to find of a mole of an element one looks Section Advance Study Assignment: Dete

Question

to find of a mole of an element one looks Section Advance Study Assignment: Determination of a Chemical Formula I. To find the mass of a mole of an element, one looks up the atomie mass of the elemnent in a table of atomic masses (see Appendix IlI or the Periodic Table) The molar mass of an element is simply the mass in grams of that element that is numerically equal to its atomic mass For a compound substance, the molar mass is equal to the mass in grams that is numerically oqual to the sum of the atomic masses in the formula of the substance Find the molar mass of Cu 2. If one can find the ratio of the number of moles of the clements in a compound to one another, one can find the formula of the compound In a certain compound of copper and oxygen, Cu, we find that a sample weighing 0.6349 g contains 0.5639 g Cu a How many moles of Cu are there in the sample? No moles mass Cu moles b. How many grams of O are there in the sample? (The mass of the sample equals the mass of Cu plus the mass of O.) c. How many moles of O are there in the sample? moles d what is the mole ratio (no moles Cuno moles) in the sample? e. What is the formula of the oxide? (The atom ratio equals the mole ratio, and is expressed using the smallest integers possible.) f. What is the molar mass of the copper oxide? g/mol

Explanation / Answer

1. Molar masses are as below,

Cu = 63.546 g

Cl = 35.45 g

H = 1.008 g

O = 15.999 g

H2O = 18.02 g

2. a. Moles of Cu = g/molar mass of Cu

                            = 0.5639/63.546

                            = 0.0089 moles

b. Grams of O = total mass of sample - mass of Cu in sample

                        = 0.6349 - 0.5639

                        = 0.071 g

c. moles of O = mass of O/molar mass of O

                      = 0.071 / 15.999

                      = 0.0044 moles

d. moles ratio of Cu and O = 0.0089 : 0.0044

                                           = 2 : 1

e. Formla of the oxide is = Cu2O

f. Molar mass of Cu2O = 2 x molar mass of Cu + molar mass of O

                                     = 2 x 63.546 + 15.999

                                     = 143.091 g  

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