Quantities in chemical reactions

• What is the atomic mass of Ca-40?

  1. 40.08 OR 2. 40.00

  40.00
• What is Avogadro's constant?

  6.02x10^23
• Law of definite proportions: Compound always contains the same ratio of elements by mass


  No MATTER the mass the ratio of atom to atom the same
• When finding empirical formula, for elements of HOFBrICl use the molar mass for ONE atom
• What is a mole?


  A unit which represents a certain number of entities
• Why is mole such a large number?


  Because chemical entities are tiny! Need a large amount to be able to see and properly evaluate
• What are considered entities?


  F.U., molecules, atoms, ions
• Empirical formula: Simplest ratio of elements in a chemical formula
• Molecular formula: Th EXACT ratio of elements in chemical formula
• Precent composition: The precent composition of an element in a compound
• Ratios of elements in a chemical reaction are not compared by weight!

  But... atoms, moles, molecules etc.

  Thus, if one atom of Mg reacts with one atom of O

  One mole of Mg will react with exactly one mole of O
• Why might precent composition Mg be too high?

  Lost some MgO during lab
• Why was the magnesium metal cleaned before use in the lab?

  So it would react efficiently with oxygen
• How many moles of Al atoms are in 7.5 mol of Al2O3?

  15
• What is the mass of 3.75 mol of CS2?

  286 g
• There are 3.56 g of C and 0.896 g of H in a sample of C2H6. What is the precent of H?

  20.1%