Happy New Year! PLEASE PICK UP THE MATERIALS IN THE FRONT AND TAKE A SEAT

Happy New Year!PLEASE PICK UP THE

MATERIALS IN THE FRONT AND TAKE A SEAT

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Policies and Procedures - Test Corrections - Pink Sheets & Late Work - Notes & Practice Problems

Chapter 8 BEAT SheetCalculate the percent composition of any element in a compound

Determine the empirical formula of a compound given its percent composition

Determine the molecular formula of a compound given its percent composition and

molar mass

Determine the empirical formula of a hydrate from lab data

Perform mole road calculations to determine atoms, molecules, ions, mass, or moles

from relevant data

Describe the labs you performed this unit and what the key concept/learning was from

each lab

What is a mole?

We have talked about this

6.02 X 1023 times!

What is a mole?

A mole is the base unit used to measure the amount of a substance, abbreviated mol. One mol of anything is equal to 6.02 x 1023 pieces of that thing.

Mole Practice

1. How many moles in 5.4 x 1020 atoms of Pb?

Mole Practice

2. How many atoms in 3.5 moles of Ag?

Mole Practice

3. How many total molecules in 1 mole of glucose: C6H12O6?

Molecular and Formula Weight Last semester we learned about molecular weight and touched on formula weight. It is important to remember that a single atom’s weight in amu is the same as one mole of that atom in grams.

Example: The weight of a single atom of aluminum is 26.98 grams. Therefore 1 mol of Al weighs 26.98 grams.

Molecular and Formula Weight

This is known as the atomic mass: the mass of 1 mole of atoms of any element. This is the number that’s on the periodic table. But atoms are rarely by themselves—they are usually in compounds. How do you find the mass of a mole of a compound??


Example: Find the molecular mass of CO2

◦C: 1 x 12.0107 = 12.0107 g◦O: 2 x 15.9994 = + 31.9988 g

44.0095 g


Example: Find the formula mass of (NH4)CO3

◦N: 1 x 14.0067 = 14.0067 g◦H: 4 x 1.00794 = 4.03176 g◦C: 1 x 12.0107 = 12.0107 g◦O: 3 x 15.9994 = + 47.9982 g

78.0474 g

Molecular and Formula Weight Practice Problems

4. Find the molecular mass of C6H12O6


5. Find the molecular mass of dinitrogen pentaoxide


6. Find the Formula mass of Na2SO4


7. Find the Formula mass of potassium phosphate

Molar Mass of a Substance

When trying to find the mass of one mole of a substance we will make life easier by just referring to the molar mass of a material. It can be an atom, a molecule, or an ionic compound. We use the same technique to calculate the mass of a mole of O2, Pb, CH4, or NaCl.

Molar Mass Practice Problems

8. Find the molar mass of O2


9. Find the molar mass of Pb


10. Find the molar mass of CH4


11. Find the molar mass of NaCl


12. When do you use atomic mass, molecular weight, and formula weight to find the molar mass?

Molar Mass Conversion

Since molar mass gives you the amount of grams in one mole of a substance you can use the molar mass to convert from grams to moles or vice versa.


Examples: How many moles in 56.8 g of MnO2?


Examples: How many grams in 3.4 moles of C6H6?

Molar Mass Conversion Practice Problems

13. How many moles are in 123.5 g of HNO3


14. How many moles are in 19.5 grams of NaCl


15. How many grams are in 15 mols of AlPO4


16. How many grams are in 5.34 mols of KBr

The Volume of a Mole of Gas

Until this point we have only converted from mass to moles, but what happens when we convert from volume to moles?

Describe how we can measure the mass of a solid substance: Describe how we can measure the mass of a liquid substance: Can we measure the mass of a gaseous substance?


When we convert from volume to moles or moles to volume we use a constant of 22.4 liters per mole. This constant tells us that one mole of a gas has a volume of 22.4 liters. When using this constant we assume the gas is at STP (standard temperature and pressure) which is 1 atm and 0C


Also remember that if there is one mole of a sample of gas, that sample must have 6.02 x 1023 atoms in it! But since gases have different masses than their solid form, one mole of a gas does not weigh the same as its solid state!


Example: If the density of a gas is 2.3 g/L, what is its molar mass?


Example: What is the density of F2 at STP?

The Volume of a Mole of Gas Practice Problems

17. Since we know that the gaseous state of a substance does not have the same mass as the solid state of the same substance, what can we say about the density of the two?


18. How many moles are in 22.4 Liters of O(gas)?


19. How many milliliters of Neon gas are in 2 mols?


20. What is the molar mass of a gas that has a density of 11.33 g/L? Which diatomic gas do you think it is?


21. What is the density of Cl2 at STP?

22.4 g/L

Molar

Mass

Volume

Avogadro’s number

Moles

AtomsMass

Mole Conversion Practice Problems 22. How many moles in 9.0 liters of a gas at STP?

Mole Conversion Practice Problems 23. How many moles in 15 g of NaOH?

Mole Conversion Practice Problems 24. How many liters would 2.9 moles of CO2 occupy at STP?

Mole Conversion Practice Problems 25. How many grams would 30 L of CO2 gas weigh?

Mole Conversion Practice Problems 26. How many atoms are in 50 L of H2 gas?

Calculating Percent Composition Percent Composition is the percent by mass of each element in a compound. You find the percent composition by dividing the mass of the element by the total mass of the molecule. If you think back to the separation lab we have done this already by calculating the % of salt, % of sand, and % of iron!!

Calculating Percent Composition Example: How many students are in this class? Find the percentage of Males and the percentage of Females.

Calculating Percent Composition Example: What percentage of students in the class are 15? 16? 17?

Calculating Percent Composition Example: What is the percent composition of each element in C6H12O6?

Calculating Percent Composition Example: What is the percent by mass of each element in H2O?

Calculating Percent Composition Example: How many grams of nitrogen are in 59 g of AgNO3?

Percent Composition Practice Problems 27. Which compound has the smallest percentage of Chlorine?◦HCl◦KCl◦LiCl◦NaCl

Percent Composition Practice Problems 28. Of the following compounds, which does Strontium have the highest percent composition?◦SrCl2

◦SrI2

◦SrO◦SrS

Percent Composition Practice Problems 29. What is the percent composition of Oxygen in the compound propanal (CH3CH2CHO)?

Percent Composition Practice Problems 30. What is the percent by mass of Oxygen in H2SO4?

Percent Composition Practice Problems 31. What is the total mass of oxygen in 1.00 mol of Al2(CrO4)3?

Percent Composition Practice Problems 32. What is the percent composition of Carbon in CO?

Calculation Empirical Formulas

An empirical formula is the lowest whole number ratio of the atoms of the elements in a compound. The empirical formula may or may not be the same as the molecular formula.

Calculation Empirical Formulas Example: The molecular formula for CO2 is the same as the empirical formula for CO2 because the atoms are in the lowest whole number ratio.

Calculation Empirical Formulas Example: The molecular formula for C2H2, could be that, or it could be C6H6. But the empirical formula for both is CH, since that is the lowest whole number ratio.

Calculation Empirical Formulas

It is important to understand that the empirical formula gives you an idea of the ratio of between elements within a compound.

Calculation Empirical Formulas Example: Calculate the empirical formula of a compound made up of: 32.00% C 42.66% O 18.67 % N 6.67% H

Calculation Empirical Formulas Practice Problems 33. A compound contains 40% calcium, 12% carbon, 48% oxygen by mass. What is the empirical formula for this compound?

Calculation Empirical Formulas Practice Problems 34. Write the empirical formula for the following compound:

P4O10

Calculation Empirical Formulas Practice Problems 35. A compound is 86% carbon and 14% hydrogen by mass. What is the empirical formula for the compound?

Calculation Empirical Formulas Practice Problems 36. Which of the following is an empirical compound?

◦ C4H10

◦ C6H12O6

◦ P2O5

◦ C2H2O2

Calculation Empirical Formulas Practice Problems 37. A compound was analyzed and was found to contain 75% carbon and 25% hydrogen by mass. What is the compounds empirical formula?

Calculation Empirical Formulas Practice Problems 38. What is the simplest ration of nitrogen to oxygen in the compound nitrogen (IV) oxide

Calculation Molecular Formulas Knowing that the Molecular formula of a substance is not always equal to the Empirical Formula of the substance, what can we say about Molecular Weight vs Empirical Formula Weight?

Calculation Molecular Formulas We can determine the molecular formula we first know the molar mass and the empirical formula of the substance. We then compare the molar mass to the Empirical Formula Weight to determine the ratio.

Calculation Molecular Formulas Examples: The molar mass of a substance is 60g and its empirical formula is CH4N. Find the Molecular Formula.

Calculation Molecular Formulas Examples: The molar mass of a substance is 78g and its empirical formula is CH. Find the Molecular Formula.

Calculation Molecular Formulas Examples: Find the molecular formula for a compound that has: 54.5% C 13.6% H 31.8 % N molar mass = 88g

Calculation Molecular Formulas Practice Problems 39. What’s the molecular formula of a compound given the empirical formula P2O5 and molar mass 284 g?

Calculation Molecular Formulas Practice Problems 41. What is the molecular formula of a compound that has a molecular mass of 42 g and empirical formula of CH2?

Calculation Molecular Formulas Practice Problems 42. Find the molecular formula for a compound that has: 54.5% C 13.6% O 31.8 % N molar mass = 176 g/mol

Calculation Molecular Formulas Practice Problems 43. Find the molecular formula for a compound that has: 25.9% N 74.1% H molar mass = 108 g/mol

Calculation Molecular Formulas Practice Problems 44. Find the molecular formula for a compound that has: 22.8 g Ba 2.00 g C 8.00 g O molar mass = 197.3 g/mol

Hydrates Hydrated compounds have water molecules attached to them. CuSO45H2O is copper (II) sulfate pentahydrate. For every formula unit of CuSO4, there are 5 water molecules attached to it. There are always numerous waters for one salt.

Hydrates Example: Start with 1.54 g wet magnesium phosphate. Dry it so that there are only 1.28 g residue left. Find the formula of the hydrate.

Hydrates Example: Calculate the percent composition in NaCl 5H∙ 2O?

Hydrates Practice Problems 45. Calculate the percent composition in BaCl2 2H∙ 2O

Hydrates Practice Problems 46. What is the percent by mass of the water in the hydrate

Na2CO3 10H∙ 2O?

Hydrates Practice Problems 47. If you start with 1.54 g wet magnesium phosphate. Dry it so that there are only 1.02 g residue left. Find the formula of the hydrate.

Hydrates Practice Problems 48. Start with 1.62 g of hydrated cobalt (II) chloride. After heating, there are 0.88 g of solid reside. Find the formula of the hydrate.

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