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Gaokao Chemistry practice questions

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Question 1Physical chemistry, amounts and reactions

For N2(g) + 3H2(g) <=> 2NH3(g), what happens to equilibrium if pressure is increased at constant temperature?

  1. It shifts toward NH3 Correct answer.
  2. It shifts toward N2 and H2
  3. It is unaffected because all species are gases
  4. It stops immediately

Explanation

Increasing pressure favors the side with fewer gas moles. The reactant side has 4 mol gas while the product side has 2 mol gas, so the equilibrium shifts toward NH3.

Question 2Physical chemistry, amounts and reactions

What is the equilibrium constant expression for N2(g) + 3H2(g) <=> 2NH3(g)?

  1. K = [N2][H2]^3/[NH3]^2
  2. K = [NH3]^2/[N2][H2]^3 Correct answer.
  3. K = [NH3]/[N2][H2]
  4. K = [N2][H2]/[NH3]

Explanation

Products appear in the numerator and reactants in the denominator, each raised to its stoichiometric coefficient. Thus K = [NH3]^2 / ([N2][H2]^3).

Question 3Physical chemistry, amounts and reactions

What is the pH of 0.010 mol/L HCl, assuming complete ionization?

  1. 1
  2. 2 Correct answer.
  3. 7
  4. 12

Explanation

HCl is a strong acid, so [H+] = 0.010 M = 10^-2 M. pH = -log[H+] = 2.

Question 4Physical chemistry, amounts and reactions

For a reaction mixture at a given temperature, Q < K. Which direction will the reaction proceed to reach equilibrium?

  1. Forward, forming more products Correct answer.
  2. Reverse, forming more reactants
  3. No change because Q and K are unrelated
  4. Both directions stop

Explanation

If Q < K, the mixture has too few products relative to equilibrium. The net reaction proceeds forward until Q increases to K.

Question 5Physical chemistry, amounts and reactions

For N2O4(g) <=> 2NO2(g), what is the relation between Kp and Kc?

  1. Kp = Kc(RT) Correct answer.
  2. Kp = Kc/(RT)
  3. Kp = Kc(RT)^0
  4. Kp = Kc(RT)^3

Explanation

Kp = Kc(RT)^Delta n, where Delta n = gas product moles - gas reactant moles = 2 - 1 = 1. Therefore Kp = Kc(RT).

Question 6Physical chemistry, amounts and reactions

If Ksp for AgCl is 1.0 x 10^-10, what is the molar solubility of AgCl in pure water?

  1. 1.0 x 10^-10 M
  2. 1.0 x 10^-5 M Correct answer.
  3. 1.0 x 10^-2 M
  4. 1.0 x 10^5 M

Explanation

For AgCl(s) <=> Ag+ + Cl-, Ksp = s^2 in pure water. Thus s = sqrt(1.0 x 10^-10) = 1.0 x 10^-5 M.

Question 7Physical chemistry, amounts and reactions

Which mixture is a typical buffer solution?

  1. Strong acid and strong base in equal amounts
  2. Weak acid and its conjugate base Correct answer.
  3. Pure distilled water
  4. A salt of two neutral atoms only

Explanation

A buffer contains a weak acid and its conjugate base, or a weak base and its conjugate acid. The pair consumes added acid or base and resists pH change.

Question 8Physical chemistry, amounts and reactions

Adding NaCl to a saturated AgCl solution generally has what effect on AgCl solubility?

  1. It increases solubility because Na+ dissolves solids
  2. It decreases solubility through the common-ion effect Correct answer.
  3. It makes Ksp larger at the same temperature
  4. It converts AgCl to a gas

Explanation

NaCl adds Cl-, a common ion in the AgCl dissolution equilibrium. Increasing [Cl-] shifts the equilibrium left and lowers the molar solubility of AgCl.

Question 9Physical chemistry, amounts and reactions

100 mL of 0.10 M HCl is mixed with 100 mL of 0.10 M NaOH. What is the approximate pH of the final solution at 25 C?

  1. 1
  2. 7 Correct answer.
  3. 10
  4. 13

Explanation

The moles of strong acid and strong base are equal: 0.010 mol each. They neutralize completely to form NaCl and water, so the final solution is approximately neutral at pH 7.

Question 10Physical chemistry, amounts and reactions

For an exothermic equilibrium reaction, what is the effect of increasing temperature?

  1. It favors the endothermic reverse direction Correct answer.
  2. It always favors the exothermic forward direction
  3. It has the same effect as adding a catalyst
  4. It makes all concentrations equal

Explanation

Heat can be treated as a product for an exothermic forward reaction. Increasing temperature adds heat, so equilibrium shifts toward the endothermic reverse direction.

Question 11Physical chemistry, amounts and reactions

For A(g) <=> B(g), Kc = 4.0. Starting with 1.0 mol/L A and no B, what is [A] at equilibrium?

  1. 0.20 mol/L Correct answer.
  2. 0.25 mol/L
  3. 0.50 mol/L
  4. 0.80 mol/L

Explanation

Let x be the amount of A converted to B. Then Kc = [B]/[A] = x/(1.0 - x) = 4. Solving gives x = 0.80, so [A] = 0.20 mol/L.

Question 12Physical chemistry, amounts and reactions

For AgCl, Ksp = 1.8 x 10^-10. What is [Ag+] in a saturated solution that already contains 0.10 mol/L Cl-?

  1. 1.8 x 10^-9 mol/L Correct answer.
  2. 1.8 x 10^-10 mol/L
  3. 1.8 x 10^-5 mol/L
  4. 1.8 x 10^-1 mol/L

Explanation

Ksp = [Ag+][Cl-]. With [Cl-] = 0.10 M, [Ag+] = 1.8 x 10^-10 / 0.10 = 1.8 x 10^-9 M.

Question 13Physical chemistry, amounts and reactions

A buffer contains equal concentrations of CH3COOH and CH3COO-. If pKa of CH3COOH is 4.76, what is the buffer pH?

  1. 2.38
  2. 4.76 Correct answer.
  3. 7.00
  4. 9.52

Explanation

By the Henderson-Hasselbalch equation, pH = pKa + log([A-]/[HA]). Equal concentrations give log 1 = 0, so pH = 4.76.

Question 14Physical chemistry, amounts and reactions

For 2NO2(g) -> N2O4(g), Delta H is negative. Which change increases the equilibrium yield of N2O4?

  1. Raising temperature and lowering pressure
  2. Lowering temperature and raising pressure Correct answer.
  3. Adding a catalyst and lowering pressure
  4. Removing all NO2 instantly

Explanation

The forward reaction is exothermic and reduces gas moles from 2 to 1. Lower temperature favors the exothermic direction, and higher pressure favors the side with fewer gas molecules, both increasing N2O4 yield.

Question 15Physical chemistry, amounts and reactions

In industrial ammonia synthesis, why are moderate temperature, high pressure, and an iron catalyst used rather than simply the lowest possible temperature?

  1. Low temperature favors yield but makes the reaction too slow, so a compromise plus catalyst is used Correct answer.
  2. Low temperature makes ammonia decompose completely
  3. High pressure favors the side with more gas molecules
  4. A catalyst changes the equilibrium constant to nearly infinity

Explanation

Ammonia formation is exothermic, so lower temperature favors equilibrium yield, but very low temperature gives an impractically slow rate. High pressure favors fewer gas moles, and an iron catalyst increases rate without changing K.

Question 16Organic chemistry and macromolecules

Which type of hydrocarbon readily decolorizes bromine water by addition across a carbon-carbon double bond?

  1. Alkane
  2. Alkene Correct answer.
  3. Arene under ordinary conditions
  4. Cycloalkane without a double bond

Explanation

Alkenes contain C=C double bonds that undergo addition with bromine, removing the brown color. Saturated hydrocarbons do not usually react this way under mild conditions.

Question 17Organic chemistry and macromolecules

What functional group is present in ethanol, CH3CH2OH?

  1. Carboxyl
  2. Hydroxyl Correct answer.
  3. Aldehyde
  4. Ester

Explanation

Ethanol contains an -OH group bonded to a carbon chain, which is the hydroxyl group of an alcohol. This group largely determines ethanol's chemical behavior.

Question 18Organic chemistry and macromolecules

An ester is commonly formed by reacting which pair of substances under acidic conditions?

  1. Alcohol and carboxylic acid Correct answer.
  2. Alkane and water
  3. Salt and base
  4. Metal and oxygen

Explanation

Esterification typically reacts an alcohol with a carboxylic acid in the presence of acid catalyst. The products are an ester and water.

Question 19Organic chemistry and macromolecules

What is the major product when HBr adds to propene under ordinary Markovnikov conditions?

  1. 1-bromopropane
  2. 2-bromopropane Correct answer.
  3. propane
  4. propanal

Explanation

Markovnikov addition places H on the carbon already bearing more hydrogens and Br on the more substituted carbon. Propene therefore gives mainly 2-bromopropane.

Question 20Organic chemistry and macromolecules

Strong oxidation of ethanol with acidified permanganate can produce which compound?

  1. Ethane
  2. Ethanoic acid Correct answer.
  3. Ethene only
  4. Benzene

Explanation

Primary alcohols such as ethanol can be oxidized first to aldehydes and further to carboxylic acids. Strong oxidation gives ethanoic acid.

Question 21Organic chemistry and macromolecules

Bromoethane reacts with aqueous hydroxide ion to form ethanol. What type of reaction is this?

  1. Addition
  2. Substitution Correct answer.
  3. Combustion
  4. Polymerization

Explanation

The hydroxide ion replaces the bromine atom in bromoethane, forming ethanol. Replacement of one group by another is a substitution reaction.

Question 22Organic chemistry and macromolecules

Hydrolysis of an ester under acidic conditions produces which type of products?

  1. Alcohol and carboxylic acid Correct answer.
  2. Alkene and hydrogen gas
  3. Amine and salt only
  4. Two alkanes

Explanation

Acidic ester hydrolysis reverses esterification, producing an alcohol and a carboxylic acid. The reaction is usually equilibrium-limited under acidic conditions.

Question 23Organic chemistry and macromolecules

Which reagents are commonly used for nitration of benzene?

  1. H2 and Ni
  2. Br2 water only
  3. Concentrated HNO3 and concentrated H2SO4 Correct answer.
  4. NaOH(aq) only

Explanation

Benzene nitration uses concentrated nitric acid with concentrated sulfuric acid to generate the nitronium ion electrophile. Benzene then undergoes electrophilic aromatic substitution.

Question 24Organic chemistry and macromolecules

How many structural isomers does C4H10 have?

  1. 1
  2. 2 Correct answer.
  3. 3
  4. 4

Explanation

C4H10 has two structural isomers: straight-chain butane and branched 2-methylpropane. They have the same molecular formula but different carbon skeletons.

Question 25Organic chemistry and macromolecules

PET polyester is formed from a diol and a dicarboxylic acid derivative. What type of polymerization is this?

  1. Addition polymerization without by-products
  2. Condensation polymerization Correct answer.
  3. Ionic lattice formation
  4. Radioactive decay

Explanation

Polyesters form when monomers with two functional groups react stepwise, eliminating small molecules such as water or methanol. This is condensation polymerization.

Question 26Organic chemistry and macromolecules

Which route converts ethene to ethane most directly?

  1. Add H2 with a Ni catalyst Correct answer.
  2. React with acidified KMnO4 strongly
  3. Add Br2 in CCl4
  4. Heat with concentrated H2SO4 then water

Explanation

Hydrogenation adds H2 across the C=C double bond of ethene to form ethane, commonly using a Ni catalyst. This saturates the alkene.

Question 27Organic chemistry and macromolecules

Which reagent can distinguish ethanal from propanone by giving a silver mirror with ethanal?

  1. Tollens reagent Correct answer.
  2. Bromine water only
  3. Sodium chloride solution
  4. Limewater

Explanation

Tollens reagent oxidizes aldehydes such as ethanal and is reduced to metallic silver, forming a silver mirror. Simple ketones such as propanone do not give this positive test under ordinary conditions.

Question 28Organic chemistry and macromolecules

A compound with formula C3H6O gives a positive Tollens test. Which structure is most consistent?

  1. Propanone
  2. Propanal Correct answer.
  3. Propan-2-ol
  4. Propene oxide

Explanation

A positive Tollens test indicates an aldehyde. Among the choices, propanal is the aldehyde with formula C3H6O.

Question 29Organic chemistry and macromolecules

What is the degree of unsaturation for C6H6?

  1. 1
  2. 2
  3. 4 Correct answer.
  4. 6

Explanation

For hydrocarbons, degree of unsaturation = (2C + 2 - H)/2. For C6H6, (14 - 6)/2 = 4, matching benzene's ring plus three pi bonds.

Question 30Physical chemistry, amounts and reactions

A student has 58.5 g of NaCl. Using a molar mass of 58.5 g/mol, how many moles of NaCl are present?

  1. 0.50 mol
  2. 1.00 mol Correct answer.
  3. 2.00 mol
  4. 58.5 mol

Explanation

Moles equal mass divided by molar mass: 58.5 g / 58.5 g/mol = 1.00 mol. This is a direct amount-of-substance calculation.

Question 31Physical chemistry, amounts and reactions

What is the approximate mass percentage of hydrogen in H2O? Use H = 1 and O = 16.

  1. 5.6%
  2. 11.1% Correct answer.
  3. 22.2%
  4. 88.9%

Explanation

One mole of water has mass 18 g, of which 2 g is hydrogen. The hydrogen mass percentage is 2/18 x 100% = 11.1%.

Question 32Physical chemistry, amounts and reactions

For the balanced reaction 2H2 + O2 -> 2H2O, what mole ratio of H2 to O2 is required?

  1. 1:1
  2. 1:2
  3. 2:1 Correct answer.
  4. 2:2

Explanation

The coefficients in a balanced equation give mole ratios. The reaction consumes 2 mol H2 for every 1 mol O2.

Question 33Physical chemistry, amounts and reactions

For 2Al + 3Cl2 -> 2AlCl3, how many moles of Cl2 are required to react completely with 0.30 mol Al?

  1. 0.20 mol
  2. 0.30 mol
  3. 0.45 mol Correct answer.
  4. 0.60 mol

Explanation

The balanced equation requires 3 mol Cl2 for every 2 mol Al. Required Cl2 = 0.30 x 3/2 = 0.45 mol.

Question 34Physical chemistry, amounts and reactions

For N2 + 3H2 -> 2NH3, 1.0 mol N2 is mixed with 2.0 mol H2. What is the maximum amount of NH3 that can form?

  1. 0.67 mol
  2. 1.0 mol
  3. 1.33 mol Correct answer.
  4. 2.0 mol

Explanation

Hydrogen is limiting because 1.0 mol N2 would require 3.0 mol H2, but only 2.0 mol is present. From 3 mol H2 to 2 mol NH3, 2.0 mol H2 produces 2.0 x 2/3 = 1.33 mol NH3.

Question 35Physical chemistry, amounts and reactions

5.85 g NaCl is dissolved and diluted to 500 mL. What is the molar concentration? Use M(NaCl) = 58.5 g/mol.

  1. 0.020 mol/L
  2. 0.10 mol/L
  3. 0.20 mol/L Correct answer.
  4. 1.00 mol/L

Explanation

Moles NaCl = 5.85/58.5 = 0.100 mol. Volume is 0.500 L, so concentration = 0.100/0.500 = 0.20 mol/L.

Question 36Physical chemistry, amounts and reactions

At standard conditions where molar gas volume is 22.4 L/mol, how many moles are in 11.2 L of O2?

  1. 0.25 mol
  2. 0.50 mol Correct answer.
  3. 1.00 mol
  4. 2.00 mol

Explanation

Moles = volume / molar volume = 11.2 L / 22.4 L/mol = 0.50 mol. The identity of the gas does not change this molar volume assumption at standard conditions.

Question 37Physical chemistry, amounts and reactions

A compound is 40.0% C, 6.7% H, and 53.3% O by mass. Which empirical formula is most consistent with the data? Use C=12, H=1, O=16.

  1. CH2O Correct answer.
  2. C2H4O
  3. CHO2
  4. C2HO

Explanation

In 100 g, moles are C 40/12 = 3.33, H 6.7/1 = 6.7, O 53.3/16 = 3.33. Dividing by 3.33 gives about 1:2:1, so the empirical formula is CH2O.

Question 38Physical chemistry, amounts and reactions

A reaction has a theoretical yield of 10.0 g and an actual yield of 8.0 g. What is the percent yield?

  1. 20%
  2. 80% Correct answer.
  3. 100%
  4. 125%

Explanation

Percent yield = actual yield / theoretical yield x 100% = 8.0/10.0 x 100% = 80%.

Question 39Physical chemistry, amounts and reactions

Propane burns according to C3H8 + 5O2 -> 3CO2 + 4H2O. If 0.20 mol C3H8 reacts with 0.80 mol O2, what is the maximum amount of CO2 formed?

  1. 0.48 mol Correct answer.
  2. 0.60 mol
  3. 0.80 mol
  4. 1.00 mol

Explanation

0.20 mol propane would need 1.00 mol O2, but only 0.80 mol O2 is available, so O2 is limiting. From 5 mol O2 to 3 mol CO2, 0.80 mol O2 forms 0.80 x 3/5 = 0.48 mol CO2.

Question 40Physical chemistry, amounts and reactions

25.00 mL of H2SO4 is neutralized by 30.00 mL of 0.100 mol/L NaOH. What is the concentration of the H2SO4?

  1. 0.0300 mol/L
  2. 0.0600 mol/L Correct answer.
  3. 0.100 mol/L
  4. 0.120 mol/L

Explanation

Moles NaOH = 0.03000 L x 0.100 mol/L = 0.00300 mol. Since H2SO4 requires 2 mol NaOH per 1 mol acid, moles H2SO4 = 0.00150 mol, and concentration = 0.00150/0.02500 = 0.0600 mol/L.

Question 41Physical chemistry, amounts and reactions

In a galvanic cell, oxidation occurs at which electrode?

  1. Cathode
  2. Salt bridge
  3. Anode Correct answer.
  4. Voltmeter

Explanation

Oxidation is loss of electrons, and it occurs at the anode in both galvanic and electrolytic cells. In a galvanic cell, electrons leave the anode through the external circuit.

Question 42Physical chemistry, amounts and reactions

Why does aqueous NaCl conduct electricity?

  1. Water molecules become electrons
  2. NaCl molecules move as neutral particles only
  3. The solution contains mobile Na+ and Cl- ions Correct answer.
  4. Solid NaCl crystals float in the solution

Explanation

Dissolved NaCl separates into hydrated Na+ and Cl- ions. These mobile charged particles carry current through the solution.

Question 43Physical chemistry, amounts and reactions

What is the oxidation number of oxygen in H2O?

  1. -2 Correct answer.
  2. -1
  3. 0
  4. +2

Explanation

In most compounds oxygen has oxidation number -2. Since two hydrogens contribute +2 total, oxygen must be -2 for neutral H2O.

Question 44Physical chemistry, amounts and reactions

In the galvanic cell Zn(s)|Zn2+(aq)||Cu2+(aq)|Cu(s), which statement is correct?

  1. Electrons flow from Cu to Zn
  2. Zn is oxidized and electrons flow from Zn to Cu Correct answer.
  3. Cu is oxidized at the anode
  4. The salt bridge supplies all electrons

Explanation

Zinc is the anode and undergoes oxidation: Zn -> Zn2+ + 2e-. Electrons flow through the external circuit from Zn to the Cu electrode, where Cu2+ is reduced.

Question 45Physical chemistry, amounts and reactions

Given Ered(Cu2+/Cu) = +0.34 V and Ered(Zn2+/Zn) = -0.76 V, what is Ecell for a Zn-Cu galvanic cell?

  1. -1.10 V
  2. -0.42 V
  3. +0.42 V
  4. +1.10 V Correct answer.

Explanation

For the spontaneous Zn-Cu cell, Cu2+ is reduced and Zn is oxidized. Ecell = Ecathode - Eanode = 0.34 - (-0.76) = +1.10 V.

Question 46Physical chemistry, amounts and reactions

During electrolysis of molten NaCl, what forms at the cathode?

  1. Na metal Correct answer.
  2. Cl2 gas
  3. O2 gas
  4. H2 gas

Explanation

In molten NaCl, Na+ and Cl- are the available ions. At the cathode, Na+ gains electrons and forms sodium metal.

Question 47Physical chemistry, amounts and reactions

How many moles of Cu can be deposited from Cu2+ solution by 1.0 mol of electrons?

  1. 0.25 mol
  2. 0.50 mol Correct answer.
  3. 1.0 mol
  4. 2.0 mol

Explanation

The reduction is Cu2+ + 2e- -> Cu. Two moles of electrons deposit one mole of copper, so 1.0 mol electrons deposits 0.50 mol Cu.

Question 48Physical chemistry, amounts and reactions

Why does iron usually rust faster in salt water than in pure water?

  1. Salt water conducts ions better, accelerating electrochemical corrosion Correct answer.
  2. Salt directly turns iron into gold
  3. Salt water contains no dissolved oxygen
  4. Pure water is always strongly acidic

Explanation

Salt water has higher ionic conductivity, which helps complete electrochemical corrosion circuits on the metal surface. Dissolved oxygen and water still participate in rust formation.

Question 49Physical chemistry, amounts and reactions

What is the oxidation number of Cr in Cr2O7^2-?

  1. +3
  2. +5
  3. +6 Correct answer.
  4. +7

Explanation

Let chromium be x. For Cr2O7^2-, 2x + 7(-2) = -2, so 2x - 14 = -2 and x = +6.

Question 50Physical chemistry, amounts and reactions

In Zn + Cu2+ -> Zn2+ + Cu, which species is the reducing agent?

  1. Zn Correct answer.
  2. Cu2+
  3. Zn2+
  4. Cu

Explanation

The reducing agent is oxidized while causing another species to be reduced. Zn loses electrons to become Zn2+, so Zn is the reducing agent.