Unit 3B (Stoichiometry) Review Packet

Directions: BE SURE YOU SHOW ALL YOUR WORK AND ALL UNITS. NOT SHOWING WORK OR UNITS WILL RESULT IN POINT DEDUCTION ON THE TEST. THEY ARE MORE IMPORTANT THAN THE FINAL ANSWER.

1. Magnesium chloride (MgCl₂) is used to melt snow. Calculate its molar mass in g/mol.

The molar mass of magnesium chloride (MgCl₂) is calculated by adding the atomic masses of magnesium (24.305 g/mol) and chlorine (35.453 g/mol × 2), resulting in a total of 95.211 g/mol.

2. Calculate the molar mass for MgSO₄.

The molar mass of magnesium sulfate (MgSO4) is calculated by adding the atomic masses of magnesium (24.305 g/mol), sulfur (32.06 g/mol), and oxygen (15.999 g/mol × 4), resulting in a total of 120.361 g/mol.

3. The molar mass of nitrogen gas (N₂) is ____.

Calculated by adding the atomic masses of nitrogen (14.007 g/mol × 2), resulting in a total of 28.014 g/mol.

4. How many moles are present in 264 grams of calcium carbonate (CaCO₃)?

• Molar Mass CaCO₃ = 100g/mol

• 1 mole = molar mass from periodic table

To find the number of moles in 264 grams of calcium carbonate (CaCO3), divide the mass by the molar mass: 264 g / 100 g/mol = 2.64 moles CaCO₃.

5. What is the mass in grams of 0.676 moles of glucose (C₆H₁₂O₆)?

   • Molar Mass CaCO₃ = 180g/mol

   • 1 mole = molar mass from periodic table

To find the mass in grams of 0.676 moles of glucose (C6H12O6), multiply the number of moles by the molar mass: 0.676 moles × 180 g/mol = 121.68 grams.

6. How many molecules of H₂O are in 5 moles of water?

   • 1 mole = 6.02×10²³

To find the number of molecules in 5 moles of water (H2O), multiply the number of moles by Avogadro's number: 5 moles × 6.02×10²³ molecules/mole = 3.01×10²⁴ molecules of H2O.

7. How many moles of silver are in 1.0 × 10²² atoms of silver?

   • 1 mole = 6.02×10²³ atoms

To find the number of moles in 1.0 × 10²² atoms of silver, divide the number of atoms by Avogadro's number: 1.0 × 10²² atoms / 6.02×10²³ atoms/mole = 0.17 moles of silver.

How many moles of carbon dioxide (CO₂) are produced when 64.20 grams of methane (CH₄) react completely with oxygen gas (O₂) according to the following balanced equation?

CH₄ + 2 O₂ —> CO₂ + 2 H₂O

• Molar Mass CH₄ = 16.05 g

• Molar Mass CO₂ = 44.01 g

To find the moles of carbon dioxide (CO2) produced from 64.20 grams of methane (CH4), first convert grams of methane to moles: 64.20 g ÷ 16.05 g/mol = 4.00 moles of CH4. From the balanced equation, 1 mole of CH4 produces 1 mole of CO2, so 4.00 moles of CH4 produce 4.00 moles of CO2.

For the reaction, 2 PN + 1 N₂ —> 2 PN₂ what is the mole ratio for PN to N₂ (HINT: you can write this as a fraction or using : as ratio)

The mole ratio for PN to N2 is 2:1.

10. Determine how many moles of water (H₂O) are needed to react exactly with 2.8 moles of Ca in the reaction:

    1 Ca + 2 H₂O —> 1 Ca(OH)₂ + 1 H₂

To determine how many moles of water (H2O) are needed to react with 2.8 moles of calcium (Ca), use the balanced equation which shows that 1 mole of Ca reacts with 2 moles of H2O. Therefore, 2.8 moles of Ca will require 2.8 × 2 = 5.6 moles of H2O.

Given the reaction: 2 NaOH + 1 H₂SO₄ —> 1 Na₂SO₄ + 2 H₂O

How many moles of NaOH are required to react with 3.6 moles of H₂SO₄

To find the moles of NaOH required to react with 3.6 moles of H2SO4, use the balanced equation which indicates that 2 moles of NaOH are needed for every 1 mole of H2SO4. Therefore, 3.6 moles of H2SO4 will require 3.6 × 2 = 7.2 moles of NaOH.

12. Given the reaction:

    1 Cu + 4 HNO₃ —> 1 Cu(NO₃)₂ + 2 H₂O + 2 NO₂

    • Molar Mass Cu = 64g

    • Molar Mass H₂O = 18g

      How many grams of H₂O is produced when 160 grams of Cu is reacted?

To determine how many grams of H2O are produced when 160 grams of copper (Cu) is reacted, first convert grams of Cu to moles using its molar mass (64 g/mol). This gives 160 g / 64 g/mol = 2.5 moles of Cu. The balanced equation shows that 1 mole of Cu produces 2 moles of H2O, so 2.5 moles of Cu will yield 2.5 × 2 = 5 moles of H2O. Finally, convert moles of H2O to grams using its molar mass (18 g/mol), resulting in 5 moles × 18 g/mol = 90 grams of H2O.

13. This particulate diagram represents the Law of Conservation of Mass. Fill in the blanksusing the word bank - note that not all words will be used.

    WORD BANK: Mass, reactants, equal to, less than, greater than

    The total mass of the _____ is ______ the total ______ of the products.

reactants is equal to products

14. How many grams of CO₂ can be created from the decomposition of 122g of NaHCO₃? The balanced reaction is provided.

    2 NaHCO₃ —> Na₂CO₃ + H₂O + CO₂

To find the grams of CO2 produced from the decomposition of 122 grams of NaHCO3, first convert grams of NaHCO3 to moles using its molar mass (84 g/mol). This gives 122 g / 84 g/mol = 1.45 moles of NaHCO3. The balanced equation indicates that 2 moles of NaHCO3 produce 1 mole of CO2, so 1.45 moles of NaHCO3 will yield 1.45 / 2 = 0.725 moles of CO2. Finally, convert moles of CO2 to grams using its molar mass (44 g/mol), resulting in 0.725 moles × 44 g/mol = 31.9 grams of CO2.

15. How many moles are in each of the following?

    139.44 g Ga, 6.02 × 10²⁴ atoms Al, 80.06 g He, 6.02 × 10²³ atoms Zn.

To find the moles in each substance, use the molar mass for grams and Avogadro's number (6.02 × 10^23) for atoms. For Ga, 139.44 g / 69.72 g/mol = 2.00 moles. For Al, 6.02 × 10^24 atoms / 6.02 × 10^23 atoms/mol = 10.00 moles. For He, 80.06 g / 4.00 g/mol = 20.02 moles. For Zn, 6.02 × 10^23 atoms / 6.02 × 10^23 atoms/mol = 1.00 mole.

16. Calculate the molar mass of Ga₂(CO₃)_3.

The molar mass of Ga2(CO3)3 is calculated by summing the atomic masses of all atoms in the formula. It consists of 2 gallium (Ga) atoms, 3 carbon (C) atoms, and 9 oxygen (O) atoms, resulting in a total molar mass of approximately 235.99 g/mol.

17. Determine the number of moles in 87.55g of Mg. (Round your final answer to two decimal places)

To find the number of moles in 87.55 grams of magnesium (Mg), divide the mass by the molar mass of magnesium (24.31 g/mol). This gives 87.55 g / 24.31 g/mol = 3.61 moles of Mg.

18. Calculate the mass of 8.44 moles of Pb. (Round your final answer to two decimal places)

To find the mass of 8.44 moles of lead (Pb), multiply the number of moles by the molar mass of lead (207.2 g/mol). This results in 8.44 moles × 207.2 g/mol = 1,752.13 g of Pb.

19. Calculate the number of moles present in 5.21 × 10²¹ atoms of He. (Round your final answer to two decimal places)

Calculate the number of moles present in 5.21 × 10²¹ atoms of He. (Round your final answer to two decimal places) \n**Definition:** To find the number of moles in 5.21 × 10²¹ atoms of helium (He), divide the number of atoms by Avogadro's number (6.02 × 10²³ atoms/mole). This results in 5.21 × 10²¹ atoms / 6.02 × 10²³ atoms/mole = 0.009 moles of He.

For questions 21-23, use the following balanced chemical equation and molar masses.

C₃H₈ + 5 O₂ —> 3 CO₂ + 4 H₂O

Molar Masses:

• C₃H₈ = 44.097 g/mol

• O₂ = 31.998 g/mol

• H₂O = 18.015 g/mol

• CO₂=44.009 g/mol

21. How many moles of O₂ would be used in the reaction if 8.65 moles of C₃H₈ are also used? (round your final answer to two decimal places)

To find how many moles of O2 are used, refer to the balanced equation C3H8 + 5 O2 → 3 CO2 + 4 H2O. According to the equation, 1 mole of C3H8 reacts with 5 moles of O2. To calculate the moles of O2 needed for 8.65 moles of C3H8: 8.65 moles C3H8 × (5 moles O2 / 1 mole C3H8) = 43.25 moles O2.

For questions 21-23, use the following balanced chemical equation and molar masses.

C₃H₈ + 5 O₂ —> 3 CO₂ + 4 H₂O

Molar Masses:

• C₃H₈ = 44.097 g/mol

• O₂ = 31.998 g/mol

• H₂O = 18.015 g/mol

• CO₂=44.009 g/mol

22. If 16.6g of C₃H₈ reacts completely with O₂ how many grams of CO₂ would be produced? (round your final answer to two decimal places)

To find the grams of CO2 produced from the reaction of 16.6 grams of C3H8, first convert grams of C3H8 to moles using its molar mass (44.097 g/mol): 16.6 g / 44.097 g/mol = 0.376 moles of C3H8. According to the balanced equation, 1 mole of C3H8 produces 3 moles of CO2. Thus, 0.376 moles of C3H8 will produce 0.376 moles × 3 moles CO2/mole C3H8 = 1.128 moles of CO2. Finally, convert moles of CO2 to grams using its molar mass (44.009 g/mol): 1.128 moles × 44.009 g/mol = 49.63 grams of CO2.

For questions 21-23, use the following balanced chemical equation and molar masses.

23. C₃H₈ + 5 O₂ —> 3 CO₂ + 4 H₂O

    Molar Masses:

    • C₃H₈ = 44.097 g/mol

    • O₂ = 31.998 g/mol

    • H₂O = 18.015 g/mol

    • CO₂=44.009 g/mol

      How many grams of H₂O would be produced if 11.9g of CO₂ were created during a chemical reaction? (Round your final answer to two decimal places)

To determine how many grams of H2O are produced from 11.9 grams of CO2, first convert grams of CO2 to moles using its molar mass (44.009 g/mol): 11.9 g / 44.009 g/mol = 0.270 moles of CO2. According to the balanced equation, 3 moles of CO2 produce 4 moles of H2O. Thus, 0.270 moles of CO2 will produce 0.270 moles × (4 moles H2O / 3 moles CO2) = 0.360 moles of H2O. Finally, convert moles of H2O to grams using its molar mass (18.015 g/mol): 0.360 moles × 18.015 g/mol = 6.48 grams of H2O.