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GIA: Mole-Mass Conversion for Elements
Learning Objectives: To correctly identify and label the “given” and “unknown” quantities in a problem. To correctly identify and label the molar mass as a conversion factor. To calculate the moles of an element given the mass, or the reverse. Working Mode: Pairs
Instructions: Students should complete each step below, alternating roles as indicated. For each quantity named, give the numerals (if known), the unit of measure, and the chemical identity for that quantity. The first question reminds you of this requirement.
Activity 1: Find the mass (in grams) of 0.15 mol of the element magnesium.
- Student 1: Identify the measure given in the problem, including the numerals, units, and name of chemical (often referred to as the “given”). Then identify the measure in the problem that is unknown (this is the one you are to find, it is often called the “unknown”). State the units and chemical identity of the unknown.
- Student 2: Identify the conversion factor that can be used to complete this problem; give the numerals, units, and chemical identity of the numerator and denominator.
- Student 1: Set up the problem correctly. Remember to begin with the measure of a known chemical, and use the units and identity for each quantity.
- Student 2: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic.
- Student 1: Round the answer to the correct number of significant figures, be sure units and identity are given, and circle the answer.
Activity 2: What is the mass of 2.32 x 10-4^ mol of the element einsteinium?
- Student 2: Identify the given and unknown (include all units and chemical identities).
- Student 1: Identify the conversion factor that can be used to complete this problem (include all units and chemical identities).
- Student 2: Set up the problem correctly (include all units and chemical identities).
- Student 1: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic.
- Student 2: Round the answer to the correct number of significant figures, be sure units and identity are given, and circle the answer.
Activity 3: A chemist uses 11.5 g of sodium. How many moles have been used? Be sure to give the units and chemical identity of each quantity.
- Student 1: Identify the given and unknown.
- Student 2: Identify the conversion factor that can be used to complete this problem.
- Student 1: Set up the problem correctly.
- Student 2: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic.
- Student 1: Round the answer to the correct number of significant figures. Circle the answer.
Activity 4: If you had 4.2 x 10-2^ g of krypton, how many moles would that be? Be sure to give the units and chemical identity of each quantity.
- Student 1: Identify the given and unknown.
- Student 1 Identify the conversion factor that can be used to complete this problem.
- Student 2: Set up the problem correctly.
- Student 1: Check to see that the units and chemical identities cancel correctly, ten do the indicated arithmetic.
- Student 2: Round the answer to the correct number of significant figures. Circle the answer.
QUESTION 1
Student 1 GIVEN = 0.15 mol Mg, UNKNOWN = mass (g) Mg
Student 2 24.3 g Mg 1 mol Mg
Student 1&2 0.15 mol Mg x 24.3 g Mg = 3.6 g Mg 1 mol Mg (units cancel)
QUESTION 2
Student 2 GIVEN = 2.32 x 10^4 mol Es, UNKNOWN = mass (g) Es
Student 1 252 g Es 1 mol Mg
Student 2&1 2.32 x 10^4 mol Es x 252 g Es = 0.585 g Es 1 mol Es (units cancel)
QUESTION 3
Student 1 GIVEN = 11.5 g Na, UNKNOWN = mol Na
Student 2 23.0 g Na 1 mol Na
Student 1&2 11.5 g Na x 1 mol Na = 0.500 mol Na 23.0 g Na (units cancel)
QUESTION 4
Student 2 GIVEN = 4.2 x 10-2^ g Kr, UNKNOWN = mol Kr
Student 1 83.80 g Kr 1 mol Mg
Student 2&1 4.2 x 10-2^ g Kr x 1 mol Kr = 5.0 x 10-4^ mol Kr
83.80 g Kr (units cancel)
ANSWER KEY
QUESTION 1
Student 1 GIVEN = 0.3722 mol La, UNKNOWN = atoms La Student 2 6.022 x 10^23 atoms La 1 mol La Student 1& 0.3722 mol La x 6.022 x 10^23 atoms La = 2.241 x 10^23 atoms La 1 mol La (units cancel)
QUESTION 2
Student 2 GIVEN = 6.8 x 10-12^ mol Fm, UNKNOWN = atoms Fm Student 1 6.022 x 10^23 atoms Fm 1 mol Fm Student 2& (6.8 x 10-12^ mol Fm) (6.022 x 10^23 atoms Fm) = 4.1 x 10-12^ atoms Fm 1 mol Fm (units cancel)
QUESTION 3 Student 1 GIVEN = 7.4 x 10-21^ mol Pm, UNKNOWN = atoms Pm Student 2 6.022 x 10^23 atoms Pm 1 mol Pm Student 1& 7.4 x 10-21^ mol Pm x 6.022 x 10^23 atoms Pm = 4,400 atoms Pm 1 mol Pm (units cancel)
QUESTION 4
Student 2 GIVEN = 8.4 x 10^18 atoms Yb, UNKNOWN = mol Yb Student 1 6.022 x 10^23 atoms Yb 1 mol Yb Student 2& 8.4 x 10^18 atoms Yb x 1 mol Yb = 1.4 x 10-5^ mol Yb 6.022 x 10^23 atoms Yb (units cancel)
Student 1: The answer does NOT depend on the identity of the element. Student 2: The question is only about the COUNT of atoms or moles. None of the quantities depend on any intensive property of the element.
GIA: Atom-Mass Conversion for Elements
Learning Objectives: To correctly identify and label the “given” and “unknown” quantities in a problem. To correctly identify and label the molar mass and Avogadro’s number as conversion factors. To calculate the moles of an element given the mass, or the reverse.
Working Mode : Pairs
Instructions : Students should complete each step below, alternating roles as indicated. For each quantity named, give the numerals (if known), the unit of measure, and the chemical identity for that quantity. The first question reminds you of this requirement.
Activity 1: What mass in grams would 1.8066 x 10^25 atoms of gadolinium have?
! Student 1: Identify the measure given in the problem, including the numerals, units, and name of chemical (often referred to as the “given”). Then identify the measure in the problem that is unknown (this is the one you are to find, it is often called the “unknown”). State the units and chemical identity of the unknown. ! Student 2: Identify the conversion factors that can be used to complete this problem; give the numerals, units, and chemical identity of the numerator and denominator. ! Student 1: Set up the problem correctly. Remember to begin with the measure of a known chemical, and use the units and identity for each quantity. ! Student 2: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic. ! Student 1: Round the answer to the correct number of significant figures, be sure units and identity are given, and circle the answer.
Activity 2: A reactor produces 0.002 1 g of plutonium. How many atoms is this?
! Student 2: Identify the given and unknown (include all units and chemical identities). ! Student 1: Identify the conversion factors that can be used to complete this problem (include all units and chemical identities). ! Student 2: Set up the problem correctly (include all units and chemical identities). ! Student 1: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic. ! Student 2: Round the answer to the correct number of significant figures, be sure units and identity are given, and circle the answer.
Activity 3: A small sample of osmium contains 4.77 x 10^10 atoms. How many grams is this? Be sure to give the units and chemical identity of each quantity.
! Student 1: Identify the given and unknown. ! Student 2: Identify the conversion factors that can be used to complete this problem. ! Student 1: Set up the problem correctly. ! Student 2: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic. ! Student 1: Round the answer to the correct number of significant figures. Circle the answer.
Activity 4: If an experimenter produces 6.605 x 10–18^ mg of seaborgium, how many atoms would that be? Be sure to give the units and chemical identity of each quantity.
! Student 2: Identify the given and unknown. ! Student 1: Identify the conversion factor that can be used to complete this problem. ! Student 2: Set up the problem correctly. ! Student 1: Check to see that the units and chemical identities cancel correctly, then do the indicated arithmetic. ! Student 2: Round the answer to the correct number of significant figures. Circle the answer.
Mole Conversion Answers
Mole-Mass
st
= 3.6 g Mg
nd
= 5.85 x 10
g Es
rd
= 0.500 mol Na
th
= 5.0 x 10
mol Kr
Mole-Atom
st
= 2.24 x 10
23
atoms La
nd
= 4.1 x 10
12
atoms Fm
rd
= 0.012 mol Pm
th
= 1.5 x 10
mol Yb
Atom-Mass
st
= 4,718 g Gd
nd
= 5.2 x 10
18
atoms Pu
rd
= 1.51 x 10
g Os
th
= 15 atoms Sg (fractions of atoms do not exist)
