Element M has two isotopes,^104M and ^106M.

1 answer:

3 0

To calculate atomic mass, you have to take to weighted average of the isotopes' masses. What that means is M = RA*106 + (1 – RA)*104, where RA is relative abundance expressed in decimal form. If you simplify the right side of that equation, you get M = 2*RA + 104. Doing a little more algebra yields RA = (M –104)/2 = (104.4 – 104)/2 = 0.4 / 2 = 0.2, which is 20%. So the answer is B.

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During a laboratory experiment, a 2.36-gram sample of NaHCO3 was thermally decomposed. In this experiment, carbon dioxide and wa

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Answer:

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Explanation:

1) Chemical equation (given)

2NaHCO₃ → Na₂CO₃ + H₂CO₃

2) Theoretical yield

a) Convert mass of NaHCO₃ to moles:

n = mass in grams / molar mass
molar mass = 84.007 g/mol
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b) Mole ratio:

2 mol NaHCO₃ : 1 mol H₂CO₃

c) Proportionality:

2 mol NaHCO₃ / mol H₂CO₃ = 0.02809 mol NaHCO₃ / x

⇒ x = 0.2809 / 2 mol H₂CO₃ = 0.01405 mol H₂CO₃

3) Actual yield

a) Mass balance: 2.36 g - 1.57 g = 0.79 g

b) Convert 0.79 g of carbonic acid to number of moles:

n = mass in grams / molar mass

molar mass = 62.03 g/mol

n = 0.79 g / 62.03 g/mol = 0.01274 mol

4) Percentage yield, y (%)

y (%) = actual yield / theoretical yield × 100

y (%) = 0.1274 mol / 0.1405 mol × 100 = 90.68%

The answer must show 3 significant figures, so y(%) = 90.7%.

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