The Grass Doctor

Chemistry Question please help?

A lawn fertilizer is rated as 6.00% nitrogen, meaning 6.00 g of N in 100. g of fertilizer. The nitrogen is present in the form of urea, (NH2)2CO. How many grams of urea are present in 107 g of the fertilizer to supply the rated amount of nitrogen?

Public Comments

1. pffft...don't have a clue, good luck with that. :):):):)
2. Hey!....It's me again. I think this is the toughest one yet. Well, lets take it apart. They want this stuff to be 6% nitrogen. How many grams of nitrogen do you need to get 6% in 107 grams? Well, obviously it's going to be a little more than 6 grams, but not much. If you take 6% of 107 you get 6.42 g. So the stuff has to have 6.42g of nitrogen in 107g to be 6 % nitrogen. It would be easy at this point if urea was pure nitrogen because all we'd have to do is add 6.42 grams of urea. Unfortunately it's not. So the next question is how much of this stuff do we need to get 6.42 grams of nitrogen? Well, what percent of urea IS nitrogen? Beats me, but we can figure that out too. urea = ( NH2)2CO Molecular weight = 60g / mole What percent of that 60 grams is nitrogen? Well, there's 28 g in 60g of urea.so 28 / 60 = 46.7% Okay, So Sad, we're almost there. If the stuff is 46.7% nitrogen and we need 6.42 g of nitrogen, how many grams of urea do we need? We can set up a simple algebraic equation where we let "x" equal the amount of urea we need to get 6.42g of nitrogen. 0.4 67 (x) = 6 .42 g Then x = 6.42g /0.467 which equals 13.76 g. And that's the answer. Fun, ain't it?