Chemistry Past Paper Questions PDF

9/27/24 What is the most likely bond angle in SO2? A. 180o B. 120o C. 109.5o D. 107o E. 104.5o Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 3 3 How do chemists describe the three-d...

9/27/24 What is the most likely bond angle in SO2? A. 180o B. 120o C. 109.5o D. 107o E. 104.5o Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 3 3 How do chemists describe the three-dimensional shape of molecules? 4 2  9/27/24 Draw the best Lewis structure for OCS. What is the O-C-S bond angle? How do you know? A. 180o B. 120o C. 109.5o D. 90o Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 9 9 Reference: Linear Electron Domain Geometry Single Molecular Shape (Linear) In the linear electron domain geometry, there is only one molecular shape: linear. Note: If there are only two atoms in the molecule, the molecule will be linear no matter what number of pairs around an atom. 10 5  9/27/24 Draw the best Lewis structure for BF3. What is the F-B-F bond angle? How do you know? A. 180o B. 120o g Follow-up: What is the C. 109.5o ·Fi.. molecular shape of BF3? D. 90o :F B-f :. trigonal planar Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 11 11 Reference: Trigonal Planar Electron Domain Geometry 2 Molecular Shapes SN = # electron domains around central atom 12 6  9/27/24 Draw BH3 and BH2─ and compare H-B-H bond angles 13 Reference: Nonbonding Pairs and Bond Angle Nonbonding pairs occupy a larger volume than bonding pairs. [Why?] Therefore, their repulsions are greater; this tends to compress bond angles. Best Lewis structures H H H Wedge-and-dash H structures 14 7  9/27/24 Multiple Bonds and Bond Angles Double and triple bonds occupy a larger volume than single bonds. [Why?] They exert a greater repulsive force than single bonds, making their bond angles greater. HCO angle > HCH angle in formaldehyde, right, as a result 15 Draw the best Lewis structure for methane, CH4. What is the H-C-H bond angle? A. 180o B. 120o C. 109.5o D. 90o Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 16 16 8  9/27/24 Exam-type Question: What is the angle between the hydrogens in PH3 (the H-P-H bond angle)? Draw the 3D structure using wedge-and-dash notation. A. 109.5o - B. A bit > 109.5o & C. A bit < 109.5o D. 90o , ↳ Think & Solve: 1 min; on your own demain +tetrahedral Discuss: 30 sec; share and compare [189 50 Answer: iClicker. 19 19 Exam-type question: Draw the best Lewis structure for each of the following molecules and determine the electron domain & geometry and molecular shape: 1. SO3 i trigonal planar Domain : shape : trigonal planar 2. H3O+ Domain : tetrahedral [H-0 4] + shape : - trigonal pyramidal Think & Solve: 4 min; on your own Discuss: 30 sec; share and compare Answer: volunteer, when prompted 20 20 10  9/27/24 Molecular Shapes Within Larger Molecules For larger molecules, we can look at the geometry about each atom rather than the molecule as a whole. 21 Name the electron domain geometry of the indicated atom in the amino acid tryptophan (the one blamed for making you sleepy after a turkey dinner) A. Linear B. Trigonal planar C. Bent D. Trigonal pyramidal E. Tetrahedral Think & Solve: 30 sec; on your own Answer: iClicker 22 22 11  9/27/24 Name the electron domain geometry of the indicated atom in the amino acid tryptophan (the one blamed for making you sleepy after a turkey dinner) A. Linear & B. Trigonal planar C. Bent D. Trigonal pyramidal E. Tetrahedral Think & Solve: 30 sec; on your own Answer: iClicker 23 23 Name the electron domain geometry of the indicated atom in the amino acid tryptophan (the one blamed for making you sleepy after a turkey dinner) A. Linear B. Trigonal planar C. Bent D. Trigonal pyramidal D E. Tetrahedral Think & Solve: 30 sec; on your own Answer: iClicker 24 24 12  9/27/24 Exam-level question: Give the bond angles around each of the carbons in this molecule: : Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: Volunteer 25 To Do: q SW Warm-up Lesson 17 due W, 8am q Recitation 4 begins Wednesday – Remember your PRQs! 26 26 13  9/27/24 Comparison of the Polarity of Two Molecules A nonpolar molecule A polar molecule 5 5 A)Yes Is CCl4 polar? B) No g ↓ - C- I Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 6 6 3  9/27/24 A)Yes What about B) No chloroform, CHCl3? Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 7 7 What about ozone, O3? 8 8 4  9/27/24 Exam-type Question: Is SO2Cl2 polar? Explain your answer. A. Yes B. No Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 9 Vibrating Bonds and the Greenhouse Effect Covalent bonds are not rigid—they vibrate, stretch, and bend. As bonds vibrate, the vibrational frequencies of their electric fields match those of infrared radiation. 10 5  9/27/24 Vibrating Bonds and the Greenhouse Effect Why is methane (CH4) a greenhouse gas? As bonds vibrate, the vibrational frequencies of their electric fields match those of infrared radiation. https://www.youtube.com/watch?v=Quz7xGgN0Tk 11 Exam-type Question: Which of the molecules listed below are polar (= have a molecular dipole)? Select all that apply. q A. CS2 q B. NO2 q C. BF3 q D. NF3 q E. H2 Think & Solve: 4 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (short answer) 12 6  9/27/24 Orbital Overlap and Bonding We think of covalent bonds forming through the sharing of electrons by adjacent atoms. Orbitals on the two atoms overlap. Sigma bonds are characterized by Head-to-head overlap. Cylindrical symmetry of electron density about the internuclear axis. 5 5 Valence Bond Theory: Orbital Overlap What two atoms might combine in each of the following ways to form a sigma bond? Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: volunteer 6 6 3  9/27/24 Single Bonds A single bond is always a s bond, because extent of s electron overlap is greater than in a π bond, resulting in a stronger bond and more energy stabilization (lowering). 7 7 Atomic Orbitals Cannot Explain VSEPR Models Alone Recall the following information about carbon: Write the electron configuration for carbon: _________ How many valence electrons does carbon have? _________ What are the orbitals in the valence shell? _______ Write the energy level diagram for the valence shell of C: E 8 8 4  9/27/24 Atomic Orbitals Cannot Explain VSEPR Models Alone Energy level diagram 2p Energy (Carbon) 2s Recall: What are the shapes of the valence atomic orbitals in carbon? Recall: What is the bond angle observed for CH4? _______ Evaluate: Each bond in CH4 is identical. How do we rationalize that we have 4 identical bonds coming from 4 unique orbitals? 9 9 Valence orbital hybridization A mathematical combination of wavefunctions Hybridized orbitals can ONLY make sigma bonds! 10 10 5  9/27/24 Hybrid Orbitals: sp3 hybridization Carbon has ____ regions of electron density. Atomic Orbitals Hybridized Orbitals used to make 2p Energy hybridize covalent used bonds to make 2p Energy 2p covalent bonds Energy 2sp3 2sp3 2s 11 Hybrid Orbitals: sp3 Is carbon the only atom that can be sp3 hybridized? How do we identify if an atom is sp3 hybridized? 12 12 6  9/27/24 https://www.youtube.com/watch?v=H5gRGcguId8 13 What is the hybridization of the nitrogen in NH2- ? A. sp B. sp2 C. sp3 D. Cannot determine Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 14 14 7  9/27/24 Which orbitals (one on each atom) overlap to form the N-H bond circled in the molecule below? Select all that apply. q A. s q B. p q C. sp q D. sp2 q E. sp3 Isoetharine – treatment for Think & Solve: 1 min; on your own asthma Discuss: 30 sec; share and compare Answer: iClicker (short answer) 15 15 Pi (p) Bonds Pi bonds are characterized by Side-to-side overlap. Bond electron density is above and below internuclear axis in pi (π) bonds Formed between unhybridized p orbitals 16 16 8  9/27/24 Multiple Bonds In a double or triple bond, one of the bonds is a s bond and the rest are p bonds. 17 17 According to the data in the table, which type of bond is stronger? A. σ-bonds B. π-bonds C. They are the same Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 18 18 9  10/4/24 In which orbitals do the lone pairs on the oxygen in formaldehyde, H2CO, exist? A. s B. p C. sp2 D. sp3 E. Cannot determine Think & Solve: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 5 5 Formaldehyde explained The unhybridized p orbitals on carbon used to make 2p Energy and oxygen overlap covalent bonds to form the p bond. 2sp2 6 6 3  10/4/24 Hybridization: sp hybridization In acetylene, carbon has ___ electron domains. It needs ____ hybridized orbitals and has ___ p orbitals unhybridized. Hybridized Orbitals and Atomic Orbitals Unhybridized p Orbitals used to make 2p hybridize 2p Energy Energy covalent bonds 2sp 2s 7 If you hold on to one carbon atom in acetylene, can you rotate the: i) Other carbon atom? ii) Hydrogen atom? A. Yes B. No C. Sometimes D. Cannot determine Think & Solve: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (short answer) 8 8 4  10/4/24 What is the hybridization of the nitrogen in N2? A. sp B. sp2 C. sp3 D. Cannot determine Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 9 9 Follow-up: How many unhybridized p orbitals are on each nitrogen atom in N2, and how many pi bonds are in N2? A. 2, 2 B. 1, 2 C. 3, 1 D. 4, 2 Think & Answer: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 10 10 5  10/4/24 Exam-type question: What is the hybridization on the carbon in carbonate, CO32-? A. sp B. sp2 C. sp3 D. Cannot determine Think & Answer: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 13 13 Exam-type question: How many σ and π bonds are in acetone (nail polish remover)? A. 8 σ, 1 π B. 9 σ, 1 π 1 2 3 C. 10 σ, 0 π D. 8 σ, 2 π Follow-up: What is the hybridization of each carbon atom? Think & Answer: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 14 14 7  10/4/24 What is the hybridization of each atom indicated in tryptophan? A. sp B. sp2 C. sp3 D. sp4 E. unhybridized Think & Answer: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 15 15 What is the hybridization of each atom indicated in tryptophan? A. sp B. sp2 C. sp3 D. sp4 E. unhybridized Think & Answer: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 16 16 8  10/4/24 What is the hybridization of each atom indicated in tryptophan? A. sp B. sp2 C. sp3 D. sp4 E. unhybridized Think & Answer: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 17 17 What is the hybridization of each atom indicated in tryptophan? A. sp B. sp2 C. sp3 D. sp4 E. unhybridized Think & Answer: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 18 18 9  10/4/24 Magnetism Atoms or molecules that are paramagnetic are weakly attracted to a magnetic field Paramagnetism indicates the presence of ____________ electrons Diamagnetism indicates ______________ electrons. Which of the following atoms is/are paramagnetic? Select all. q A. P q B. Ti q C. Zn q D. Ca Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (short answer) 3 Use the Lewis Structures for N2, O2 and NO to predict whether each one is paramagnetic or diamagnetic. Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: volunteer 4 2  10/4/24 Is N2 diamagnetic as predicted? To see whole video visit: https://www.youtube.com/watch?v=Lt4P6ctf06Q 5 Make a Prediction What will happen when you pour liquid O2 between the poles of a magnet? A. It will all evaporate before it gets to the magnet B. It will flow through C. It will get stuck D. Some will flow through and some will https://www2.dawsoncollege.qc.ca/dbaril/NYA/Handout/MO/MO.htm get stuck Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 6 3  10/4/24 Combining 1s orbitals: Compare the MO Diagrams for H2 and He2. Why is helium not a diatomic molecule? H2 He2 σ*1s σ*1s E 1s 1s 1s 1s σ1s σ1s 25 Follow up: Calculate bond order of He2 25 Combining 1s orbitals: Compare the MO Diagrams for H2+ and H2-. What is the bond order of each ion? H2+ H2- σ*1s σ*1s E 1s 1s 1s 1s σ1s σ1s Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 26 13  10/4/24 Exam type question: If an electron in H2 absorbed enough energy (a photon) to be promoted to the LUMO, what do you predict would happen? A. The excited electron would drop back down to the ground σ*1s state and release a photon. B. The molecule will break apart. E 1s 1s C. Nothing will happen. σ1s Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare 27 Answer: iClicker 27 To Do: q SW Warm-up Lesson 21 due W, 8am 28 28 14  10/4/24 Based on the picture and the cartesian coordinates shown below, which p orbitals will combine to form bonding and antibonding sigma (σ) MOs? A) px B) py C) pz D) none, p- orbitals do not form σ bonds Think & Solve: 30 sec; on your own Discuss: 30 sec Answer: iClicker 7 MO Theory: What about atoms with p orbitals? pz orbitals combine to form bonding and antibonding sigma (σ) MOs 8 4  10/4/24 Why are two orbitals formed? pz orbitals combine to form bonding and antibonding sigma (σ) MOs 9 Molecular Orbitals: Apply your knowledge When the two orbitals below are combined in a constructive manner, what kind and what shape molecular orbital results? + A. pi B. pi C. pi* Think & Solve: 1 min; on your own D. pi E. pi* Discuss: 30 sec.; share and compare Answer: iClicker 10 5  10/4/24 MO Theory: What about atoms with p orbitals? Together, the six p orbitals create six MOs: σ*2p π*2p Energy π2p 2py 2px 2pz 2pz 2py 2px s2p 13 Why is there a greater energetic difference between σ and σ* orbitals than between π and π* orbitals? Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: volunteer 14 7  10/4/24 Exam-type question: According to MO Theory, how many unpaired electrons are in O2 ? σ*2p A.0 B.2 π*2p π*2p C.4 D.6 E π2p π2p σ2p σ*2s Think & Solve: 3 min; on your own Discuss: 30 sec Answer: iClicker σ2s 15 15 Exam-type question: According to MO Theory, what is the bond order of O2? Which are the highest occupied and lowest unoccupied molecular orbitals? (HOMO and LUMO) Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: volunteers 16 16 8  10/4/24 Exam-type question: According to MO Theory, how many unpaired electrons are in F2? σ*2p A.0 σ* B.2 π*2p 2p π*2p π*2p π*2p C.4 2p π2p π 2p D.6 π2p2p E π2p σσ2p2p σ* σ*2s 2s 2s 2s Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare σ2s σ2s Answer: iClicker 17 17 Exam-type question: What is the bond order of F2? Which are the HOMO and LUMO? σ*2p σ* π*2p 2p π*2p π*2p π*2p 2p π2p π 2p π2p2p E π2p σσ2p2p σ* σ*2s 2s 2s 2s Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare σ2s σ2s Answer: iClicker 18 18 9  10/4/24 Summary Molecular Orbital Theory üExplains why H2 forms a Energy s*1s covalent bond but He2 doesn’t 1s 1s üExplains why O2 is s1s paramagnetic Valence Bond Theory üExplains shapes of molecules 19 Ground States vs. Excited States in MO σ*2p Electrons occupy lowest σ*2p energy levels in ground π*2p π*2p state π*2p π*2p π2p π2p Electrons can move to π2p π2p higher energy levels when σ2p σ2p excited σ*2s O2 → O2* σ*2s σ2s σ2s 20 20 10  10/11/24 Does the diagram depict an attraction or repulsion between molecules? What is the sign on the potential energy in this case? A) Attraction; positive (PE > 0) B) Attraction; negative (PE < 0) C) Repulsion; positive (PE > 0) D) Repulsion; negative (PE < 0) Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 5 Potential energy on the atomic scale Q+Q─ Eel = k Energy vs distance d 10 5 Eel Potential Energy (Eel) 0 d -5 -10 Distance between particles (d) 6 3  10/11/24 Draw two HF molecules in an orientation to depict a repulsive interaction. What is the sign on the potential energy term for repulsion? For repulsion: A. PE > 0 B. PE < 0 C. PE = 0 D. PE may be greater than, less than, or equal to zero. Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 7 Three types of attractive intermolecular forces between molecules within pure substances 1. London Dispersion forces 2. Dipole-dipole interactions 3. Hydrogen bonding 8 4  10/11/24 Evidence-based reasoning: What trend do you observe in these data? Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: volunteer 9 London Dispersion Forces (LDFs) All molecules can interact via temporary dipoles. Nonpolar molecules only have London Dispersion Forces (LDFs) The strength of these London dispersion forces depend on several factors: Size of the atoms/molecules Shape of the molecules 10 5  10/11/24 Exam-Type Question: Which substance has the higher boiling point? Why? A) tetrafluoromethane, CF4 B) tetrachloromethane, CCl4 Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 13 Which molecule exhibits the greatest dispersion forces? A. n-pentane (C5H12) B. 2,2-dimethylpropane (C5H12) C. Both have the same LDFs because Think & Solve: 45 sec; on your own they have the same chemical formula Discuss: 30 sec; share and compare Answer: iClicker 14 7  10/11/24 Recall: Molecular Polarity Molecules—such as HF and H2O— + are POLAR. That is, they have a H + dipole moment. The polar H2O O H molecule will turn to align with an electric field. Two factors that cause a molecule to be polar: 1. Differences in electronegativity 2. Asymmetrical structure 17 Which substance has the higher boiling point? A. Dimethyl ether B. Ethanol C. Too close to tell Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 18 9  10/11/24 Dipole-Dipole Interactions All other things being similar, the more polar the molecule, the higher is its boiling point. 19 Which substance has the larger dipole? How do you know? A) difluoromethane, CH2F2 B) dichloromethane, CH2Cl2 Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 20 10  10/11/24 Why does dichloromethane have the higher boiling point? A) difluoromethane, CH2F2, BP = -52 oC B) dichloromethane, CH2Cl2, BP = 40 oC Think & Solve: 45 sec.; on your own Discuss: 30 sec; share and compare Answer: volunteer 21 To Do: q SW Warm-up Lesson 23 due W, 8am q Recitation 5 starts Today! Remember your PRQs 22 22 11  10/11/24 Why is the boiling point of H2O so much higher than HF, since they all exhibit hydrogen bonding? Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: Volunteer 5 H-bonds play critical roles in biology H-bonds hold the two strands of DNA together and are critical for protein structure and function Side note: biologists and biology textbooks don’t always draw the lone pairs. But you should! 6 3  10/11/24 Which isomer of propanol, C3H7OH, has the higher boiling point? A) n-propanol B) iso-propanol C) Both have the same boiling point since they’re both C3H7OH and both exhibit hydrogen bonding. Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 7 Exam type question: Draw three NH3 molecules and indicate all hydrogen bonds by circling the atoms involved in those hydrogen bonding interactions. Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: Volunteer 8 4  10/11/24 Applications of Intermolecular Forces: Drugs For ibuprofen, ibuprofen Put a triangle around all atoms that could be hydrogen bond donors Circle the hydrogen bond acceptors. Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: Random call 9 Exam-type question: Place the following substances in order of increasing normal boiling point: A) F2 B) HBr C) NH4Cl D) HF Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (short answer) 10 5  10/11/24 What intermolecular forces exist between HF and H2O? I. Dispersion Forces II. Dipole-dipole forces III. Hydrogen bonding A. III only B. I and II only C. II only D.I, II and III Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 11 Ion–Dipole Interactions Cations and anions can interact with molecules that have a permanent dipole. Each type of ion will be + attracted to a different - t - end of the polar molecule. Ionic salts can interact with polar water molecules, causing them to dissolve in water. 12 12 6  10/11/24 Trends in Solubility: Like Dissolves Like Liquids that are soluble in any proportion are miscible with each other. Strength and number of interactions among solute particles and interactions of solvent molecules determine solubility. Nonpolar solutes may dissolve in water due to dipole-induced dipole interactions. 15 What is the primary reason that hexane (C6H14) does not dissolve in water? A) dipole-dipole attraction between hexane molecules. B) ion-dipole attraction between water and hexane molecules. C) London dispersion forces between hexane molecules. D) hydrogen bonds between water molecules. Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 16 8  10/11/24 Exam-type question: In each pair, determine which compound is likely to be more soluble in water and explain why in a sentence of 25 or fewer words. A B I. CH3CH2OH vs CH3CH2CH2CH2OH II. CH3CH2OH vs CH3OCH3 III. Ca(OH)2 vs KOH Think & Solve: 2 min; on your own IV. KOH vs NaOH Discuss: 30 sec; share and compare Answer: iClicker (short answer) 19 To Do: q SW Warm-up Lesson 24 due F, 8am q Recitation 5 (Today/Th/F). Don’t forget the PRQs! q SW Mastery Assignment #7 due M, 8am 20 20 10  10/11/24 Phase diagram of sulfur How many triple points exist in this phase diagram of sulfur? Which states are in equilibrium at each triple point? Which solid form is more stable under ordinary atmospheric conditions (1 atm, 25°C)? Describe the phase change(s) that would occur when sulfur at 1 atm is heated from 25°C to 200°C. 5 Exam-type question: A phase diagram of a pure compound has a triple point at 1.5oC and 0.3 atm, a normal melting point of 5.0oC, and a normal boiling point of 105oC. Which of the following statements about this compound is/are true? Select all that apply. q A) It exists as a liquid at room temperature and 1 atm pressure. qB) D(liquid) > D(solid). qC) As pressure is reduced from 1.05 atm to 0.10 atm at a constant temperature of 15oC, evaporation occurs. Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (short answer) 6 3  10/11/24 Properties of Water On Earth and in our bodies, water is everywhere. The ability of water to form hydrogen bonds results in some remarkable properties including an unusually high boiling point for its size, a high surface tension, an increase in the density of water as it gets colder, and the ability to flow against Starry Night over the Rhone – Vincent van Gogh gravity. 7 7 How can a stainless steel razor blade float on water? Dsteel = 8.05 g/cm3 Dwater = 1.00 g/cm3 Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: volunteers 8 4  10/11/24 Surface Tension The ability of the surface of a liquid to resist an external force is call its surface tension. The water molecules at the surface are held together by hydrogen bonds and will not easily separate. Water strider; Family Gerridae 9 9 Which substance exhibits stronger cohesive forces in a glass container: & A) Hg or B) H2O Think & Solve: 30 sec; on your own Hg H 2O Discuss: 30 sec; share and compare In glass test tubes Answer: iClicker 10 5  10/11/24 Capillary action In the red liquid, which interaction is stronger? A)Cohesion B) Adhesion Think & Solve: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 13 Capillary action The adhesion of water molecules to the walls of a narrow tube allows water to rise up the tube. This capillary action helps water to flow against gravity. 14 7  10/25/24 What product will form when aluminum combines with oxygen gas? What is its name? A. AlO B. Al2O3 C. Al3O2 D. AlO2 Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 7 Decomposition Reactions In a decomposition reaction one substance breaks down into two or more substances. In the air bag, solid sodium azide releases nitrogen gas quickly: NaN3(s) → Na(s) + N2(g) Given a substance (like NaN3), you should be able to predict the elemental products and balance the reaction. 8 4  10/25/24 Exam-type question: Write the balanced chemical reactions. No need to include states of matter. A) Carbon reacts with sulfur dioxide to produce carbon disulfide and carbon monoxide. B) Sodium cyanide combines with sulfuric acid (H2SO4) to produce hydrogen cyanide and sodium sulfate. Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: volunteer 11 Stoichiometry Basics Stoichiometry: quantitative relationship between substances consumed and produced in a reaction 1 cup mix 6 oz milk 1 egg 8 pancakes 12 6  10/25/24 Given the combustion of sucrose: C12H22O11 + 12 O2 → 12 CO2 + 11 H2O A) How many moles of water are produced when five moles of sucrose react? Think & Solve: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 15 Given the combustion of sucrose: C12H22O11 + 12 O2 → 12 CO2 + 11 H2O B) How many molecules of sucrose are required to produce 96 molecules of carbon dioxide? Think & Solve: 30 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 16 8  10/25/24 Given the combustion of sucrose: C12H22O11 + 12 O2 → 12 CO2 + 11 H2O C) How many molecules of water are produced when 18 moles of CO2 are produced? Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 17 Given the combustion of sucrose: C12H22O11 + 12 O2 → 12 CO2 + 11 H2O D) What mass of oxygen (g) is required to completely combust 1.00 mole of sucrose? Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 18 9  10/25/24 Given the combustion of sucrose: C12H22O11 + 12 O2 → 12 CO2 + 11 H2O E) If I start with 2.5 mol sucrose and 24 mol oxygen, how many moles of CO2 can I produce? Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 19 Exam-type question: The complete combustion of 2.0 moles of butane gas, C4H10, will: A. consume 13 mol O2 and produce 8.0 mol H2O. B. consume 5.0 mol O2 and produce 13 mol CO2. C. consume 7.0 mol O2 and produce 8.0 mol CO2. D. produce 8 mol CO2 and 5.0 mol H2O. E. consume 13 mol O2 and produce 8.0 mol CO2. Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 20 10  10/25/24 Exam Type Question: How many grams of iron(III) chloride are produced when 26.0 g of hydrogen sulfide gas are produced in the following reaction? Fe2S3(s) + 6 HCl(g) → 2 FeCl3(s) + 3 H2S(g) A. 17.3 g FeCl3 B. 26.0 g FeCl3 C. 60.8 g FeCl3 D. 82.5 g FeCl3 Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 21 To Do: q SW Warm-up Lesson 26 due W, 8am q Recitation 6 starts today! Remember your PRQs 22 22 11  10/25/24 Limiting Reactants Which reactant is the limiting reactant in the picture below, where CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)? In this example, the O2 is the excess reactant. The limiting reactant is the reactant present in the smallest stoichiometric amount. In other words, it’s the reactant you’ll run out of first 3 20.0 g of CH4 reacts with 50.0 g of O2(g). Which reactant is the limiting reactant? A. CH4 CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) B. O2 C. CO2 D. H2O E. There is no limiting reactant Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 4 2  10/25/24 20.0 g of CH4 reacts with 50.0 g of O2(g). What is the theoretical yield of CO2 (44.01 g/mol)? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 5 20.0 g of CH4 reacts with 50.0 g of O2(g). What mass (g) of the excess reactant remain unreacted? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 6 3  10/25/24 Reaction Yield The theoretical yield is the amount of a given product that can be made (calculated through the stoichiometry problem) CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) The actual yield is the amount actually produced and measured The percent yield is a comparison of the actual yield to the theoretical yield : -./0-1 23415 percent yield = ×100 /ℎ4784/3.-1 23415 7 20.0 g of CH4 reacts with 50.0 g of O2(g). Suppose 29.8 g CO2 is collected. What is the percent yield for this experiment? CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(g) Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 8 4  10/25/24 Exam-type question: Propane, C3H8 (MM = 44.09 g/mol), is a common fuel used for cooking and home heating. What is the mass of carbon dioxide (MM = 44.01 g/mol) produced when 3.00 grams of C3H8 and 2.00 grams of O2 are combined to heat S your skillet. A. 8.98 g B. 1.65 g C. 12.0 g D. 1.60 g Think & Solve: 5 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 9 9 Exam-type question: According to the balanced reaction, 2 H2(g) + O2(g) → 2 H2O(l) When 1.80 moles of hydrogen gas is combined with 1.00 mole of oxygen gas…. A) 0.80 moles of hydrogen remain unreacted B) 0.10 moles of hydrogen remain unreacted C) 0.90 moles of oxygen remain unreacted - D) 0.10 moles of oxygen remain unreacted E) 0.20 moles of oxygen remain unreacted Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 10 5  10/25/24 Exam type question: Molten gallium (Ga, Z = 31) reacts with arsenic (As, Z = 33) to form the semiconductor GaAs which is used in solar cells: Ga(l) + As(s) → GaAs(s) If 4.00 kg Ga is reacted with 5.50 kg As, how much of the excess reactant (kg) remains at the end of the reaction? A) 1.20 kg As B) 1.50 kg As C) 4.30 kg As D) 1.20 kg Ga Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 11 11 To Do: q Check your final exam schedule! Fill out the EEF if you have a conflict q SW Warm-up Lesson 27 due F, 8am q SW Mastery Assignment #8 due M, 8am q Recitation 6 Today/Th/F – remember your PRQs! 12 12 6  10/25/24 Calculating empirical formulas – from % composition What is the empirical formula of the compound that is 20.20% Mg, 26.63% S, and 53.17% O by mass? Think & Solve: 2 min; on your own Discuss: 30 sec, share and compare Answer: volunteer 3 Exam-type question: What is the name of the compound that is 20.20% Mg, 26.63% S, and 53.17% O by mass? A.Magnesium sulfite B.Magnesium sulfide C.Magnesium sulfate D.Manganese sulfate E. Manganese sulfide tetroxide Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 4 2  10/25/24 Exam-type question: What is the molecular weight (amu) of a single molecule of Vitamin K1? It is 7.11% oxygen by mass, and each molecule contains two oxygen atoms. !"## %& '('!')* % by mass = ∗ 100 !"## %& !%('+,(' Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 5 Exam-type question: A certain element, M, is a main-group metal that reacts with chlorine to give a compound with the chemical formula MCl2; M reacts with oxygen to give the compound MO. a) To which group in the periodic table does element M belong? b) The chlorine compound contains 34.0% chlorine by mass. What is M? Think and plan: 1 min 6 3  10/25/24 What property of M do we need to determine its identity? Exam-type question: A certain element, M, is a main-group metal that reacts with chlorine to give a compound with the chemical formula MCl2; M reacts with oxygen to give the compound MO. b) The chlorine compound contains 34.0% chlorine by mass. What is M? Think & Solve: 30 sec; on your own Answer: volunteer 7 What are the units of this property? Exam-type question: A certain element, M, is a main-group metal that reacts with chlorine to give a compound with the chemical formula MCl2; M reacts with oxygen to give the compound MO. b) The chlorine compound contains 34.0% chlorine by mass. What is M? A. g B. mL C. g/mol D. mol Think & Solve: 30 sec; on your own Answer: iClicker 8 4  10/25/24 What information from the problem can you use to get these units? Exam-type question: A certain element, M, is a main-group metal that reacts with chlorine to give a compound with the chemical formula MCl2; M reacts with oxygen to give the compound MO. b) The chlorine compound contains 34.0% chlorine by mass. What is M? Think & Solve: 1 min; on your own Answer: volunteer 9 Solve part B! Exam-type question: A certain element, M, is a main-group metal that reacts with chlorine to give a compound with the chemical formula MCl2; M reacts with oxygen to give the compound MO. b) The chlorine compound contains 34.0% chlorine by mass. What is M? A. Mg B. Ca C. Sr D. Ba Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 10 5  10/25/24 Combustion Analysis Combustion analysis involves the complete combustion of a compound followed by an analysis of the products of the reaction. The moles of CO2 can be used to determine the C! H" + excess O# * moles of C in the sample. The moles of H2O can be → CO# * + H#O * used to determine the (unbalanced) moles of H in the sample. Masses of other elements must be determined using conservation of mass. 11 Exam-type question: Combustion of eicosene, a hydrocarbon (CxHy) similar to the mating pheromone secreted by the Japanese beetle, produces 44.0 g CO2 and 18.0 g H2O. A) Which is the empirical formula of eicosene? How many moles of CO2 were produced? How many moles of C were in the original sample? A. CH B. CH2 C. CH3 How many moles of H2O were produced? D. CH4 How many moles of H were in the original sample? Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker What is the ratio of C:H? 12 6  10/25/24 Exam-type question: Combustion of eicosene, a hydrocarbon (CxHy) similar to the mating pheromone secreted by the Japanese beetle produces 44.0 g CO2 and 18.0 g H2O. B) Mass spectrometry analysis shows that the molecular mass of eicosene is 280 amu. What is its molecular formula? A. C28H56 B. CH2 C. C20H40 D. C12H24 Think & Solve: 1 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 13 To Do: q Check your final exam schedule! Fill out the EEF if you have a conflict! q SW Warm-up 28 due M, 8am q SW Mastery Assignment #8 due M, 8am 14 14 7  10/31/24 The CDC recommends that utilities like OWASA (that provides drinking water to UNC campus) provide 0.7 mg fluoride per liter tap water to ensure residents’ dental health. What is this concentration in ppm? Dwater = 1.00 g/mL A) 0.7 B) 7 C) 70 D) 700 Think & Solve: 60 sec; on your own Discuss: 30 sec, share and compare Answer: iClicker 5 Concentration units: Molarity The concentration of an aqueous solution describes the quantity of solute dissolved in a specific quantity of either solvent or total solution. Mole-to-volume ratio Molarity M,[solute] #$%&' $) *+,-./ 4 != = %01&2 $) *+,-.3+4 5 6 3  10/31/24 What mass of NaOH(s) must you dissolve in enough water to make 5.00 x 102 mL solution in order to create a 0.267 M solution? A) 5.34 g B) 5.34 kg C) 21.4 g D) 7.49 x 10-2 g Think & Answer: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 7 Exam-type question: Ascorbic acid (Vitamin C, C6H8O6, 176.1g/mol) is a water-soluble vitamin and found in popular supplements like Emergen-C. We make a solution by dissolving 20.5 g of ascorbic acid in 2.10 x 102 g of water; the solution has a density of 1.08 g/mL at 35°C. Calculate the molarity of ascorbic acid in the solution. A. 0.524 M B. 0.603 M C. 0.105 M D.Other molarity Think & Answer: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker 8 4  10/31/24 Dilution Total moles of solute don’t change 9 Exam-type question: In prepping for a CHEM 101 Lab, a lab worker wishes to dilute 5.00 x 102 mL of 18.0 M HCl to a concentration of 0.250 M. What volume of distilled water (L) must they add to the initial solution to achieve this lower concentration? Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 10 5  10/31/24 Which of the following solutes would cause the light bulb to be the brightest when 1.0 mole of that solute is added to the water in the picture below? Assume that all electrolytes dissociate completely. A. NH4NO3 B. C12H22O12 C. NaCl D. Al(NO3)3 Think & Solve: 45 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker 13 Exam-level question: Rank the following solutes in order of increasing brightness of the light bulb for each solution. Assume that all electrolytes dissociate completely. A. 2.0 M NH4NO3 B. 6.0 M C12H22O12 C. 3.0 M NaCl D. 2.0 M Al(NO3)3 Think & Solve: 60 sec; on your own Discuss: 30 sec; share and compare Answer: iClicker (free response) 14 7  10/31/24 Exam-level question: The Department of Transportation for the state of North Carolina purchases calcium chloride every year; calcium chloride, when combined with water to form a salt solution, can be sprayed on roads and sidewalks to reduce the freezing point of water and create slush out of ice precipitated during winter storms. The solubility of calcium chloride is 59.5 g per 1.000 x 102 g water. If the density of a solution is 1.1 g/mL, what is the molarity of the ions in a saturated solution (maximum amount of solute dissolved)? Think & Solve: 2 min; on your own Discuss: 30 sec; share and compare Answer: iClicker (numeric) 15 To Do: q SW Warm-up 29 due Wednesday, 8am q Recitation 7 starts Wednesday – remember your PRQs! 16 16 8  10/31/24 Which anions are insoluble with most cations (except the few cations that are soluble with everything)? $# $$ !!" = κ % 5 Exam Type Question: 1.00 moles of each of the following compounds is added to 1.00 L of water. Rank the resulting solutions in order of increasing number of solute particles. A. 2