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pshichka [43]
3 years ago
12

Write the symbol for the ion formed when each element gains electrons and attains a noble-gas electron configuration. Br, H, Se.

Chemistry
2 answers:
Bad White [126]3 years ago
8 0
Br^-
H^-
Se^2-

(^ - superscript)
Aneli [31]3 years ago
5 0

Explanation:

When an atom gain electrons then it acquires a negative charge whereas when an atom loses electrons then it acquires a positive charge.

For example, atomic number of bromine is 35 and its electronic distribution is 2, 8, 18, 7. So, in order to gain stability bromine accepts one electrons and thus it acquires a negative charge as Br^{-}.

Therefore, the symbol for the ion formed when each given element gains electrons and attains a noble-gas electron configuration are as follows.

  • Br changes into Br^{-}.
  • H changes into H^{-}.
  • Se changes into Se^{2-}.

 

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The energy produced by burning : -32.92 kJ

<h3>Further explanation</h3>

Delta H reaction (ΔH) is the amount of heat change between the system and its environment

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The enthalpy and heat(energy) can be formulated :

\tt \Delta H=\dfrac{Q}{n}\rightarrow n=mol

The enthalpy of combustion of naphthalene (MW = 128.17 g/mol) is -5139.6 kJ/mol.

The energy released for 0.8210 g of naphthalene :

\tt Q=\Delta H\times n\\\\Q=-5139.6~kJ/mol\times \dfrac{0.8210~g}{128.17~g/mol}~\\\\Q=-32.92~kJ

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Calculate the theoretical yield of aspirin obtained when 2.0 g of salicylic acid and 5.0 mL of acetic anhydride (density = 1.08
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Answer:

The percent yield would be 73%

Explanation:

The balanced reaction for the obtention of acetylsalicylic acid (aspirin) is the following:

Salicylic acid + acetic anhydride → acetylsalicylic acid + acetic acid

C₇H₆O₃          +          C₄H₆O₃        →         C₉H₈O₄           +    C₂H₄O₂

According to the reaction, 1 mol of salicylic acid reacts with 1 mol of acetic anhydride to give 1 mol of acetylsalicylic acid (aspirin) and 1 mol of acetic acid.

1 mol aspirin (C₉H₈O₄) = (9 x 12 g/mol) + (8 x 1 g/mol) + (4 x 16 g/mol)

                                     = 180 g

1 mol salicylic acid (C₇H₆O₃) = (7 x 12 g/mol) + (6 x 1 g/mol) + (3 x 16 g/mol)

                                              = 138 g

1 mol acetic anhydride (C₄H₆O₃) = (4 x 12 g/mol) + (6 x 1 g/mol) + (3 x 16 g/mol)

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The stoichiometric ratio is = 138 g salicylic acid/102 g acetic anhydride= 1.35

We have:

2.0 g salicylic acid

acetic anhydride = 5.0 mL x 1.08 g/mL = 5.4 g

The reactants ratio is = 2.0 g salicylic acid/5.4 g acetic anhydride = 0.37

0.37 < 1.35 , therefore <em>salicylic acid is the limiting reactant</em>.

Now, we use the amount of salicylic acid to calculate the theoretical amount of aspirin. For this, we know that 1 mol of aspirin (180 g) is obtained from 1 mol of salycilic acid (138 g):

theoretical yield= 180 g aspirin/138 g salycilic acid x 2.0 g salycilic acid = 2.61 g aspirin

actual yield = 1.9 g

Finally, we calculate the yield:

percent yield = actual yield/theoretical yield x 100

        = 1.9 g/2.6 g x 100 = 72.8% ≅ 73%

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