Assignment 2 Avogadro’s Constant

Introduction Avogadro’s Constant, also called Avogadro’s number, represents the number of particles that make up one mole of anything. It was named in honour of an Italian scientist, Amadeo Avogadro di Quaregna, who helped clarify the difference between atoms and molecules.

Atoms are very small. They are so small that it would seem impossible to find the mass of a single atom yet the Periodic Table does give the atomic mass of every element. How were they able to determine this?

If you were asked to determine the mass of one salt crystal how would you do it? The easiest way would be to find the mass of a certain quantity of salt, then estimate the number of crystals in that quantity, and then calculate the average mass of one crystal: mass of salt = 2.5 g number of particles ~ crystals mass of 1 crystal = = g 2.5 = 1.0 x g

Scientists use the mole when dealing with quantities of atoms or molecules. A mole is actually defined as the number of carbon atoms in exactly 12 g of pure carbon-12. Through many years of experimentation it was determined that one mole of anything consists of the same number of particles.

1 mole = 6.02 x particles = Avogadro’s Constant Remember this number. It will be used a lot in Chemistry 1 mole of any substance represents this number of particles. 1 mole of Hydrogen atoms = 6.02 x atoms 1 mole of Hydrogen molecules = 6.02 x molecules 1 mole of C 6 H 12 O 6 = 6.02 x molecules

Converting the number of particles to Moles If we know that 1 mole is equal to 6.02 x particles we can use this relationship to convert the number of particles in a sample to moles: #moles = the number of particles x _____1 mole______ 6.02 x particles Question: How many moles of magnesium is 1.25 x atoms of magnesium? #moles = 1.25 x atoms x _____1 mole______ 6.02 x particles = mol Mg (moles of magnesium)

Converting the number of moles to the number of particles How many particles of sucrose are in 3.5 mol of sucrose? We use the same relationship as on the previous page. 1 mole = 6.02 x particles Therefore 3.5 moles x 6.02 x particles = 2.11 x 6.02 x particles 1 mole

Assignment Questions due date: Saturday October 3, 2009 All students: 1.Read pages 9-10 of the Chemistry Course Companion. 2.How many moles contain each of the following? a) 5.75 x atoms Al b) 2.50 x atoms Fe 3.Calculate the number of particles in a) 11.5 mol of water b) 2.50 mol Zn 4.Arrange these samples from smallest to largest in terms of number of representative particles: 1.25 x atoms of zinc; 3.56 mol of iron; 6.78 x molecules of glucose HL: continued next page

HL only Using read the speech given for the Nobel prize in Physics. Rewrite the speech by summarizing each paragraph in such a way as to be easily understood by a high school Chemistry student.