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Chemistry lab question spectroscopy percent brass in copper

my lab: Percent Copper in Brass by using spectroscopy
I have Copper(II) nitrate solution
Copper(II) sulfate solution
Iron(III) nitrate solution
Iron(III) chloride solution
Zinc nitrate solution
Zinc sulfate solution
 
 
Do Zn2+ ions absorb visible light? Discuss the answer in term of (a) the color and appearance of Zn2+ aqueous solutions and (b) the electonic structure of Zn2+ ions. Hint: See the background section for the information on the electronic transitions of transition metals ions.
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2 Answers

I think the short answer to this would be no. Zn2+ ions have a filled d-shell with an empty s-shell, therefore there are no electrons to excite. Zn(NO3)2 solution should be colorless. 
Here is an abstract from pubmed, you may search it for additional and most relevant information.
 
Naina B
 
Physiol. 1969 February; 44(2): 255–261.

PMCID: PMC396071
Absorption of Copper, Zinc, and Manganese by Sugarcane Leaf Tissue 1
John E. Bowen

aPlant Physiology Department, Hawaii Agricultural Experiment Station, University of Hawaii, Hilo, Hawaii 96720
1 Journal Series No. 1026 of the Hawaii Agricultural Experiment Station.
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Abstract
The absorption of Cu2+, Zn2+, and Mn2+ by leaf tissue of 4-month old sugarcane plants (Saccharum officinarum L., var. H53-263) has been investigated. After the “apparent free space” fraction was desorbed, the absorption of Cu2+, Mn2+, and Zn2+ yielded a curve typical of many ion uptake processes when measured as a function of the external concentration. However, only 1 absorption mechanism was evident for each cation. The pH optimum for Cu2+ and Zn2+ uptake was 5.0 to 6.0, whereas that for Mn2+ absorption was 4.5 to 6.0. Absorption was competitively inhibited by H+, and this inhibition was reversible when 0.5 mm Ca2+ was present. Cu2+ and Zn2+ were absorbed through the same carrier sites, as concluded from their mutually competitive activities. Mn2+ was absorbed through a second, independent mechanism. Uptake of each cation was strongly inhibited by uncouplers of oxidative phosphorylation, by Amytal and Nembutal2, by 5 × 10−2m succinate, and by ADP and Pi. Absorption of Cu2+, Zn2+, and Mn2+ was concluded to be coupled to oxidative phosphorylation, and specifically to energy-conservation Site I.