And Dimensional Analysis Mole Questions And Dimensional Analysis

OUTCOME QUESTION(S): Vocabulary & Concepts Avogadro’s number C11-3-12 MOLAR CALCULATIONS Understand the importance of the concept of the mole and calculate the molar mass of various substances. Interpret a balanced equation in terms of moles, mass, and volumes of gases. Include: molar volume Solve problems requiring interconversions between moles, mass, volume, and number of particles. Include: density Vocabulary & Concepts  Avogadro’s number

Just like a “dozen” means 12... To make life easy, in chemistry we count particles by large groups called moles (n). One mole is 6.02 x 1023 particles Just like a “dozen” means 12... This weird amount was chosen as it is exactly how many atoms of carbon needed to weigh 12.011 grams 6.02 x 1023 particles (or 1 mole) of a substance will have a mass in grams equalling its formula mass.

The mass of 1 mole of anything is the molar mass - (g/mol) Mass of 1 atom of K = 39.10 amu Mass of 1 mole of K atoms = 39.10 g/mol So this number represents two things – the mass of a single atom and the mass of a mole of atoms The molecular mass of water (H2O) is 18.0 amu 1 mole of H2O = 2 H + 1 O = 2(1.0) + 1(16.0) So...the molar mass of water is 18.0 g/mol

What is the molar mass of calcium nitrate? Ca(NO3)2 Breakdown the compound: 1 Ca(NO3)2 particle = 1 Ca atom + 2 N atoms + 6 O atoms 1 Ca(NO3)2 mole = 1Ca mole + 2 N moles + 6 O moles = (40.0) + 2(14.0) + 6(16.0) So the molar mass of Ca(NO3)2 is 164.0 g/mol

Mole is abbreviated mol or n What is the molar mass of ammonium dichromate? (NH4)2Cr2O7 Breakdown the compound: 1 (NH4)2Cr2O7 mole = 2 N mol+ 8 H mol + 2 Cr mol + 7 O mol Mole is abbreviated mol or n = 2(14.0) + 8(1.0) + 2(52.0) + 7(16.0) So the molar mass of (NH4)2Cr2O7 is 252.0 g/mol

Find the molar masses of these compounds: You will need to write the formula in some cases. Cu3(PO4)2 copper(II) phosphate 3Cu + 2P + 8O 381 g/mol magnesium hydroxide Mg(OH)2 Mg + 2O +2H 58 g/mol dinitrogen trioxide N2O3 2N + 3O 76 g/mol

We call this Avogadro’s Number (NA) One mole is 6.02 x 1023 particles We call this Avogadro’s Number (NA) 6.02 x 10 23 particles 1 mole 6.02 x 10 23 particles 1 mole or The term "particle" refers to the known value: atoms, molecules, ions, etc. 6.02 x 1023 pencils is 1 mole of pencils 6.02 x 1023 carbon atoms is 1 mole… 6.02 x 1023 water molecules is 1 mole…

Rules for Dimensional Analysis Start with what you know Identify (or create) the conversion factor Put units you want to cancel on bottom Put units you need on the top Multiply across top, divide across bottom Dimensional Analysis is a way to convert units: (make the value the same but in different units) Some people simplify this notation with added bars – called “factor label line” How many pizzas would 250 pieces of pepperoni make? 1 pizza 250 pepperoni = 13.2 Pizzas 19 pepperoni

String multiple conversion factors together… How many eggs in 25.0 dozen? 12 eggs 25.0 dozen = 300 eggs 1 dozen How many centimetres in 150 km? String multiple conversion factors together… 150 km 1000 m 100 cm = 1.5 x 107 cm 1 km 1 m

1 mol 1 mol How many atoms in 25.0 moles of copper? atoms are the “particle” 25.0 Cu mol 6.02 x 1023 particles = 1.51 x 1025 Cu atoms 1 mol How many molecules of water in 1.50 x 10–5 mol? molecules are the “particle” 1.50 x 10-5 H2O mol 6.02 x 1023 particles = 9.03 x 1018 H2O molecules 1 mol

atoms are the “particle” How many moles is 5 atoms of zinc? atoms are the “particle” 5 Zn atoms 1 mol = 8.31 x 10-24 Zn mol 6.02 x 1023 particles Note: all conversion factors can be flipped “upside down” depending on the need 6.02 x 10 23 particles 1 mole 6.02 x 10 23 particles 1 mole or So 5 atoms of Zinc is the same as 8.31 x 10-24 moles

Now lets add the molar mass to our dimensional analysis work… What is the mass of 1.20 x 10–5 moles of carbon tetrachloride, CCl4? Now lets add the molar mass to our dimensional analysis work… CCl4 = 1 C + 4 Cl = 1(12.0) + 4(35.5) = 154.0 g/mol 154.0 g 1 mol 154.0 g 1 mol What you know Add conversion factor Units to cancel on bottom Units in need on the top Multiply top, divide bottom or 1.20 x 10-5 mol CCl4 1 mol 154.0 g = 1.85 x 10-3 g

The mole allows the conversion between mass and number of particles

1 mol = 0.556 mol of H2O 18 g = 3.34 x 1023 H2O molecules 1 mol How many molecules of water in a 10.0 g sample? H2O = 18.0 g/mol Whenever the question involves mass (g) find the molar mass 10.0 g H2O 18 g 1 mol = 0.556 mol of H2O 0.556 mol 1 mol 6.02 x 1023 particles = 3.34 x 1023 H2O molecules This will take two steps…

Put the two equations together! 10.0 g H2O 1 mol 6.02 x 1023 particles = 3.34 x 1023 molecules of H2O 18 g 1 mol There are 3.34 x 1023 molecules in 10.0 g of water. String multiple conversion factors together… to solve in one step!

This will take two steps… How many particles of sodium chloride in 25.0 g? NaCl = 58.5 g/mol Need the molar mass… 1 mol 25.0 g NaCl 6.02 x 1023 particles = 2.57 x 1023 particles of NaCl 58.5 g 1 mol There are 2.57 x 1023 particles of NaCl in 25.0 g. This will take two steps…

1 mol 30 g 1 mol = 3.61 x 1023 atoms in total 1 particle How many total atoms in 6.0 g of lithium oxide? Li2O = 30 g/mol Here our “particle” is NOT an atom; but, a compound How does this change things? 1 mol 6.0 g Li2O 6.02 x 1023 particles 3 atoms 30 g 1 mol 1 particle ? atoms 1 particle = 3.61 x 1023 atoms in total We need to create a conversion factor!

CAN YOU / HAVE YOU? Vocabulary & Concepts Avogadro’s number C11-3-12 MOLAR CALCULATIONS Understand the importance of the concept of the mole and calculate the molar mass of various substances. Interpret a balanced equation in terms of moles, mass, and volumes of gases. Include: molar volume Solve problems requiring interconversions between moles, mass, volume, and number of particles. Include: density Vocabulary & Concepts  Avogadro’s number