Chemistry, 03.07.2019 16:30 kathleensumter5100

Combustion analysis of toluene, a common organic solvent, gives 8.20 mg of co2 and 1.92 mg of h2o. if the compound contains only carbon and hydrogen, what is its empirical formula?

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For the purpose of proper representation in this item, we let the number of moles of carbon in the compound be x, that of H is y. The equation of toluene now becomes,
CxHy
The combustion reaction is,
CxHy + O2 --> CO2 + H2O

The equation presented above may not be balanced yet. Then, we determine the number of mmols of C, H, and O in the product using the given masses.

(1) 8.20 mg CO2
(8.2 mg CO2)(1 mmol CO2/44 mg CO2) = 0.186 mmol CO2
which means,
0.186 mmol C
0.373 mmol O

(2) 1.92 mg H2O
(1.92 mg H2O)(1 mmol H2O/18 mg H2O) = 0.107 mmol H2O
which means
0.2133 mmol H
0.107 mmol O

Thus, the equation for toluene is,
C(0.186)H(0.2133)

Dividing the numbers by the lesser value,
CH(8/7)
To eliminate the fraction, we multiply by the denominator. Thus, the final answer would be,
C7H8

Answer from: Quest

assuming that your periodic table has eighteen columns, you should highlight the four elements in the third column from the left of the table.

explanation

neutral atoms of elements after calcium contain d electrons. the energy of d orbitals of a particular main shell lies between the energy of the s and p orbitals of the next main shell. for example, electrons in the $3d$ have energy higher than those in the $4 s$ orbital while lower than those of the $4 p$ orbital.

by the aufbau principle, electrons fill orbitals one at a time, starting from those of the lowest energy. the $4s$ orbital is therefore filled right after $3p$ orbitals and before $3 d$ orbitals.

potassium has electron configuration $[\text{ar}] 4 s^{1}$ and calcium $[\text{ar}] 4 s^{2}$ . the s orbital of a main shell holds a maximum of two electrons. the next element would thus have the electron configuration $[\text{ar}] 4 s^{2} \; 3d^{1}$ and satisfy the requirements.

a neutral atom of the element contains three electrons on top of the most recent noble gas element. it should thus be placed in the third column of the periodic table. both scandium and yttrium would satisfy the conditions. an aufbau diagram indicates that the 4f orbital is filled before the 5d. however, it appears that exceptions exists for both lanthanum and actinium. neutral atoms of the two d-block elements also demonstrate the $ns^{2} \; (n-1) p^{1}$ and should be highlighted as well.

Answer from: Quest

answer; talc and gypsum;

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Combustion analysis of toluene, a common organic solvent, gives 8.20 mg of co2 and 1.92 mg of h2o. i...

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