Gases Review

Things to remember about gases Calculations: Density (D)= m/V, thus m= Dx V, for gases V is in Liters, m is still in g! Molar mass MM=dRT/P PV=nRT You can use PV=nRT to solve for Charles’ Boyles and other gas laws. Cross out what is constant! Ptot= PA +PB +PC … Pgas= Ptot-PH2O, when you collect GAS over WATER

More calculations: Rms = √3RT/MM Graham’s law of diffusion Rate1 = √MM2 Rate2 √MM1 PA= χA Ptot χA= mols A/total moles in system - Smaller MM gases effuse faster and diffuse faster than larger MM gases

More things about gases Ideal gases act more “real” at low temp and high pressure because the molecules are close together so IMFs matter. You MAY have to use a chart or graph to get some of the data you need to solve a problem… be aware! If you are given PP of water vapor, you will have to use it!

More things about gases Kinetic Molecular Theory: All gases are in constant motion All gases have completely elastic collisions Gases don’t have IMFs Gases average kinetic energy is the same at the same temperature

Relationships between variables: 1) When P goes up, V does this??? 2) When Temp goes up, V does this??? 3) How do moles affect P??? 4) Can you use moles interchangeably with P???

Things to KNOW in general: Percent error= |actual-experimental| x 100 actual Percent errors you want to be LOW Percent yield= actual x 100 theoretical Percent yields you want to be HIGH How do you find actual??? How do you find theoretical?

Stoichiometry Review BE able to do the following: Go from gram of a reactant to grams of a product. (either chart or dimensional analysis) Go from moles of a reactant to moles of a product. Go from grams or moles of a reactant to grams/ moles of another reactant. WHY? WHEN?

Stoichiometry Review KNOW THESE TO GET TO MOLES: g/MM M x Vin L Atoms or molecules / 6.022 x 1023 Gas at STP only: V/22.4

Stoichiometry Review Recognize limiting reactant problems!!!! MOST OF THE TIME THEY WILL NOT TELL YOU IT’S LIMITING REACTANT! So, how do you know? Be able to solve for moles given volume and molarity. KNOW MOLARITY COLD!!!! What is the definition of molarity?

Stoichiometry Review Be able to calculate percentages! Part/whole x 100 Be able to use percentages to find out info in problem! For example: your actual yield is 89% of your theoretical yield…. How can you make a solution? STEP BY STEP What if you start from g… what if you start from a solution? Why do you ALWAYS add conc acid to water when diluting? Never water to conc acid!

Stoichiometry Review Use the dilution equation to dilute solutions: Mdil Vdil =Mconc Vconc You will only need to solve for 1 variable! Know the mass spec idea. Why do we use it? Understand how to solve for problems in which you make something…. Lab problems! Gravimetric analysis

Stoichiometry Review Beer’s Law: abc= A Where: a= molar absorptivity b= path length of cell (usually 1 cm) c= concentration A= absorbance Why do we need beer’s law???? We can use the absorbance of light to determine concentration when compared against a calibration curve!

Stoichiometry Review What is a calibration curve???? - A set of measurements that includes points before and after the points you are interested in… Example: percent of sugar by mass of soft drinks…. You can create a calibration curve…

Types of Chemical Reactions 1) Synthesis… how do you know? You start with 2 elements or an element and compound or two compounds…. BUT you make 1 product: Examples: Metal oxides + water  metal hydroxides Metal hydrides + water  metal hydroxide + H2 Group I metal + water  metal hydroxide + H2 Element + element  compound Nonmetal oxide + water  acid

Types of Chemical Reactions Synthesis: metal oxide + CO2  metal carbonate Combustion: Hydrocarbons or alcohols + O2  H2O + CO2 Hydrocarbons have only H and C Alcohols have H, C and O only!

Types of Chemical Reactions 2) Decomposition How do you know? You start with one compound!!!!! ALWAYS! To know: H2O2  O2 + H2O (not balanced) Metal hydroxides metal oxide + H2O Acids nonmetal oxide + H2O

Types of Chemical Reactions 3) Single replacement: How do you know?? Start with an element and a compound. Cation replacement: Switch the free metal with the one in the compound! Ex: Zn + HCl  H2 + ZnCl2 (not balanced) Anionic replacement: Switch the halogens! Ex: Cl2 + NaBr  NaCl + Br2 (not balanced)

Types of Chemical Reactions 4) Double Replacement How do you know? You start with 2 ionic compounds! What is the goal of double replacements??? To form a precipitate, a gas or a weak acid How do you know if it is a gas? Here are the common ones: CO2, SO2, SO3, NO2, NO, NH3

Types of Chemical Reactions How do you know if it precipitates? SOLUBILITY RULES: Know this…. If it has a group 1 metal in the compound, it is soluble! If it has a nitrate in the formula, it is soluble! If it is soluble, it DOES NOT form a precipitate! If it is a strong acid, it will always ionize! (SOLUBLE!) What are they????

For those of you that really care: Halides (group 17) are mostly soluble except: Pb, Ag, and Hg Sulfates are soluble except: Ca, Sr, Ba Pb Hydroxides are only soluble with group 1 and Ca, Sr, Ba (a little) Phosphates are NOT soluble Sulfides are NOT soluble