b) Given the mass spectrum of benzene, identify the molecular weight and give the molecular formula.

Video transcript

Hi everyone. This problem reads the empirical formula for nap filin is C five H four. Using the mass spectrum of naphthalene. What are its molecular formula and molecular weight. Okay, so we're given the mass spectrum below and molecular mass is the most intense peak with the highest mass to charge ratio. So looking at our mass spectrum, our most intense peak is 128. Okay, so that means that this is going to be our molecular weight and this molecular weight is in grams per mole. So we know what the molecular weight is and we're able to look at that or figure that out by looking at the mass spectrum. So now we need to write out the molecular formula. Okay, so in order for us to write out the molecular formula, we first need to calculate the empirical mass. Okay, so we know that the empirical formula is C five H four. So this means we have five carbons and four hydrogen. We're going to multiply both of these by their atomic weights so that we can get the empirical mass. Alright, so we'll write that are empirical mass is going to equal For carbon. We have five carbons times its molecular weight is 12.01 plus we have four hydrogen times its molecular weight is 1.008. Okay, so this gives us an empirical mass of 64.082. That's the empirical mass. So now what we're going to do is we're going to take the molecular mass and divide it by the empirical mass. Okay, so that we can get a ratio. So we're going to take the molecular mass and divided by the empirical mass. Okay, we know what the molecular masses we saw. It's 100 and 28 by looking at the mass spectrum and the empirical mass we just calculated is 64.82. So we get 1.997 which we're going to round 22. So this ratio is what we're going to use to multiply our empirical formula by. Alright, so we know that our empirical formula Alright, E F. R empirical formula is C five H four are molecular formula. Alright, MF is going to equal our empirical formula. So we're going to take C5, we're going to take that five and multiply two and then we're going to take our H four and multiply by two. And so we get our molecular formula is going to equal C 10 H eight. Okay, so this is going to be our final answer for molecular formula. Molecular formula is C 10 H eight and our molecular weight is 100 and 28 g per mole. Alright, so that is it for this problem? I hope this was helpful