1. Unit 4: Mole Calculations
CH1120

2. Avogadro’s Number and the Mole
Even the smallest samples contain enormous numbers of atoms, ions, or molecules
Teaspoon of water (5mL) contains 2 x water molecules
1.67 x 1022 dozen
We need a new counting unit to describe the number of atoms, molecules, or ions of a substance

3. Avogadro’s Number and the Mole
We use the mole as our counting unit
One mole is the amount of matter that contains as many objects (atoms, molecules, ions, formula units, etc.) as the number of atoms in exactly 12g of pure carbon-12
NA = x 1023particles/mol

4. Molar Mass
The molar mass of a substance can be found in the periodic table
This molar mass describes the average mass of each of the elements
The molar mass of a compound is the sum of all of the elements it contains (in their specific ratios)

5. Molar Mass O2
C2H6
Mg(ClO3)2

6. Conversions Mols to Mass
Use the molar mass as a conversion factor in dimensional analysis
Example:
Calculate the mass, in grams of 0.433mol of calcium nitrate.

7. Conversions Mass to Mols
Use the molar mass as a conversion factor in dimensional analysis
Example:
Calculate the number of moles of glucose (C6H12O6) in 5.380gC6H12O6.

8. Conversions Mols to Particles
Particles can be ions, atom, molecules, formula units, etc.
Always use Avogadro’s number
Example: How many Calculate the number of H atoms in 0.350mol C6H12O6.

9. Conversions Particles to Mols
We will still use Avogadro’s number for this conversion
Remember NA = x 1023particles/mol
Arrange your conversion factor so you cancel the units you don’t want and keep the units you need
Example: Calculate the number of mols of NaCl in a sample of x 1023 formula units.

10. Conversions Mass to Particles
Example: How many glucose molecules are in 5.23g of C6H12O6?
We can also take this one step further to determine how many atoms of a certain element are contained in a sample
Using data from the last question, how many oxygen atoms are in this sample?

11. Conversions Particles to Mass
Remember always make sure the units you don’t need cancel
Given a sample of 4.23 x 1023 atoms of Ca calculate its mass in grams.

12. Solutions Solute: substance being dissolved in a solution
Solvent: the majority of a solution (the substance dissolving the solute)
Solubility: the maximum amount of the solute that can dissolve in a given amount of the solvent at a specified temperature

13. Solutions Homogeneous mixtures
Mixtures of substances that have uniform composition

14. Solutions
Unsaturated: the maximum amount of solute has not been reached, the solvent is able to dissolve more of the solute
Saturated: the maximum amount of the solute that the solvent is able to dissolve at the given temperature has been reached
Supersaturated: an amount of solute greater than that needed to form a saturated solution has been dissolved (usually by heating a solution)

15. Solutions

16. Solutions

17. Seed Crystals
Adding a seed crystal means to add more solute to your solution
Unsaturated solution: seed crystal dissolves
Saturated solution: seed crystal not dissolved, found in bottom of container
Supersaturated solution: seed crystal provides template for crystallization, excess solute will crystallize giving saturated solution with excess solute in solid form

18. Seed Crystals

19. Solutions Can be found in any state Most common solid-solid: alloys
Liquid
Gas
Most common solid-solid: alloys
Most common liquid-liquid: amalgams

20. Solutions Miscible liquids dissolve in one another
Can’t see individual parts of the solution
Mix in all proportions with each other
Immiscible liquids do not dissolve in one another
Can see layers
Do not mix

21. Solutions

22. Solutions Like dissolves likes Polar dissolves polar
Non-polar dissolves non-polar
Look at polarity of molecules, if they are both polar or both non-polar they will dissolve (miscible)

23. Solutions
Solubility of solids and gases in liquids also depends on intermolecular forces
The stronger the attractions between solute and solvent molecules the greater the solubility of the solute in that solvent

24. Solubility
Remember: solubility is the mass of solute that can be dissolved by a solvent at a given temperature
We can use a solubility table to figure out whether or not an ionic compound is soluble in water (will dissolve) or insoluble in water (will form a solid/precipitate)

25. Solubility Determine whether the following at soluble or insoluble
NaCl
Ag2SO4
H3PO4
VPO4

26. Solubility Solubility of solids in liquids depends on temperature
Salt in water
Solubility of gases in liquids depends on temperature and pressure
Hot pop in car
Opening a bottle of pop

27. Concentration
The quantity of solute present in a given quantity of solvent or solution
Usually given as molarity (M) or molality (m)
Units:
M = mols of solute/L solution
M = mols solute/kg solvent

28. Standard Solutions
Contain a specific amount (g) of solute and specific amount (L) solution

29. Molarity
We can calculate molarity given mols of a substance and volume of solution
We can also use molarity to calculate other information about our solution

30. Molarity
What is the molarity of a 0.30L solution containing 0.50mols of NaCl?

31. Molarity
How many moles of NaCl are present in 600mL a 1.55M NaCl solution?

32. Molarity
How many liters of solution are needed to make a 1.66M solution containing 2.11mols of KMnO4?

33. Molarity
How many grams of Ca(OH)2 are needed to produce 500mL of 1.66M Ca(OH)2 solution?

34. Concentration as a Percent
Concentration can be represented by a percentage that compares:
Mass/mass
Mass/volume
Volume/volume
Also known as a percent by mass

35. Concentration as a Percent
%(m/v) = [grams solute/mL solution] x 100
Calculate the %(m/v) KCl for 2.50g KCl in 50.0mL of solution.

36. Percent by Mass
For compounds we can find the percent by mass of the elements by using the molar mass of the individual elements and the compound as a whole
What is the percent by mass of all elements in the following:
Ca(OH)2
Co2(C2O4)3

37. Parts Per Million (ppm)
Just like percent is out of 100, ppm is out of
1mg per 1L (m/v)
1mg per 1kg (m/m)

38. Parts Per Million (ppm)
What is the concentration of a solution, in parts per million, if 0.02g NaCl is dissolved in 1kg of solution?

39. Ion Concentrations
Ionic substances dissociate (split apart) into ions when dissolved in water
Some molecular substances (mostly acids) ionize (split apart to create ions) when dissolved in water

40. Ion Concentrations
We know how to find the concentration of compounds in solution (mols/L)
We can take this one step further and determine the mols/L of elements found in these compounds
All you have to do is look at the subscripts

41. Ion Concentrations
Given a 4.6M solution of H2SO4 what concentration of H+ ions are found when this substance completely ionizes in solution.

42. Ion Concentrations
What is the molar concentration of the ions in a 0.20M calcium nitrate solution?