Brady Chapter04 - Chapter 4 The Mole Atomic mass provides a means to count atoms by measuring the mass of a sample The periodic table on the inside

Brady Chapter04 - Chapter 4 The Mole Atomic mass provides a...

This preview shows page 1 - 8 out of 27 pages.

Chapter 4: The Mole Atomic mass provides a means to count atoms by measuring the mass of a sample The periodic table on the inside cover of the text gives atomic masses of the elements The mass of an atom is called its atomic mass When using atomic masses, retain a sufficient number of significant figures so the atomic mass data contributes only slightly to the uncertainty of the result
Image of page 1
The molecular mass allows counting of molecules by mass The molecular mass is the sum of atomic masses of the atoms in the compounds formula – For example the molar mass of water, H 2 O, is twice the mass of hydrogen (1.008) plus the mass of oxygen (15.999) = 18.015 Strictly speaking, ionic compounds do not have a “molecular mass” because they don’t contain molecules
Image of page 2
The mass of the formula unit is called the formula mass Formula masses are calculated the same way as molecular masses For example the formula mass of calcium oxide, CaO, is the mass of calcium (40.08) plus the mass of oxygen (15.999) = 56.08 One mole of a substance contains the same number of formula units as the number of atoms in exactly 12 g of carbon-12
Image of page 3
One mole of a substance has a mass in grams numerically equal to its formula mass The mass of one mole of a substance is also called its molar mass One mole of any substance contains the same number of formula units This number is called Avogadro’s number or constant 1 mol formula units = 6.02 x 10 23 formula units
Image of page 4
Counting formula units by moles is no different than counting eggs by the dozen (12 eggs) or pens by the gross (144 pens) Avogadro’s number is huge because atoms and molecules are so small: a huge number of them are needed to make a lab-sized sample Avogadro’s number links moles and atoms, or moles and molecules and provides an easy way to link mass and atoms or molecules
Image of page 5
Using water (molar mass 18.015) as an example: 1 mole H 2 O 6.022 x 10 23 molecules H 2 O 1 mole H 2 O 18.015 g H 2 O 18.015 g H 2 O 6.022 x 10 23 molecules H 2 O Within chemical compounds, moles of atoms always combine in the same ratio as the individual atoms themselves so: 1 mole H 2 O 2 mole H
Image of page 6
Stoichiometry is the study of the mass relationships in chemical compounds and
Image of page 7
Image of page 8

You've reached the end of your free preview.

Want to read all 27 pages?

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes