Moles Activity & Practice Name ______Date ______Unit 2 Assignment 6

Introduction - When we work with chemical quantities, we use the unit called a mole. This is because we work with an enormously large number of particles in each chemical reaction experiment and we need to be able to count them quickly! - A mole is like a dozen in that it is a unit that represents a set number of particles. - We can relate 1 mole to the number of particles, which is 6.02×10!"particles - We can relate 1 mole to the mass of a specific substance. The mass of 1 mole is the molar mass. - We do not relate the number of particles to the mass of a specific substance directly. We must do this in two steps using the two relationships involving the mole. Practice As we know, 1 dozen = 12 particles and in chemistry, we use Avogadro’s number to define 1 mole. 1 mole = 6.02×1023 particles (you can see why we don’t count them individually!). A ‘particle’ can mean an atom or a molecule or a formula unit – we’ll learn about molecules and formula units later in the semester. ! !"# Abbreviate mole as mol. Use this equivalence as a set of conversion factors: and !.!"×!"!" !"#$%&'() !.!"×!"!" !"#$%&'()

! !"#

1) Calculate moles for each of the following: a. 2.45 x 1023 atoms of carbon (C) c. 4.6 x 1020 atoms calcium

b. 1921 atoms of bromine (Br) d. 8.24 x 1022 apples

2) Calculate the number of particles for each of the following: a. 1.25 moles of oxygen (O) c. 0.073 moles of potassium (K)

b. 0.446 moles of lithium (Li) d. 8.245 moles of apples

1 The relationship between moles and mass is called the molar mass. The molar mass is the mass of one mole of a substance. We get this mass from the periodic table. Remember the atomic mass? That value is the ! value of the molar mass, but with units of grams per mole, or . For example, the molar mass of carbon is !"# ! 12.011 . !"#

3) Determine the molar mass for each of the following (note: molar mass can be rounded to two digits after the decimal point):

a. Chlorine (Cl): ______d. Sodium (Na): ______

b. Potassium (K): ______e. Silver (Ag): ______

c. Beryllium (Be): ______f. Nickel (Ni): ______

Now that you know how to find the molar mass of a substance, you can use the molar mass as a conversion !!.!" ! ! !"# factor. For iron, the conversion factor can be used as: or ! !"# !!.!" !

4) Calculate the number of moles equivalent to each of the following: a. 152.2 grams of iron (Fe) b. 34 grams of copper (Cu)

5) Calculate the mass of each of the following: a. 0.743 moles of aluminum b. 4.2 moles of silicon (Si)

6) Multi-step problems: Use multiple conversion factors: Avogadro’s number and the molar mass. a. How many grams are there in 3.4 x 1024 atoms of helium (He)?

b. How many atoms are there in 4.25 grams of silver (Ag)?

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