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ololo11 [35]
2 years ago
14

How many moles of boron (B, 10.81 g/mol) are in 37.8 grams of boron? [?] moles

Chemistry
1 answer:
madreJ [45]2 years ago
3 0

Answer:

37.8g/ 10.81g/mol = 3.4968...moles

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The effective nuclear charge is the amount of charge experienced by an electron taking into account any shielding effects from o
Agata [3.3K]

Answer:

The nuclear charge increases from boron to carbon, but there is no additional shielding( that is no additional shells).

Explanation:

First of all, we must know the electron configuration of carbon and boron.

Boron- 1s2 2s2 2p1

Carbon- 1s2 2s2 2p2

Moving from boron to carbon, the effective nuclear charge increases without a corresponding increase in the number of shells. Remember that shielding increases with increase in the number of intervening shells between the outermost electron and the nucleus. Since there isn't an increase in shells, boron experience a lower screening effect.

From

Zeff= Z- S

The Z for carbon is 6 while for boron is 5 even though both have the same number of screening electron S(4 screening electrons). Hence it is expected the Zeff(effective nuclear charge) for boron will be less than that of carbon.

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3 years ago
A scientist observes how a particular South American bird cares for its young. Why is a field study an appropriate type of scien
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Who first argued that all matter is made up of particles so small that they could not possibly be divided
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3 years ago
How long is 5 half lives if the half life is 2.6 hours? Remember to round to the correct number of significant figures and use u
Dmitry [639]

Answer:

\Delta t = 13\,h

Explanation:

Half time is period required to desintegrating the half of the initial number of atoms. Then, the total time is:

\Delta t = 5\cdot (2.6\,h)

\Delta t = 13\,h

3 0
3 years ago
In their notebook you see that it takes 9 hours for a sixth of a 0.5M solution of BC2 to react. Unfortunately, you have somewher
trasher [3.6K]

Complete Question

The complete question is shown on the first uploaded image

Answer:

The concentration of BC_2 that should used originally is C_Z_o = 0.4492M

Explanation:

     From the question we are told that

         The necessary elementary step is  

                  2BC_2 ----->4C + B_2

          The  time taken for sixth of 0.5 M of reactant to react t = 9 hr

           The time available is t_a = 3.5 hr

             The desired concentration to  remain C  = 0.42M

Let Z be the reactant ,   Y be the first product and X the second product

Generally the elementary rate  law is mathematically as

                    -r_Z = kC_Z^2 = - \frac{d C_Z}{dt}

Where k is the rate constant ,  C_Z is the concentration of Z

From the elementary rate law we see that the reaction is second order (This because the concentration of the reactant is raised to power 2 )

 For second  order reaction

            \frac{1}{C_Z}  - \frac{1}{C_Z_o}  = kt

Where C_Z_o is the initial concentration of Z which a value of   C_Z_o = 0.5M

       From the question we are told that it take  9 hours  for the concentration of  the reactant to become

                 C_Z =  C_Z_o - \frac{1}{6}  C_Z_o

                  C_Z = 0.5  - \frac{0.5}{6}

                       = 0.4167 M

So      

                     \frac{1}{0.4167}  - \frac{1}{0.50}  =  9 k

                          0.400 = 9 k

                =>    k = 0.044\  L/ mol \cdot hr^{-1}

  For   C_Z = 0.42M

                \frac{1}{0.42} - \frac{1}{C_Z_o}  = 3.5 * 0.044

                2.38 -  0.154  =    \frac{1}{C_Z_o}

                           2.226  =    \frac{1}{C_Z_o}

                            C_Z_o = \frac{1}{2.226}

                             C_Z_o = 0.4492M

                       

           

             

         

4 0
3 years ago
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