CHEMISTRY SHENANIGANS

In today's class, we did a lab. Last class, we had to complete the prelab which involved our prediction for the outcome of the experiment.

The Experimental Design: 2.00 g of Strontium nitrate is dissolved in 50mL of water and then reacted with excess Copper (II) sulphate (3.00g). The product is a precipitate (Strontium sulphate and Copper (II) nitrate. After mixing the solutions, the precipitate will be seprated by filtration, dried and weighed.

My group's prediction results:

1. What is the balanced chemical equation for this reaction?
Sr(NO₃)₂ + CuSO₄ --> SrSO₄ + Cu(NO₃)₂

2. If 2.00 g of Strontium nitrate completely reacts, how many grams of Strontium sulphate should be produced?
2.00 g Sr(NO₃)₂ x (1 mol/211.6g) x (1 mol/SrSO₄/1 mol Sr(NO₃)₂) x 183.7g/mol = 1.74 g



We completed the first part of the lab (dissolving the chemicals, forming a precipitate, and seprating it through filtration) and the second half (drying and weighing) will occur next class.

Ex. When 2.0g of oxygen reacts with nitrogen monoxide, how many moles of nitrogen dioxide are produced?
O2+2NO >>> 2NO
2.0gx (1 mol of O2/32.0g) x (2mol NO2/1mol O2) = 0.125 mol of NO2

Ex. If 3.0g of O2 with nitrogen monoxide, what volume of nitrogen dioxide is produced at STP?
1. O2 + 2NO2 >>> 2NO2
2. 3.0g x (1mol O2/ 32.0g) x (2mol NO2/1mol O2) x (22.4L/mol) = 4.2L

Ex. In the formation of Copper(II) Oxide, 4.0g of copper react. How many moles of copper oxide are produced?
1.2Cu + O2 >>> 2CuO
2. 4.0g x (2 Cu/63.5g) x (2mol of CuO/ 2mol Cu) = 0.126 mol CuO

Ex. What mass of water is produced when 5.5L of hydrogen is burnt(reacted w/O2)?
1. 2H2 + O2 >>> 2H2O
2. 5.5L x ( mol/22.4) x (18.0g/mol) = 4.4 g

Ex. Lead (IV) Nitrate reacts with 2.0g of potassium iodide. How many moles of leader (IV) nitrate are needed?
1. Pb (NO3)4 + 4KI >>> PbI4+ 4KNO3
2. 2.0g x (1mol PbI4/ 714.8g) x (1 mol Pb(NO3)4/ 1mol PbI4) = 2.8x 10-3 mol

-Coefficients in balanced equations represent moles
-Also conversion factors

Ex. (In class) If a 0.15 mole sample of methane reacts with oxygen. How many moles of each product are produced?
1)CH4+2O2--->CO2+2H20
2)0.15molCH4 x 1molCO2/1molCH4 = 0.15 mol CO2
3)0.15molCH4 x 2molH2O/1molCH4= 0.30 mol H20

-Always what you need/what you know
-Converting to mass requires one addtional step

Ex. (In class)How many grams of Bouxite are required to produce 3.5 mol of Al?
1) 3.5molAl x 2molAl2O3/4molAl = 1.75 mol Al2O3
2) 1.75mol x102g/1mol=178.5g

Today, we went over the Molar Enthalpy and Combustion worksheet and did a lab. In our lab, we placed water in a can and lit a candle underneath for several minutes. Afterwards, with the measurements we took, we tried to make an educated guess of how much energy was released or absorbed in the experiment. It looked a lot like this:



Questions from the homework:

1. A car engine burns 250g of octane (C8H18). If 1.19x10^3 kJ of heat are produced, what is the molar enthalpy of the combustion of Octane?
Answer: 250g ÷ 114g/mol (of Octane) = 2.19 mol
1.19x10^3 kJ ÷ 2.19 mol = 543 kJ/mol

4. When ethanol C2H5OH is burned, heat is released. For every mole of ethanol burned, 1300 kJ of heat are released.
a) If 2.5g of ethanol are burnt, how much heat will be released?
Answer: 2.5g x mol/46g x 1300kJ/mol = 70.65 -> 71 kJ

Questions for practice:

ex. What is the molar enthalpy of CO2 (g) in the reaction for the burning of butane below?
2 C4H10 (l) + 13 O2 (g) 8 CO2 (g) + 10 H2O (g) H = -5315 kJ
Answer: Molar enthalpy, change in H = 5315 kJ ÷ 8 mol = 664 kJ / mol.

Calorimetry
To measure heat absorbed/released by water we need to know THREE important things

1) Temperature change ( 'C)
2) Amount of water (g,kg, mL, L)
3) Specific heat capacity (KJ/ Kg 'C)

deltaH= mCdeltaT

m= mass of water
C= specific heat capacity
deltaT= change of temperature *liquid water is 4.19 KJ/Kg '


MOLAR ENTHALPY
Heat obsorbed/ realeased by one mole

When a candle (C H ) is burnt, heat is released according to reaction"
25 52

C H + 380 ---> 25CO + 26H O+ 11000 KJ
25 52 2 2 2

ex. 9.0 grams of charcoal were completely consumed in a bomb calorimeter. If 2.0 L of water absorbed all of the heat released by the charcoal, and if the temperature of the water increased from 20.25 to 56.04oC, what is the molar enthalpy of carbon?
Answer: deltaH= mCdeltaT
= 2000g(4.19 J/(g C))(56.04-20.25)
= 299 920 J
dH = - C = - 299 920 J = -299.92 kJ
n = 9.0g / 12.01 g/mole = 0.7493 mole
DH/n = -299.92 kJ/ 0.7493 mole = -400.27kJ/mole of C = - 4.0 X 102 kJ/mole

- Rxns that release heat are exothermic (hot)
- Rxns that absorb heat are endothermic (cold)

Heat is a form of energy
All chemicals have energy stored in them. Stored chemical energy is called enthalpy.
Enthalpy is stored chemical energy.

Enthalpy of gasoline > Enthalpy of water

Exothermic rxns convert enthalpy into heat.
2C8H18 + 25O2 >>> 16CO2 + 18 H2O + Heat
high enthalpy low enthalpy

Enthalpy has a symbol H
Change in enthalpy is Delta H (triangle H)

Exothermic

• delta H is negative
• products are lower than reactants
• heat is released

Endothermic

• delta H is positive
• reactants are lower than products
• heat is absorbed

Delta H and Moles
coefficients can stand for moles or molecules

1)Synthesis
2Al+3F2--->2AlF3

2)Decomposition
*always assume the products are elements*
4H3PO4--->6H2+P4+8O2

3)Single Replacement
*compounds must always have a metal and a nonmetal*
3Mg+2Al(NO3)3--->2Al+3Mg(NO3)2

4)Double Replacement
MgCl2+K2SO4--->MgSO4+2KCl

5)Neutralization
*Between acids and bases*
*always forms H2O*
H2SO4+2KOH--->2H2O+K2SO4

6)Combustion (burning)
2Mg+O--->2MgO --Metallic
CH4+2O2--->CO2+2H20 --Hydro carbon

In today's class, we discussed how to balance equations involving carbon, hydrogen, and oxygen. We learned that in combustion reactions, the products will always be carbon dioxide and water.

ex. (in-class) CH₄ + 0₂ -> CO₂ + H₂O
becomes CH₄ + 20₂ -> CO₂ + 2H₂O

Also, we found out that we could use fractions while balancing equations. Because the number in front of the atom or compound says how many moles of it there is, it is possible to have a fraction as there can be 1/2 or 7/2 of a mole.

ex. (in-class) C₈H₁₈ + O₂ -> CO₂ + 9H₂O
becomes C₈H₁₈ + 25/2 O₂ -> 8 CO₂ + 9H₂O

Briefly, we discussed alcohols.
CH₃OH - methanol
C₂H₅O₅ - ethanol

In addition, we were given a number of acids we should know.
Hydrochloric acid (HCl)
Nitric acid (HNO₃)
Sulfuric acid (H₂SO₄)
Phosphoric Acid (H₃PO₄)
Acetic Acid (CH₃COOH)

Try some for yourself!
1. CO₂ + H₂ -> CH₄ + H₂O
2. C₂H₆ + O₂ -> CO₂ + H₂O

Answers:
1. CO₂ + 4H₂ -> CH₄ + 2H₂O
2. 2C₂H₆ + 7O₂ -> 4CO₂ + 6H₂O

Need to some more help or examples? Check out the videos below: