CHEM 1127Q Lecture Notes - Lecture 6: Molar Mass, Molar Concentration

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Molarity: represented by m (stands for moles/liter, concentration (moles/liter, anything in square brackets [x] = concentration, the tests will be more clear, but this is good to know. Abbreviations: mm = molar mass, m = moles per liter, n = number of moles. Molarity is a unit to use to figure out how many moles there are in a solution: normally the unit is grams, but in solution it won"t be solid it will be dissolved, so m works better. Example 1: moles/liter, convert grams --> moles, use the molar mass (can be calculated from the periodic table) 19. 4 g x: 0. 100 moles/liter = 0. 1 m. 0. 100 moles k2cro4 x 2 = 0. 200 moles k: this is because there are two k+"s for every k2cro4"s, so you multiply it by 2. Mass percentages: these work for solutions just like they do liquids.

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I know its a lot of questions but anything helps! please help me im so lost!

1. Using the Beerâs law equation, A=Îµbc, where A - the unit-less absorbance, c - the molarity of the solution, and b - the path length in centimeters, find the units for the molar extinction coefficient, Îµ. Show your work. Donât include numbers. (10 pts)

2. Given the following data for a colored solution, find the concentration of the unknown sample given. You will need to print a graph of absorbance vs. concentration as discussed in the experiment to do this. This cannot be done by hand for credit. Please remember to include the graph with your prelab and label each axis. A title should be given to all graphs. (10 pts)

Trial	Concentration, (moles/liter)	Absorbance (unit-less values)
1	0.080	0.399
2	0.16	0.715
3	0.24	0.950
4	0.32	1.136
5	0.40	1.429
Unknown Solution A	X	1.337

The concentration of unknown solution A is (moles/liter) ________________________

Show your calculation with units here:

3. Determine the total amount of the stock solution you will need for this experiment. Record that volume here and then in the procedure where thereâs a blank for it: ________________________________mL of stock solution is needed for this experiment. (10 pts)

4. This multiple part question deals with concentrations.(10 pts)

A) What is the final concentration of iron(III) sulfate made if 17.804 grams of the solid is added to a 100.00 mL volumetric flask and then distilled water is added to the graduation. Assume the solid is anhydrous iron sulfate.

B) What is the concentration of sulfate ion in the solution?

C) What is the concentration of Fe3+ in the solution? Show your work.

5. You need 0.5000 M copper(II) sulfate solution for this experiment. Remember that copper(II) sulfate exists as a pentahydrate. (10 pts)

A) What is a hydrate?

B) What is the formula for copper (II) sulfate pentahydrate? What is the formula mass of this compound?

C) How would you, exactly, make 50.00 mL of a 0.515 M copper (II) sulfate solution?

D) Tell the exact mass of the solid needed.

1. Consider the unbalanced equation for the reaction of solid lead with a silver nitrate solution.

_____Pb (s) + ______AgNO3 (ac) â ______Pb(NO3)2 (ac) + _______Ag (s)

a. Balance the equation.

b. How many moles of silver nitrate are required to react completely with 9.3 mol of lead?

c. How many moles of silver, Ag, are formed by the complete reaction of 28.4 mol of Pb?

2. For the following reaction: _____CaO (s) + _____CO2 (g) â _____CaCO3 (s), Calculate how many grams of CaCO3, are formed when 2.4 g of CaO Do they react completely with CO2?

3. For the following reaction: 2 Li (s) + F2 (g) â 2 LiF (s), find the reagent limiting with the amounts of 1.0 mol of Li and 1.0 mol of F2.

4. For the next reaction, determine the limiting reagent, calculate the yield Theoretical product in grams with 5.5 g of Al and 19.8 g of Cl2.

2 Al (s) + 3 Cl2 (g) â 2 AlCl3 (s)

5. Consider the reaction between NiS2 and O2:

2 NiS2 (s) + 5 O2 (g) â 2 NiO (s) + 4 SO2 (g)

When 11.2 g of NiS2 react with 5.43 g of O2, 4.86 g of NiO are obtained. Determine the limiting reagent, the theoretical yield of NiO and the% yield for the reaction.

6. How many atoms of mercury are in 5.8 mol of mercury?

7. Complete the following table:

Element Moles Mass Number of molecules

8. How many grams of sodium are there in 1.00 g of each of the following compounds?

a. Na3PO4

b. NaC7H5O2

c. Na2C6H6O7

9. A sample of 4.78 g of aluminum reacts completely with oxygen to form 6.67 g of aluminum oxide. Use the data to calculate the percent of composition by mass.

10. Citric acid, the compound responsible for the bitter taste in lemons, has the following composition: C - 37.51%

H - 4.40%

O - 58.29%

Calculate the empirical formula.

11. A compound containing phosphorus and oxygen has a molar mass of 219.9 g / mol and an empirical formula of P2O3. Find the molecular formula of compound.

12. It is a term used in chemistry, to describe a system in which a

or more substances, are mixed or dissolved homogeneously in another

substance.

a. Mixture

b. Solution

c. Compound

d. None of the above

13. It is the component that is in a solution, in smaller quantity.

a. Solution

b. Solvent

c. Solvent

d. Soluto

14. It is the component that is in a solution in greater quantity.

a. Solution

b. Solvent

c. Solvent

d. The answers b and c are correct.

15. The quantitative expression of the dissolved amount of solute in a quantity determined solvent is known as:

a. Solution

b. Volume

c. Concentration

d. Stoichiometry

16.Express the moles of solute among the liters of solution

a. Molality

b. Molarity

c. % weight by volume

d. % weight by weight

17.Express the moles of solute between kg of solvent

a. Molarity

b. ppm

c. ppt

d. Molality

18. What is the molarity of a solution prepared by dissolving 7.50 g of nitrate of magnesium, Mg (NO3) 2 in enough water to prepare 25.0 mL of solution?

a. 10.3 M

b. 5.6 M

c. 6.5 M

d. 2.03 M

19. How many grams of sodium chloride, NaCl are needed to prepare 125 mL of 0.037 M NaCl solution

a. 1.021 M

b. 0.268 M

c. 0.201 M

d. 0.500 M

20. Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.

21. A solution of ethylene glycol contains 21.2 g of ethylene glycol (C2H6O2) in 85.4 mL of water. Calculate the freezing point and the boiling point of the solution. (Assume the water density is 1.00 g / mL)

22. At what volume should you dilute 75 mL of a 10.0 M solution of H2SO4 to obtain a 1.75 M solution of H2SO4.

CHEM 1127Q Lecture Notes - Lecture 6: Molar Mass, Molar Concentration

CHEM 1127Q Full Course Notes

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