CHE 102 Exam 2 Review Answers F24

# CHE 102 Exam 2 Review- Answers ## PART 1- The Mole, Stoichiometry 1. How does the Law of Conservation of Matter apply to balancing equations? The total type and number of atoms in the reactants must equal the total type and number of atoms of the products. Atoms rearrange, but atoms are not lost o...

# CHE 102 Exam 2 Review- Answers ## PART 1- The Mole, Stoichiometry 1. How does the Law of Conservation of Matter apply to balancing equations? The total type and number of atoms in the reactants must equal the total type and number of atoms of the products. Atoms rearrange, but atoms are not lost or gained in a chemical reaction. Coefficients are used to balance chemical equations to represent reactions that obey this law. 2. Balance the following equations: - N2H4 + 2 H2O2 → N2 + 4 H2O - 2 HCl + Zn → H2 + ZnCl2 - Na2CO3 + Ca(NO3)2 → CaCO3 + 2 NaNO3 - C7H16 + 11 O2 → 7 CO2 + 8 H2O 3. How many items do the following units refer to? - 1 pair? 2 - 1 dozen? 12 - 1 mole? 6.02 x 10^23 4. What is the mass in grams on 1 mole of... - Gold, Au 197.0 g - Bromine, Br2 159.8 g - Calcium Nitrate, Ca(NO3)2 164.1 g Remember: Molar mass = mass in grams for 1 mole of a substance 1 mole = 6.02 x 10^23 atoms, molecules, or formula units *rounded all mass values to 1 decimal place 5. An apple contains 12.6 grams of fructose, C6H12O6. How many molecules of fructose is this? 12.6 g C6H12O6 x 6.02 x 10^23 molecules C6H12O6 = 4.21 x 10^22 molecules C6H12O6 180.0 g C6H12O6 6. A recipe calls for 4.0 grams (approximately 1 teaspoon) of cream of tartar. How many moles of cream of tartar is this (KC4H5O6) is this? 4.0 g KC4H5O6 x 1 mol KC4H5O6 = 0.021 mol KC4H5O6 188.1 g KC4H5O6 7. Consider the following reaction: Fe2O3(s) + 3CO(g) → 2 Fe(s) + 3CO2(g) - How many moles of CO are required to produce 6 moles of Fe? 6 moles Fe x 3 moles CO = 9 moles CO 2 moles Fe - How many grams of CO2 will be produced from 2250 grams of iron (III) oxide, assuming an excess of carbon monoxide, CO? 2250. g Fe2O3 x 1 mol Fe2O3 x 3 mol CO2 x 44g CO2 = 1,856 g CO2 160 g Fe2O3 1 mol Fe2O3 1 mol CO2 - In order to yield 1 kg of iron, Fe, how many grams of iron ore, Fe2O3 are required? 1 kg Fe = 1000g Fe 1000. g Fe x 1 mol Fe x 1 mol Fe2O3 x 160 g Fe2O3 = 1428 g Fe2O3 55.8 g Fe 2 mol Fe 1 mol Fe2O3 8. Consider the recipe for making a club sandwich: 3 slices of bread + 2 pieces of cheese + 6 strips of bacon + 2 pieces of lettuce + 4 slices of turkey → 1 sandwich If you have 15 slices of bread, 10 pieces of cheese, 24 strips of bacon, 8 pieces of lettuce and 12 slices of turkey, how many club sandwiches can you make? 3 According to each ingredient, the following number of sandwiches can be made: - Bread-5 - Cheese-5 - Bacon-4 - Lettuce-4 - Turkey-3 What is the limiting reagent? turkey slices 9. If 6.4 grams of sulfur dioxide gas reacts with 4.0 grams of oxygen gas, how many grams of the product, sulfur trioxide, can be produced? 2SO2 (g) + O2 (g) → 2SO3 (g) 6.4 g SO2 X 1 mol SO2 x 2 mol SO3 = 0.10 mol SO3, SO2 is the limiting reactant 64.1 g SO2 2 mol SO2 4.0 g O2 X 1 mol O2 x 2 mol SO3 = 0.25 mol SO3 32.0 g O2 1 mol O2 Theoretical yield = 0.10 mol SO3 x 80.1 g SO3 = 8.0 g SO3 1 mol SO3 ## PART 2- Properties of Solutions 10. Predict whether the following ionic substances would be soluble in water. Check solubility rules - Pb(NO3)2 SOLUBLE - CaCO3 INSOLUBLE - KCI SOLUBLE - Na2CO3 SOLUBLE 11. When aqueous solutions of Sr(NO3)2 and K2SO4 are mixed, a white solid forms. Write out the overall balanced equation and identify the formula of the solid precipitate. Sr(NO3)2 (aq) + K2SO4 (aq) → SrSO4 (s) + 2KNO3 (aq) 12. Consider the graph: At 60C, 40g of KCl are dissolved in 100 g of water. Is this solution saturated, unsaturated, or supersaturated? Below the line for KCI so unsaturated Under what conditions is it possible to form a supersaturated solution? If a saturated solution at an elevated temperature cools and the excess solute does not crystalize out of the solution, then at the lower temperature, a supersaturated solution exists. 13. a. Why are carbonated beverages best when consumed cold and immediately after they are opened? Gas solubility decreases with an increase in temperature, and gas solubility decreases when the pressure of that gas over the solution decreases. When a can of soda is opened, pressure decreases, and gas solubility decreases- you can hear the CO2 fizzing or "escaping” the solution. Carbon dioxide is also less soluble at higher temperatures, like in a warm soda. b. Why is heat applied when making a syrup with sugar and water? In general, the solubility of a solid in a liquid increases with increasing temperature, so at higher temperatures, more sugar will dissolve in the same amount of water. c. When scuba diving, why is it important to ascend slowly to the surface after swimming deep underwater? At greater depths, pressure is much higher, so a diver must breathe compressed air. Nitrogen present in the air mixture becomes more soluble in the blood at this pressure. When ascending, the pressure decreases, so nitrogen will begin to come out of solution. This release of nitrogen must occur slowly to avoid the formation and expansion of gas bubbles in the body. 14. Which would dissolve the fastest and why? - 5 g sugar cube in hot tea, 5 g sugar cube in iced tea, 5 g of granulated sugar in hot tea, or 5 g granulated sugar in iced tea? 5 g granulated sugar in hot tea... more surface area and higher temperature increases the rate of dissolving for sugar. 15. Provide 2 examples of units that are used to represent the concentration of a solute in a solvent. For example, ppm or parts per million, used in monitoring levels of contaminants in drinking water - Blood Alcohol Concentration (BAC)- g ethanol/ mL of blood - Vinegar- g acetic acid/g of solution - Rubbing Alcohol- mL isopropyl alcohol/mL of solution 16. Which solution has the highest molarity? Molarity = molsolute/Lsolution - 87.8 g NaCl in 2.0 L solution - 87.8 g NaCl x 1 mol NaCl = 1.50 mol NaCl = 0.6 M 58.5 g NaCl M = 1.50 mol/2.0L = 0.75 M - OR 1.75 mol NaCl 1.75 mol NaCI/ 3 L 17. How many grams of Na2CO3 are required to make 3.0 L of a 0.50 M aqueous solution of Na2CO3? M = molsolute 0.50 M = mol Na2CO3 L solution 3.0 L of solution = 1.5 mol Na2CO3 To make 3 L, you would need 3X the moles of Na2CO3, so 1.5 mol Na2CO3 1.5 mol Na2CO3 x 106.0 g Na2CO3 = 160 g Na2CO3 (rounded to 2 sig figs) 1 mol Na2CO3 ## PART 3- Water- Properties and Quality Issues 18. Water has some unique properties due to hydrogen bonding interactions between its polar molecules. Connect this theoretical model of particle structure and interparticle interactions to explain the observable properties below: - High Boiling Point: Water has a higher normal boiling point than other molecules of similar molecular mass and size because it requires more energy to break the hydrogen bonding attractive forces between particles. - High Surface Tension: Water molecules at the surface form strong hydrogen bonding attractions between other water molecules at and below the surface. Surface molecules cannot hydrogen bond with the nonpolar air molecules above the surface. - Solid State Density: As water freezes, it expands due to the space introduced between the particles as they “lock” (attract due to hydrogen bonding interactions) into a crystal lattice structure. - Universal Solvent: Water is a small, polar molecule that can dissolve some ionic compounds (such as NaCl), small nonpolar molecules (such as O2), and polar molecules (such as ethanol and sugar molecules). 19. a. Where does most of our drinking water come from? Groundwater, local lake, or local river b. What are the general steps conducted in most municipal water treatment plants to purify water? - Coagulation (flocculants added to remove suspended particles), - Filtration (gravel, sand, and charcoal to remove smaller particles and impurities), - Disinfection (chlorine or ozone added to kill harmful microorganisms), - Some plants include addition steps- Aeration (to improve taste), fluoride addition, pH adjustment, anticorrosion control Check out examples of water quality reports in Illinois: https://amwater.com/ilaw/water-quality Illinois American Water- water treatment diagram https://amwater.com/ilaw/water-quality/water-treatment 20. How does reverse osmosis purify water (a process common for bottled water)? Osmosis- water (the solvent) flows toward diluting the more concentrated solution on the left until the volume of this solution corresponds to the osmotic pressure. Reverse Osmosis-pressure greater than the osmotic pressure is applied to force water across the membrane to the right to purified water (this is the opposite of osmosis). 21. How does the process of distillation purify water? The solution (impure water) is heated to produce water vapor. The water vapor is then cooled by running cold water over the condenser tube to condense the water from a vapor to a liquid. The pure water is collected in a separate flask. 22. What are some steps or measures you can take at home to reduce the amount of lead and other contaminants from your potable (drinkable) water? - Flush tap for two minutes prior to using water for cooking or drinking. - Use cold water. - Check and clean faucet screens regularly. - Use lead-free plumbing materials. - Use a faucet filter or filter water prior to drinking (pitcher, refrigerator). ## PART 4- Acids and Bases 23. Complete the table. Refer to notes on acids and bases. | Definition | ACID | BASE | |---|---|---| | Arrhenius Definition | | | | Bronsted-Lowry Definition | | | | Lewis Definition | | | | Observable properties | | | 24. Match the type of acid or base with the specific example of a dissociation equation. [picture removed] - Strong acid (high concentration of H3O+, complete dissociation) - Strong base (high concentration of OH, complete dissociation) - Weak base (low concentration of OH at equilibrium) - Weak acid 25. Write out the neutralization reaction between H2SO4 and NaOH. Identify the acid, base, and salt in the reaction. Salt H2SO4 (aq) + 2NaOH (aq) → 2H2O (l) + Na2SO4 (aq) Acid Base 26. In the box, insert the correct symbol, >, <, or =. - In a solution with a pH of 7, the H3O+ • ОН¨. = - In a solution with a pH of 10, the H3O+ OH. <, less than - In a solution with a pH of 3, the H3O+ • OH. >, greater than 27. a. How does the hydrogen ion concentration of a solution at a pH of 1 compare to the hydrogen ion concentration of a solution at a pH of 2? A solution at a pH of 1 has ten times the [H+] as a solution at a pH of 2. ## PART 5- Intro to Organic Chemistry 28. What does the term "organic" mean in chemistry? Organic chemistry is the study of carbon-containing molecules. 29. Why are the diverse compounds of life carbon-based? 30. What is a hydrocarbon? Is it a polar or nonpolar molecule? Hydrocarbons contain carbon and hydrogen only. They are NONPOLAR. 31. Draw ethane (alkane), ethylene (alkene), and acetylene (alkyne). Circle the compound(s) that are considered to be saturated with hydrogens. [picture removed] 32. An important reaction of hydrocarbons is exothermic combustion, which make them a good fuel source. Write out the balanced combustion reaction of pentane, C5H12. C5H12 + 8O2 → 5CO2 + 6 H2O 33. Alkenes participate in combustion and many other reactions. For example, alkenes are used as monomers to make large polymer molecules present in plastic materials that we use every day. Alkenes will also participate in addition reactions across the double bond. One such reaction is the hydrogenation of unsaturated fats. Why are vegetable oils high in unsaturated fats hydrogenated? What is an unhealthy consequence of the hydrogenation process? What is the difference between cis and trans isomers? Hydrogenation is used to change the consistency of vegetable oils. An example of this is margarine. Margarine has been processed to become spreadable like butter. Trans fatty acids do not occur naturally in the body and are a product of the hydrogenation process. 34. For the following molecules, identify the functional groups and calculate the molar mass. - Ibuprofen [picture removed] carboxylic acid - Oxycodone, Molar Mass, 315 g (C18H21NO4) [picture removed] - Ether - Alcohol - Amine - Ketone - Ether 35. Calculate the molar mass of ibuprofen using the line structure provided above. Molar Mass- 206 g (C13H18O2) ## PART 6- Biomolecules 36. a. List the fat-soluble vitamins. A, D, E, and K b. List the water-soluble vitamins. C and B vitamins c. What properties do all of these vitamins share in common? Essential micronutrients that must be obtained through the diet. Many vitamins serve as cofactors to enzymes that catalyze cellular reactions. 37. a. Identify the following vitamins as water-soluble or fat-soluble. [picture removed] - Water-soluble (polar) - Fat-soluble (nonpolar, predominately a hydrocarbon structure) 38. Which vitamin would need to be replenished more often? Water-soluble vitamins (Fat-soluble vitamins can be stored in fat tissue whereas excess amounts of water-soluble vitamins can be flushed out of the body in urine.) 39. Why would it be more beneficial to obtain your daily allowance of vitamins by eating a variety of foods including fruits and vegetables instead of simply taking a vitamin supplement? Many plant-based foods contain disease-fighting phytochemicals in addition to the recommended daily vitamins. Large doses of some fat-soluble vitamins can be harmful. Some vitamins may be better absorbed when consumed from a food source. In addition, foods rich in soluble and insoluble fiber promote a healthy digestive system and could lower bad cholesterol and help manage weight. 40. What functional group(s) are present in the following important biomolecules: - Monosaccharide- in cyclic form- ether and alcohol - Amino acid- carboxylic acid and amine - Triglyceride- ester 41. What type of functional group is formed when amino acids form a peptide bond? Amide 42. What is the role of starch and cellulose in plants? Starch is energy storage of glucose for plants. Cellulose is a structural component. 43. What is the role of starch, glycogen, and cellulose in the human body? - Starch- complex carbohydrate, energy - Glycogen- storage of excess glucose, energy reserves - Cellulose- insoluble dietary fiber 44. A person with type A blood cannot donate to a person with B blood type. Why? Specific carbohydrate sequences (oligosaccharide) present on the surface of a red blood cell determine blood type. A person with B blood does not contain the A oligosaccharide on its red blood cells. Therefore, it has A antibodies that would trigger an immune response upon exposure of A antigens present in A blood. 45. How does a virus, such as the HIV virus, target its host cell? The virus recognizes its host cell based on the carbohydrate structure present on the cell membrane. 46. Why do saturated fats have higher melting points than unsaturated fats? Saturated fats do not contain double bonds, and the fatty acid chains are able to pack closer together and interact through London dispersion forces. 47. What are cell membranes primarily composed of? How are these molecules arranged? Cell membranes consist primarily of a bilayer of phospholipids. These phospholipids are amphiphilic meaning there are polar and nonpolar regions in the molecule. The polar ends of the bilayer are located on the exterior and are exposed to the aqueous environments inside and outside the cell. The nonpolar fatty acids are buried within the bilayer. 48. What is the difference between “good” cholesterol and “bad” cholesterol? "Good" cholesterol actually refers to the type of cholesterol containing lipoprotein complex. HDL (high density lipoprotein) or good cholesterol acts to remove cholesterol from arteries, keeping blood vessels clear. LDL (low density lipoprotein) or bad cholesterol can cause a build-up of cholesterol and clog up arteries. 49. Discuss three reasons why cholesterol is important to the human body. Cholesterol is an important structural component of cell membranes, adding rigidity. Cholesterol is an important precursor molecule of some hormones (chemical messengers). Cholesterol can be converted to vitamin D with exposure to sunlight. 50. List at least 5 functions proteins can serve in the body. - Enzymes- catalyze reactions in the body - Structural- proteins make up hair, nails, connective tissue, etc. - Regulatory- regulate important processes in the body - Transport- transport substances throughout the bloodstream or allow substances to travel in and out of a cell - Protection- immune system response, defense mechanisms, blood clotting 51. Identify the important stabilizing forces present within a protein. [picture removed] Intermolecular forces such as London dispersion forces, hydrogen bonding, and ion-dipole occur between the amino acid side chain groups and between the amino acid side chain groups and water (on the outside of the protein). Two cysteine amino acid side chain groups can form a covalent bond, which is a strong, stabilizing force within a protein. 52. Why is it important to have the correct balance of energy nutrients? Carbohydrate (glucose/glycogen reserves) is the first type of macronutrient to be mobilized and metabolized for energy. When exercising strenuously for long periods, fatty acids can be oxidized and used for energy to spare glucose. Fatty acids can also be converted to ketone bodies that can fuel the brain (used when carbs are absent). The body does not have a lot of protein stores; however, some amino acids can be converted into glucose. Because this process produces ammonia (which must be converted to urea), using protein for energy (high protein diet) can be harmful on the liver and kidneys. Diets low in carbs and high in fats can cause ketosis due the production of ketones for fuel. Ketoacidosis is an extreme condition when ketone bodies accumulate enough to lower blood pH. ## HELPFUL | Group | Structure | Example of Compound | |---|---|---| | Alkyl halide | R-X | CI-CH CI | | Alcohol | R-OH | H3C-CH2-OH | | Phenol | | | | Ether | R-O-R' | H3C-O-CH3 | | Aldehyde | | | | Ketone | | | | Carboxylic acid | | | | Ester | | | | Amine | | | | Amide | | | [picture removed] [picture removed] [picture removed]