next generation chemistry i kaye truitt, don bratton, tina wagner msms
TRANSCRIPT
Next Generation Chemistry IKaye Truitt, Don Bratton, Tina WagnerMSMS
Hess's Law: Determining the Enthalpy of Combustion of Mg
Easy and impressive demonstration
Difficult to measure the heat released by this reaction
Great investigation for the use of Hess's Law
Hess’ Law Great results from
simple technology
Inexpensive and easy to use
Works with standard alcohol thermometer OR data logger temperature probe
Graphs of DT
Hess’ Law1) Mg(s) + HCl(aq) → MgCl2(aq) + H2(g) ΔH1
2) MgO(s) + HCl(aq) → MgCl2(aq) + H2O(g) ΔH2
3) H2(g) + ½O2(g) → H2O(l) ΔH3
Carry out first 2 reactions and measure the ΔH; use literature value for reaction 3
Hess’ Law Measure the DT of the solution
and use q= mCDT to determine heat absorbed
Heat absorbed by solution = heat released by reaction
Manipulate equations to achieve the target equation Mg(s) + ½O2(g)→ MgO(s)
Hess’ Law
Mg(s) + HCl(aq) → MgCl2(aq) + H2(g) ΔH1
MgCl2(aq) + H2O(g) → MgO(s) + HCl(aq) (-ΔH2)
H2(g) + ½O2(g) → H2O(l) ΔH3
Mg(s) + ½O2(g)→ MgO(s) ΔH = ΔH1+(-H2)+ΔH3
Hess’ LawAnalysis
Use literature value of ΔH of combustion of Mg and calculate % error (experience has shown a low (< 5%) error rate on this investigation).
To make more inquiry-based, offer a series of reactions and have students determine which would best combine to achieve target equation.
Standards MS Chemistry Framework:
Inquiry 1 C: use of scientific inquiry methods to conduct/evaluate
lab investigations (DOK 3) D: organize data, draw conclusions, make inferences
(DOK 3) E: evaluate procedures,data, conclusions to critique
validity (DOK 3) F: data analysis (DOK 3) G: use of technology to create formal presentation (DOK
3) Physical Science 4
D: explain thermodynamics associated with physical and chemical concepts related to temperature, enthalpy and heat energy (DOK 2)
Standards Next Generation Science Standards:
HS-PS1-4: Develop a model to illustrate that the release or absorption of energy from a chemical reaction system depends on the changes in total bond energy
Science & Engineering Practices: Planning and carrying out investigations Using mathematics and computational thinking
Disciplinary Core Ideas: PS1.B Chemical processes and whether energy is stored or released
can be understood in terms of collisions of molecules and the rearrangement of atoms into new molecules and consequent changes in sum of all bond energies.
Cross-cutting Concepts: Energy and Matter Changes of energy and matter in a system can be described in
terms of energy and matter flows into, and out of, and within that system.
Aluminum Alchemy MCF Alignment (Chemistry)
3.c Classify chemical reactions by type. (DOK 2)
3.d Use stoichiometry to calculate the amount of reactants
consumed and products formed. (DOK 3) 5.c
Analyze a reduction/oxidation reaction (REDOX) to assign oxidation numbers (states) to reaction species and identify the species oxidized and reduced, the oxidizing agent, and reducing agent. (DOK 2)
Plus nearly every inquiry standard
Aluminum Alchemy NGSS Alignment
HS-PS1-2: Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties
HS-PS1-7: Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction
Aluminum Alchemy Materials
Aluminum foil 0.25 – 0.5 M copper (II) sulfate 1.0 M or greater concentration of acid 250 mL beaker Stirring rod Funnel Filter paper Balance
Aluminum Alchemy Safety and Disposal
Lab coats and goggles should be used due to presence of acid
Reaction is slightly exothermic Check MSDS for disposal of solution
Flinn Scientific suggests that aluminum sulfate solutions may be disposed of down a municipal drain system
Aluminum Alchemy Concepts
Stoichiometry Percent yields on this experiment are quite
good Oxidation can take yield over 100%
Types of reactions Excellent example of single replacement Excellent example of redox reactions
Aluminum Alchemy Keys to success
Allow filters to dry completely Do not allow copper powder to sit out for
long periods – it will oxidize Be careful handling filters after drying –
the powder may spill
NSES Content Standards being met Content standards Science as Inquiry The standards on inquiry highlight the
ability to conduct inquiry and develop understanding about scientific inquiry.
Students at all grade levels and in every domain of science should have the opportunity to use scientific inquiry and develop the ability to think and act in ways associated with inquiry, including asking questions, planning and conducting investigations, using appropriate tools and techniques to gather data, thinking critically and logically about relationships between evidence and explanations, constructing and analyzing alternative explanations, and communicating scientific arguments.
Antacid: Regular vs. Extra Strength The major function of the antacid is to
neutralize excess HCl in gastric juice. The antacid is a buffer that maintains the pH of the stomach.
Is it worth the money to buy ultra strength antacid versus the regular strength?
TumsRegular – 500 mg CaCO3 - $5.79 (150)
Ultra Strength – 1000 mg CaCO3 - $5.79 (72)
3.86 cents per tablet8.04 cents per tablet
Neutralization reactionCaCO3(s) + HCl(aq) CaCl2(aq) + H2O(l) + CO2(g)
In this lab you will perform a titration for two antacids to find which absorbs the most acid.Costs comparisons will then be calculated to see which is the best value for the consumer.
Procedure: Mass one antacid tablet and grind it to a powder.
Record mass. Pour the measured amount into a 100 ml beaker. Add 25 mL of distilled water and mix well. Make
qualitative observations. Add ten drops of BTB indicator to the solution. BTB
is used because its color changes at a pH of 6-7 Titrate the solution to the end point with 0.1M HCl.
Record the number of drops needed to cause the color change.
Repeat steps 1-5 with the ultra strength antacid.
# drops to titrate x (1 ml/20 drops) xnumber of grams of antacid used = grams of HCl neutralized
Mississippi 2010 FrameworkINQUIRY - 1. Apply inquiry-based and problem-solving processes and skills to scientific investigations. c. Demonstrate the use of scientific inquiry and methods to
formulate, conduct, and evaluate laboratory investigations (e.g., hypotheses, experimental design, observations, data analyses, interpretations, theory development). (DOK 3)
d. Organize data to construct graphs (e.g., plotting points, labeling x-and y-axis, creating appropriate titles and legends for circle, bar, and line graphs), draw conclusions, and make inferences. (DOK 3)
g. Collect, analyze, and draw conclusions from data to create a formal presentation using available technology (DOK 3)
Physical Science3. Develop an understanding of the periodic table. c. Classify chemical reactions by type. (DOK 2)
Single displacement, double displacement, synthesis (combination), decomposition, combustion, or precipitation. Products (given reactants) or reactants (given products) for each reaction type
d. Use stoichiometry to calculate the amount of reactants consumed and products formed. (DOK 3)
5. Compare factors associated with acid/base and oxidation/reduction reactions.a. Analyze and explain acid/base reactions. (DOK 2) Properties of acids and bases, including howthey affect indicators and the relative pH of the solution. Formation of acidic and basic solutionsb. Classify species in aqueous solutions according to the Arrhenius and Bronsted-Lowry definitions, respectively and predict products for aqueous neutralization reactions. (DOK 2)
