Stoichiometry Investigation Lab - Jan 28, 2010 Class

LAB:

Stoichiometry Investigation
Testing the Stoichiometric Method

The purpose of this lab is to test if Stoichiometry accurately predicts the mass of the products produced in chemical reactions.

Experimental Design:

2.00g 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 separated by filtration, dried and weighed.

Prediction:(What is the theoretical mass of the precipitate?)

1. What is the balanced chemical equation for this reaction?
Sr(NO3)3 + CuSO4 -> SrSO4 + Cu(NO3)2


2. If 2.00g of Strontium nitrate completely reacts, how many grams of Strontium sulphate should be produced?








Procedure:

1. Carefully measure about 3.00g of Copper (II) sulphate.
2. Crush the Copper (II) sulphate into a fine powder using a mortar and pestle
3. Dissolve the Copper (II) sulphate in 50mL of water
4. Carefully measure 2.00g of Strontium nitrate and dissolve it in 50mL of water
5. Slowly pour the two solutions together
6. Stir the mixture to complete the reaction
7. Write your group name on a piece of filter paper
8. Find and record the mass of the filter paper
9. Using a funnel and an Erlenmeyer flask, place the filter paper in the funnel. Slowly pour the mixture into the funnel
10. Pour the filtrate into the waste collection bottle
11. Place the filter paper in the drying oven and record the mass when its dry.

Mass to Mass Problems - Jan26 Class

Lead (IV) Nitrate reacts with 5.0 g of potassium iodide. How many grams of lead (IV) nitrate are required?






Potassium Iodide:

















How many grams of O2 are produced from the decomposition of 3.0g of potassium chlorate?







If 5.0g of potassium chlorate decomposes, what volume of O2 at STP is produced?





If a 100mL solution of 2.0 M H2SO4 is neutralizd by sodium hydroxide, what mass of water is produced?




Percent Yield
- The theoretical yeild of a rxn is the expected (calculated) amount.
- The experimental amount is the actual yield:
% = Actual/theoretical x 100
Example: The production of urea CO(NH2)2 is given by: 2 NH3 + CO2 --> CO(NH2)2 + H2O

If 47.7 g of urea are produced when 1 mole of CO2 reacts, find the actual yield, theoretical yield and percent yield.
Actual yield: 47.7g
Theoretical yield: 1mol CO2 x 1 CO(NH2)2/1 mol CO2 x 60.1g / 1 mol = 60.1g
Percent yield: 47.7g / 60.1g x 100 = 79.4%

Stoichiometry - Jan. 22

In today's class we learned about Stoichiometry and did many examples.

Stoichiometry
- Coefficients in balanced equations represent moles
- They are also conversion factors

*Always write a balanced equation

Examples:
If a 0.3 mole sample of methane reacts with oxygen, how many moles of each product are produced?





Converting to mass requires one additional step

Example
How many grams of water are produced if 0.84 mol produced of phosphoric acid is neutralized by Barium hydroxide?

Jan 18 Class - Lab
Heat of Combustion of Candle (paraffin) Wax

Materials:

• candle
• matches
• weigh scale
• lab stand
• wire mesh or triangle
• thermometer
• water

Procedure:

1. Set up the lab stand and wire mesh (low enough for fire to heat up)
   
2. Measure 150 mL of cold water and pour it into the metal can, using a graduated cylinder.
3. Record the temperature of the watter.
   
4. Record the mass of the candle before lighting it.
5. Place the candle under the can and carefully light it
6. Let the candle burn for aprx. 5 minutes. Record the new temperature of the water. Record the mass of the candle after the experiment.
7. Clean up your lab station.

Observations:
These are my groups observations...
Volume of water used: 150 mL
Initial Temperature of Water: 21°C
Initial Mass of Candle: 10.46g
Final Temperature of Water: 26°C
Final Mass of Candle: 9.8g

The accepted value for the molar heat of combustion of Paraffin Wax is aprx. 14500. We concluded that it was 1652. We were 88% wrong. Some possible sources of error were when the water and wax spilled, when we did not leave the thermometer in long enough, and when we did not record as precisely.

Calorimetry - Jan14 Class

Calorimetry
- To measure heat absorbed/released by water we need to know 3 things:
1) Temperature change °C
2) Amount of water (g, kg, ml, L)
3) Specific heat capacity (kJ/kg °C)

∆H = mC∆T
m = mass of water
C = specific heat capacity 4.19kJ/kg °C
∆T = change in temperature

Examples: Calculate the heat required to warm 400g of water from 20°C to 50°C
∆H = mC∆T
∆H = (0.400kg)(4.19 kJ/kg °C)(50° - 30°)
∆H = 50 kJ

75.0 kJ are added to 850 ml of water initially at 25.0°C. What will the final temperature be?

∆H = mC∆T

∆H = mC (Tf - Ti)

Molar Enthalpy: Heat absorbed/released by one mole

When a candle (C25H52) is burnt, heat is released according to the reaction:
C25H52 + 38 O2 -> 25 CO2 + 26 H2O + 11 000 kJ
If 1.0g of wax is burnt, how much energy is released?
1.0g x 1.0mol/352g = 0.00284mol

11 000kJ / 1mol C25H52 x 0.00284 mol C25H52 = 31.3 kJ

CALORIMETRY OF A BOMB!

Heat & Enthalpy - Jan. 12

In today's lesson we learned about Heat, Enthalpy, and the reactions.

-Reactions that release heat are exothermic. (Hot)
-Reactions 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 of Gasoline > Enthalpy of Water







- Enthalpy has a symbol H
- Change in enthalpy is:






Enthalpy Diagrams (Exothermic & Endothermic)
Exothermic
- H is negative
- Products are lower than reactants
- Heat is released

Endothermic
- H is positive
- Reactants are lower than products
- Heat is absorbed




Two ways to write enthalpy in reactions













- Coefficients can stand for moles or molecules








1 mole of N2 produces 46.3 kJ
3 mole of H2 produces 46.3 kJ
2 mole of NH3 produces 46.3 kJ

This gives conversion factors:
46.3 kJ/ 1 mol N2
46.3 kJ/ 3 mol H2
46.3 kJ/ 2 mol NH3


Ex. Find the amount of heat released if 7.0 mol of N2 are consumed.
46.3 kJ/ 1 mol N2 x 7.0 mol of N2 = 324.1 kJ

Jan 6 Class Balancing Chemical Equations

Balancing with C, H & O (combustion)
To make combustion questions easier to balance, you can do them in particular steps.
1. carbons
2. hydrogens
3. oxygens

2C8H18 + 25O2 -> 16CO2 + 18H2O
C8H18 + 25/2O2 -> 8CO2 + 9H2O
Both are the same.

Alcohols
C2H5OH + 3O2 -> 2CO2 + 3H2O

Words -> Balanced Equations
EX: Sodium Chloride is mixed with Potassium Carbonate. Sodium Carbonate and Potassium Chloride are formed. Write a balance equation.

2NaCl + K2CO3 -> Na2CO3 + 2KCl


ACIDS
Name Formula
Hydrochloric acid HCl
Nitric Acid HNO3
Sulphuric Acid H2SO4
Phosphoric Acid H3PO4
Acetic Acid CH3COOH

Hydrogen makes it acid. -> (almost all)

EX: Nitric Acid is neutralized by barium hydroxide.
2HNO3 + Ba(OH)2 -> Ba(NO3)2 + 2HOH