Monday November 26, 2012 (Discussion and Worksheet – Moles and Molar Mass)

it’s a small burrowing mammal What is a “mole?”

it’s a skin blemish

What is a “mole?” it’s a spicy sauce

What is a “mole?”... and it’s also a unit of measurement used in chemistry to express amounts of a chemical substance.

Last six-weeks I was very lenient concerning turning in late worksheets and remediating Quizzes well past their “last days.” Also, as you may have noticed, students were allowed to retake quizzes after they had been released back to their owners. Merry Christmas! Here are the new policies for this six-weeks, and there can be no exceptions (sorry): Formatives (worksheets, labs, daily grades, etc.) These must be turned in by Friday of the week they are given to you. No worksheets will be given to you after Tuesday of any week. No late turn- ins and no remediations. Summatives (Quizzes and Projects) These must be remediated no later than two weeks after the grade appears in Gradespeed. If you miss a Quiz due to absence, it must be taken by 5:00 on your second day back in class. Otherwise, it will count as a remediation with a maximum grade of 90. Quiz remediations will involve a different Quiz from the original one. Announcements

Assignment Currently Open Summative or Formative? Date IssuedDate Due Date Into GradeSpeed Final Day QUIZ 11S111/9 11/30 QUIZ 12S211/16 12/7

What is a “mole?” A mole is defined as an amount of a substance that contains as many elementary entities (e.g., atoms, mo lecules, ions, electrons) as there are atoms in 12 grams of pure carbon-12, the isotope of carbon wi th an atomic mass of 12 amu.

Questions How many eggs are in a dozen eggs? How many roses are in a dozen roses? How many donuts are in a dozen donuts? 12

A Dozen A “dozen”, therefore, is a term we use to designate 12 of anything.

Questions How many pennies are in a mole of pennies? How many marshmallows are in a mole of marshmallows? How many water molecules are in a mole of water molecules? x 10 23

A Mole A “mole”, therefore, is a term we use to designate x of anything.

A Mole By the way, if you had a mole of marshmallows, it would cover the surface of the continental United States to a depth of 1170 miles.

A Mole Here’s another way to try to grasp the enormity of this number. If you split a mole of dollars between every man, woman, and child on Earth, each would get $ That’s 86 trillion dollars each! In case you’re curious, each person would get about 100 times more US dollars than are currently in existence.

The Mole In chemistry, the “mole” is the standard unit that indicates the amount of substance present. A mole is the amount of a substance that contains as many particles as there are atoms in exactly 12g of the carbon-12 isotope, which is: x or, Ex.) 12g of the C-12 isotope contains x C-12 atoms. This is Avogadro’s Number – the number of particles in exactly one mole of a pure substance. This number can always be reduced and rounded to the correct number of significant figures.

Molar Mass The mass of one mole of a pure substance is called the molar mass of that substance. A molar mass of an element contains one mole of atoms. Ex.) 4.00g of He, of Li and g of Hg all contain a mole of atoms.

Moles and Molar Mass A mole is the amount of a substance that contains an Avogadro’s number of particles. What is the approximate mass of one mole of helium atoms? g. The mass of one mole of a pure substance is called the molar mass of that substance. Molar mass is usually written in units of g/mol.

Moles and Molar Mass Sample Problem To two decimal places, what is the relative atomic mass and the molar mass of the element chlorine, Cl? If we consult the Periodic Table, we find that the relative atomic mass of chlorine is amu. Therefore, the molar mass of chlorine is grams/mole. This means that the mass of a mole of chlorine atoms is grams, and that mole contains x chlorine atoms.

Determine the mass in grams of the following: Moles and Molar Mass Sample Problem 3.00 mol of sulfur On the Periodic Table, the mass number of sulfur is amu. Therefore, sulfur’s molar mass is g/mol. If there are grams of mass in one mole of sulfur, there are three times that much mass in three moles moles S x g/mol = g S

Determine the mass in grams of the following: 3.01 x atoms of fluorine There is no direct conversion from number of atoms to mass in grams. You must first convert atoms to moles, then moles to grams. Moles and Molar Mass Sample Problem 3.01 x atoms F X 1 = atoms F mol F g F X mol f 1 g F x 10 23

Worksheet Moles and Molar Mass