Chemistry - Answers to Chemistry Problems - Quick Guides

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Study GuideChemistry – Answers to Chemistry Problems1.A compound contains nitrogen, hydrogen, and chlorine. Given that the compound has a molarmass of about 53.5 g/mol and contains 1 N atom, 4 H atoms, and 1 Cl atom, calculate the percent bymass of each element.Answer:By mass, the compound is 26.19% nitrogen, 7.55% hydrogen, and 66.26% chlorine.2.Given the following masses in a compound:•Potassium: 35.91 g•Copper: 29.19 g•Fluorine: 34.90 gDetermine the empirical (simplest) formula of the compound.Answer:The simplest formula is K2CuF4.

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Study Guide3.How many moles of C₆H₅Br are present in 1000 grams of the compound?Answer:There are 6.37 moles of C6H5Br.4.What is the mass of neon gas in 5.0 liters at STP?Answer:The neon has a mass of 4.5 grams.5.If 1.00 gram of methane (CH₄) reacts completely with oxygen according to the balanced equation,how many liters of oxygen gas are required at STP?Answer:The reaction coefficients denote the relative volumes, so the volume of O2is twice that of6.Three nuclei are shown. Two have mass numbers of about 24, and one has a different atomicnumber.Which nuclei are isotopes, and which element do they represent?Answer:Nuclei B and C are isotopes of magnesium, the element with atomic number 12. Nuclei Aand B both have a mass of approximately 24 atomic mass units because their nucleons sum to 24.

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Study Guide7.Natural silver has an average atomic mass of 107.868 amu. Given the isotopes silver-107 andsilver-109, determine the percent abundance of Ag-109.Answer:Natural silver is 48.15% silver‐109.8.An alpha particle is emitted from a radioactive nucleus. The resulting nucleus has an atomicnumber of 88 and a mass number of 226.Identify the element, atomic number, and mass number of the daughter nucleus.Answer:The nucleus is radium‐226, also written ²²⁶₈₈Ra The atomic mass decreased by four, themass of the alpha particle. The atomic number decreased by two because the alpha particle carriedoff two protons. The problem asks for the mass number “226,” the atomic number “88,” and the nameof the element “radium.”9.How many valence electrons does aluminum have? How many does oxygen have?Answer:Aluminum has three valence electrons; whereas oxygen has six. Remember that you countcolumns from the left margin of the periodic table.10.Draw the Lewis structure for hydrogen sulfide (H₂S).Answer:The Lewis diagram for H2S is11.The electronegativity of chlorine is 3.0 and magnesium is 1.2.Calculate the electronegativity difference and classify the type of bond formed.

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Study GuideAnswer:The electronegativity difference of magnesium and chlorine is 1.8,which corresponds to a bond with 52% ionic character and 48% covalent character. Such anintermediate bond is called polar.12.C₅H₁₂has three structural isomers.Draw and name the three isomers and explain how their carbon bonding differs.Answer:The three isomers of C5H12are shown in the following example. The essential feature is thebonding of carbons. In the first molecule, no carbon is bonded to more than two carbons, the secondmolecule has a carbon bonded to three carbons, and the third molecule has a carbon bondedto fourcarbons.13.Acetylene reacts with hydrogen to form ethane.If 100 liters of acetylene react, how many liters of hydrogen gas are required at the same conditions?Answer:The addition of hydrogen converts acetylene to ethane:Because the number of moles of hydrogen is twice that of acetylene, the reaction requires 200 litersof hydrogen, double that of acetylene.

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Study Guide14.Identify the functional group and name the compound with the structural formula H–C(=O)–H.Answer:It is an aldehyde with the structural formula:15.What is the minimum pressure required to liquefy carbon dioxide at its critical temperature?Answer:The minimum pressure for liquid CO2is 5.1 atmospheres.16.At what temperature does solid carbon dioxide sublime at standard pressure?Answer:At–64°C, the solid CO2sublimates to the gas state.17.Calculate the total heat required to warm ice from −40°C to water at 20°C, including phasechanges.Answer:The total heat needed is 49,831 joules.18.Convert 611 mm Hg to atmospheres.Answer:The pressure equals 0.804 atmosphere.

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