You need a 45% alcohol solution. on hand, you have a 480 ml of a 40% alcohol mixture. you also have 85% alcohol mixture. how much of the 85% mixture will you need to add to obtain the desired solution?

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

the formula mass of a molecule or a compound is the sum of the atomic weights of the atoms in its empirical formula

(that's what i know about formula mass)