Moles and Molecules Moles and Chemical Reactions Moles, Chemical Reactions, and Molarity All done as UNIT CONVERSIONS!!! …and practice, practice, practice

• Moles and Molecules• Moles and Chemical Reactions• Moles, Chemical Reactions, and Molarity

• All done as UNIT CONVERSIONS!!!

• …and practice, practice, practice

Chemical Calculations

CHM 1010 - Sinex

Mass of substance in grams

Moles of substance

Number of particles of substance(atoms, molecules, or ions)

Molar mass of substance - g/mole

Avogrado’s number -6.02 x 1023 particles/mole

Mass-moles-particles conversions

Conversion factors

Molar mass – sum of atomic masses from periodic table2

3

How many atoms of carbon?

atoms C = 9 atoms/molecule * 3.3 x 1021 molecules = 3.0 x 1022 atoms

Now find molecules:

molecules = 0.0055 moles * 6.02x1023 molecules/mole = 3.3 x 1021 molecules

First find moles:

moles = 1000 mg *1g/1000mg * 1mole/180g = 0.0055 moles

How many molecules of aspirin (C9H8O4) in a dose of 1000 mg?

Find MM of aspirin:

MM = 9*12+8*1+4*16 = 180 g/mole

Conversion factors in boxes

from the formula

4

For 12.6g NaHCO3, how many moles do you have?

Mass of substance A Moles of substance AMM

How many CO2 molecules in 0.17 moles CO2?

Moles of substance A Molecules of substance A6.02 x 1023

5

Another way to find moles…

Molarity = moles of solute/volume of solution in liters (moles/L)

A unit of concentration – amount solute per amount solution or solvent

Rearranging the definition of molarity:

moles = M x VL

For a solution (homogeneous mixture), there are two components:solute (substance being dissolved) and solvent (dissolving medium, usually water)

Another way to find moles!

How many moles NaCl in 50 mL of 0.28 M NaCl?

50 mL x 1L/1000 mL x 0.28 mole/L = 0.014 mole NaCl

6

What is the molarity if 35g KCl are dissolved to make 350 mL of solution?

How many moles are in 300 mL of a 0.23 M NaOH solution?

Moles of substance A Volume of substance AMolarity

7

2C4H10 + 13O2 8CO2 + 10H2O

2 13 8 104 26 16 20

20 130 80 1001 6.5 4 5

61.3

3250

1.37 X 13/2 X 8/2 X 10/2

1.37 8.91 5.48 6.85

Mole ratios

The ratio of moles in a reaction

Click for answers

81 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 2 mole HCl

Moles of substance A Moles of substance BMole ratio

This comes from the balanced chemical reaction!…and it relates substances in the reaction!

Mole-to-mole conversions

2HCl + CaCO3 CaCl2 + H2O

How many moles of HCl react with a mole of CaCO3?

mole ratio

9


Mass of substance A

Molar mass of substance A

Mass of substance B

Molar mass of substance B

Volume of substance A Volume of substance B

Molarity of solution A Molarity of solution B

Stoichiometry

Molarity (M) = moles of solute/volume in liters of solution – moles/L

Conversion factors

10


Mass of substance A


Mass of substance B




How many grams of O2 are required to reaction with 10g C3H8?

10g C3H8 x 1 mole/44g = 0.23 moles C3H8

0.23 moles C3H8 x 5 moles O2/1mole C3H8 = 1.15 moles O2

1.15 moles O2 x 32.0g/mole = 37 g O2

C3H8 + 5O2 3CO2 + 4H2O

This is a classic stoichiometry problem!

Conversion factors in boxes

11


Mass of substance A


Mass of substance B




How many grams of O2 are required to reaction with 10g C3H8?

10g C3H8 x 1 mole/44g = 0.23 moles C3H8

0.23 moles C3H8 x 5 moles O2/1mole C3H8 = 1.15 moles O2

1.15 moles O2 x 32.0g/mole = 37 g O2

C3H8 + 5O2 3CO2 + 4H2O

1

2

3

Step 1

Step 3

Step 2

Another view of solving

12


Mass of substance A


Mass of substance B




C3H8 + 5O2 3CO2 + 4H2O

If 74g O2 react, how many grams of CO2 will be produced?

13


Mass of substance A


Mass of substance B





What volume of stomach acid, 0.16 M HCl, reacts with 1.0 g CaCO3?

0.010 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 0.020 mole HCl

1.0 g CaCO3 x 1 mole/100g = 0.010 mole CaCO3

0.020 mole HCl x 1L/0.16 moles = 0.13 L = 130 mL stomach acid

14


Mass of substance A


Mass of substance B




This is a classic titration problem!

CH3COOH + NaOH CH3COONa + H2O

What volume of 0.25 M CH3COOH will reaction with 25.0 mL of 0.37M NaOH?

25.0 mL x 1L/1000 mL x 0.37 mole/L = 0.0093 moles NaOH

0.0093 moles NaOH x 1 mole CH3COOH/1 mole NaOH = 0.0093 mole CH3COOH

0.0093 mole x 1L/0.25 moles = 0.037 L = 37 mL CH3COOH

15

Could you find one of the conversion factors?


Mass of substance A


Mass of substance B





Suppose 2.0g CaCO3 reacted with 25.0 mL of HCl. What is the molarity of the HCl?

2.0 g CaCO3 x 1 mole/100g = 0.020mole CaCO3

0.020 mole CaCO3 x 2 mole HCl/1 mole CaCO3 = 0.040 mole HCl

Molarity = moles/ VL = 0.040 mole HCl / (25.0 mL x 1L/1000mL) = 1.6 M HCl

Moles of substance B Volume of substance B

16


Mass of substance A


Mass of substance B




Al(OH)3 + 3HCl AlCl3 + 3H2O

How many grams of Al(OH)3 will react with 100 mL of 0.15 M HCl?

17

2Al2O3 (l) + 3C (s) 4Al (l) + 3CO2 (g)

For a 1.0 kg of Al2O3, how much aluminum metal, in grams, can be produced?

How many atoms of carbon are consumed for the problem above?

18

CH3COOH + NaOH CH3COONa + H2O

How many grams of CH3COOH are needed to react with 27.3 mL of 0.21 M NaOH?

HX + NaOH NaX + H2O

If 0.121g HX react with 26.2 mL of 0.229 M NaOH, what is the molar mass of HX?

What is element X?

19

What if two reagents are added, how much product do you get?

2Na + Cl2 2NaCl

Suppose 10 g Na and 10 g Cl2 are mixed together. How much NaCl can be produced?

First find the moles of each reactant:

10 g Cl2 x 1 mole/71.0 g = 0.14 mole Cl2

10 g Na x 1 mole/23.0 g = 0.43 mole Na

Find the moles of NaCl produced for each reactant:

0.14 mole Cl2 x 2 mole NaCl/1 mole Cl2 = 0.28 mole NaCl

0.43 mole Na x 2 mole NaCl/2 mole Na = 0.43 mole BrCl

This is what can be produced! Cl2 is limiting reagent.

2 1

Have 0.43

Need 0.22

Need 0.28

Have 0.14

2Na + 1Cl2

20

A chemical analysis problem

A chemist decides to check the molarity of H2SO4 in her car battery. A 10.0 mL sample is reacted with 31.03 mL of 2.73M NaOH. What is the molarity of H2SO4?

H2SO4 + 2NaOH Na2SO4 + 2H2O

21

Answers to problems by slide number:

4- 0.15 mole NaHCO3; 1.0 x 1023 molecules CO2

6- 1.3 M KCl; 0.069 mole NaOH

12- 61g CO2

16- 0.39g Al(OH)3

17- 5.3 x 102g Al; 8.9 x 1024 atoms C

18- 0.34g CH3COOH; MM = 20.2 g/mole; X = F

20- 4.2M H2SO4

Documents

Moles and Molecules Moles and Chemical Reactions Moles, Chemical Reactions, and Molarity All done as UNIT CONVERSIONS!!! …and practice, practice, practice