Question

This is an inroganic chemistry question, I just need help with number 7 but included everything so you can get background. Please only answer if you can answer it correctly.

a) Obtain two 50 mL beakers. Into one beaker add 1.0 M Zn(NO302 and into the other add 1.0 M Cu(NO302. Adjust the liquid depths in each beaker such that they are approximately equal and 1-2 cm deep b) Cut a strip of filter paper that is long enough to extend between the solution in the two beakers. Wet the strip of filter paper with 0.5 M NaNO3 solution and place each end of the paper into the beakers, such that the paper is in contact with the both solutions as shown below: Figure 2: Constructing a Galvanic Cell c) obtain a voltmeter (Wavetek Digital Multimeter) and strips of Cu and Zn metal. Immerse the bottom of a strip of Cu metal in the Cu(NO32 solution. Then, immerse the bottom of a strip of Zn metal in the Zn(NO3)2 solution. Ensure that the strips are NOT touching each other at the top. Turn on the voltmeter and turn the dial on the meter to the number 20 in the "V region of the meter. Touch the red probe to one of the metals and the black probe to the other metal. d) Record the voltage obtained from the voltmeter to the nearest 0.01 volts. If you obtain a negative voltage you should switch the red and black probes (such that the probes touch the opposite metals. Allow the reading to stabilize before you record the voltage. Answer the questions that follow 1. What is the experimental voltage for the cell? 0.85 2. Draw a diagram of the cell you constructed. Label the cathode and anode. Indicate in the drawing which metal was touching the red probe and which was touching the black probe.

Answer 1

QUESTION 7

When excess ammonia (or ammonium hydroxide) is added slowly into copper (II) nitrate, hydroxide ions are formed in the solution. As ammonia is a weak base, it removes hydrogen ions from water, to form hydroxide ions.

$NH_3+H_2O\rightarrow NH_{4}^{+}+OH^-$

First, these hydroxide ions will react to form an insolubale pale blue, copper (II) hydroxide.

$Cu^{2+}+2OH^-\rightarrow Cu(OH)_2$

Upon further addition, the colour of the solution turns dark blue, due to the formation of a copper-ammonia complex as follows.

$Cu^{2+}+4NH_3\rightarrow [Cu(NH_3)_4]^{2+}$

The drop in voltage can be attributed to the dilution of the cathodic electrolyte. When the copper solution is diluted with the ammonia solution, the concentration of the cathodic electrolyte decreases, and the voltage of the cell decreases. (The nernst equation can be used to explain this)

$E_{cell}=E^0_{cell}-\frac{0.0592}{n}log\frac{[Zn^{2+}]}{[Cu^{2+}]}$