Mole Review Molar mass The molar mass is calculated by adding atomic _____________ (found underneath an element’s symbol). ! molar mass = the mass of ______________ of particles ex: Let’s calculate the molar mass of Na2SO4: The atomic mass of any element in GRAMS, will always contain ______________________ of atoms of that element. We often need the molar mass to perform conversions. ex: 2.60 moles of NaSO4 = ______________ grams Of course, as we learned last class, we have to remember our sig figs! ! this calculation involved ______________________, meaning we’re looking for the least number of _____________________________. ! our answer should be rounded to _______ sig figs ***When doing a series of calculations, do NOT round your answer UNTIL THE END!!! If you do it each step, you will lose a huge amount of accuracy AND precision! 1 ex: 1053.24 grams of K2Se = _____________ moles Mole Calculations Avogadro and his number -­‐ Italian chemist (1776 – 1856) -­‐ didn’t determine/find the number but did a lot of preliminary research/theorizing about atoms and molecules -­‐ ________________________________ o the numerical value of one mole Your turn! a) How many atoms are there in 44g of neon? b) What is the mass of 1.5 x 1024 atoms of sodium? 2 Avogadro’s Hypothesis Equal volumes of different gases at the same temperature and __________________ contain the same number of particles. One mole of any gas occupies _________________ at STP. STP -­‐ standard temperature = ___________ ! chosen because this is the ___________________ point of water and is easily reproduced (a basic foundation for the scientific method) ! absolute zero = ___________ = _______________ -­‐ standard pressure = ______________ ! normal pressure at ____________________________ Your turn! c) How many moles of N2(g) are there in a sample with a volume of 15.0 litres at STP? d) What volume will 10.0 grams of helium gas occupy at STP? 3 Stoichiometry The relationship between the amount of ____________________ used in a reaction and the amount of __________________ produced by a reaction. The coefficients of a balanced chemical equation give the relative ________________ of each substance, NOT their relative masses. If the mass of a substance is given, it must be converted to a _____________ quantity. Then, the mole _________________ from the coefficients of the balanced equation can be applied. First, let’s balance the equation below: C2H5OH(l) + O2(g) ! CO2(g) + H2O(l) Now, using the above equation, solve the problems below: e) What mass of CO2 can be produced when 3.6 moles of O2 completely react? f) What mass of CO2 is produced along with 10.8 grams of H2O? 4 Molarity Molarity is defined as the ________________ of solute per litre of solution. ! Molarity = M = [ ] = ____________________ = __________________ = ________ ***note: this is not per litre of water!!! g) If 4.2 moles of KNO3 are dissolved to make 2000.mL of solution, what is the molar concentration of the solution? h) If 8.0g of NaOH is dissolved to make 100. mL of solution, what is the molar concentration of NaOH(aq)? i) If [Pb(NO3)2] = 0.10M, how many grams of Pb(NO3)2 are in 500.mL of solution? 5 j) What volume of 0.250M KCl solution can be prepared using 5.00g of KCl(s)? Dilution C1V1 = C2V2 [final] = [initial] x initial volume final volume k) What is the resulting concentration of KBr(aq) when 200. mL of water are added to 150. mL of 0.150M KBr(aq)? l) What is the concentration of each solute when 100. mL of 0.200 M NaCl(aq) are added to 150. mL of 0.100M KBr(aq)? 6 m) Calculate the concentration of each ion present when 15.0mL of 0.75M MgCl2 is mixed with 30.0mL of 0.60M CaBr2. 7