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Dafna1 [17]
2 years ago
6

131i has a half-life of 8.04 days. assuming you start with a 1.53 mg sample of 131i, how many mg will remain after 13.0 days ___

_______?
a.0.835
b.0.268
c.0.422
d.0.440
e.0.499
Chemistry
1 answer:
inn [45]2 years ago
8 0
For this problem we can use half-life formula and radioactive decay formula.

Half-life formula,
t1/2 = ln 2 / λ

where, t1/2 is half-life and λ is radioactive decay constant.
t1/2 = 8.04 days

Hence,         
8.04 days    = ln 2 / λ                         
λ   = ln 2 / 8.04 days

Radioactive decay law,
Nt = No e∧(-λt)

where, Nt is amount of compound at t time, No is amount of compound at  t = 0 time, t is time taken to decay and λ is radioactive decay constant.

Nt = ?
No = 1.53 mg
λ   = ln 2 / 8.04 days = 0.693 / 8.04 days
t    = 13.0 days 

By substituting,
Nt = 1.53 mg e∧((-0.693/8.04 days) x 13.0 days))
Nt = 0.4989 mg = 0.0.499 mg

Hence, mass of remaining sample after 13.0 days = 0.499 mg

The answer is "e"

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What is the iupac name of this structure?
alexgriva [62]

Answer:

3–ethyl–4–methylhexane.

Explanation:

To name the above compound, do the following:

1. Determine the functional group of the compound.

2. Locate the longest continuous carbon chain. This gives the parent name of the compound.

3. Identify the substituent group attached to the compound.

4. Give the substituent the lowest possible count.

5. Combine the above to name the compound.

Now, we shall name the compound given in the question above as follow:

1. The compound contains only single bond. Therefore, the compound belong to the alkane family.

2. The longest continuous carbon chain is 6 i.e hexane.

3. The substituent group attached are:

i. Methyl, CH3.

ii. Ethyl, CH2CH3.

4. we shall name the substituents alphabetically i.e ethly will come before methyl. Therefore,

Ethyl is located at carbon 3.

Methy is located at carbon 4.

5. Therefore, the name of the compound is:

3–ethyl–4–methylhexane.

5 0
2 years ago
15. Using the information below, calculate ΔHf° for PbO(s)
Svet_ta [14]
ΔH(reaction) = ΔH(formation of products) - ΔH(formation of reactants) 
ΔH(reaction) = ( 1*ΔH(Pb(s)) + 1*ΔH(CO2(g)) ) - ( 1*ΔH(PbO(s)) + 1*ΔH(CO(g)) ) 
ΔH(reaction) = ( 0 + -393.5 ) - ( ΔH(PbO(s)) + -110.5 ) 
ΔH(reaction) = -283 - ΔH(PbO(s)) 
-131.4 = -283 -ΔH(PbO(s)) 
ΔH(PbO(s)) = -151.6 kJ

So, the best answer is A.
5 0
2 years ago
Read 2 more answers
A solution is prepared by adding 6.24 g of benzene (C 6H 6, 78.11 g/mol) to 80.74 g of cyclohexane (C 6H 12, 84.16 g/mol). Calcu
tekilochka [14]

Answer:

x_B=0.0769

m=0.990m

Explanation:

Hello,

In this case, we can compute the mole fraction of benzene by using the following formula:

x_B=\frac{n_B}{n_B+n_C}

Whereas n accounts for the moles of each substance, thus, we compute them by using molar mass of benzene and cyclohexane:

n_B=6.24g*\frac{1mol}{78.11g}=0.0799mol\\ \\n_C=80.74g*\frac{1mol}{84.16g} =0.959mol

Thus, we compute the mole fraction:

x_B=\frac{0.0799mol}{0.0799mol+0.959mol}\\ \\x_B=0.0769

Next, for the molality, we define it as:

m=\frac{n_B}{m_C}

Whereas we also use the moles of benzene but rather than the moles of cyclohexane, its mass in kilograms (0.08074 kg), thus, we obtain:

m=\frac{0.0799mol}{0.08074kg}=0.990mol/kg

Or just 0.990 m in molal units (mol/kg).

Best regards.

7 0
2 years ago
If Maria winks exactly 5 times every minute while she is awake and she sleeps exactly 8 hours a day, how many times does Maria w
irina1246 [14]
24 minus 8 is 16
5 times 60 is 300
300 times 16 is 4800.
She winks 4800 times a day
5 0
2 years ago
Which of these correctly defines the pOH of a solution? the log of the hydronium ion concentration the negative log of the hydro
Likurg_2 [28]

Answer : The correct option is, the negative log of the hydroxide ion concentration.

Explanation :

pOH : It is defined as the negative logarithm of hydroxide ion concentration. It is a measure of the alkalinity of the solution.

Formula used :

pOH=-log[OH^-]

[OH^-] is the concentration of OH^- ions.

When pOH is less than 7, the solution is alkaline.

When pOH is more than 7, the solution is acidic.

When pOH is equal to 7, the solution is neutral.

4 0
2 years ago
Read 2 more answers
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