Atomic Spectra

Atoms give off light when heated or otherwise excited. The light emitted by excited atoms consists of only a few wavelengths, rather than a full rainbow of colors. When this light is passed through a prism, the result is a series of discrete lines separated by blank areas. The visible lines in the series of the hydrogen spectrum are caused by emission of energy accompanying the fall of an electron from the outer shells to the second shell. The wavelength (λ) of the lines can be calculated using the Balmer-Rydberg equation

1λ=R(1m2−1n2)

where m is an integer, n is an integer greater than m, and R=1.097×10−2 nm−1 is the Rydberg constant.

In the Balmer-Rydberg equation, what value of m is used to determine the wavelengths of the Balmer series?

What Is The Wavelength?

What is the wavelength in meters of an FM radio wave with frequency ν = 141.5MHz ?

What is the wavelength of a medical X ray with ν = 9.60×10^¹⁷Hz ?

Electromagnetic Radiation

Electromagnetic radiation behaves both as particles (called photons) and as waves. Wavelength (λ) and frequency (ν) are related according to the equation

c=λ×ν

where c is the speed of light (3.00×108 m/s). The energy (E in joules) contained in one quantum of electromagnetic radiation is described by the equation

E=h×ν

where h is Planck’s constant (6.626×10−34 J⋅s). Note that frequency has units of inverse seconds (s−1), which are more commonly expressed as hertz (Hz).

A microwave oven operates at 2.50GHz . What is the wavelength of the radiation produced by this appliance?

Precipitation Reactions and Solubility Rules

How would you prepare the following substances by a precipitation reaction?
* Al(OH)₃
* FeS
* CoCO₃

 

 

What Is The Total Molar Concentration of Ions?

What is the total molar concentration of ions in each of the following solutions? Assuming complete dissociation.

1.)   .750 M of K2CO3

2.)   .355 M of AlCl3

 

Hydrogen Cyanide Poisoning

Hydrogen cyanide, HCN, is a poisonous gas. The lethal dose is approximately 300. mg HCN per kilogram of air when inhaled. The density of air at26 ∘C is 0.00118 g/cm3.

Calculate the amount of HCN that gives the lethal dose in a small laboratory room measuring 12.0 ft×15.0 ft×8.50ft.

Consider the formation of HCN by the reaction of NaCN(sodium cyanide) with an acid such as H2SO4 (sulfuric acid):

2NaCN(s)+H2SO4(aq)→Na2SO4(aq)+2HCN(g)

What mass of NaCN gives the lethal dose in the room?

HCN forms when synthetic fibers containing Orlon^® or Acrilan^®burn. Acrilan^® has an empirical formula of CH2CHCN, so HCN is 50.9% of the formula by mass. A rug in the laboratory measures 12.0× 15.0ft and contains 30.0 oz of Acrilan^® fibers per square yard of carpet. If the rug burns, what mass of HCNwill be generated in the room? Assume that the yield of HCNfrom the fibers is 20.0% and that the carpet is 37.0% consumed.

Calculations Involving Consecutive Reactions

Melamine, C3N3(NH2)3, is used in adhesives and resins. It is manufactured in a two-step process in which urea, CO(NH2)2, is the sole starting material, isocyanic acid, HNCO, is an intermediate, and ammonia, NH3, and carbon dioxide, CO2, gases are byproducts.

In the first step of this reaction, urea is broken down into isocyanic acid and ammonia:

CO(NH2)2(l)→HNCO(l)+NH3(g)

In the second step of this reaction, isocyanic acid reacts to form melamine and carbon dioxide:

HNCO(l)→C3N3(NH2)3(l)+CO2(g)

Balance this reaction and enter the coefficients below.

What mass of melamine, C3N3(NH2)3, will be obtained from 124.0kg of urea, CO(NH2)2, if the yield of the overall reaction is 84.0% ?

Theoretical, Actual, and Percent Yields

Ethyl butyrate, CH3CH2CH2CO2CH2CH3, is an artificial fruit flavor commonly used in the food industry for such flavors as orange and pineapple. Its fragrance and taste are often associated with fresh orange juice, and thus it is most commonly used as orange flavoring.

It can be produced by the reaction of butanoic acid with ethanol in the presence of an acid catalyst (H+):

CH3CH2CH2CO2H(l)+CH2CH3OH(l)H+⟶CH3CH2CH2CO2CH2CH3(l)+H2O(l)

Given 7.50g of butanoic acid and excess ethanol, how many grams of ethyl butyrate would be synthesized, assuming a complete 100% yield?

A chemist ran the reaction and obtained 5.25g  of ethyl butyrate. What was the percent yield?

The chemist discovers a more efficient catalyst that can produce ethyl butyrate with a 78.0% yield. How many grams would be produced from 7.50g of butanoic acid and excess ethanol?

Concentration of an Aqueous Soultion

The concentration of an aqueous solution of NaOCl (sodium hypochlorite; the active ingredient in household bleach) can be determined by a redox titration with iodide ion in acidic solution: OCl−(aq)+2I−(aq)+2H+(aq)→Cl−(aq)+I2(aq)+H2O(l)Assume that the blue spheres in the buret represent I− ions, the red spheres in the flask represent OCl− ions, the concentration of the I−ions in the buret is 0.140M , and the volumes in the buret and the flask are identical.

What is the concentration of NaOCl in the flask?

What percentage of the I− solution in the buret must be added to the flask to react with all the OCl− ions?

 

What Is The Mass Percent?

A sample weighing 14.98g and containing a small amount of copper was treated to give a solution containing aqueous Cu^2+ ions.  Sodium iodide was then added ti yield solid copper (I) iodide plus I3^- ion, and the I3^- was titrated with thiosulfate, S2O3^2-.  The titration required 10.49mL of .100M Na2S2O3 for complete reaction.  What is the mass percent copper in the sample?  The balanced equations are…

2Cu^2+(aq)+5I^-(aq)—->2CuI(s)+I3^-(aq)

I3^-(aq)+2S2O3^2-(aq)—->3I^-(aq)+S4O6^2-(aq)