Homogenized whole milk contains \(4 \%\) butterfat by volume. How many milliliters of fat are there in a glass \((250 \mathrm{~mL})\) of milk? How many grams of butterfat \((d=0.8 \mathrm{~g} / \mathrm{m} \mathrm{L})\) are in this glass of milk?

Understanding solution concentration is central to many areas in chemistry, particularly when dealing with mixtures such as milk, which comprises various substances including butterfat. Solution concentration typically refers to the amount of a substance (a solute) dissolved in a specific volume of solvent. In our exercise, the concentration of butterfat in milk is given as a percentage: 4%. This means that for every 100 milliliters of milk, there are 4 milliliters of butterfat.

To calculate the volume of butterfat in a different quantity of milk, we multiply the total volume of milk by the concentration percentage, converting that percentage to a decimal form. This straightforward method allows us to readily understand the proportion of butterfat in any given quantity of milk. Remember, when you encounter terms like '4% by volume', it's indicating how much volume of butterfat is present compared to the total volume of the milk, not its mass or weight.

Density is a fundamental concept in chemistry that relates the mass of a substance to its volume. It is typically expressed in grams per milliliter (g/mL) for liquids. If you're given the density and the volume of a substance, you can easily find its mass, which is what we do in our exercise for butterfat in milk.

Density conversion involves using the formula \( \text{Density} = \frac{\text{Mass}}{\text{Volume}} \) to find one of the three variables if the other two are known. In simpler terms, if you multiply the density of a substance by its volume, you get the mass, which is an example of volume-to-mass conversion. In the exercise, this allows us to convert the volume of butterfat to its corresponding mass in grams, providing a practical approach to quantify the amount of butterfat rather than just knowing its volume.

Volume-to-mass conversion is an essential technique in chemistry, especially when dealing with ingredients or substances in the liquid state. By knowing a liquid's density, you can convert the volume of the liquid into mass. This process is useful since mass is often a more valuable measurement in chemical equations and reactions than volume.

To perform volume-to-mass conversion, like we did with the butterfat content in the milk, we employ the simple equation: \( \text{Mass} = \text{Volume} \times \text{Density} \) where mass is in grams, volume is in milliliters, and density is in grams per milliliter. It's crucial to note that the accuracy of this conversion depends on the consistency of the substance's density. Inhomogeneous substances might have varying densities, which could introduce errors in the calculation. Also remember, when measurements are involved, keeping consistent units throughout the calculation is key to obtaining a correct and meaningful result.