Unit 4 Review

     In unit 4, we learned all about toxins. The definition of a toxin is a substance that interacts with a living thing and causes harm. Toxins can enter the body and will often react with water. They can be molecular, ionic, or metallic-bonded substances.
     When we first started unit 4, we learned what it means to interpret a chemical equation. That includes basically looking at an equation and the phase changes (the italicized letters next to chemical compounds) in it and writing in words what's happening. This could possibly sound like "solid ___ reacts with an aqueous ___solution to form solutions of ___ and ___." The italicized letters can act as clues to whether a reaction is a physical or chemical change.
     A huge part of this toxins unit was balancing equations. It's crucial for a chemical equation to be balanced on both sides, otherwise the reaction will be unstable. A lot of reactions will produce toxic substances. Not only do equations need to be balanced for the safety of the chemists, but also to abide by the law of conservation of mass, which states that no atoms can be lost or gained. Balancing equations and predicting products go hand in hand; there are four different types of reactions: combination, decomposition, single exchange, and double exchange. If ever an atom moves places between the reactant side and the product side, you have to make sure it's present in equal quantities on both sides.
     Obviously, we also learned about toxicity in this unit. All substances can be toxic if ingested in large enough qualities, and the amount of substance needed to kill an organism or poison it is called the LD-50. LD stands for "lethal dose". To calculate how much substance you need to harm an organism of a certain weight in pounds, convert those pounds to kilograms and multiply by the LD-50.
     pH is important to consider when dealing with contaminated substances or substances which you don't know the toxicity of. On a logarithmic scale, anything with a pH of lower than 7 is an acid, and anything above 7 is a base. 7 is neutral.  PH is determined by the concentration of hydrogen and hydroxide ions in a solution. An acid or base can be diluted with water, and certain mL of water can decrease the acidity or basicness by tenfold.
     The final, and possibly hardest, skill that we learned in this unit was stoichiometry, which uses coefficients in BALANCED chemical equations to determine the number of moles of a substance. By constantly converting moles to grams and back to moles, you can find out how much reactant is needed to make a certain amount of product and vice versa. You can also figure out limiting reactant, a reactant that puts a limit on how much product can be made.

Problems: 

Jogkvsjdajfsk (to be added soon)