Name_____Average 6.1/10_________________________

                            Chemistry 101                               

Quiz #4—Chapters 4 and 5(part)    

 

1.   A typical bacterial cell has a diameter of 1 uM and a volume of

 5.2 x 10 –19 m3 and contains 10 molecules of DNA polymerase III, the enzyme responsible for copying the cell’s DNA.  During the course of purification of the DNA polymerase, 10 9 bacterial cells are broken up or lysed and mixed with water such that the final volume is 15.0 mL.

What is the final molar concentration of DNA polymerase III?

 

This is a lesson in when not to use M1V1 = M2V2

 

10 DNA pol / cell x 10 9 cells = 10 10 DNA pol

 

10 10 DNA pol x 1 mol / 6.02 x 10 23 DNA pol = 1.66 x 10 –14 moles DNA pol

 

[DNA pol] = 1.66 x 10 –14 moles DNA pol / 0.015 L = 1.1 x 10 –12 M

 

 

2.         Some commercial drain cleaners contain two components: sodium hydroxide and aluminum powder.  When the mixture is poured down a clogged drain, the following reaction occurs:

2 NaOH (aq) + 2 Al (s) + 2 H2O  à 2 NaAl(OH)4 (aq) + 2 H2 (g)

The heat generated in this reaction helps melt away obstructions such as grease, and the hydrogen gas released stirs up the solids clogging the drain.

Calculate the volume of H2 formed at 25 °C and 1.0 atm if 3.12 g of Al is treated with an excess of NaOH and water.

 

Strategy 1) find the number of moles of Al 2)find the number of moles of H2 3)Find the volume of H2

 

3.12 g x 1 mol/ 26.98 g = 0.116 moles Al

 

0.116 moles Al x 2 moles H2 / 2 moles Al = 0.116 moles H2

 

V = nRT /P = 0.116 moles x 0.0802 L atm/ K mol x (273 + 25 K) / 1 atm

V = 2.8 L (2 sf)

 

Potentially Useful Information-- Na = 6.022 x 10 23 atoms or molecules / mole.

R = 0.082 L. atm./ K. mol = 8.314 J/ K.mol

1 L = 1 dm 3                                                            T  in Kelvin = 273.15 + T (°C)

Element

Atomic Number

Mass ( g /mol)

H

1

1.008

Al

13

26.98

Good luck and have a great Fall break!