Question

How would you prepare \(500 \mathrm{~mL}\) of \(0.33 \mathrm{M}\) solution of \(\mathrm{CaCl}_{2}\) from solid \(\mathrm{CaCl}_{2} ?\) Specify the glassware that should be used.

Short answer

Weigh 18.31 g of \( \mathrm{CaCl}_{2} \), dissolve in water, and dilute to 500 mL in a volumetric flask.

Step-by-step solution

Calculate Moles of Solute

To find the amount of calcium chloride needed, we first calculate moles using the formula \( n = M \times V \), where \( n \) is moles, \( M \) is molarity, and \( V \) is volume in liters. Here, \( M = 0.33 \; \mathrm{M} \) and \( V = 0.500 \; \mathrm{L} \). So, \( n = 0.33 \times 0.500 = 0.165 \; \mathrm{moles} \).

Convert Moles to Grams

Next, we convert moles of \( \mathrm{CaCl}_{2} \) to grams using the molar mass. The molar mass of \( \mathrm{CaCl}_{2} \) is approximately \( 110.98 \; \mathrm{g/mol} \). Thus, grams required = \( 0.165 \; \mathrm{moles} \times 110.98 \; \mathrm{g/mol} = 18.3127 \; \mathrm{g} \).

Weigh the Calcium Chloride

Use a balance to weigh \( 18.31 \; \mathrm{g} \) of \( \mathrm{CaCl}_{2} \) solid. Ensure the balance is calibrated before measuring for accuracy.

Dissolve Calcium Chloride in Water

Place the weighed \( \mathrm{CaCl}_{2} \) in a beaker and add distilled water gradually while stirring until the entire solid is dissolved.

Transfer and Dilute the Solution

Transfer the dissolved solution into a 500 mL volumetric flask. Rinse the beaker with distilled water adding the rinsings to the flask to ensure all solute is transferred. Add distilled water to the flask until the bottom of the meniscus is at the 500 mL mark.

Mix the Solution

Stopper the flask and mix by inverting the flask several times to ensure homogeneity of the solution.

Key concepts

Calcium Chloride

Calcium chloride, with the chemical formula \( \mathrm{CaCl}_2 \), is a salt composed of calcium and chloride ions. It is highly soluble in water and widely used in different applications such as de-icing roads, as a drying agent, and in food preservation. In laboratories, calcium chloride is a common source of calcium ions and is used in the preparation of chemical solutions. When preparing a solution, it's crucial to measure an accurate amount of calcium chloride to ensure the desired concentration. This means starting with the correct number of moles, which are then converted to grams for practical use. Understanding the properties of calcium chloride, including its solubility and molarity in solutions, is key for effectively preparing accurate solutions.

Moles to Grams Conversion

Converting moles to grams is a fundamental concept in chemistry, crucial for preparing accurate chemical solutions. The conversion process involves using the molar mass of a substance, which is the mass of one mole of its molecules. For calcium chloride, the molar mass is approximately \( 110.98 \, \mathrm{g/mol} \).

• First, calculate the number of moles needed using the equation \( n = M \times V \), where \( n \) is the number of moles, \( M \) is the molarity, and \( V \) is the volume in liters.
• Once the moles are determined, convert them to grams by multiplying by the molar mass. This step translates theoretical calculations into a tangible amount of substance you can physically measure.

Converting moles to grams ensures that you have the exact amount of solute needed to achieve the desired concentration in your solution.

Volumetric Flask

A volumetric flask is an essential piece of glassware in preparing solutions with precise concentrations. It's designed with a flat bottom and a long neck with a single calibration mark that indicates a specific volume, such as 500 mL in this exercise.

• The flask's precise calibration guarantees that the solution reaches exactly the intended volume, helping maintain the accuracy of the prepared solution's molarity.
• To use it, after dissolving the solute in a smaller volume of water, transfer the solution into the volumetric flask.
• Rinse any remaining traces from the initial container into the flask and add distilled water until the liquid hits the calibration mark. Always check the meniscus from eye level to ensure correct volume.

The volumetric flask ensures that your solution is consistent and reliable for experimental use.

Chemical Solution Concentration

Chemical solution concentration refers to the amount of solute present in a given volume of solvent, usually expressed in molarity (\( M \)). Molarity is defined as moles of solute per liter of solution, making it a key measurement in solution preparation.

• Start by calculating the moles of solute required using \( n = M \times V \), where \( M \) is molarity and \( V \) is volume.
• Convert these moles into a measurable quantity in grams as precise as possible. This step is crucial for maintaining the desired concentration.
• Properly dilute the solution by ensuring the solute is entirely dissolved and accurately adjusted to the target volume in a volumetric flask. This guarantees a uniform concentration throughout the solution.

Understanding concentration helps in ensuring that the prepared solutions meet the experimental needs and produce reliable results.