Chemistry 1027A/B Study Guide - Midterm Guide: Hexavalent Chromium, Stereoisomerism, Bioavailability

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2. How Can It Contain the same Elements Yet Be Different?
Key Learning Outcome
Define terms such as speciation, constitutional/structural isomerism, stereoisomerism, enantiomers, etc.
Use the above terms to identify the relationships between chemical substances, and provide examples of
substances that are related by those terms
Describe the different properties (physical, biological, etc.) of substances that are related by the terms
above
Describe and identify the basic shapes of molecules
Section A : Speciation
Speciation : Different chemical forms of the same element i.e. Cr3+ & C4+ are examples of chemical speciation
- Cr6+ Hexavalent chromium (carcinogen) while cr3+ is trivalent chromium body needs to function
Parts per Billion/ Parts per Million Example :
EPA says current standard is 100 parts per billion of all forms of chromium
Failies told ell ater is’t safe at 7 parts per illio
There’s a thousand million in a billion therefore water concentration is 7000 parts per billion does’t eet
standards
Concentration (Parts Per Billion) - PPB = mass of substance/ total mass x 1 billion
Bioavailability: Determines how well something is getting absorbed into your body
i.e. Iron Tablets, Iron Sulphate has a lower bioavailability then Iron Bisglyceine (protein carriers bring to blood
stream)
i.e. Mercury : Volatile easily goes from liquid to gas
Common Forms of Mercury(HG)
Elemental; liquid mercury in thermometers, mercury is the only metal at room temperature metals conduct heat
very well
Fluorescent Light bulbs (Mercury coated on gas tube gives off light) are conductive to electricity
Gaseous Mercury VERY dangerous esp. if its inhaled into your lungs gets absorbed into your body
- Oxidizes (removes electrons) Hg(g) Hg2+ (Toxic) Chemical Speciation
o Become inorganic mercury due to oxidization
Inorganic Cinnabar Hg2+ Hgo
- Organic - Organomercury Hg-CH3 * Most Toxic Methy Mercury (MeHg) reaches brain then gets turned
into Hg2+
o Bio magnification scavenger fish eating little fish & garbage on bottom higher mercury
concentration
- 50-75% of Hg released into the environment is due to human activity (Electricity generation, burning coal,
garbage incineration, smelting), balance is from natural events olcao eruptio’s etc.
- Small Scale gold mining (20% of world gold) also add to atmospheric Hg
o Au + Elemental Hg(Liquid) mix to form an amalgam, later heated to drive off Hg, leaving Au
Section B: Structural/Constitutional Isomers
Any given molecule will have a defined connectivity that is based on the electronic structure of the atoms
o Single bonds rotate freely
o Same molecular formula but different connectivity (Order in which atoms are connected)
o Different molecule different physical properties
Section C: Stereoisomerism
Have the same connectivity but not normally interconnecting (cannot be converted from one to another
by rotating a bond) - different chemical species
Different properties
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