Chapter 3 (CIC) and Chapter 3, 18 (CTCS)

• Read in CTCS Chapter 3.4, 6, 7, and 18.4 (pgs. 697-699)

• Problems in CTCS: 3.29, 31, 33, 35, 39, 41, 59, 63, 69, 71, 73, 79, and 18.27

How Much CO2 is 3 bmt of C?

• Several ways to solve (%C in CO2 and stoichiometric relationships)

Q: What is the %C in CO2?

A: 27.3%

• This is equivalent to dividing 3 by 0.273 (27.3%)

22

3 bmt C 44 bmt CO = 11 bmt CO

1 12 bmt C

Stoichiometric Relationships• C + O2 CO2

• Since a bmt is so much larger than an amu, it is helpful to work on a larger scale than an amu – such as grams

• If a 12C atom weighs 12.0000…amu by definition, how many 12C atoms does it take to weigh 12.000…g? 6.02 x 1023 (Avogadro’s number)

• Dozen, Gross, Ream, Mole

12 -24

23

C atom 12 g 1.66 x 10 g =

12 amu 6.02 x 10 C atoms amu

Inverted: 6.02 x 1023 amu/g

• How big is Avogadro’s number?

• 1 mol of seconds = 4 million times as long as Earth has existed

• We use Avogadro’s number to count individual atoms, molecules, electrons, etc.

62 2 2

262 2

3 bmt C 10 g C 1 mol C 1 mol CO 44 g CO 1 bmt CO = 11 bmt CO

1 1 bmt C 12 g C 1 mol C 1 mol CO 10 g CO

Stoichiometry LabFor MgCO3 we were finding ~ 0.40 g CO2 released. Had we not known it was a carbonate, could we have figured it out knowing that 0.73 g of HCl was used in the reaction?

CO32- + 2 HCl H2O + CO2 + 2 Cl-

HCO3- + HCl H2O + CO2 + Cl-

How many g of that 0.40 g is due to C (27.3%)?

2 22

2

0.73 g HCl 1 mol HCl 1 mol CO 44 g CO = 0.44 g CO

1 36.5 g HCl 2 mol HCl 1 mol CO

2 2

2 2

0.40 g CO 1 mol CO 1 mol C 12 g C = 0.11 g C

1 44 g CO 1 mol CO 1 mol C

How do you know it was Mg?• Suppose the slope of the line in the 1st week’s

data had been 0.5g CO2/1 g XCO3.

• ? = 88 g XCO3 and of that 88g, 44 + 16 (or 60g) of it was due to the CO3. This means that 28 g of it was due to X. If X was an alkaline earth metal then it must mass 28g. If X was an alkali metal X must mass 14 g because the formula is X2CO3.

2 2

3 3

0.50 g CO 44 g CO =

1 g XCO ? g XCO

Q: If volcanoes release 19 mmt SO2, how much S is “combusted”?

A: 9.5 mmt S

Q: If a lighter holds 5.0g of butane (C4H10), how many grams of CO2 are produced upon combustion?

A: 15 g CO2

g (reactant) mol (reactant) mol (product) g (product)

Limiting ReagentCO3

2- + 2 H+ H2O + CO2

• When adding small amounts of the carbonate a pink solution remained. – What was the limiting reagent? – What was the excess (xs) reagent? – Could you tell by looking at the solution?

• When large amounts of carbonate were added, a white solid and colorless solution appeared. – What was the limiting reagent? – What was the excess (xs) reagent? – Could you tell by looking at the solution?

• At what point on the graph could you use the stoichiometric relationships?

Percent Yield (actual/theoretical x 100)• In reality, we ended up getting about 0.35 g CO2

from the MgCO3 instead of the 0.44 g that is the theoretical amount. See next slide for the graph!

Q: What is the percent yield of CO2 that was obtained?

A: 80%

• What does this mean?– HCl concentration was not 0.73 g– A poor yielding reaction is not suitable for this lab

Stoichiometry Laby = 0.3453x

R2 = 0.724

y = -0.0013x + 0.3382

R2 = 0.0004

0

0.1

0.2

0.3

0.4

0 0.5 1 1.5 2 2.5 3 3.5 4

g XCO3

g C

O2

Other Gases and What We Know• CH4 is 30x as effective as a greenhouse gas as CO2 but

its’ concentration is only at 1.7 ppm• CFC’s – 25,000x effective and [CFC] is at 0.28 ppb• Modeling earth’s Temp is still crude• We know

– CO2 increases global Temp

– [CO2] increased over the last century

– [CO2] increased due to human activity

– Global Temp increased over last century

• Uncertain about– CO2 and other gases are responsible for increased Temp

– Avg global Temp will continue to increase as anthropogenic greenhouse gases increase

What Should We Do?• Act now! Is the cure worse than the disease?

– Fertilize ocean with iron to increase phytoplankton– Release S containing compounds into air

– Pump CO2 to bottom of ocean

– Pollution Rights• US has a great head-start over undeveloped countries

• Study the problem more

• Nothing – It’s inevitable - Adapt– Fossil fuels are too valuable to just combust