Explore BrainMass

various chemical questions

Please see the attached file.

1. Answer the following problems about gases.

a) The average atomic mass of naturally occurring neon is 20.18 amu. There are two common isotopes of naturally occurring Neon as indicated in the table below.
(i) Using the information above, calculate the percent abundance of each isotope.
(ii) Calculate the number of N2-22 atoms in a 12.55 g sample of naturally occurring neon.

b) A major line in the emission spectrum of neon corresponds to a frequency of 1.34 x 10 14 s1. Calculate the wavelength, in nanometers, of light that corresponds to this line.

c) In the upper atmosphere, ozone molecules decompose as they absorb ultraviolet (UV) radiation, as shown by the equation below, Ozone serves to block harmful ultraviolet radiation that comes from the sun.

A molecule of O3(g) absorbs a photon with a frequency of 1.00 x 10^15 s-1.
(i) How much energy, in joules, does the O3(g) molecule absorb per photon?
(ii) The minimum energy needed to break and oxygen-oxygen bond in ozone is 387 kJ mol-1. Does a photon with frequency of 1.00 x 1015 s-1 have enough energy to break this bond? Support your answer with a calculation.

2. The following questions relate to the synthesis reaction represented by the chemical equation in the box above.
(a) Calculate the value of the standard free energy change, ΔSo298, for the reaction.
(b) Determine the temperature at which the equilibrium constant Keq, for the reaction is equal to 1 .00 (Assume that ΔHo and ΔSo are independent of temperature).
(c) Calculate the standard enthalpy change, ΔHo, That occurs when 0.256 mol sample of NF3(g) is formed from N2(g) and F2(g) at 1.0 atm and 298K.

The enthalpy change in a chemical reaction, is the difference between energy absorbed in breaking bonds in the reactants and energy released by bond formation, in the products.

(d) How many bonds are formed when two molecules of NF3 are produced according to the equation in the box above?
(e) Use both the information in the box above and the table of average bond enthalpies below to calculate the average enthalpy of the F - F bond.

3. 3. Answer the following questions that relate to the analysis of chemical compounds.

(a) A compound containing the elements C, H, N and O is analyzed. When a 1.2359 g sample is burned in excess oxygen, 2.241 g of C02(g) is formed. The combustion analysis also showed that the sample contained 0.0648 g of H.

(i) Determine the mass, in grams, of C in the 1.2359 g sample of the compound.
(ii) When the compound is analyzed for N content only, the mass percent of N is found to be 28.84 percent. Determine the mass, in grams, of N in the original 1.2359 g sample of the compound.
(iii) Determine the mass, in grams of O in the original 1.2359 g sample of the compound.
(iv) Determine the empirical formula of the compound.

(b) A different compound, which has the empirical formula CH2Br, has a vapor density of 6.00 g L-1 at 375 K and 0.983 atm. Using these data, determine the following.

(i) The molar mass of the compound.
(ii) The molecular formula of the compound.

Answer question 4 below. The section II score weighting for this question is 10 percent.

4. For each of the following three reactions in part (i) write a balanced equation for the reaction and in part (ii) answer the question about the reaction, In part (i), coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances extremely ionized. Omit formulas for any ions or molecules chat are unchanged by the reaction. You may use the empty space at the bottom of the 'next page for scratch work but only the equations that are written in the answer boxes provided will be graded,

(a) A solution of sodium hydroxide is added to a solution of lead(II) nitrate.
(i) Balanced equation
(ii) If 1.0 L volumes of 1.0 M solutions of sodium hydroxide and lead(II) nitrate are mixed together, how many moles of the product(s) will be produced? Assume the reaction goes to completion.

(b) Excess nitric acid is added to solid calcium carbonate.
(i) Balanced equation
(ii) Briefly explain why statues made of marble (calcium carbonate) displayed outdoors in urban areas are deteriorating.

(c) A solution containing silver(1) ion (un oxidizing agent) is mixed with a solution containing iron(II) ion (a reducing agent).
(i) Balanced equation
(ii) If the contents of the reaction mixture described above are filtered, what substance(s), if any, would remain on the filter paper.


Solution Summary

It provides detailed explanations of various chemical questions. The solution was rated '5/5' by the student who originally posted the questions.