How do you find the number of moles in a substance if you have the density and the molecular weight?

#moles = grams/molar mass. You don't need the density if you have grams.

Okay I think I wrote the question wrong.

You need to find the number of moles in 5mL of the substance given the density and the molecular weight.

To find the number of moles in a substance given the density and the molecular weight, you can use the formula:

Number of moles = Mass / Molecular weight

First, you need to find the mass of the substance. You can calculate this by multiplying the density of the substance by its volume:

Mass = Density x Volume

Once you have the mass, you can divide it by the molecular weight of the substance to find the number of moles:

Number of moles = Mass / Molecular weight

Let's say we have an example where the density of a substance is 2.5 g/mL and the molecular weight is 40 g/mol. If we are given the volume of 10 mL, we can calculate the number of moles as follows:

First, calculate the mass:
Mass = Density x Volume
Mass = 2.5 g/mL x 10 mL = 25 g

Then, calculate the number of moles:
Number of moles = Mass / Molecular weight
Number of moles = 25 g / 40 g/mol = 0.625 mol

So, in this example, we have 0.625 moles of the substance.