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Fuad Mansour

Fuad M.

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INSTANT ANSWER

1. A sample of \( 0.50 \mathrm{~g} \) of an organic compound was treated according to Kjeldahl's method. The ammonia evolved was absorbed in \( 50 \mathrm{ml} \) of 0.5 \( \mathrm{M} \mathrm{H}_{2} \mathrm{SO} 4 \). The residual acid required \( 60 \mathrm{~mL} \) of \( 0.5 \mathrm{M} \) solution of \( \mathrm{NaOH} \) for neutralization. Find the percentage composition of nitrogen in the compound.

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INSTANT ANSWER

[5 Mark An electron in an orbit of principal quantum number \( n_{i} \) in a hydroge tom makes a transition to an orbit of principal quantum number 2 . The proton emitted has a wavelength of \( 434 \mathrm{~nm} \). Calculate \( n_{i} \). \[ \left[R_{H}=2.179 \times 10^{-18} \mathrm{~J} ; \mathrm{h}=6.626 \times 10^{-34} \mathrm{~J} . \mathrm{s} ; \mathrm{c}=3.0 \times 10^{8} \mathrm{~ms}^{-1}\right. \] \( [5 \mathrm{MI} \)

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INSTANT ANSWER

g. A physical chemist believes that the energy lost by the hydrogen atom, \( \Delta \mathrm{E}=\mathrm{E}_{f}-\mathrm{E}_{j} \) where \( \mathrm{E}_{f} \) is the final energy level and \( \mathrm{E}_{i} \) is the initial energy level. \( \mathrm{E}_{r} \) is found at the final quantum number \( \mathrm{n}_{r} \) and \( \mathrm{E}_{1} \) is located at the initial quantum number n. Use Niels Bohr formula \( E=-\frac{R_{H}}{n^{2}} \) for the calculation of the energy of the electron in the liydrogen atom to show that: \[ \frac{1}{\lambda}=\frac{R_{H}}{h c}\left(\frac{1}{n_{f}^{2}}-\frac{1}{n_{l}^{2}}\right) \] [3 Marl

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INSTANT ANSWER

[4 marks] .) The blue colour of the sky results from the scattering of sunlight by air molecules. The blue light has a frequency of about \( 7.5 \times 10^{14} \mathrm{Fz} \). (i.) Calculate the wavelength, in \( \mathrm{nm} \), associated with this radiation? (ii.)Calculate the energy, in joules, of a single photon associated with this frequency. [4 marks]

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INSTANT ANSWER

(b.) (i.) Calculate the energy required to excite the hydrogen electron from level \( n=1 \) to level \( n=4 \). (ii) Also calculate the wavelength of light that must be absorbed by a hydrogen atom in getting to the excited state in 1(b.) (i) above from its ground state. \[ \left(\mathrm{h}-6.626 \times 10^{-36} \mathrm{Js}^{-1}\right. \text { ) } \] [4 marks] (c.) In the Lihium atom, what information do we get for the values of the quantur numbers for the third electron? [4 marks] (d.) For principal quantum level \( \mathrm{n}=4 \), determine the number of subshells (diffe values of 1) and give the orbital designation of each. [4 marks] (e.) How many electrons would be in an atom with the following sets of qui numbers? \( \quad n=4 \quad C=1 m=+k \quad n / s=d 1 / 2 \)

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ANSWERED

(b.) (i.) Calculate the energy required to excite the hydrogen electron from level \( n=1 \) to level \( n=4 \). (ii) Also calculate the wavelength of light that must be absorbed by a hydrogen atom in getting to the excited state in 1(b.) (i) above from its ground state. \[ \left(\mathrm{h}-6.626 \times 10^{-36} \mathrm{Js}^{-1}\right. \text { ) } \] [4 marks] (c.) In the Lihium atom, what information do we get for the values of the quantur numbers for the third electron? [4 marks] (d.) For principal quantum level \( \mathrm{n}=4 \), determine the number of subshells (diffe values of 1) and give the orbital designation of each. [4 marks] (e.) How many electrons would be in an atom with the following sets of qui numbers? \( \quad n=4 \quad C=1 m=+k \quad n / s=d 1 / 2 \)

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INSTANT ANSWER

a compound that is 85.6% C and 14.4%H and has a molar mass of 56g reacts with water amd sulphuric acid to produce a compound that reacts with acidic potassium dichromate solution to produce ketone. what is the name of the original compound? Draw the structure of three isomers of original compound and give their Iupac names

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