Find the correct coefficients so that the following equation balances.  Some answers may be used more than once, some may not be used. ____ Mg(s) + _____ Cr3+(aq) –> ____ Mg2+(aq) + _____ Cr(s)

Choose the best labels for the diagram of an electrochemical cell. electrochemical_cell_labsl.png 

Complete the following passage with the best answers.  Some answers may be used more than once, some may not be used. In a(n) 1)_______________________ reaction, two aqueous solutions of soluble ionic species are combined which results in at least one pairing of ions producing an insoluble solid.  This type of reaction belongs to a larger class of reactions called 2)____________________ reactions, in which two species ‘swap’ bonding partners.  There are several ways to express such a reaction with a chemical reaction equation.  In a(n) 3)______________________ equation, the reactant and product species are written as complete formulas, with ions paired together as salts.  Subscripts of (aq) or (s) may denote whether each compound is soluble or insoluble, but otherwise, no dissociation is depicted.  This type of equation can be expanded into a 4)___________________ equation, where each soluble ion is written separately, expressing its state of being dissociated in solution, while insoluble compounds remain written as complete formulas.  In such an equation, 5)______________________ can be clearly seen, appearing both on the reactant and product side of the equation, indicating that they are not interacting with other ions or participating in the formation of the solid.  Eliminating these inactive species gives a(n) 6)________________________ where only the ions which come together to react and form the solid are shown, as well as the solid produced.

For the following reaction, calculate the volume of hydrogen gas that will be produced if grams of zinc metal is completely reacted with HCl.  Report your calculated answer in liters, but leave off the units when entering your answer.  Ambient conditions:  Torr of pressure, °C. Zn + 2 HCl –> ZnCl2 + H2

Match the following terms with their best definition or description.  Some answers may be used more than once, some may not be used.

A liter tank of compressed nitrogen (N2) with a pressure of psi is sitting in a warehouse at a temperature of °C.  How much volume would this nitrogen occupy if it were released to the atmosphere at °C?  Give your answer in liters.  (Note — 1 atm = 14.696 psi)

What is the concentration of sodium ions in a % (m/v) solution of sodium phosphate (Na3PO4, MW = 163.94 g/mol)?  Give your answer as a molarity (just the number, no units).

Complete the following passage with the best answers.  Some answers may be used more than once, some may not be used. There are many ways to express the concentration of a solution, which can often lead to confusion and errors in calculation if their definitions are not understood or improperly applied.  There are three common methods of expressing concentration in terms of percent.  1)______________________ expresses concentration in terms of mass of solute per mass of solution.  2)____________________ expresses concentration in terms of volume of solute per volume of solution.  3)_______________________ expresses concentration in terms of mass of solute per volume, and this way of expressing concentration in particular often leads to confusion and improper calculation.  Very dilute solutions are often expressed with a different convention that borrows from the conventions using percent.  4)____________________ expresses concentrations in terms of mass of solute per mass of solution — or sometimes in terms of volume of solution — times 106.  Likewise, 5)____________________ expresses concentrations in terms of mass of solute per mass of solution — or sometimes in terms of volume of solution — times 109.  Sometimes they are expressed with the shorthand “milligrams per kilogram” or “micrograms per kilogram”, respectively.  Care should be taken with these definitions, especially whether they are made in terms of mass or volume and even more expecially when the solvent is not water.  Another important and frequently encountered method for expressing concentration is in terms of moles of solute per liter of solution, which is known as 6)___________________.  This term is most commonly encountered in the chemical laboratory.

Complete the following passage with the best answers.  Some answers may be used more than once, some may not be used.   The strength and concentration of acids and bases can be measured in multiple ways.  Perhaps the simplest, oldest, and most common methods involve the use of pH 1)____________________, which change color in the presence of acid or base.  One type is called 2)____________________ paper, which generally changes to blue in the presence of base, and pink (or red) in the presence of acid.  Another type, which goes by the generic name of 3)_________________________ uses several different compounds which change color at different pH values, generating a spectrum of different colors and allowing a more accurate estimate of the pH of the solution.  For even more precise results, a digital 4)________________________ can be used, which is an electronic instrument with an electrode that is immersed in the solution to give a digital readout of pH.  Such instruments do require frequent calibration, however.  A different sort of measure involves an actual stoichometric experiment — in a 5)_______________________, a solution with a very precisely known concentration is reacted with the unknown acid or base until the exact point of complete reaction is reached, at which point the volume and concentration are used to calculate the concentration of the unknown.  In such an experiment, a common visual indicator known as 6)________________________ can be used, which changes color from clear to a purple-pink color very close to neutral pH, with the pink color seen in the basic pH range and clear when the solution is acidic.

A unit is manufacturing synthetic oil and using a hydrogenator to reduce olefin content in the product.  The hydrogenator uses compressed hydrogen and a catalyst to react with any remaining olefins (alkenes) in the material to make a saturated, more stable product.  Under current operating conditions, moles of hydrogen are required per ton of process material passing through the hydrogenator, and the unit produces tons per hour, 24 hours per day, 7 days per week.  The hydrogenator is fed by a hydrogen storage tank holding liters of hydrogen, currently at psi, with the ambient temperature stable at °C.  If an operator has just come in for a seven day shift, what should he expect the pressure reading to be on the last day of his shift (seven whole days later)?  Give your numerical answer in psi. (Note:  1 atm = 14.696 psi)