Chem HWK

Hello Team,Kindly assist with the attached 

CHE011 Homework 6 Name:

You can either type your calculations and answers directly into this document or you can write them out on the piece of paper.

For numerical problems, calculation set up must be shown

To calculate molar masses, use the values of atomic masses with 2 DP from the Periodic Table provided at the last page. 

1. You have a 329.4-gram sample of gold(III) sulfide, Au2S3. After various chemical and physical processes, you are able to separately measure 264.8 grams of gold and 64.6 grams of sulfur.

What are the experimental mass percents of the two elements in this compound?

Answer: %Au =

% S =

2. Use molar masses to calculate the theoretical percent of gold and sulfur in gold(III) sulfide, Au2S3.

Answer: %Au = % S =

3. Suppose a certain compound is known to be 47% copper, by mass. How many grams of copper will there be in a 12.5 gram sample of this compound?

Answer:

4. Fill in what items are being counted for each substance. The choices are: molecules, atoms, formula units. Include the substance in your answer.

a. 1 mole of silver, Ag = 6.022⨯1023 _____ __________

b. 1 mole of methane, CH4 = 6.022⨯1023 ______ __ _____

c. 1 mole of chlorine gas, Cl2 = 6.022⨯1023 ______ __ _________

d. 1 mole of gold(III) sulfide, Au2S3 = 6.022⨯1023 _______ __________

5. Calculate the molar mass for each of the following substances. Use the Periodic Table provided at the last page. Use these calculated values for questions #6-13 as needed.

a. ammonia, NH3 __

b. glucose, C6H12O6 ____

c. carbon dioxide, CO2 ____

For questions #6-13, fill in the requested information to figure out how to set up the calculation. Then do the calculation a separate sheet of paper and round off the answer to the correct significant figures.

6. How many ammonia molecules are there in 16.78 moles of NH3 ?

Starting Unit (include substance):

Ending Unit (include substance):

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Answer:

Calculation set up:

7. How many moles of ammonia molecules are there in 789 grams of NH3 ?

Starting Unit (include substance):

Ending Unit (include substance):

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Answer:

Calculation set up:

8. How many moles of tin, Sn are needed to give 1.39×1022 tin atoms ?

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Ending Unit (include substance):

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Answer:

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9. How many grams of glucose, C6H12O6 are there in 5.7×1021 glucose molecules ?

Starting Unit (include substance):

Ending Unit (include substance):

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Answer:

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10. How many moles of chromium are there in 24.61 moles of aluminum dichromate, Al2(Cr2O7)3 ?

Starting Unit (include substance):

Ending Unit (include substance):

Tool(s) needed:

Answer:

Calculation set up:

11. How many grams of carbon dioxide are there in 0.0364 moles of CO2 ?

Starting Unit (include substance):

Ending Unit (include substance):

Tool(s) needed:

Answer:

Calculation set up:

12. How many glucose molecules are there in 7.649 grams of glucose, C6H12O6 ?

Starting Unit (include substance):

Ending Unit (include substance):

Tool(s) needed:

Answer:

Calculation set up:

13. How many oxygen atoms are there in 64 moles of carbon dioxide, CO2 ?

Starting Unit (include substance):

Ending Unit (include substance):

Tool(s) needed:

Answer:

Calculation set up:

Summary of Mole Calculation Tools

1. Avogadro’s Number

· What it’s used for: moles ⟷ # of items

· Value: 6.022×1023 items = 1 mole

· Examples:

· molecular compound – water: 1 mole H2O = 6.022 x1023 H2O molecules

· monatomic element – helium: 1 mole He = 6.022 x1023 He atoms

· diatomic element – hydrogen: 1 mole H2 = 6.022 x1023 H2 molecules

· ionic compound – calcium chloride: 1 mole CaCl2 = 6.022 x1023 CaCl2 formula units

2. Molar Mass

· What it’s used for: moles ⟷ grams

· Value: Add up atomic masses from the periodic table for all atoms in the formula.

· Examples:

· H2O

molar mass = 2(1.008) + 1(16.00) = 18.02 g/mol

⇒ 18.02 g H2O = 1 mol H2O

· Ca3(PO4)2

molar mass = 3(40.08) + 2(30.97) + 8(16.00) = 310.18 g/mol

⇒ 310.18 g Ca3(PO4)2 = 1 mol Ca3(PO4)2

3. Subscripts in a Formula

· What it’s used for: moles of atoms ⟷ moles of molecule or formula unit

· Examples:

· H2O: ⇒ 1 mole H2O = 2 moles H

⇒ 1 mole H2O = 1 mole O

· Ca3(PO4)2: ⇒ 1 mole Ca3(PO4)2 = 3 moles Ca

⇒ 1 mole Ca3(PO4)2 = 2 moles P

⇒ 1 mole Ca3(PO4)2 = 8 moles O

MOLE CALCULATIONS

· Using Subscripts in Chemical Formulas to Relate Moles

The subscripts in a chemical formula, like P4O10 represent how many atoms of each element are in one molecule.

But, they also represent the number of MOLES of each kind of atom in one MOLE of molecules.

In this example, we could write two conversion-factor statements:

1 mole of P4O10 = 4 moles of P and 1 mole of P4O10 = 10 moles of O

When subscripts are used in a calculation, they are considered to be exact numbers, so the significant figures for the answer is determined by the other numbers in the calculation.

· Examples: Using Subscripts to Relate Moles of Element to Moles of Compound

(1) How many moles of hydrogen atoms are in 6.455 moles of water?

water is H2O so 1 mole H2O = 2 moles H

6.455 mol H2O ⨯ =
12.91 mol H
(4 SF)

(2) How many moles of silver phosphate, Ag3PO4 are there if there are 0.13 moles of silver?

1 mole Ag3PO4 = 3 moles Ag

0.13 mol Ag ⨯ =
0.043 mol Ag3PO4
(2 SF)
· Examples: Using Two Mole Tools in One Problem
(3) How many nitrogen atoms are there in 7.05 moles of N2O5 ?
Starting unit: moles N2O5 Ending unit: N atoms
Tools: Formula subscript for moles N2O5 to moles N
Avogadro’s number for moles N to N atoms

7.05 mol N2O5 ⨯ ⨯ =
8.49
⨯1024 N atoms
(3 SF)

(4) How many dinitrogen pentoxide molecules are there in 675 grams of N2O5?
Starting unit: grams N2O5 Ending unit: N2O5 molecules
Tools: Molar mass of N2O5 for grams N2O5 to moles N2O5
Avogadro’s number for moles N2O5 to N2O5 molecules
molar mass N2O5 = 2(14.01) + 5(16.00) = 108.02 g/mol

375 g N2O5 ⨯ ⨯ =
2.09
⨯1024 N
2O5 molecules
(3 SF)
(5) What is the mass (grams) of 1.5⨯1019 copper atoms ?
Starting unit: Cu atoms Ending unit: grams Cu
Tools: Avogadro’s number for Cu atoms to moles Cu
Molar mass of Cu for mole Cu to grams Cu
molar mass Cu = 63.55 g/mol

1.5⨯1019 Cu atoms ⨯ ⨯ =
0.0016 g Cu
(2 SF)
4.