Unit 4 Review:

In unit 4, we started with toxins. Toxins can enter the body in a limited number of ways, also they can react with H2O in the body. Toxins may be molecular, ionic, or metallic substances. The definition of toxins are substances that interact with living organisms and cause harm. Something important to know is how to write an interpretation, NaVN(s) + HCL (aq) ----> NaCl (aq) + HCN (g) solid sodium cynics reacts with aqueous hydrochloric acid to produce aqueous sodium chloride and gaseous hydrogen cyanide. Then we moved on to equations, which allow you to track changes in matter on an atomic level. Also, a physical change is a change in a matter in which a substance changes form but not identity, and a chemical change is a change in matter that results in the the formation of a new substance or substances with new properties. Something important to know is that ionic compounds do not dissolve in the same way as molecular solids. The dissolving of ionic solids can be shown with a type of equation that stresses the formation of ions in solution. Very important!! If a gas is one of your products, the mass of the products will be less than the mass of the reactants unless you trap the gas. Then we moved on to balancing chemical equations which is an equation that shows the true mathematical relationship between the reactants and the products in a chemical reactant. When balancing equations, you can only change the coefficients. Coefficients in a chemical equation indicate how many "units" of an element or compound you have. Important! Combination: A + B--> AB, decomposition: AB-->A + B, single: A + BC--> AC + B, double: AB + CD ---> AD + CB. Then we moved into the chart again! A lethal dose is the amount of an ingested substance that kills 50% of test sample of animals, it is expressed in mg/ kg, or milligrams of substance per kilogram of body weight. We learned how to find the LD 50 or solve for it in the chart! Then we went into percent error, which is observed value - actual value times 100 / actual value. Chemists use the percent error to express how close their measurements are to the accepted value. Then we moved into scientific notation! Hopefully you all know how to find a mole! If not (learn it!!! Charts!). Then we talked about a solution which is a mixture of two substances that is uniform throughout. A solute is the substance dissolved in a solution. And a solvent is the substance in which the solute dissolves in a solution. Concentration refers to the amount of solute that is dissolved in a solution. Molarity is M= mole over liter. Very important!!! The relationship between the number of moles of particles in a solution is proportional. Then we moved into pH and acids and bases ect. An indicator is a molecular substance that changes color when it comes into contact with an acid or a base. Left side from 0 to 7 is an acid, and 7- 14 is a base. At 7 is neutral, water is a neutral substance. That is why you can dilute an acid or base with water. In order to find the pH of a substance it is -log (H+) H+ is the hydrogen concentration, and OH - is the hydroxide concentration. OH and H+ must equal 1.0 times 10 to the -14. There are two definitions for an acid and base. Starting with the Arrhenius, an acid is a solution which adds hydrogen to the solution, and a base adds hydroxide to the substance. And Bronsted-Lowry Definiton is an acid is a portion donor and a base is a proton acceptor. Each time the H+ concentration is diluted tenfold, the pH number goes up one unit. A strong acid and base, dissociate completely in a solution, and a weak acid and weak base don't dissociate completely in a solution. When strong acid and bases are mixed, the pH approaches 7, but never reaches it completely. Titration is a procedure in which a neutralization reaction is monitored with an indicator allowing you to calculate the unknown concentration of an acid or base. When the equivalence point is reached, the number of moles of H+ ions equals the number of OH- moles. Something important to know is that a precipitate is a solid produced in a chemical reaction between two solutions(chart). Lastly! We learned about stoichiometry! G-->mol, molar ratio, mol--> g. When doing a stoichiometry problem, the number with the lowest grams in the end is the limiting reactant. You can use the limiting reactant when finding the percent yield which is: actual decided by theoretical times one hundred. Good luck on the test! :) a few problems below!

 

 

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