The Half-Life of Pa-234 is 6.75 hours. How much (what fraction) of a sample of this isotope remains after 20.25 hours?

1 answer:

6 0

So in one hour half the amount remains (that's what half life means). In two hours 1/4 (or half of half) would remain and in three hours 1/8 would remain.
So the answer is 1/8

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In hydrate ratio does the mass of salt come first or does the mass of water

frutty [35]

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In the formula of the hydrate, on the first place is the salt and on the second of water. so in ration on the first place should be salt also.

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3 years ago

If 15 g of C₂H₆ reacts with 60.0 g of O₂, how many moles of water (H₂O) will be produced?

IceJOKER [234]

Answer:

$n_{H_2O}=1.5molH_2O$

Explanation:

Hello,

In this case, the undergoing chemical reaction is:

$2C_2H_6 + 7O_2 \rightarrow 4CO_2 + 6H_2O$

Next, we identify the limiting reactant by computing the available moles of ethane and the moles of ethane consumed by 60.0 grams of oxygen:

$n_{C_2H_6}^{available}=15g*\frac{1mol}{30g} =0.50molC_2H_6\\n_{C_2H_6}^{reacted}=60.0gO_2*\frac{1molO_2}{32gO_2}*\frac{2molC_2H_6}{7molO_2} =0.536molC_2H_6$

Thus, we notice there are less available moles, for that reason, the ethane is the limiting reactant. Finally, we can compute the produced moles of water by:

$n_{H_2O}=0.50molC_2H_6*\frac{6molH_2O}{2molC_2H_6}\\\\n_{H_2O}=1.5molH_2O$

Best regards.

5 0

2 years ago

Which of the following is not the same as 12.5 millimeters? 0.0000125 km 0.00125 hm 0.0125 m 1.25 cm

erma4kov [3.2K]

1 mm (millimeter) = 0.000001 km (kilometer)
12.5 mm = 0.0000125 km

1 mm = 0.00001 hm (hectometer)
12.5 mm = 0.000125 hm

1 mm = 0.001 m (meter)
12.5 mm = 0.0125 m

1 mm = 0.1 cm (centimeter)
12.5 mm = 1.25 cm

So the only one of the answer choices that doesn't equal 12.5 mm is 0.00125 hm, since 12.5 mm is 0.000125 hm.

Answer:
0.00125 hm

Hope this helps!

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