Chemistry 141- Problem Session 1

McMurry and Fay

Chapters 1, 2, 3 & 4

1.       Give the name or formula as required:

2.       A macadamia nut grove has 130 trees per square km.  Each tree produces 930 nuts per year and 24 nuts are needed to make a box of chocolate covered macadamia nuts which sell for $6.49 per box (cost of production = $2.37/box).  How many acres of macadamia nut trees must be planted to earn a profit of $150,000 per year.  (1 acre = 43,560 ft²)

3.       Silicon occurs as three isotopes;  ²⁸Si with a mass of 27.9769 amu, comprises 92.2% of the natural abundance and ²⁹Si at 28.9765 amu is 4.67%.  The atomic mass of silicon is 28.0855. Identify the third isotope.

4.       Write the a) conventional, b) total ionic and c)net ionic equations for the reactions which    occur  when the following aqueous solutions are mixed:

a.     HBr(aq)   +   Ca(HSO₃)₂(aq)  à

b.     Fe(NO₃)₃(aq)  +  NH₃(aq)    à

c.     AgNO₃(aq)  +  K₃PO₄(aq)     à

d.     Na₂C₂O₄(aq)  +  HCl(aq)         à

e.     K₂CO₃(aq)  +  HCl(aq)     à

5.       A solution of 35.00% zinc nitrate has a density of 1.3678 g/cm³.  What is the volume of a sample of this solution that contains 25.00 g of zinc nitrate?

         6.        Balance the following equations using the half-reaction method:

HClO(aq)  +  Mn²⁺(aq)  à  Cl₂(g)  +  MnO₄^-(aq)  (in acid)

Sn²⁺(aq)  +  NO₃^-(aq)  à  Sn⁴⁺(aq)  +  NO(g)  (in acid)

MnO₄^-(aq)  +  NO₂^-(aq)  à  MnO₂(s)  +  NO₃^-(aq)  (in base)

7.        If 15.00 g of a mixture of 25.00% CaCl₂ and 75.00% inert material are dissolved in 1.000 liter of water, how many mL of 0.500 M silver nitrate solution will be required to precipitate all of the chloride?  The reaction equation is:

2 AgNO₃   +   CaCl₂   à   Ca(NO₃)₂   +   2 AgCl

8.        A sample of sodium phosphate dodecahydrate, Na₃PO₄·12H₂O contains 15.0g of sodium. 

(1)               What is the mass of the sample?

(2)               How many water molecules are in the sample?

(3)               How many moles of phosphorus are present?

(4)               What is the mass of oxygen in the sample?

9.        A 0.2417 gram sample of a compound known to be composed of C, H, O and Cl only, is burned in oxygen yielding 0.4964 grams of carbon dioxide and 0.0846 grams of water.  A separate 0.1696 gram sample of the compound is fused with sodium metal, the products dissolved in water and the chloride quantitatively precipitated with silver nitrate to yield 0.1891 grams of AgCl.  What is the simplest empirical formula for the compound?

10.     Sulfur dichloride reacts with sodium fluoride according to the equation:

3 SCl₂(l)  +  4 NaF(s)  à  SF₄(g)  +  S₂Cl₂(l)  +  4 NaCl(s)

If 30.00 g of SCl₂ and 20.00 g of NaF react to yield 8.00 g of SF₄, what is the percent yield of SF₄?

11.   A 7.500 g sample of chloroacetic acid (CH₂ClCO₂H) is dissolved in enough water to prepare 250.0 mL of solution.  A 20.00 mL aliquot of the solution requires 31.03 mL of sodium hydroxide solution to achieve a phenolphthalein endpoint.  What is the molarity of the sodium hydroxide solution?

12.   A 354 mL aliquot of 0.228 M FeCl₃ is mixed with a 652 mL aliquot of 0.410 M KOH.  Write the balanced equation for the reaction that occurs and identify any precipitate formed.  Determine the mass of the precipitate and the molar concentrations of all ions present after mixing.

13.   The volumes of a 20.00 mL pipet, a 50.0 mL graduated cylinder  and a 250.0 mL volumetric flask were determined by weighing the amount of water they delivered (pipet and cylinder)  or contained (the flask). The pertinent information is given in the table; all volumes are in mL.   For each device rate the precision and accuracy as good, fair or poor .  The balance used for the measurements was calibrated and thereby known to be accurate.

14.   A salesman wishes to sell you a gold nugget with a mass of 39.85 ± 0.03 grams for $25.00.  This seems like a good bargain, but is the nugget really gold??  You determine the volume by displacement of water, the data follows.  Calculate the density (g/mL) of the gold nugget and estimate the absolute error in this value.

Volume water in graduated cylinder             25.00 ± 0.02 mL

Volume water + nugget                    27.39 ± 0.02 mL