is used to accurately weigh the solid CaF2. Proper use of these tools ensures the solution's concentration is accurate and reproducible.