All of the substances listed here are fertilizers that...

All of the substances listed here are fertilizers that contribute nitrogen to the soil. Which of these is the richest source of nitrogen on a mass percentage basis? (a) Urea, $\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO}$ (b) Ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$ (c) Guanidine, $\mathrm{HNC}\left(\mathrm{NH}_{2}\right)_{2}$ (d) Ammonia, $\mathrm{NH}_{3}$

All of the substances listed here are fertilizers that contribute nitrogen to the soil. Which of these is the richest source of nitrogen on a mass percentage basis?
(a) Urea, $\left(\mathrm{NH}_{2}\right)_{2} \mathrm{CO}$
(b) Ammonium nitrate, $\mathrm{NH}_{4} \mathrm{NO}_{3}$
(c) Guanidine, $\mathrm{HNC}\left(\mathrm{NH}_{2}\right)_{2}$
(d) Ammonia, $\mathrm{NH}_{3}$

Key Concepts

Fertilizers

Fertilizers are substances added to soil to provide essential nutrients that enhance plant growth. A key nutrient in many fertilizers is nitrogen, which plays a crucial role in plant metabolism and development.

Molar Mass and Elemental Percentage Calculation

Calculating the molar mass of a compound and then determining the mass percentage of an element involves summing the atomic masses of all atoms in the molecule and identifying the contribution of the target element. This analysis is fundamental in comparing the nutrient content across different chemical substances.

Stoichiometry and Molecular Formulas

Understanding a compound’s molecular formula allows for the determination of the stoichiometric ratios of its constituent elements. This is essential for evaluating how much of a specific element, such as nitrogen, is present relative to the overall molecular mass.

Transcript

00:01 So for this question, we're supposed to compare the percent nitrogen of four different fertilizers.

00:08 And you're supposed to find the one that has the highest mass percentage of nitrogen.

00:12 So the way that we're going to do this is we're going to find how much nitrogen is each fertilizer.

00:17 Divide that by the overall molecular mass, multiply by 100%, and that'll give us the percent nitrogen.

00:23 So the first fertilizer that we have is urea.

00:28 So the first thing we need to do is want to find how much the nitrogen is in here or the mass of the nitrogen.

00:36 Well, we have two nitrogen atoms because it's two distributes.

00:41 So the mass of the nitrogen is just 2 times 14 .01, it's 28 .02.

00:51 So now we need to find the total molecular mass.

00:56 Well, we know that the total molecular mass.

01:00 Mass is going to include two nitrogen atoms.

01:04 We also have four hydrogen atoms because that two also distributes, so we have four times 1 .00.

01:12 And we have a carbon atom and an oxfarin atom.

01:15 And the amus for both of those elements are 12 .01, 16 .00 respectively.

01:25 And plug that into the calculator will get that the total molecular mass is 60 .066.

01:32 Amu.

01:34 So now we just take the mass of the nitrogen, divided by the total molecular mass, multiply by 100, and you guys at the percent nitrogen is 46 .65%.

01:49 So that is the answer to part a.

01:54 Now for part b, for part b, we have ammonium, a nitrate, or nh4, and03.

02:02 So once again, you want to find the mass of the nitrogen.

02:05 We have two nitrogen atoms.

02:07 One here and one there, so it's just two times the amu of nitrogen, which is 14 .01, and that yields 28 .02 atomic mass units of nitrogen.

02:19 Now the total molecular mass.

02:24 Well, like before, it's going to include those two atoms of nitrogen, and we also have four atoms of hydrogen, which is four times 1 .08, and then three oxygens, which is 16 .00.

02:40 And when we multiply all this together, you get that the total molecular mass of the entire compound is 80 .04, amu.

02:54 So we take the mass of the nitrogen, divided by the total molecular mass, multiply by 100, and we get our answer is 35 .2.

03:06 0 % nitrogen.

03:12 Part c...

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