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cestrela7 [59]
3 years ago
11

Lithium-6 has a mass of 6.0151 amu and lithium-7 has a mass of 7.0160 amu. The relative abundance of Li-6 is 7.42% and the relat

ive abundance of Li-7 is 92.58%. Based on this data alone, calculate the average atomic mass for lithium to the correct number of significant digits.
Chemistry
2 answers:
horsena [70]3 years ago
3 0
Average atomic mass is the weighted average atomic masses with regard to the relative abundance of the isotopes 
average atomic mass of Li = relative abundance of Li-6 x mass of Li-6 + relative abundance of Li-7 x mass of Li-7
average atomic mass of Li = (7.42% x 6.0151 a.m.u) + (92.58% x 7.0160 a.m.u)
                                           = 0.446 + 6.495
                                           = 6.941 amu
average atomic mass of Li is 6.941 amu
Bezzdna [24]3 years ago
3 0

Answer: The average atomic mass of Lithium is 6.94 amu.

Explanation:

Mass of isotope Li-6 = 6.0151 amu

% abundance of isotope  Li-6 = 7.42%= \frac{7.42}{100}=0.0742

Mass of isotope Li-7=  7.0160

% abundance of isotope Li-7 = 92.58% = \frac{92.58}{100}=0.9258

Formula used for average atomic mass of an element :

\text{ Average atomic mass of an element}=\sum(\text{atomic mass of an isotopes}\times {{\text { fractional abundance}})

A=\sum[(6.0151\times 0.0742)+(7.0160\times 0.9258)]

A=6.94

Therefore, the average atomic mass of Lithium is 6.94 amu.

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konstantin123 [22]

Answer:

See explanation and picture below

Explanation:

First, in the case of methyloxirane (Also known as propilene oxide) the mechanism that is taking place there is something similar to a Sn2 mechanism. Although a Sn2 mechanism is a bimolecular substitution taking place in only step, the mechanism followed here is pretty similar after the first step.

In both cases, the H atom of the HBr goes to the oxygen in the molecule. You'll have a OH⁺ in both. However, in the case of methyloxirane the next step is a Sn2 mechanism step, the bromide ion will go to the less substitued carbon, because the methyl group is exerting a steric hindrance. Not a big one but it has a little effect there, that's why the bromide will rather go to the carbon with more hydrogens. and the final product is formed.

In the case of phenyloxirane, once the OH⁺ is formed, the next step is a Sn1 mechanism. In this case, the bond C - OH⁺ is opened on the side of the phenyl to stabilize the OH. This is because that carbon is more stable than the carbon with no phenyl. (A 3° carbon is more stable than a 2° carbon). Therefore, when this bond opens, the bromide will go there in the next step, and the final product is formed. See picture below for mechanism and products.

4 0
3 years ago
23) What is the volume of 2.454 x 1024 atoms of nitrogen gas at STP?
earnstyle [38]

Answer:

d) V =  91.3 L

Explanation:

Given data:

Volume of nitrogen = ?

Temperature = standard = 273.15 K

Pressure = standard = 1 atm

Number of atoms of nitrogen = 2.454×10²⁴ atoms

Solution:

First of all we will calculate the number of moles of nitrogen by using Avogadro number.

1 mole = 6.022×10²³ atoms

2.454×10²⁴ atoms × 1 mol / 6.022×10²³ atoms

0.407×10¹ mol

4.07 mol

Volume of nitrogen:

PV = nRT

1 atm × V = 4.07 mol ×0.0821 atm.L /mol.K ×273.15 K

V =  91.3 atm.L /1 atm

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