By Vincent Summers Updated Aug 30, 2022

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Urea (chemical formula H₂N‑CO‑NH₂) is a colorless solid that the body eliminates as a waste product. In agriculture it serves as a primary nitrogen source for crops, often applied as a liquid solution of a defined concentration. Preparing such a solution is straightforward once you understand urea’s molecular weight and the two most common concentration units: weight‑percent (either of urea or nitrogen) and molarity.

Step 1: Calculate Urea’s Molecular Weight

Using the atomic masses (H = 1, N = 14, C = 12, O = 16) and the molecular formula (C₁N₂H₄O₁), the calculation is: (4×1) + (2×14) + 12 + 16 = 60 g mol⁻¹.

Step 2: Determine Nitrogen Content and Molarity Basics

Urea contains 28 g of nitrogen per 60 g of molecule, giving a nitrogen percentage of (28/60)×100 = 47 %. Molarity is the number of moles of solute per liter of solution; for urea, 1 M equals 60 g dissolved in 1 L of water.

Step 3: Prepare the Solution Using Your Preferred Method

1. Weight‑Percent Urea

For a 4 % w/w solution, weigh 40 g of urea and 960 g of water in a beaker. Stir until fully dissolved. This yields a homogeneous 4 % urea solution.

2. Molarity

To make a 0.25 M solution, weigh 15 g of urea (0.25 × 60 g) into a 1‑L graduated beaker, then add water up to the 1‑L mark while stirring.

3. Weight‑Percent Nitrogen

For a 3 % w/w nitrogen solution, convert to urea weight percent: 3 % × (60/28) ≈ 6.5 %. Thus, add 65 g of urea to 935 g of water and stir.

Materials Needed

• Urea (anhydrous)
• Distilled or deionized water
• Weighing scoop
• Scale or balance
• 1‑L graduated beaker (or other suitable container)
• Funnel (optional)
• Stirring rod or magnetic stirrer with stir bar

Following these steps ensures a precisely concentrated urea solution suitable for agricultural or laboratory use.