chem review thingy
The density of a gas changes inversely with which of the following?
The density of a gas is directly related to pressure (P) and molar mass (M), and inversely related to temperature (T). The polarity has no effect on density other than to indicate the freezing or condensing point. D = PM/RT
What is the best explanation for why ionization energy generally increases left to right across the periodic table?
The electrons of elements in the same period are all in the same shell and roughly the same distance from the nucleus. The increase in the number of protons and the effective nuclear charge causes the increase of ionization energy across a period.
What is the sum of the coefficients when the following equation is balanced with the most reduced whole numbers? Al(OH)3 + H2SO4 → Al2(SO4)3 + H2O
2Al(OH)3 + 3H2SO4 → Al2(SO4)3 + 6H2O. Adding the coefficients: 2 + 3 + 1 + 6 = 12.
Upon combustion, a 30 g sample of a compound containing only carbon, hydrogen, and oxygen produces 44.0 g of carbon dioxide and 18.0 g of water. Find the empirical formula of the compound.
44 g carbon dioxide = 1 mole of carbon dioxide. 1 mole of carbon dioxide contains 1 mole of carbon or 12 g. 18 g of water = 1 mole of water. 1 mole of water contains 2 moles of hydrogen or 2.02 g. Subtract to find oxygen: 30 g sample - 12 g carbon - 2 g hydrogen = 16 g of oxygen or 1 mole of oxygen. The correct empirical formula needs to have a 1:2:1 ratio of C to H to O.
One mole of which of the following contains the most ions when dissolved in 250. mL to make a solution?
A 4 M solution of strontium hydroxide, a strong base, completely dissolves producing three ions per mole in solution. A 4 M solution of potassium chloride, a strong electrolyte, produces 2 ions per mole in solution. Even though lead (II) iodide contains three ions per molecule, lead (II) iodide is virtually insoluble due to the force of attraction between the cation and anions as described by Coulomb's Law, leading to almost no ions in solution. Calcium carbonate is also not soluble in solution.
Which of the following is an ambiguous change?
A and B are physical changes since intermolecular forces are changing while C is a chemical change that will produce carbon dioxide gas bubbles and bonds have rearranged in the process. D is ambiguous because ionic bonds are breaking apart as the water dissolves the potassium chloride crystal lattice and the temperature decreases. KCl can be obtained again through evaporation of the water.
What is the conjugate base in this reaction: H2S(g) + H2O(l) ⇄ H3O+(aq) + HS-(aq)?
A conjugate base is formed when an acid donates a proton (H+). H2S donates a proton to water (making it an acid) and thus turns into the conjugate base, HS-.
Analyze the two chemical reactions above. Which conjugate base is the strongest?
A conjugate base is formed when an acid donates a proton (H+). The stronger the acid, the weaker the conjugate base. H2SO4 is a strong acid so its conjugate is weaker. HC2H3O2 is a weak acid so it will make a stronger conjugate base, C2H3O2-.
What is the electron configuration of V2+?
A positive charge on an atom means that electrons were removed from the electron configuration. For transition metals we remove the highest n-value orbitals first (4s), even if it does not correspond to the reverse order of filling.
. The dissolution in water of which of the following substances is endothermic?
Acids, bases, and alkali metals are always exothermic, but ammonium compounds are endothermic when dissolved in water. This is due to the polar covalent nature of the cation in the compound because breaking of the lattice structure of NH4Cl requies more energy than the energy of hydration of the ions provides. The result is an overall drop in temperature of the system.
What is the electron configuration of a ground state of an ion of an alkali metal?
Alkali metals have a general electron configuration ending in ns1. Alkali metals form a 1+ ion. Removing an electron to make cation will give an electron configuration isoelectronic to the noble gases (np6).
Consider the following unbalanced reaction: Sc(NO3)3 + NaOH → Sc(OH)3 + NaNO3. If one mole of scandium nitrate and three moles of sodium hydroxide react, how many moles of ions are present in this chemical reaction? Assume that insoluble substances produce no measureable amounts of ions.
All species are soluble in water except scandium hydroxide. Scandium hydroxide is a weak electrolyte and a weak base. It does not dissociate fully in water and will not make any ions. Scandium nitrate will make 4 ions when it dissolves in water (3 nitrate ions and 1 scandium ion). Three sodium hydroxide compounds are needed to balance the equation and each sodium hydroxide breaks up into 2 ions for 6 total ions. Three sodium nitrate compounds are needed to balance the equation and each sodium nitrate breaks up into 2 ions for 6 total ions. Adding all of the ions: 4 + 6 + 6 = 16 total ions.
Which of the following substances is amphoteric?
Amphoteric means that the species can act as either a proton (H+) donator or acceptor (acid or base). In this case all substances are types of bases. Most bases will accept, but not donate a proton. Aluminum hydroxide is unique. It can accept or donate protons by forming a complex ion. Base (neutralizing an acid): Al(OH)3 + 3 HCl → AlCl3 + 3H2O and Acid (neutralizing a base): Al(OH)3 + NaOH → Na[Al(OH)4]. Zinc, tin, lead, aluminium, and beryllium and most metalloids form amphoteric oxides or hydroxides, but their amphoterism depends on the oxidation state of the oxide.
Which of the following is an isotope of Sulfur-32?
An isotope has the same number of protons but different number of neutrons. The mass number is equal to protons plus neutrons. Sulfur-32 has 16 protons and 16 neutrons. An isotope will need 16 protons and some other number of neutrons other than 16
A laboratory analysis produced the following mass percent data: 48.5% C, 3.9% H, and 47.5% O. Find the empirical formula of the compound.
Assume 100 g of substance (and round percents to a whole number to simplify mental math) to get 49 g of C, 4 g of H, and 48 g of O. Convert mass to moles by dividing by the molar mass: 49 g / 12 g/mol = 4 moles of C, 4 g / 1 g/mol = 4 moles of H, and 48 g / 16 g/mol = 3 moles of O. The 4:4:3 ratio is the most reduced or simpliest mole ratio possible. Therefore the mole values obtained are the subscripts of the empirical formula: C4H4O3.
What is the net ionic equation for a acid-base reaction between solutions of Ba(OH)2 and H2S?
Barium hydroxide is a strong base and a strong electrolyte, therefore, dissociating 100% into ions. Hydrosulfuric acid is a weak acid and a weak electrolyte and does not dissociate completely into ions. The salt formed, barium sulfide, is insoluble and does not dissociate into ions. Water is a liquid and also does not dissociate. It is a misconception that all acid-base reactions share the net ionic equation as seen in answer B. Only reactions between strong acids and bases have a net ionic reaction as B.
Besides concentration, what two other factors affect a visible spectrometry or colorimetry absorbance according to Beer's Law?
Beer's Law is A = abc where A is absorbance and c is concentration. The other two factors involve path length and molar absorptivity of the solution.
A student preforms a titration between monoprotic KHP, an acid, and an unknown concentration of NaOH using phenolphthalein as an indicator. At the end of the titration, the student overshot the endpoint when their flask was a darker pink than desired. If the student calculates the molarity of the unknown NaOH solution using the data they obtained in this experiment, the calculated molarity would be:
Calculations for a simple acid base titration with a 1:1 ratio involve MV = MV. Since KHP is monoprotic (donates one H+), the reaction is a 1:1 ratio of acid to base. To find the concentration of the unknown: (Mknown x Vknown)/Vunknown = Munknown. In this experiment the student titrated the known with too much unknown. The volume of the unknown will be higher that it is supposed to be, resulting in a lower concentration according to the equation.
Substance Y is an oxocarbon, composed of carbon and oxygen. Mass data was collected showing that 0.39 g of carbon atoms react with 1.00 g of oxygen atoms in substance Y. What is substance Y?
Carbon is 12 g/mol while oxygen is 16 g/mol. To help with mental math, round and convert numbers to scientific notation: 4 x 10-1 g C and 1 x 100 g O. Divide by molar masses: 4 x 10-1 g C /12 g = 0.333 x 10-1 or 0.0333 and 1 x 100 g O/16 = 0.0625. There is about double the amount of oxygen by mass in the compound. Carbon dioxide is CO2 and best fits the data.
What would be the molecular geometry of the OCS molecule?
Carbon would be the central atom, forming a double bond with the oxygen atom on one side and a double bond with the sulfur atom on the other side. This would lead to a linear molecular structure. Drawing the Lewis structure helps.
Consider the reaction: 2 ZnS + 3 O2 → 2 ZnO + 2 SO2 This reaction has an 80.0% yield. What mass of ZnO is produced when 50.0 g ZnS is heated in an open vessel until no further weight loss is observed?
Convert mass of ZnS to moles by dividing by the mass on the periodic table: 50/100 (approx.) = 0.5 moles of ZnS. The mole to mole ratio between ZnS and ZnO is 2:2 or 1:1 so moles of ZnS = moles of ZnO. Convert moles of ZnS to grams by multiplying by the molar mass: 0.5 x 80 (approx.) = 40 g of ZnS produced. Multiply by the percent yield to determine the actual mass obtained in lab: 40 x 0.8 = 32 g (approx. due to rounding). The closest answer is 33.4 g.
A nitrogen and oxygen containing molecule is decomposed into its elements. It is found to contain 14 g of nitrogen and 40 g of oxygen. Find the empirical formula of the compound.
Convert the masses to moles by dividing by the molar mass. There is about 1 mole of nitrogen and about 2.5 moles of oxygen. Divide by the smallest mole value to simplify the ratio (it is already simplified). Multiply both mole values by 2 to get whole number subscripts.
Why is Cs larger than Cs+?
Cs has an electron configuration ending in 6s1 while Cs+ ends is 5p6. There are more shells in Cs compared to Cs+ (that lost an electron). The additional inner core shell in Cs shields the 6s1 electron from the nuclear charge, making it bigger.
0.543 g of copper oxide is heated in a crucible. Its final mass after heating is 0.519 g. What is the best explanation for this change in mass?
Decomposition reactions usually involve heating the reactant. In this case, oxygen gas was produced. This gas left the crucible, lowering the mass of the product left in the crucible.
Find the delta Go of a galvanic cell with Ag and Al?
Delta Go = -nFEcell. First find the voltage of the cell: 0.80 + 1.66 = 2.46 V. Remember to not multiply the voltages by the values you multiply to balance the electrons. There are 3 moles of electrons that are transferred. Plug the values into Delta Go = -nFEcell where n = moles of e- and F = 96485 C: Delta Go = -(3)(96000)(2.5) = -720,000 J or -720 kJ.
A compound is found to contain 1.32 moles of Li, 0.66 moles of Se, and 2.64 moles of O. Find the empirical formula of the compound.
Divide all mole values by the smallest value (0.66) to determine the subscripts.
How many moles are present in 2.1 x 1024 atoms of calcium
Divide by Avogadro's number to find the number of moles. Convert 2.1 x 1024 to 21 x 1023 to make the mental math easier. 21 x 1023/6.02 x 1023 = 21/6 = 3.5
Consider the following elements: S, Na, O, Ne. Which element has the highest electronegativity
Electronegativity increases up and to the right on the periodic table. Electronegativity is the ability of an atom in a molecule to attract shared electrons to itself. Ne is not an option because it is a noble gas and does not form molecules
. The polarity of a molecular compound results from an imbalance of the sharing of electrons in the bond based on electronegativity differences and atomic structure. Which of the following gases would be the LEAST polar?
Even though carbon and hydrogen have an electronegativity difference, the bonds between carbon and hydrogen are considered to be nonpolar. Ethane is a nonpolar molecule because all of the bonds are carbon and hydrogen only, making the molecule nonpolar. The other three compounds have a permanent dipole moment between the nitrogen atom and the other corresponding atoms bonded to it.
When 1.00L of a 0.500M LiBr solution is tripled by dilution with water, what is the number of moles of lithium in the new solution?
Even though the volume of the solution was changed, the number of moles of solute remains constant. Changing the volume affects the molarity, but not the amount of solute in solution. To find the number of moles of solute, multiply molarity by volume: MxV = mole solute. For every one mole of solute, there is one mole of lithium
When 32 g of methane (CH4) and 32 g of oxygen gas react, 20.g of carbon dioxide is produced along with some water. What is the percent yield of carbon dioxide in this reaction?
First convert the masses to moles by dividing by the molar mass: 32/16 = 2 moles of methane and 32/32 = 1 mole of oxygen gas (oxygen is diatomic). Write and balance the chemical equation: CH4 + 2O2 → CO2 + 2H2O. Convert both to carbon dioxide, keeping in mind limiting reactants: 2 x 1/1 = 2 moles produced by methane and 1 x 1/2 = 0.5 moles produced with oxygen. Oxygen produces the least amount of product so it is the limiting reactant. Convert to mass of carbon dioxide using the limiting reactant (oxygen) and multiplying by the molar mass of carbon dioxide: 0.5 x 44 = 22 g of carbon dioxide. To find percent yield take the actual mass and divide by the theoretical mass and multiply by 100: 20g/22g x100 = 91% yield
Consider the reaction: 2 Na3PO4 + 3 ZnCl2 → Zn3(PO4)2 + 6 NaCl. 0.40 moles of sodium phosphate solution is mixed with 0.50 moles of zinc chloride solution. Which lists the ions in solution after the reaction occurs, in order of increasing concentration?
First figure out how many ions are present in the reaction: 0.4 x 3 = 1.2 moles sodium ions, 0.4 x 1 = 0.4 phosphate ions, 0.5 x 1 = 0.5 zinc ions, and 0.5 x 2 = 1 mole chloride ions. Then determine how many ions will end up in a solid (zinc phosphate) and not dissolved in solution at the end of the reaction. The sodium phosphate and zinc chloride react in a 2:3 ratio. All of the zinc chloride will react while some of the sodium phosphate will be left over. All of the zinc ions therefore will be in the solid and no ions will be present in solution. Zinc will have the lowest concentration. Some of the phosphate ions will be left over and not in the solid and it will therefore have the second lowest concentration of ions. Sodium and chloride ions remain aqueous the entire reaction. Sodium has the most dissolved ions with 1.2 moles and chloride is second with 1 mole of ions. 9
. What occurs most often in nature: oxidation or reduction?
For every electron lost by a substance, an electron must be gained. Therefore both processes occur equally. It is a common misconception that one occurs more than the other.
What is the major reason that physical properties do not differ much among gaseous compounds?
Gases can be polar, have higher masses, and can exist at lower temperatures. However, the nature of gases indicates that the molecules are far apart and have almost no intermolecular forces among particles, leading to a smaller variation in physical properties
Which electron transition produces light of the highest frequency in the hydrogen atom?
High frequency waves have a large energy. The largest transition will require the most energy. 5p to 2s is the largest difference in energy levels, therefore it will emit the highest frequency wave.
. Which laboratory procedure will produce the data necessary to determine the waters of hydration in a hydrate?
Hydrates are ionic compounds that trap water molecules in their crystal lattice. Since there is a big difference in boiling points between water and an ionic solid, the hydrate can be heated to remove the water via evaporation.
Consider the following balanced chemical reaction: SnO2(s) + 2 H2(g) → Sn(s) + 2 H2O(g). If 1 L of hydrogen gas is reacted with excess tin (IV) oxide, how many liters of water vapor will be produced?
Hydrogen and water react in a 2:2 or 1:1 ratio according to the balanced equation. Since volumes of a gas are directly proportional to number of molecules or moles, they can be used similar to a mole to mole ratio. If 1 L of hydrogen reacts in a 1:1 ratio with water, 1 L of water will be produced.
Based on the following structures, which of the following does not exhibit Hydrogen bonding as one of the molecule's intermolecular forces?
Hydrogen bonding only occurs when hydrogen is bonded directly to fluorine, nitrogen, or oxygen. In hydrogen cyanide, the hydrogen is separated from the nitrogen by a carbon atom, so there is no Hydrogen bonding present.
Classify the following reaction: 2 MnO4- + 5 H2C2O4 + 6 H+ → 2 Mn2+ + 10 CO2 + 8 H2O.
In this reaction, oxidation numbers change, making it a redox reaction. While a combustion reaction produces carbon dioxide and water, this reaction does not involve burning in the presence of oxygen gas. This reaction does have an acid in it, the key chemical change does not involve neutralization of the hydronium ions. Decomposition reactions typically start with one compound and it breaks up into smaller components. This reaction does not do that.
List the elements in order of increasing atomic radius
K is the largest because it has the most filled shells or energy levels. Na is larger than Si because it has a lower effective nuclear charge than Si.
Calculate the mass fraction of a solution that contains 15 grams of methanol in 45 grams of water.
Mass fraction is found by dividing the mass of solute by total mass of solution (mass solute + mass solvent): 15 g methanol/ (15 g methanol + 45 g water) = 15/60 = 1/4 = 0.25.
What is the concentration of an NaOH solution if it takes 12.50 mL of a 0.100 M HCl solution to titrate 25.00 mL of the NaOH solution?
Molarity = mol/L. Since HCl (strong acid) and NaOH (strong base) react in a 1:1 ratio according to the balanced equation: HCl + NaOH → H2O + NaCl, we can use the equation MV = MV for this titration. 12.5 x 0.100 = 1.25 millimoles of acid. When the titration is complete and at the endpoint, moles of acid = moles of base according to the mole ratio in the balanced equation (1:1). There is 1.25 millimoles of base. 1.25/25 = 0.05 M.
For a 0.400M solution of cobalt (II) iodide, how many moles of iodide ions can be found in 0.200 L of solution?
Molarity is moles of solute divided by volume of solution. Rearranging the equation gives molarity times volume equal to moles of solute: 0.400M * 0.200L = 0.0800 mol compound. For every one mole of cobalt (II) iodide, there are 2 moles of iodide ions, so 0.0800mol * 2 = 0.160mol iodide ions.
Which element has the highest second ionization energy?
Na has the highest second ionization energy because when 2 electrons are removed from sodium, you are removing the last electron from a stable p6 configuration. This will require a higher than normal energy. Rb will also have a higher than normal second ionization energy; however since it is lower on the periodic table and has more shielding it will have a smaller IE than Na.
Which of the following represents the oxidation half reaction for the unbalanced redox equation: Cu + HNO3 → Cu(NO3)2 + NO2?
Oxidation is the loss of electrons while reduction is the gain of electrons. Remember that the oxidation number for elements in their stable state is 0. Copper is being oxidized since its oxidation number is changing from 0 to 2+ and it is losing 2 electrons. Since copper is losing 2 electrons, it should be written as a product in the chemical equation.
Which of the following is not a redox reaction?
Oxidation numbers change in a redox reaction. Follow the oxidation number rules to determine the oxidation numbers of every element. Notable rules for this question include: elements in their stable state = 0, alkali metals = 1+, halogens = 1- (generally), and oxygen = 2- (when not as peroxide). The silver chloride reaction does not have a change in oxidation numbers. The silver ion remains 1+ and the chloride ion remains 1- for the entire reaction.
Which of the following can not be classified as an ionic compound based on basic bonding concepts?
PCl3 is a molecular compound, so it does not exhibit ionic bonding properties. Ionic bonds are produced by the attraction between oppositely charged particles where the electrons have been transferred from the cation to the anion. Molecular compounds share electrons.
A compound MCl3, where M is a cation, has a melting point of -112oC. The compound can be identified as which of the following?
Phosphorus trichloride is a molecular liquid, the other compounds are ionic solids. Liquids and gases have very low melting points (generally well below 0oC) due to the intermolecular forces and kinetic energy of the molecules. Solids, especially ionic solids, have extremely high melting points.
Which of the following increases with the number of electrons in the molecule and is often attributed to pi bonding?
Polarizability is increased with pi bonding which is the overlap of additional orbitals seen in double and triple bonds between non-metal atoms. The other three trends do increase in a period with increasing number of valence electrons, but they do not contribute to pi bonding.
The rate of reaction for a concentrated strong acid with a concentrated strong base is least affected by which of the following?
Pressure changes only affect a system that involves at least one gas. The reaction between a concentrated strong acid and a concentrated strong base forms a salt in water and would not include any compound in the gas phase, so pressure would have no effect. Addition of a catalyst and increasing temperature would both increase the rate. Increasing reaction concentration of one or both reactants would increase the rate, while decreasing the concentration of one or both reactants would decrease the rate.
. What evidence led scientists to discard the plum-pudding model of the atom (random arrangement of positive and negative charge) and adopt a model with a tiny, dense, positively charged nucleus?
Rare alpha particle deflection demonstrated the existence of a very tiny nucleus. Alpha particles were deflected by the positive charge from the nucleus. Deflection was rare since the nucleus was so tiny and the atom is mostly empty space.
Which of the following equations represents the largest ionization energy?
Removing a 2nd electron from sodium will require more energy than the others. Na experiences a higher effective nuclear charge since its valence electrons are closer to the nucleus and experiences less shielding from core electrons. Removing a second electron with require more energy than the first since the electron is removed from an electron configuration isoelectronic to a noble gas.
The identity of an unknown alkali metal carbonate needs to be obtained. 1.379g of the unknown is reacted with 100. mL of 0.300 M calcium chloride. 0.986g of calcium carbonate was obtained. Which of the following alkali metal carbonates could be the unknown?
Round the given numbers to make the mental math eaiser. Use the molar mass of the potential unknown to help identify. Molar mass = g/mol. Find moles of the unknown by first dividing the mass of the product by its molar mass: 1/100 = 0.01 moles of calcium carbonate. All of the carbonate in calcium carbonate came from the unknown carbonate in a 1:1 mole ratio. Therefore, there are 0.01 moles of the unknown carbonate. Take the mass of the unknown carbonate used in the reaction and divide by the number of moles of the unknown carbonate that reacted to find the molar mass: 1.38/0.01 = 138 g/mol. Potassium carbonate (K2CO3) is the best match to this molar mass.
Which of the following would have the highest melting point?
Silicon is a metalloid which forms a solid with oxygen. The other three cations are non-metals and all form gases with oxygen. The solid will have the highest melting point due to the strong intramolecular forces present in the covalent network structure of the solid.
When silver reacts with phosphorus, the resulting empirical formula is represented by which of the following?
Silver violates Hund's rule, promoting one s electron to fill the d orbital, giving the ion a +1 charge. Phosphorus has an ionic charge of -3 due to the half full p orbital. When the charge magnitude is crossed, the resulting compound is Ag3P.
The first ionization energy for Na is 495 kJ/mol. The best estimate for sodium's second ionization energy would be:
Sodium's second ionization energy is significantly larger than the first because an electron is being removed from an electron configuration isoelectronic to a noble gas. It is a very stable, low energy configuration and it will take much more energy to remove the electron.
Which of the following can be used to measure the decrease in concentration of aqueous reactants over time?
Spectroscopy uses Beer's Law to determine the decrease in reactants or increase of products over time. Reduced turbidity would apply if measuring the decrease in colloids for a solution. Pressures would only be affected if a gas were present. Paper chromatography would be useful for separating and determining concentrations for colored compounds in a solution.
Which of the following two bonds are most similar in polarity?
Starting at fluorine and moving further down or to the right on the periodic table, electronegativity of the elements decreases. Oxygen and chlorine have almost identical electronegativity values, so the polarity of each bonded to fluorine, the most electronegative element, would be most similar.
In order to create a 0.500M solution of HCl for use in a laboratory experiment, how much distilled water must be used to dilute 100.mL of a 3.00M HCl solution?
The 100.mL of the original solution must be diluted down to a total volume of 600.mL, based on calculation for the new solution and the original data: M1V1 = M2V2. Solving for V2 = (100mL * 3.00 M)/(0.500 M) = 600. mL. Total volume of new solution = water added + acid. Since the HCl is 100.ml, the amount of water added must be 500.mL to yield the 600.mL of new solution.
The average atomic mass of bromine is 79.90 amu. Bromine consists of two isotopes: Bromine-79 and Bromine-81. Which of the following is the best approximate relative abundance of these two isotopes?
The average atomic mass is about halfway between 79 and 81 at approximately 80 amu. That means each isotope has an abundance of 50%
What is the average mass of one mole of naturally occuring, pure carbon?
The average atomic mass represents the weighted average of all of the naturally occuring isotopes in a sample. The average mass of any large number of atoms, like a mole (6.02 x 1023 atoms), of a naturally occurring sample of a given element is always the same as the average atomic mass on the periodic table, regardless of isotopes (different mass numbers) or allotropes (different bonding structure).
Which describes the final laboratory observations when 0.40 moles of NaOH(s) is added to 0.50 liters of 0.60 M CuCl2 solution?
The balanced reaction is 2 NaOH + CuCl2 → Cu(OH)2 + 2 NaCl. 0.40 moles of sodium hydroxide is reacting in a 2:1 ratio with 0.5x0.6 = 0.3 moles of copper (II) chloride solution. This is a limiting reactant scenario. All of the sodium hydroxide will react and 0.1 moles of copper (II) chloride will remain unreacted. This means that extra copper ions will be in solution. Solid copper (II) hydroxide is formed
The rate constant for the reaction between oxygen and nitrogen monoxide to form NO2 at 353oC has been shown to be less than one. In order to determine if the reaction is exothermic, what other information must be considered?
The exothermic nature of a reaction can only be determined from a table of enthalpies. The overall enthalpy of the reaction can be calculated using Hess' Law and the enthalpy values from the table based on a balanced equation. If the overall enthalpy of the reaction is negative, the reaction is exothermic.
Why did the Quantum Mechanical Model replace the Bohr atomic model?
The fundamental flaw in Bohr's model dealt with its ability to predict phenomena. While Bohr's mathematical model predicted the emission spectra of hydrogen, it was not able to predict the colors emitted by other elements
Through the process of photosynthesis, 5.00 g of glucose (C6H12O6) is created by a corn plant. This corn is eaten by a herd of deer who migrate to a different habitat and eventually die. How much of the carbon in the 5.00 g of glucose produced by the original corn plant is still present on Earth after the deer die?
The law of conservation of mass applies. All of the carbon is present, but in different forms in the carbon cycle on Earth
. Consider the reaction: Cl2 + 2 KI → I2 + 2KCl. Which species will be reduced at the cathode?
The oxidation number of chlorine gas is 0 since it is in it's stable elemental diatomic state. The oxidation number of Cl in KCl is 1- since alkali metals tend to have an oxidation number of 1+. Chlorine's oxidation number is being reduced (0 to 1-) since it is gaining electrons. Since Cl2 is undergoing this process, it is being reduced and at the cathode.
Beer's Law states A= abc, where A is absorbance, a is the molar absorptivity constant, b is the path length, and c is the molar concentration. Which of the following would be an incorrect application of Beer's Law?
The path length must be constant for all samples, otherwise it will affect the calculated molar concentration values for an unknown sample. The use of Beer's Law with a spectrophotometer will give a more accurate molar concentration than simple visual comparison, unknown concentrations are easily determined from the graph of a standard curve, and molar concentration is directly related to absorbance.
The main reason for the extremely low solubility of carbon dioxide in benzene (C6H6) at room temperature is due to which of the following?
The question states that carbon dioxide does NOT dissolve in benzene, both non-polar molecules. Generally, substances with similar polarities dissolve in eachother. However, since both are non-polar, there are only dispersion forces present, and the solute will not be strongly attracted to the solvent by intermolecular forces. Increased disorder would indicate a greater dissolving of solute in solvent, usually due to strong solute-solvent interaction from dipole or Hydrogen bonding.
Given the rate law for a reaction as: rate = k[A]2[B]3, what is the overall order for the reaction
The reaction order is simply the sum of the powers of the reactant concentrations in the reaction. 6. A multi-step
Arrange the following atoms by increasing first ionization energy: Atom A (radius 160 pm), Atom B (radius 246 pm), Atom C (radius 32 pm), and Atom D (radius 138 pm)
The smaller the radius, the stronger the coulombic attraction felt by the electrons from the nucleus. This will result in a higher ionization energy since more energy will be required to overcome the coulombic attraction to remove the electron.
. A student would like to use gravimetric analysis to determine the percent by mass of magnesium chloride in a contaminated mixture containing magnesium chloride. Which of the following compounds would be the best substance to react the contaminated mixture with to determine the mass percent?
The student needs to form a precipitate that they can weigh to determine the amount of magnesium or chlorine in the contaminated sample. Knowledge of the solubility rules is necessary for this question. Group 1 elements, nitrates, and acetates always form soluble compounds. Halogens are usually soluble except with silver, lead and mercury. Silver nitrate will be the only substance to form a precipitate. Magnesium chloride and silver nitrate will react to form a silver chloride precipitate.
Which of the following compounds does not have a trigonal planar geometry?
The sulfite ion has three single bonded oxygen atoms and one unbonded pair of electrons around the central atom. The unbonded pair of electrons forces the three oxygen bonds to push down into an overall trigonal pyramidal geometry. All of the other molecules have a trigonal planar configuration with no lone pairs on the central atom. Boron trihydride has three single bonds, the carbonate ion has one double and two single bonds, and the nitrate ion forms two double and one single bond.
At constant temperature, the behavior of a real gas more closely approximates that of an ideal gas as its volume increases due to which of the following?
The temperature did not change, so the average kinetic energy and average molecular speed did not change. The molecule size does not change either, so the molecule could not have "expanded". The distance between the molecules increases causing a decrease in intermolecular forces, thus reducing the interaction between the molecules.
2 KMnO4 + 5 H2C2O4 + 3 H2SO4 → K2SO4 + 2 MnSO4 + 10 CO2 + 8 H2O How many moles of MnSO4 are produced when 1.5 mol of KMnO4, 3.5 mol of H2C2O4, and 2.5 mol of H2SO4 are mixed?
This is a limiting reactant problem since you are given an initial amount of more than one reactant. The moles of manganese sulfate produced will be limited by the limiting reactant, the reactant that runs out first. Convert each reactant to moles of manganese sulfate using the mole ratio in the balanced equation: 1.5 x 2/2 = 1.5 moles produced by potassium permanganate, 3.5 x 2/5 = 1.4 moles produced by oxalic acid, and 2.5 x 2/3 = 1.66 moles produced by sulfuric acid. 1.4 moles is the least amount produced since oxalic acid is the limiting reactant and therefore is the amount of manganese sulfate produced.
Consider a spontaneous electrochemical cell: Cd2+ I Cd II Ag I Ag+ The reduction potentional of Cd is 0.403 V and Ag is 0.799 V. What is the balanced equation for the reaction that is occurring and what is the electrochemical cell voltage?
Two electrons are transferred in this reaction. Therefore the silver redox equation needs to be multiplied by 2. When you multiply the reaction by 2, do not multiply the voltage by 2 as it is an intrinsic property. From the reduction potentials, you will need to flip one reaction for oxidation. The reaction to flip is the one that will make the voltage positive. When the reaction is reversed, change the sign of the voltage: 0.799 + 0.403 = 1.200 V. Another way of looking at this is to compare the reduction values and use the equation: Eocell = Eored(cathode) - Eored(anode). The more positive reduction value will be at the cathode. 0.799 - (-0.403) = 1.200 V.
What type of spectroscopy would be the best tool to analyze the concentration of the carotene molecule, which gives the orange color to carrots, in carrot juice?
UV and the visible spectrum is used to analyze concentration of a colored substance in a mixture
Which wavelength of light has the lowest frequency?
Use the equation c = frequency x wavelength. It is an inverse relationship. As frequency increases, wavelength decreases. 20 mm is the longest length and therefore the longest wavelength. The longest wavelength corresponds to the smallest frequency.
How much energy is contained in 1 mole of 400. nm photons?
Use the equations and constants on your AP equation sheet to derive the equation: E = hc/wavelength. Convert nm to m so that all units match. 400 nm = 4 x 10-7 m. Use estimation: (hc = 6.6x10-34)(3x108) = 20 x 10-26. 20 x 10-26/4 x 10-7 = 5 x 10-19. This represents the energy for one photon. Multiply by 6.022 x 1023 to get 1 mole of photons: 5 x 10-19 x 6 x 1023 = 30 x 104 or about 300,000 J
The "alum" used in cooking is potassium aluminum sulfate hydrate, KAl(SO4)2 • x H2O . To find the value of x, a sample of the compound is heated. The mass of the empty crucible is 20.01g. The alum hydrate was added to the crucible until the total mass of the crucible and hydrate was 24.75 g. The sample was heated in the crucible until the final mass of the crucible and anhydrous product was 22.59g. What is the value of x?
Use the law of conservation of mass to determine the mass of water and the mass of the anhydrous compound: 24.75g - 22.59g = 2.16 g water and 22.59g - 20.01g =2.58 g anhydrous. Divide by the molar mass to find moles: 2.58/258 = 0.01 and 2.16/18 = 0.12. Divide by the smallest mole value: 0.01/0.01 = 1 and 0.12/0.01 = 12. X = 12.
. Rank the following elements by increasing ease of oxidation: Cd, Cu, Ni, Fe?
Use your reduction potential chart. All of the reactions listed are reduction reactions. They will need to be reversed and the sign of the voltage will need to be reversed to represent oxidation reactions. The oxidation half reaction with the largest voltage is most easily oxidized. Fe is the most with 0.44 V and Cu is the least with -0.34 V. Since the oxidation half-reaction is written: Fe → Fe2+ + 2e-, the solid states should be used instead of the ions. The ions would represent the reduction reaction.
A 34.1 g sample of a copper (II) chloride hydrate was heated to drive off the water. The remaining anhydrous sample was 26.9 g. Find the number of waters of hydration in the hydrate.
Waters of hydration are the number of water molecules per formula unit of copper (II) chloride in the hydrated sample. Find the mass of water that was driven off during heating by subtracting. 34.1-26.9 = 7.2 g water. Divide the mass of copper (II) chloride and water by their respective molar masses to determine moles: 26.9/134.5 = 0.2 moles copper (II) chloride and 7.2/18 = 0.4 moles water. Divide both mole amount by the smallest value. 0.2/0.2 = 1 and 0.4/0.2 = 2. The water of hydration is 2.
A 2.00 mole sample of an ideal gas is placed into a rigid 2.00L vessel at 1.00 atm. What will the temperature of the gas be when the volume of the gas is reduced to 0 L?
Zero Kelvin is the temperature at which all energy is potential. Since a gas requires a large amount of kinetic energy, a gas will not exist at zero Kelvin, thus the volume of the gas would be zero.
Which statement is true concerning electron shielding of nuclear charge?
Core electrons are in the inner-most electron shells whereas the valence electrons are in the outer-most electron shells. Core electrons block or shield the attractive force of the nucleus from the valence electrons.
