Algebra II: Chemical Compounds

Question

it would really help me if I knew the process to get the answer step by step.

A beaker oh PH3 contains 372 grams of hydrogen. What is the total weight in the beaker? (P:31, H:1)

Answer 1

Hello, Sally,

We can calculate the percentage of PH3 that is hydrogen by taking the molar mass of PH3 (34 g/mole) and take the 3 hydrogens @ 1 g/mole each and divide : 3 g H/34 g PH3. That gives a percent H of 8.82%. We have 372 grams of H. To find the amount of H, multiply the percent H times the total mass. But in this case, it is the mass of H that is the known and the mass of PH3 (X) that is the unknown, so use:

0.0882X = 372

I hope this helps,

Bob

Answer 2

Let's think of this in terms of balls labelled P and H. Looking at the question: if the total weight of the H balls is 372g, and each ball weighs 1g, then there are 372 balls labelled H. The chemical formula PH3 tells us that there are 3 times as many H balls as there are P balls, or in other words that there are 372/3 = 124 P balls. Furthermore, each P ball weighs 31 times as much as an H ball. So all in all we have 372 balls weighing 1 gram each, and 124 balls weight 31 grams each. From here, all that's left is simple multiplication and addition.