Question

Two Chem word questions!?

23. Magnesium oxide (Mg0) forms wh (a) Ir 1.25 g og MgO g of (b) What is the mass percent of O in Mg0? (c) How many micrograms of oxygen are in 534 kg of Mg en magnesium metal burns in air contains 0.754 g of Mg what is the mass percent of Mg in Mg0? 24. Boron has two naturally occurring isotopes: Bo ron-10 and Boron-11. If the atomic mass of boron(listed on the periodic table) is 10.81 amu, what is the %abundance of each of the two isotopes?

Answer 1

a)

Mass percent of Mg in MgO =

$=\frac{Mass\ of\ Mg}{Mass\ of\ MgO}\times 100$

$=\frac{0.754}{1.25}\times 100$

b)

Mass percent of O in MgO = 100 - 60.3 = 39.7 %

c)

Amount of O present in 534 kg MgO =

$=534\ kg\ of\ MgO \times\frac{1000\ g}{1\ kg} \times \frac{1\ mol\ MgO}{40.3\ g}\times \frac{1\ mol\ O}{1\ mol\ MgO}\times \frac{16\ g}{1\ mol\ O}$

= 212, 009 g O

=212 Kg

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24)

formula,

Atomic mass = % isotope 1 x mass of isotope 1 + % isotope 2 x mass of isotope 2

let percentage abundance of boron-10 be x

so another isotope percentage abundance = 100 - x

$10.81=\frac{x \times 10 + (100-x) \times 11}{100}$

$10.81=\frac{10x + 1100 -11x}{100}$

percentage abundance of B-10 = 19%

Percentage abundance of B-11 = 100 - 19 = 81%