Basic Questions General Chemistry Exam PDF

This is a list of the "basic questions" related to the General Chemistry examiniation. The questions summarize the most important "basic" knowledge related to the study material. Conciese answers are also provided. As a start of the exam five questions should be answered by 80% efficiency from the l...

This is a list of the "basic questions" related to the General Chemistry examiniation. The questions summarize the most important "basic" knowledge related to the study material. Conciese answers are also provided. As a start of the exam five questions should be answered by 80% efficiency from the list in test format (the proper answer should be selected from a list). In some cases for the answer a simple calculation might be needed (all can be done by heart). In such cases the numerical values may vary. Characterize the molecular lattice! Lattice points are occupied by molecules (isolated atoms), held together by secondary forces (H-bridge, dispersion, van der Waals interactions. eg.: CH4, NH3, H2O, CO2, Kr, P4, SiH4, PH3, H2S, AsH3, Cl2, I2. Usually characterized by low melting point, often sublimable, do not conduct electricity, and are soluable either in polar or apolar solvents (depending on their polarity). Characterize the atomic lattice! Lattice points are occupied by atoms bound by strong covalent bonds. eg.: C(diamond), SiO2, P (red), Si, Ge, Te (grey) Usually characterized by high melting point, large hardness, do not conduct electricity, and are insoluable. Characterize the ionic lattice! Lattice points are occupied by ions bound by ionic bonds, eg.: NaCl, KCl, MgSO4 KF, LiBr Medium to high melting points, soluable in polar solvents. Non-conductive but mecome conductive in molten form. Characterize the metallic lattice! Lattice points are occupied by cations bound by a delocalized cloud of electrons. eg: Na, K, Mg, Al, Fe, W, Cu, Ag, Au Melting points vary, physically insoluable (but alloy formation), conductive. Characterize the states of the matter! Property Gas Liquid Solid Free path large small No Translation + ± - Rotation + + - Vibration + + + Compressibility large small very small Structure Disordered Disordered Ordered* * crystalline Draw the (p-T) phase diagram for water! Show the area corresponding to the three phases, important points and curves (continuous line) representing phase equliria!  T: Triple point with corresponding temperature (TH) and pressure (pH) C: critical point with corresponding temperature (TK) and pressure (pK) op op: melting curve; s: sublimation curve; t: vapour tension (boiling point) curve Define sublimation! Sublimation: phase transition, where solid becomes directly vapour, without forming any liquid phase. Define sublimation vapour pressure! Sublimation vapour pressure is the pressure of the vapour, which is in equlibrium with the solid. Is sublimation heat larger than heat of evaporation? Give reasoning! Sublimation heat is larger than heat of evaporation by the heat of fusion. Give a definition for partial pressure! Partial pressure is the notional pressure of a component of a gas mixture, which would be observed if the given component were present alone in the given volume and temperature. What is the statement of Dalton's law? Dalton's law: The pressure of a gas mixture (ps [Pa].) is the sum of the component's partial pressures (pi [Pa]) ps= ∑ Pi What is the statement of Amagat's rule? Amagat's rule: The volume of a gas mixture (V s [m3].) is the sum of the component's partial volumes (Vi [m3]) Vs= ∑ Vi Give the definition of vapour pressure (vapour tension)! Vapour pressure is at the given temperature the pressure of a vapour, which is in equlibrium with a condensed phase (eg. liquid) Give the definition of vapour! Vapour is a gas phase substance below the critical temperature. (Vapour can be condensed at the given temperature by incresing the pressure. Give the temperature dependence of vapour pressure (Clausius-Clapeyron equation) Vapour pressure has an exponential temperature dependence: 𝐿 𝑝 ∗= 𝑝𝑜 ∗ 𝑒 −𝑅𝑇 p* – vapour pressure (tension) [Pa] Po* – preexponential factor [Pa] R – gas constant [8,314 J/(mol*K)] L – latent heat (heat of evaporation or heat of sublimation) [J/mol] T – absolute temperature [K] Define the concept of gas! Gasous phase compound above the critical temperature, thus cannot be condensed by increasing the pressure. Define critical temperature! Critical temperature is the temperature belonging to the critical point. At temperatures larger than the critical temperature, the substance can not be condensed. Define critical pressure! Critical pressure is the pressure belonging to the critical point. At pressure larger than the critical pressure, the substance can not be in the gaseous state. Define the triple point! At the triple point three phases are in equlibrium. What is the statement of Avogardro's rule? Different (ideal) gases contain the same number of molecules under the same conditions (p, T, V). Define the Avogardro number! Avogadro number: NA = 6*1023 mol-1; one mol of substance consists of 6*1023 particle (atom, ion, molecule). How does the temperature change during the melting of a pure compound? For pure compounds the temperature remains constant during melting. In a closed container the measured pressure of a gas equals to its vapour pressure. What happens with the pressure, if the volume is reduced by 40% while the temperature remains unchanged! The pressure remains unchanged, since some vapour condenses. In a closed container the measured pressure of a gas equals to its vapour pressure. What happens with the pressure, if the volume is reduced by 40% while the temperature remains unchanged? The pressure remains unchanged, since some vapour condenses. How does the pressure change for an ideal gas at a given temperature (above the critical value) if the volume is reduced by 50%? For ideak gas: p1*V1=p2*V2. Accordingly the pressure will be doubled. What determines the freezing point depression for a given solvent? The molar freezing point depression, and the Raoult concentration of the particles in the solution. Give a definition for dilute solution? A solution is dilute, if the laws of dilute solutions are valid. How can the molecular mass be determined using the freezing point depression? Since the measured freezing point depression depends only on the known molar freezing point depression, and the Raoult concentration, for a given solution the Raoult concentration can be determined from the measured data. Since the mass/1000 g solvent concentration can also be determined, by weight measurement of the solute and solvent, respectively, the molar ass can be calculated. Under what circumstances is the rule of freezing point depression valid? For sufficiently dilute solutions. If no reaction (in particular dissociation, association) takes place between solvent and solute. Only solvent is freezing off from the solution. Under what circumstances is the rule of boiling point elevation valid? For sufficiently dilute solutions. If no reaction (in particular dissociation, association) takes place between solvent and solute. Only solvent is evaporating from the solution. What is the osmotic pressure depending on? Osmotic pressure depends on the molar concentration and the temperature. What is the definition of isotonic solution? The osmotic pressure of the given solution equals to that in the cell. What is the relationship between the composition of the vapour and the (single phase) liquid in case of a binary, non-azaeotropic mixture? The concentration of the more volatile component is larger in the vapour, than in the liquid phase. Define the boiling temperature, and boiling point? Boiling temperature is reached, if the vapour pressure of the liquid equals to the outer pressure, allowing bubble formation inside the liquid. In case of the atmospheric outer pressure boiling temperature is called boiling point (normal boiling point). Is boiling point depression possible? Yes, if not only the solvent evaporates (eg. a more volatile compound is added to the solvent). Is there any temperature change during the distillation of a two component mixture? Yes, the temperature is increasing steadily, since the concentration of the liquid phase is changing during the process. What is the azeotropic composition? At the azeotropic composition the concentration in the liquid equals to the concentration in the vapour (in equlibrium). Define the Dew point curve (V vapour curve)! The points of the Dew point curve give such vapour concenctrations at the given temperature, whereby the vapour is in equlibrium with the liquid. Define the boiling point (bubble point) curve (L liquid curve)! The points of the boiling point curve give such liquid concenctrations at the given temperature, whereby the liquid is in equlibrium with the vapour. Define the concept of acid and base according to Arrhenius! According to Arrhenius: acids provide H+, while bases OH- in a wateric solution. The reaction product is salt + water. Define the concept of acid and base according to Bronsted! According to Bronsted: acids provide H+ yielding a corresponding base, while bases take up H+ yielding a corresponding acid. Define the concept of acid and base according to Lewis! According to Lewis: acids are electron pair acceptors (with low lying empty orbital), while bases are electron pair donors (with a high energy lne pair). The reaction of acids and bases yields a complex bound by a dative bond. Can a compound behave as acid and also as a base according to Bronsted? Yes, the reactivity depends on the partner. Eg. water can release, but also can take up a proton. How can the strength of an acid described? The strength of an acid can be characterized by the dissociation equlibrium constant K a corresponding to the reaction AcH = Ac- + H+. Larger Ka value indicates stronger acidity. What is smoke? Smoke is solid dispersed in gas. What is fog? Fog is liguid dispersed in gas. What is suspension? Suspension is solid dispersed in liquid. What is the definition of heat of formation? Heat of formation is the reaction heat for one mol of substance at standard conditions, when it forms from the most stable allotropic forms of the constituting elements. Which substances have zero heat of formation? The most stable allotropic forms of the elements have zero heat of formation by definition. What is the statement of Hess's law (Constant Heat Summation)? Hess's Law states that regardless of the multiple stages or steps of a reaction, the total standard reaction heat is the sum of all heats of formation (using the corresponding stoichiometric ratio). This law is a manifestation that reaction heat is a state function. Give the sign convention of the reaction heat! The reaction heat is negative for exothermic, and positive for endothermic reactions. Give the statement of the Le Chatellier-Brown principle! Disturbing an equlibrium system, will result in a new equlibrium, whereby the effect of the perturbation is reduced. How can the equlibrium of an exothermic reaction be shifted towards product formation? According to the van 't Hoff equation the reduction of the temperature increases the equlibrium constant (c.f. Le Chatellier-Brown principle). How can the equlibrium of a chemical reaction be characterized! For a chemical reaction xj(Ri) = aj(Pj) 𝑎 ∏𝑗[𝑃𝑗 ] the equlibrium constant 𝐾 = ∏𝑖[𝑅𝑖 ]𝑥 holds; square brackets representing concentrations. How can the equlibrium of an exothermic reaction be shifted towards product formation? According to the van 't Hoff equation the reduction of the temperature increases the equlibrium constant (c.f. Le Chatellier-Brown principle). What kind of compounds are acid-base indicators? Acid-base indicators are weak acids, where the colour of the acid differs from that of its conjugate base. What is the transient region of an acid-base indicator? The transient region of an acid-base indicator is the pH range about the pK value (generally ± 0.5-1 pH unit) of the weak acid, where the colour change is well visible. Define the concept of pH! pH is defined as pH= -lg [H+]; [H+] standing for the proton concentration (activity) of a solution. Give the neutral pH in wateric solution at standard conditions! The pH in water at 25 oC is 7. This is the neutral pH value. Give the pH value for a 0.01 mol/l NaOH solution! The pH of this solution is 12. Give the pH value for a 0.01 mol/l HCl solution! The pH of this solution is 2. Dissolving sodium-acetate in water, which pH range can be expected? Give reasoning! The pH of this solution is expected to be basic. Since acetic acid is a weak acid, the corresponding base (acetate ion) is able to deprotonate some water, increasing the OH - concentration of the solution. Define the concept of buffer capacity! Buffer capacity is the amount of a strong (monoprotic) acid or base that must be added to one liter of a solution to change it by one pH unit. Calculate the pH of a sodium-acetate(2m)/acetic acid(1m) buffer Ka= 2x10-5! nacid Since: pH = −lg (K a ∗ ) = 5,0 nsalt Define the bubbling standard hydrogen electrode! Standard hydrogen electrode consists of a Pt electrode immersed into a pH=0 solution, surrounded by bubbling hydrogen at standard conditions. Define anode! Anode is the electrode, where oxidation takes place. Define cathode! Cathode is the electrode, where reduction takes place. Define the concept of electrolyte! Electrolytes conduct electricity by the movement of ions. Usually liquids, either solution or molten salt. Give the formula describing the potential () of a hydrogen electrode at standard conditions!  = -0.059pH How to measure the potential of a given electrode! The electrode potential is determined by the terminal voltage of the battery made from the given eletrode and the standard hydrogen electrode. Comparing two systems, which redox step takes place at the more positive electrode potential? The system with the more positive redox potential will be the oxidizing agent. Give the anode and the cathode processes, if the ion concentration of the solutions is 1 mol/l! Zn | Zn2+(aq) || Cu2+(aq) | Cu; ε°(Zn2+/Zn)= −0,762 V; ε°(Cu2+/Cu) = +0,342 V For 1 mol/l solutions the electrode potential equals to the normal potential. Thus, at the more positive electrode reduction takes place (cathode: Cu 2+ (aq) + 2 e− → Cu (s)), while at the more negative electrode oxidation takes place (anode: Zn (s) → Zn2+ (aq) + 2 e−) What is the statement of Faraday's (1th) law! The mass of the electrolyzed material is proportional to the charge used in the electrolytic process. How much time is needed to obtain 27g (1 mol) aluminum from the electrolysis of Al2O3 if the constant current is 26.8 A? Since 26.8 Ah charge gives 1 eqv Al, the get Al3+ reduced 3 hours electrolysis is needed. Define the reaction rate (speed of the reaction)! Reaction rate can be defined by the concentration change in unit time: 1 𝑑[𝐴] 𝑣(𝑡) = − 𝜐𝐴 𝑑𝑡 𝜈 – reaction rate [mol*dm-3*s-1]; t – time [s]; [A] – Concentration of the A starting material [mol*dm-3] υA – stoichiometric number [-] Give the temperature dependence of the rate constant (k) (Arrhenius's law)! 𝐸𝑎 𝑘 = 𝐴𝑒 −𝑅𝑇 k – rate constant [unit depends on several parameters] A – preexponential factor tényező [unit the same as for k] e – Euler number, 2,718… [-]; Ea – activation energy [J*mol-1]; R – gas constant [8,314 J*mol-1*K-1], T – temperature [K] Define the order of a reaction! The reaction order is the sum of the exponentiations of the concentrations in the rate equation. Generally, this value (exception: elementary reaction) differs from the sum of the soichiometric numbers. What is catalyst! Catalysts increase the rate of the reaction by reducing the reaction barrier. Catalysts recover after the reaction is completed. Eg. Pd or Pt are excellent catalysts of hydrogenation reactions (double bond saturation), since they store hydrogen in atomic form in their lattice. Give a definition for covalent bond! The covalent bond is formed between two atoms, by a shared electron pair on the bonding orbital, while there is no electron on the antibonding orbital. Give a definition for the ionic bond! Ionic bond forms between two oppositely charged ions due to Coulomb interaction. Give a definition for the dative covalent bond! The dative covalent bond is formed between two atoms, having a (rather high energy) lone pair of electrons and an empty orbital (with rather low energy), respectively. Compounds formed by dative bond are complexes. Define the atomic number! Atomic number is the number of protons in the nucleus. Define the atomic weight! Atomic weight is the number of protons+neutrons in the nucleus. List the atoms of group 1 of the periodic table! Li, Na, K, Rb, Cs. List the atoms of group 2 of the periodic table! Be, Mg, Ca, Sr, Ba. List the atoms of group 13 (3rd main group) of the periodic table! B, Al, Ga, In, Tl. List the atoms of group 14 (4th main group) of the periodic table! C, Si, Ge, Sn, Pb. List the atoms of group 15 (5th main group) of the periodic table! N, P, As, Sb, Bi. List the atoms of group 16 (6th main group) of the periodic table! O, S, Se, Te. List the atoms of group 17 (7th main group) of the periodic table! F, Cl, Br, I. List the atoms of group 18 (8th main group) of the periodic table! He, Ne, Ar, Kr, Xe. Define the ionization energy! Ionization energy is the energy need to remove an electron from an atom or molecule in the gasous state to infinity. Define the electron affinity! The electron affinity of an atom or molecule is defined as the amount of energy released when an electron attaches to a neutral atom or molecule in the gaseous state to form an anion. What is the geometrical arrangement in the sp hybrid state? The sp hybrid is linear. What is the geometrical arrangement in the sp2 hybrid state? The sp2 hybrid is trigonal planar. What is the geometrical arrangement in the sp3 hybrid state? The sp3 hybrid is tetrahedral. What is the geometrical arrangement in the sp3d hybrid state? The sp3d hybrid is a trigonal bipyramid. What is the geometrical arrangement in the sp3d2 hybrid state? The sp3d2 hybrid is octahedral. What is the basic principle of the VSEPR theory? According to VSEPR theory the geometry about a given atom is determined by the repulsion of the (independent) valence electron pairs, which try to avoid each other as much as possible. Thus their number will determine the geometry. What is the statement of the Pauli principle? According to the Pauli principle in an atomic system, there are notwo electrons with identical quantum numbers. Thus no orbital can be occupied by more than two electrons (which should then have opposite spins). What is the statement of Hund's rule? According to Hund's rule degenerate orbitals (such as sub-shells) should be occupied by as many unpaired electrons as possible.