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Grade 12 Chemistry national exam, 2012 E.C. (2020 G.C.)
76 questions · 120 minutes. The first 5 answers are shown with explanations; sit the whole paper timed in the app to get your score and the textbook page behind every question.
- 1.According to World Health Organization (WHO), the standard for the concentration of alcohol used to prevent COVID-19 virus is 70%. How much water has to be added to prepare the standard alcohol for 1L of 96% alcohol?
- A. 1371.4 ml
- B. 371.4 L
- C. 371.4 ml
- D. 30 ml
Answer: C. The key idea is that dilution keeps the amount of alcohol the same while increasing the solution volume. The alcohol amount is $0.96\,\mathrm{L}$; the final volume must be $0.96/0.70=1.3714\,\mathrm{L}$, so add $1.3714-1.0000=0.3714\,\mathrm{L}=371.4\,\mathrm{mL}$ of water. A gives the final volume, not the water to add; B has the wrong unit and size; D is too little water. Textbook: Grade 10, unit 2 · section 2.5. - 2.In which of the following solvents would you expect the solubility of NaCl to be greatest?
- A. Carbon tetrachloride (CCl4)
- B. Water (H2O)
- C. Methanol (CH3OH)
- D. Methanol (CH3OH)
Answer: B. Water dissolves ionic substances such as sodium chloride well because it is polar, meaning its charges are unevenly spread. So sodium chloride is most soluble in water among these choices. A is wrong because carbon tetrachloride is non-polar. C is wrong because methanol is less effective than water at dissolving sodium chloride. D is wrong for the same reason as C; it is also the same solvent listed again. Textbook: Grade 10, unit 2 · section 2.2. - 3.Which of the following substances might stabilize a colloidal suspension of oil in water?
- A. Sodium stearate NaCO2(CH2)16CH3
- B. Sodium bicarbonate (NaHCO3)
- C. H2O
- D. CaCl2
Answer: A. The question tests how a substance can keep oil droplets dispersed in water. Sodium stearate can do this because one part interacts with water and its long hydrocarbon part interacts with oil. Sodium bicarbonate and calcium chloride are not surfactants; water alone does not keep oil dispersed. Textbook: Grade 10, unit 2 · section 2.1. - 4.How many moles of unknown weak acid (HA) in a 100 L solution are required to produce a solution with pH = 2? Ka of the unknown weak acid (HA) = 5×10^-3.
- A. 3×10^-3
- B. 0.3×10^-3
- C. 3
- D. 0.3
Answer: C. For a weak acid, the amount that ionizes determines its $pH$. Since $pH=2$, $[\mathrm{H^+}]=10^{-2}=0.01\,\mathrm{M}$; then $K_a=x^2/(C-x)$ gives $C=0.01+(0.01)^2/(5\times10^{-3})=0.03\,\mathrm{M}$. In $100\,\mathrm{L}$, the amount is $0.03\times100=3\,\mathrm{mol}$. A and B are too small, and D is one tenth of the required amount. Textbook: Grade 12, unit 1 · section 1.2.2. - 5.If different processes are used to bring about the same change the enthalpy changes during these processes are the same, this is the statement of
- A. Hess's law
- B. Standard Enthalpy
- C. 1st law thermodynamics
- D. 2nd law thermodynamics
Answer: A. The key idea is that enthalpy change depends on the starting and ending states, not on the route taken. Hess's law (A) says that enthalpy changes are the same for different processes that bring about the same overall change. Standard enthalpy (B) refers to an enthalpy change under standard conditions; the first law (C) concerns conservation of energy; the second law (D) concerns the direction of natural processes. Textbook: Grade 10, unit 4 · section 4.4. - 6.Which of the following 0.1 M solutions has the lowest pH?
- A. NaNO2
- B. KClO4
- C. NH4Cl
- D. NH3
Answer, explanation and textbook page: open in the app. - 7.The pH of a 0.1 M weak base B is 9. What is the Kb for B?
- A. 9.2×10^{-4}
- B. 2×10^{-6}
- C. 1×10^{-4}
- D. 1×10^{-9}
Answer, explanation and textbook page: open in the app. - 8.Addition of HCl to an aqueous buffer solution containing NH3 and NH4Cl cause which of the following to occur? I. pH of the solution increase II. pH of the solution decrease III. NH4+ concentration increase IV. NH3 concentration increase
- A. I
- B. II
- C. I and III
- D. II and III
Answer, explanation and textbook page: open in the app. - 9.What is the equivalence point pH of the solution formed by the titration of 50 mL of 0.15 M CH3COOH using 25 mL of 0.3 M NaOH? [Use log 7.5 = 0.87, Kb of acetate ion = 5.6×10^{-10}]
- A. 7.44
- B. 6.22
- C. 8.44
- D. 8.87
Answer, explanation and textbook page: open in the app. - 10.The solubility of a particular salt in water is 9.9 g/mL at room temperature. If 11.1 g is completely dissolved in one milliliter of water, the solution is
- A. Saturated
- B. Supersaturated
- C. Unsaturated
- D. Dilute
Answer, explanation and textbook page: open in the app. - 12.Which one of the following best describes chemical equilibrium?
- A. Concentrations of products are higher than concentration of reactants.
- B. Forward and reverse reactions continue with no effect on the concentration of reactants and products.
- C. Reactions stop only when reactants have been converted to products.
- D. Forward and reverse reactions have stopped so that the concentration of the reactants equals the concentration of products.
Answer, explanation and textbook page: open in the app. - 13.Based on the Valence shell electron pair repulsion (VSEPR) theory which of the following would have a tetrahedral arrangement of electrons around the central atom?
- A. BH3
- B. NO2-
- C. CO3^2-
- D. SiH4
Answer, explanation and textbook page: open in the app. - 14.When the 1s-orbitals of two hydrogen atoms combine to form a hydrogen molecule, then which molecular orbitals are formed?
- A. One bonding molecular orbital only.
- B. Two bonding molecular orbitals.
- C. One bonding molecular orbital and one antibonding molecular orbital.
- D. Two antibonding molecular orbitals.
Answer, explanation and textbook page: open in the app. - 15.Which of the following solid substances contains positive ions immersed in a sea of mobile electrons?
- A. O2
- B. Cu
- C. CuO
- D. SiO2
Answer, explanation and textbook page: open in the app. - 16.Which one of the following compounds contains both covalent and ionic bond?
- A. CCl4
- B. KCl
- C. MgCl2
- D. NH4Cl
Answer, explanation and textbook page: open in the app. - 17.Oxygen, nitrogen and fluorine bond with hydrogen to form molecules. These molecules are attracted to each other by
- A. Coordinate covalent bonds
- B. Electro covalent bond
- C. Ionic bonds
- D. Hydrogen bonds
Answer, explanation and textbook page: open in the app. - 18.Given the reaction: H2 + Cl2 → 2HCl. Which statement best describes the energy changes as bonds are formed and broken in this reaction.
- A. The forming of the H-Cl bond releases energy.
- B. The forming of the H-Cl bond absorbs energy.
- C. The breaking of the H-H bond releases energy.
- D. The breaking of the Cl-Cl bond releases energy.
Answer, explanation and textbook page: open in the app. - 19.The reaction CHCl3(g) + Cl2(g) → CCl4(g) + HCl(g) has the rate law: Rate = k[CHCl3][Cl2]. If the concentration of CHCl3 is increased by a factor of five while the concentration of Cl2 is kept the same, the rate will be
- A. Stay the same
- B. Increased by a factor of five
- C. Decreased by a factor of five
- D. Doubled
Answer, explanation and textbook page: open in the app. - 20.What are the four quantum numbers of 4d^6 orbital? (Options in table)
- A. n=4, l=1, ml=1, ms=±1/2
- B. n=4, l=2, ml=-2, ms=-1/2
- C. n=4, l=0, ml=0, ms=-1/2
- D. n=4, l=2, ml=1, ms=-1/2
Answer, explanation and textbook page: open in the app. - 21.Lava is a foam colloid. The dispersed phase and dispersion medium are respectively:
- A. gas-liquid
- B. solid-gas
- C. liquid-gas
- D. gas-solid
Answer, explanation and textbook page: open in the app. - 22.Which of the following salts would form an acidic solution? I. KCl II. NaF III. NH4Cl IV. CaCO3
- A. I and III
- B. I and IV
- C. III and IV
- D. only III
Answer, explanation and textbook page: open in the app. - 23.Which of the following is a Lewis acid but not a Brønsted acid?
- A. HBr
- B. BBr3
- C. NH3
- D. CH4
Answer, explanation and textbook page: open in the app. - 24.What is the percentage dissociation of a 0.1 M unknown weak acid (HA) solution? [Use Ka of HA = 9×10^{-9}]
- A. 9×10^{-9}
- B. 3×10^{-9}
- C. 9×10^{-2}
- D. 3×10^{-2}
Answer, explanation and textbook page: open in the app. - 25.A chemist adds water to 120 mL of a 6 M solution of HCl until the final volume is 2 L. What is the molarity of the resulting solution?
- A. 0.94 M
- B. 2.3 M
- C. 0.36 M
- D. 8.7 M
Answer, explanation and textbook page: open in the app. - 26.Which of the following is the correct increasing order of the atomic size of Mg+, Na, Si^3+, and Al^2+?
- A. Na < Mg+ < Al2+ < Si3+
- B. Si3+ < Al2+ < Mg+ < Na
- C. Al2+ < Mg+ < Na < Si3+
- D. Si3+ > Al2+ > Na > Mg+
Answer, explanation and textbook page: open in the app. - 27.The standard enthalpy of formation of Nitrogen (N2) is?
- A. 1
- B. 0
- C. -1
- D. 4
Answer, explanation and textbook page: open in the app. - 28.We have three aqueous solutions of NaCl labeled 'A', 'B', and 'C' with concentrations 0.1 m, 0.01 m, and 0.001 m, respectively. The van't Hoff factor for these solutions will be
- A. iA < iB < iC
- B. iA > iB > iC
- C. iA = iB = iC
- D. iA < iB > iC
Answer, explanation and textbook page: open in the app. - 29.Which of the following is TRUE for the sublimation of solid carbon dioxide at room temperature and pressure?
- A. Change in Enthalpy is negative, and change in Entropy is positive.
- B. Change in Entropy is negative, and change in Enthalpy is positive.
- C. Change in Enthalpy and change in Entropy are positive.
- D. Change in Gibbs free energy is positive.
Answer, explanation and textbook page: open in the app. - 30.Electrons exist only at fixed levels of potential energy. However, if an atom absorbs sufficient energy, a possible result is that
- A. An electron may move to an electron shell farther out from the nucleus.
- B. An electron may move to an electron shell closer to the nucleus.
- C. The atom would become a positively charged or cation.
- D. The atom may become radioactive isotopes.
Answer, explanation and textbook page: open in the app. - 31.Consider this equilibrium reaction in a sealed container: H2O(g) ⇌ H2O(l). Which one of the following will be the effect on the equilibrium of increasing the temperature from 20°C to 30°C?
- A. More of the water will be in the gaseous state at equilibrium.
- B. More of the water will be in the liquid state at equilibrium.
- C. At equilibrium the rate of condensation will be greater than the rate of evaporation.
- D. At equilibrium the rate of evaporation will be greater than the rate of condensation.
Answer, explanation and textbook page: open in the app. - 32.Which one of the following best describes the formation of pi (π) bond?
- A. They are formed by sideways overlap of parallel orbitals.
- B. They are formed by the axial overlaps of orbitals.
- C. They are formed by the sideways overlaps of an s and p orbital.
- D. They are formed by the axial overlaps of either s or p orbital.
Answer, explanation and textbook page: open in the app. - 33.Which one is the function of iron in the Haber process?
- A. It shifts the position of equilibrium towards the products.
- B. It decreases the rate of reactions.
- C. It provides an alternative reaction pathway with lower activation energy.
- D. It reduces the enthalpy change of the reaction.
Answer, explanation and textbook page: open in the app. - 34.Which types of solid materials are typically hard, have high melting points and poor electrical conductivities? I. Ionic II. Metallic III. Covalent-network
- A. I and II only
- B. I and III only
- C. II and III only
- D. I, II, and III
Answer, explanation and textbook page: open in the app. - 35.For the reaction: H2(g) + I2(g) ⇌ 2HI(g), at a certain temperature the equilibrium concentrations in mol/L are [H2]=0.2, [I2]=0.2, [HI]=2.0. Then based on this data, which one is the equilibrium constant Kc?
- A. 0.002
- B. 20
- C. 10
- D. 100
Answer, explanation and textbook page: open in the app. - 36.Which statement is correct about the effect of adding a catalyst to a system at equilibrium? I. The rate of the forward reaction increases. II. The rate of reverse reaction increases. III. The yield of the products increases.
- A. I only
- B. III only
- C. I and II only
- D. I, II and III
Answer, explanation and textbook page: open in the app. - 37.For the reaction: N2O4(g) ⇌ 2NO2(g), Kc = 8×10^4 mol/cm^3? Actually units: 8×10^4 mol/cm^3? That is huge; likely 8×10^{-4}? Given options: [N2O4]=8×10^{-2} mol/cm^3, find [NO2]. Kc = [NO2]^2 / [N2O4] = 8×10^4? That would give [NO2]^2 = 8×10^4 × 8×10^{-2} = 6.4×10^3, [NO2]=80, not matching options. If Kc=8×10^{-4}, then [NO2]^2 = 8×10^{-4}×8×10^{-2}=6.4×10^{-5}, [NO2]=8×10^{-3}. Option C: 8.0×10^{-3}. So likely Kc=8×10^{-4}.
- A. 8.0×10^{-1}
- B. 8.0×10^{-2}
- C. 8.0×10^{-3}
- D. 4.5×10^{-4}
Answer, explanation and textbook page: open in the app. - 38.For the reaction: C2H4(g) + H2(g) → C2H6(g), ΔH = -137 kJ. Which statement about the information is correct?
- A. The total energy of the bonds broken in the reactants is greater than the total energy of the bonds formed in the products.
- B. The bonds broken and the bonds made are of the same strength.
- C. The total energy of the bonds broken in the reactants is less than the total energy of the bonds formed in the products.
- D. No conclusion can be made about the sums of the bond enthalpies.
Answer, explanation and textbook page: open in the app. - 39.Under what conditions can we absolutely say a system is at equilibrium at constant temperature and pressure?
- A. Change in Enthalpy is equal to Zero.
- B. Change in Gibbs free energy is equal to Zero.
- C. Change in Entropy is greater than Zero
- D. Change in Enthalpy is greater than Zero.
Answer, explanation and textbook page: open in the app. - 40.Which of the following substances would you expect to have the highest entropy at 1 atm of pressure?
- A. 1 mol of H2O(l)
- B. 1 mol of H2O(s)
- C. 0.5 mol of ethanol in 0.5 mol of H2O(l)
- D. a gaseous solution of 0.5 mol of CH4(g) and 0.5 mol of H2O(g)
Answer, explanation and textbook page: open in the app. - 41.Which of the following is capable of acting both as an oxidizing and reducing agent?
- A. SnCl2
- B. H2O2
- C. NaF
- D. KMnO4
Answer, explanation and textbook page: open in the app. - 42.Which of the following is NOT true about the anode of an electrolytic cell?
- A. Oxidation occurs at it.
- B. It is assigned as the positive pole.
- C. Cations in solution move away from the surface of the electrode as the redox reaction occurs.
- D. It is deficient in number of electrons.
Answer, explanation and textbook page: open in the app. - 43.The reaction MnO4- + C2O4^2- → MnO2 + CO3^2- is not balanced. If the reaction is balanced using basic medium, the coefficient of OH- and H2O will be respectively?
- A. 4 and 2
- B. 2 and 4
- C. 2 and 3
- D. 3 and 2
Answer, explanation and textbook page: open in the app. - 44.In which of the following aqueous solution can water be oxidized and O2 forms at the anode and water is reduced and H2 forms at the cathode?
- A. KBr
- B. MgSO4
- C. AgNO3
- D. NaBr
Answer, explanation and textbook page: open in the app. - 45.If you want to plate out an iron spoon with silver metal, then which of the following is TRUE?
- A. The electrolyte must contain silver ion
- B. The iron spoon must be set at the anode
- C. The silver metal must be the cathode
- D. The material to be plated must be the anode
Answer, explanation and textbook page: open in the app. - 46.The standard state of water is?
- A. Steam
- B. Liquid
- C. Ice
- D. Vapour state
Answer, explanation and textbook page: open in the app. - 47.What type of bond you observe in phenol other than 5 C-H bond?
- A. 3C=C, 3C-C and 1O-H
- B. 3C=C, 3C-C, 1C-O and 1O-H
- C. 6C-C, 1C-O and 1O-H
- D. 4C=C, 2C-C, 2C-O and 1O-H
Answer, explanation and textbook page: open in the app. - 48.Which batteries are faced with leak out and environmental problem respectively?
- A. Nickel-cadmium and fuel cells
- B. Nickel-cadmium and dry cells
- C. Dry cells and Mercury cells
- D. Dry cells and fuel cells
Answer, explanation and textbook page: open in the app. - 49.When the compounds below are listed in order of decreasing boiling point (highest to lowest) which one is the correct order? 1. Ethane 2. Fluoroethane 3. Ethanol 4. Ethanoic acid
- A. 4,3,1,2
- B. 3,4,1,2
- C. 4,3,2,1
- D. 2,1,3,4
Answer, explanation and textbook page: open in the app. - 50.Which one of the following is the formal charge on each atom in dichloromethane (CH2Cl2)?
- A. C=0, H=+1, Cl=-1
- B. C=0, H=0, Cl=0
- C. C=0, H=+1, Cl=-1
- D. C=-2, H=+1, Cl=+1
Answer, explanation and textbook page: open in the app. - 51.Which one of the following species has the same molecular geometry: CO2, H2O, BeCl2, and N2O?
- A. CO2 and N2O
- B. H2O and N2O
- C. CO2 and BeCl2
- D. CO2, BeCl2, and N2O
Answer, explanation and textbook page: open in the app. - 52.Which hybridization change does the carbon atom undergo in the combustion of methane? CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)
- A. sp → sp^2
- B. sp^3 → sp
- C. sp^2 → sp^3
- D. sp^2 → sp
Answer, explanation and textbook page: open in the app. - 53.The number of sigma and pi bonds present in benzene (C6H6) molecule is
- A. 12 sigma and 3 pi
- B. 3 sigma and 12 pi
- C. 18 sigma and 6 pi
- D. 6 pi and 18 sigma
Answer, explanation and textbook page: open in the app. - 54.Which one of the following characteristics applies to PCl3? I. Nonpolar molecule II. Polar bonds III. Trigonal- pyramidal molecular geometry IV. sp^2 hybridized
- A. I and II
- B. II and III
- C. I, II and III
- D. I, II, III and IV
Answer, explanation and textbook page: open in the app. - 55.According to molecular orbital theory, which one of the following species is most likely to exist?
- A. He2
- B. Be2
- C. Ne2
- D. Li2
Answer, explanation and textbook page: open in the app. - 56.According to molecular orbital theory, what is the bond order of O2?
- A. 1
- B. 2
- C. 2.5
- D. 1.5
Answer, explanation and textbook page: open in the app. - 57.Which of the following data gives the most precise measurement?
- A. 3.0
- B. 3.00
- C. 3.000
- D. 3.0000
Answer, explanation and textbook page: open in the app. - 58.Which one is the correct order of increasing Cl-A-Cl bond angle in the following species where A is central atom: I. BCl3, II. SiCl4, III. SCl2, IV. PCl3?
- A. III < IV < II < I
- B. II < III < I < IV
- C. IV < I < II < III
- D. I < II < III < IV
Answer, explanation and textbook page: open in the app. - 59.What substance is reduced in an alkaline-cell battery?
- A. Zn(s)
- B. Zn^2+(aq)
- C. NH4+(aq)
- D. MnO2(s)
Answer, explanation and textbook page: open in the app. - 60.When iron is 'galvanized', what metal is used to coat iron?
- A. Al
- B. Mn
- C. Zn
- D. Cr
Answer, explanation and textbook page: open in the app. - 61.What is E° for the following balanced reaction? Zn(s) + Pb^2+(aq) → Zn^2+(aq) + Pb(s). Given reduction potentials: Zn^2+/Zn = -0.763 V, Pb^2+/Pb = -0.126 V.
- A. +0.637 V
- B. -0.889 V
- C. -0.637 V
- D. +0.889 V
Answer, explanation and textbook page: open in the app. - 62.The value of E° for the reaction Zn(s) + Cu^2+(aq) → Cu(s) + Zn^2+(aq) is 1.10 V. What is the value of Ecell when the concentrations of Cu^2+ and Zn^2+ are equal to 0.025 M?
- A. 1.10 V
- B. 0.95 V
- C. 1.15 V
- D. 0.80 V
Answer, explanation and textbook page: open in the app. - 63.Natural rubber is a polymer of
- A. Butadiene
- B. Isoprene
- C. Neoprene
- D. Styrene
Answer, explanation and textbook page: open in the app. - 64.Why the name given NYLON 66 co-polymer? This is because
- A. It is discovered in 1966
- B. Both the monomers have 6 carbons each
- C. The longest chain contains 6 carbons
- D. It is the sixth polymer
Answer, explanation and textbook page: open in the app. - 65.Bakelite is obtained from phenol by reacting with
- A. HCHO
- B. (CH2OH)2
- C. CH3CHO
- D. CH3COCH3
Answer, explanation and textbook page: open in the app. - 66.The froth-flotation process in metallurgy involves which of the following?
- A. mining of an ore
- B. smelting of iron
- C. concentration of an ore
- D. reduction of metal ion
Answer, explanation and textbook page: open in the app. - 67.Which of the following substances are added to natural rubber to toughen it?
- A. Calcium
- B. Carbon
- C. Nitrogen
- D. Sulfur
Answer, explanation and textbook page: open in the app. - 68.Which will be the best method to decrease the random uncertainty of a measurement in an acid-base titration?
- A. Repeat the titration
- B. Use a different titrant
- C. Use a different analyte
- D. Use a different indicator
Answer, explanation and textbook page: open in the app. - 69.Which of the following is the most important type of solute-solvent interaction in solution NaCl(s) in water?
- A. Dispersion
- B. Ion-dipole
- C. Dipole-dipole
- D. Hydrogen bonding
Answer, explanation and textbook page: open in the app. - 70.Which of the following hydride orbital is favoring the formation of see-saw?
- A. sp^3d
- B. sp^3d^2
- C. sp^3
- D. sp^3d^3
Answer, explanation and textbook page: open in the app. - 71.A neutral molecule having the general formula AX3 has one unshared pair of electrons on A. Which is the hybridization of A?
- A. sp^3
- B. sp^3d
- C. sp^3d^2
- D. sp^3d^3
Answer, explanation and textbook page: open in the app. - 72.For lithium, enthalpy of sublimation = +161 kJ/mol, first IE = +520 kJ/mol. Dissociation energy of F2 = +154 kJ/mol, electron affinity of F = -328 kJ/mol. Lattice energy of LiF = -1047 kJ/mol. The overall enthalpy of formation for LiF is:
- A. -617 kJ/mol
- B. 2134 kJ/mol
- C. -694 kJ/mol
- D. 2066 kJ/mol
Answer, explanation and textbook page: open in the app. - 73.Which of the following statements is correct about hydrogen cyanide (HCN)?
- A. It has linear geometry with C as central atom.
- B. It has bent or angular geometry with C as central atom.
- C. It has trigonal planar geometry with N as central atom.
- D. It has bent or angular geometry with N as central atom.
Answer, explanation and textbook page: open in the app. - 74.Which one of the following electromagnetic radiations has the highest energy?
- A. X-rays
- B. Gamma rays
- C. UV rays
- D. Microwaves
Answer, explanation and textbook page: open in the app. - 75.When electrons fall down from the higher energy level to the first excited state, the spectral lines correspond to:
- A. Pfund series
- B. Paschen series
- C. Lyman series
- D. Balmer series
Answer, explanation and textbook page: open in the app. - 76.The maximum number of electrons in P-orbital with n = 6, ml = 0 is
- A. 2
- B. 6
- C. 16
- D. 14
Answer, explanation and textbook page: open in the app. - 77.Which of the following electrons, identified only by their n and l quantum numbers, have the highest energy?
- A. n=3, l=2
- B. n=4, l=1
- C. n=4, l=2
- D. n=3, l=0
Answer, explanation and textbook page: open in the app.