Rare earth metals are a group of 17 elements - lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, scandium, yttrium - that appear in low concentrations in the ground
Answer:
B. Chemical changes produce new substances; physical changes do not.
Explanation:
Physical changes only alter appearances, while chemical changes are interactions that create new chemical formulas.
Answer:
31.60% phosphorus
Explanation:
To find the percent by mass, you first calculate the total mass and then the mass of phosphorus, and finally divide phosphorus mass by total.
Phosphorus mass: the molar mass of P is 30.97 g/mol, and since there's 1 mole of P, we just have 30.97 g.
Total mass: we add all the molar masses of the components together.
We have 3 moles of H, so we multiply 3 by 1.008 g/mol = 3.024 g H.
We already calculated the mass of phosphorus: 30.97 g P.
We have 4 moles of O, so we multiply 4 by 16.00 g/mol = 64.00 g O.
The total is then the sum: 3.024 + 30.97 + 64.00 = 97.994 g ≈ 97.99 g
Now, to find the percentage, we take 30.97 g P and divide by 97.99:
30.97/97.99 ≈ 0.3160 ⇒ 31.60% P
Thus, the answer is 31.60% phosphorus.
Hope this helps!
<u><em>NOTES TO TAKE DOWN: </em></u>
<em>Apparent brightness is a human measurement, and it would change for each star if the measurement were taken from another location. The more precise counterpart of apparent brightness is called absolute brightness (or absolute magnitude) and is the measure of the luminosity of a star, but on a common scale.</em>
<u><em>ANSWER:</em></u>
<em>Absolute brightness is the actual amount of light produced by the star, whereas apparent brightness changes with distance from the observer.</em>
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