Mass percent is the percentage of the total mass of a solution that is made up of the solute.

1. Formula: Mass percent is calculated by dividing the mass of the solute by the total mass of the solution and multiplying by 100.
   Mass percent = (mass of solute ÷ mass of solution) x 100

2. Units: Mass percent is usually expressed as a percentage (%), but it can also be expressed in parts per million (ppm) or parts per billion (ppb).

3. Example: A solution contains 20 grams of salt dissolved in 100 grams of water. What is the mass percent of salt in the solution?
   Mass percent = (20 ÷ 120) x 100 = 16.7%
   The mass percent of salt in the solution is 16.7%.

4. Uses: Mass percent is commonly used in chemistry to express the concentration of a solution. It can also be used in other fields, such as in the food industry to express the fat content of a food product.

5. Limitations: Mass percent can be affected by changes in temperature and pressure, so it is important to use it at standard conditions. It also assumes that the solute and solvent are uniformly mixed throughout the solution, which may not always be the case.

6. Practice problems: To practice calculating mass percent, try solving problems that involve finding the mass percent of a solute in a solution given the mass of the solute and the total mass of the solution. Also, try solving problems that involve finding the mass of the solute in a solution given the mass percent and the total mass of the solution.