Question

Part 1: Tony has been monitoring wildlife around a stream near the Delaware Tech campus for an ongoing Biology project. During his last visit to the stream he noticed that there were rusty-red deposits on a number of the rocks. When he scooped up some of the water he saw that it. appeared to be cloudy and had a yellowish tint. He thought it smelled slightly metallic. However, he did not observe any signs that wildlife had been harmed. At lunchtime, Tony mentioned what he had observed at the stream to his friend, Jill, who is studying chemistry at Delaware Tech. He wondered if she could explain the water's color and cloudiness. Jill thought for a while, and then said that she did know that natural water usually contains traces of many different substances, most of which do not affect its color. Some are inorganic compounds that the water picks up as it filters through the ground, but there will be some organic compounds too. She thought that the metallic smell could suggest an inorganic compound. In her experience most of those compounds are ionic, like salt, and won't discolor water or stain rocks. She tried to think of colored materials she had encountered and remembered using blue crystals of CuSO45 H2O in lab. She'd also worked with solutions containing copper and they were usually blue or green. She recalled using red, orange, purple, and yellow solutions but couldn't remember the compounds involved or any metals in those compounds. She did remember that metals that produce colored solutions are primarily found in a particular area of the Periodic Table Each team member should record preliminary responses to questions 1-4 in their individual notebooks. Answer question 5 in ONE team member's lab notebook. Turn in all yellow sheets with the lab report. 1. What area or areas of the Periodic Table will you focus on considering what Jill has remembered? 2. List five elements whose ions might produce color in the water. Indicate cations and/or anions containing those elements that occur in ionic compounds.

Answer 1

1) Jill has remembered the middle portion of the periodic table. This portion of the periodic table includes Transition elements or d-block elements. Many transition metals or their ions are colored due to the presence of unpaired electrons in their d-atomic orbitals.The colors of transition metals or their ions are due to d-d transition in the visible region of electromagnetic spectrum.

2) The five elements whose ion produces color in water are Iron, Copper, Chromium, Nickel and Titanium.

Cation Anion

FeS Fe²⁺   S^2-

CuO Cu²+   O^2-

CrO   Cr²⁺ O^2-

NiS Ni²⁺ S^2-

TiCl₃ Ti³⁺ Cl^-