How would you prepare each of the following solutions? (a) 100 mL of a 155 ppm solution of urea, CH4N2O, in water

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Determine the mass of urea needed: First, understand that ppm stands for parts per million, which means milligrams of solute per liter of solution. Since you need a 155 ppm solution, calculate the mass of urea required by converting the volume of the solution from mL to L and then using the ppm concentration to find the mass in mg.

Convert the mass of urea to grams: Since the mass calculated in the previous step is in milligrams, convert it to grams for practical weighing purposes (1 g = 1000 mg).

Measure the urea: Use a balance to measure the mass of urea you calculated. Ensure accuracy as the amount is likely small.

Prepare the solution: Add the measured urea to a beaker or flask. Add a portion of the total water to dissolve the urea completely. Stir or shake until the urea is fully dissolved.

Dilute to the final volume: Transfer the urea solution to a 100 mL volumetric flask. Add distilled water to reach the calibration mark of the flask, ensuring the solution is well mixed and at the correct final volume.

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Key Concepts

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

Parts Per Million (ppm)

Parts per million (ppm) is a unit of concentration that expresses the amount of a substance in a million parts of the solution. In the context of a 155 ppm solution, it means that there are 155 grams of urea in one million milliliters of water. This measurement is particularly useful for very dilute solutions, allowing chemists to quantify small concentrations effectively.

Dilution

Dilution is the process of reducing the concentration of a solute in a solution, typically by adding more solvent. To prepare a specific concentration, such as 155 ppm, one must calculate the appropriate amount of solute and solvent needed. This concept is fundamental in solution preparation, as it ensures that the desired concentration is achieved accurately.

Molar Mass

Molar mass is the mass of one mole of a substance, expressed in grams per mole (g/mol). For urea (CH4N2O), the molar mass is approximately 60.06 g/mol. Knowing the molar mass is essential for converting between grams and moles, which is necessary when preparing solutions to ensure the correct amount of solute is used for the desired concentration.

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