I85PREP
⌘ K
Schleswig-Holstein Abitur Chemistry study materials
Schleswig-Holstein Abitur Chemistry study resources

Schleswig-Holstein Abitur Chemistry practice questions

One question at a time. Build your Schleswig-Holstein Abitur Chemistry understanding.

First 50 of 190 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Organic chemistry and macromolecules

Which functional group is responsible for the acidic properties of ethanoic acid (acetic acid), CH3COOH?

  1. The carboxyl group (-COOH) Correct answer.
  2. The hydroxyl group (-OH) alone
  3. The aldehyde group (-CHO)
  4. The ester group (-COO-)

Explanation

The carboxyl group combines a carbonyl and a hydroxyl on the same carbon, and the resulting O-H bond is acidic because the conjugate base (the carboxylate ion) is resonance-stabilized. This is what makes ethanoic acid behave as a weak acid in water.

Question 2Organic chemistry and macromolecules

What is the correct IUPAC name for CH3-CH2-CH2-OH?

  1. Propan-1-ol Correct answer.
  2. Propan-2-ol
  3. Propanal
  4. Propanoic acid

Explanation

The hydroxyl group is attached to the first (terminal) carbon of a three-carbon chain, so the compound is named propan-1-ol. The '-ol' suffix identifies it as an alcohol, and the locant '1' specifies the position of the hydroxyl group.

Question 3Organic chemistry and macromolecules

An alkane follows the general formula CnH2n+2. If an alkane has 8 carbon atoms, how many hydrogen atoms does it contain?

  1. 18 Correct answer.
  2. 16
  3. 20
  4. 8

Explanation

Substituting n = 8 into the general alkane formula CnH2n+2 gives 2(8)+2 = 18 hydrogen atoms, matching the formula of octane, C8H18. Every alkane follows this pattern because it is a fully saturated chain with no rings or multiple bonds.

Question 4Organic chemistry and macromolecules

Butane (CH3-CH2-CH2-CH3) and 2-methylpropane (isobutane) share the molecular formula C4H10 but have different atom connectivity. What type of isomerism do they show?

  1. Constitutional (structural) isomerism Correct answer.
  2. Cis-trans (geometric) isomerism
  3. Optical isomerism (enantiomers)
  4. They are not isomers, since they are actually the same compound

Explanation

Constitutional isomers share the same molecular formula but differ in how their atoms are connected. Butane has a straight four-carbon chain, while 2-methylpropane has a branched chain, so they are constitutional isomers even though both are C4H10.

Question 5Organic chemistry and macromolecules

But-2-ene can exist as distinct cis and trans isomers. What makes this possible?

  1. Rotation around the C=C double bond is restricted Correct answer.
  2. The molecule contains a stereocenter with four different groups
  3. There is free rotation around all the carbon-carbon single bonds
  4. The molecule forms a ring that locks substituents in place

Explanation

A carbon-carbon double bond consists of a sigma bond and a pi bond, and rotating around it would require breaking the pi bond. This restricted rotation locks the substituents on each carbon into fixed relative positions, allowing cis (same side) and trans (opposite side) arrangements to exist as distinct, non-interconverting isomers.

Question 6Organic chemistry and macromolecules

In the Cahn-Ingold-Prelog (CIP) system used to assign priority at a stereocenter, priority is determined primarily by comparing the...

  1. Atomic number of the atoms directly attached to the stereocenter Correct answer.
  2. Total molecular weight of each entire substituent group
  3. Alphabetical order of the substituent group names
  4. Physical (van der Waals) size of each substituent

Explanation

The CIP rules rank the four groups attached to a stereocenter by looking first at the atomic number of the atom directly bonded to that center; a higher atomic number gets higher priority. Only when there is a tie at the first atom do the rules move outward to compare the next set of attached atoms.

Question 7Organic chemistry and macromolecules

A carbon atom bonded to four different substituents is a stereocenter. Two molecules that are non-superimposable mirror images of each other at such a center are called...

  1. Enantiomers Correct answer.
  2. Diastereomers
  3. Conformers
  4. Constitutional isomers

Explanation

Enantiomers are pairs of stereoisomers that are exact mirror images of one another but cannot be superimposed, much like a left and right hand. They have identical physical properties except for the direction in which they rotate plane-polarized light and how they interact with other chiral molecules.

Question 8Organic chemistry and macromolecules

A racemic mixture contains equal amounts of two enantiomers. What net optical rotation does this mixture produce?

  1. 0 degrees, since the rotations cancel out Correct answer.
  2. Twice the rotation of either pure enantiomer
  3. Half the rotation of either pure enantiomer
  4. The mixture is always strongly dextrorotatory

Explanation

Each enantiomer rotates plane-polarized light by an equal amount but in opposite directions. In an exactly equal (racemic) mixture, the rotation from one enantiomer exactly cancels the rotation from the other, giving a net optical rotation of zero even though both individual enantiomers are optically active.

Question 9Organic chemistry and macromolecules

Replacing a hydrogen atom on an alkane with a chlorine atom, such as in the radical chlorination of methane to form chloromethane, is an example of which reaction type?

  1. Substitution Correct answer.
  2. Addition
  3. Elimination
  4. Condensation

Explanation

In a substitution reaction, one atom or group in a molecule is replaced by another atom or group without changing the overall degree of saturation. Chlorination of methane replaces a C-H bond with a C-Cl bond, so it is classified as a substitution reaction.

Question 10Organic chemistry and macromolecules

Bromine water (Br2) reacts with an alkene by adding bromine atoms across the C=C double bond. What type of reaction is this?

  1. Addition Correct answer.
  2. Substitution
  3. Elimination
  4. Condensation

Explanation

In an addition reaction, atoms are added across a multiple bond, converting it into a single bond and increasing the saturation of the molecule. Bromine adds across the alkene's C=C double bond to form a dibromo product, which is also used as a simple chemical test for unsaturation because the bromine water is decolorized.

Question 11Organic chemistry and macromolecules

Heating an alcohol with a strong acid catalyst, such as concentrated sulfuric acid, to produce an alkene and water is an example of which reaction type?

  1. Elimination Correct answer.
  2. Addition
  3. Substitution
  4. Radical reaction

Explanation

In this reaction, a hydroxyl group and an adjacent hydrogen atom are removed from the alcohol to form a new C=C double bond, with water released as a byproduct. Removing atoms from adjacent carbons to create a multiple bond is the defining feature of an elimination reaction, here specifically an acid-catalyzed dehydration.

Question 12Organic chemistry and macromolecules

Forming an ester from a carboxylic acid and an alcohol, with water released as a byproduct, is classified as a...

  1. Condensation reaction Correct answer.
  2. Addition reaction
  3. Hydrolysis reaction
  4. Substitution reaction at an sp3 carbon

Explanation

A condensation reaction joins two molecules together while releasing a small molecule, commonly water. Esterification combines a carboxylic acid and an alcohol into an ester, releasing water as the small byproduct, which is the defining pattern of a condensation reaction.

Question 13Organic chemistry and macromolecules

Radical chlorination of methane (CH4 + Cl2 -> CH3Cl + HCl) under UV light proceeds through which type of reactive intermediate?

  1. Free radicals Correct answer.
  2. Carbocations
  3. Carbanions
  4. Nucleophiles that attack the alkane directly

Explanation

UV light homolytically cleaves the Cl-Cl bond, producing two chlorine free radicals, each with a single unpaired electron. These radicals then propagate a chain reaction by abstracting a hydrogen atom from methane and forming new radicals, which is characteristic of a radical substitution mechanism.

Question 14Organic chemistry and macromolecules

According to Hückel's rule, a planar, fully conjugated ring is aromatic if it contains how many pi electrons?

  1. 4n+2 (such as 6 for benzene) Correct answer.
  2. 4n (such as 4 or 8)
  3. Exactly 6, and no other number is ever aromatic
  4. Any even number of pi electrons

Explanation

Hückel's rule states that a planar, fully conjugated ring is aromatic when it contains 4n+2 pi electrons, where n is a non-negative integer. Benzene fits this rule with 6 pi electrons (n=1), but larger aromatic systems can also be aromatic with 10, 14, or more pi electrons as long as they fit the 4n+2 pattern.

Question 15Organic chemistry and macromolecules

All six carbon-carbon bonds in benzene have the same length, intermediate between a typical single and double bond. What best explains this?

  1. Delocalization of the pi electrons evenly around the ring (resonance/mesomerism) Correct answer.
  2. Benzene actually has alternating distinct single and double bonds that simply look similar
  3. Benzene is a fully saturated ring with no double-bond character at all
  4. Each carbon forms one full, fixed double bond that does not interact with its neighbors

Explanation

Benzene's structure is best described not as fixed alternating single and double bonds but as a ring in which the six pi electrons are delocalized evenly over all six carbons. This mesomeric delocalization makes every carbon-carbon bond equivalent, with a bond length and strength intermediate between a pure single and pure double bond.

Question 16Organic chemistry and macromolecules

Nitration of benzene, converting it into nitrobenzene using a mixture of concentrated nitric and sulfuric acid, proceeds by which mechanism?

  1. Electrophilic aromatic substitution Correct answer.
  2. Nucleophilic substitution
  3. Radical substitution
  4. Electrophilic addition across the ring

Explanation

The nitronium ion (NO2+), generated from nitric and sulfuric acid, acts as an electrophile that attacks the electron-rich benzene ring. A hydrogen is then lost to restore the aromatic ring, so the overall process replaces a hydrogen with a nitro group while regenerating full aromaticity, the defining pattern of electrophilic aromatic substitution.

Question 17Organic chemistry and macromolecules

Glucose and fructose are both simple sugars that cannot be broken down into smaller sugar units by hydrolysis. What class of carbohydrate are they?

  1. Monosaccharides Correct answer.
  2. Disaccharides
  3. Polysaccharides
  4. Amino acids

Explanation

Monosaccharides are the simplest carbohydrate units, such as glucose and fructose, and cannot be hydrolyzed into smaller sugars. Disaccharides and polysaccharides, in contrast, are built from two or many monosaccharide units joined by glycosidic bonds.

Question 18Organic chemistry and macromolecules

What is the name of the bond that links two monosaccharide units together to form a disaccharide, such as in sucrose?

  1. A glycosidic bond Correct answer.
  2. A peptide bond
  3. An ester bond
  4. A hydrogen bond

Explanation

A glycosidic bond forms between the anomeric carbon of one monosaccharide and a hydroxyl group of another, releasing a molecule of water in a condensation reaction. This bond is the characteristic linkage joining sugar units in disaccharides and polysaccharides.

Question 19Organic chemistry and macromolecules

In the Fischer projection convention used for sugars, D-glucose is defined by the configuration at the...

  1. Reference stereocenter farthest from the carbonyl group, with its hydroxyl group pointing to the right Correct answer.
  2. Anomeric carbon, which determines the alpha or beta form
  3. Carbonyl carbon itself
  4. Total number of carbon atoms in the chain

Explanation

The D/L designation in the Fischer projection is based on the configuration at the stereocenter farthest from the carbonyl group, the reference carbon. If the hydroxyl group at that carbon points to the right in the standard Fischer projection, the sugar is designated D; if it points left, it is designated L.

Question 20Organic chemistry and macromolecules

Freshly dissolved alpha-D-glucose in water shows a gradually changing optical rotation until it settles at a constant value. This phenomenon, called mutarotation, occurs because...

  1. The alpha and beta anomers interconvert through the open-chain form until an equilibrium mixture is reached Correct answer.
  2. Glucose is slowly and irreversibly converted into fructose
  3. The solution's temperature changes over time, independent of any structural change
  4. The molecule permanently loses all of its chirality once dissolved

Explanation

In solution, the cyclic form of glucose can open back into its open-chain aldehyde form and then re-close, forming either the alpha or beta anomer at the new stereocenter created at the anomeric carbon. This continues until the alpha and beta forms reach a stable equilibrium ratio, and the measured optical rotation shifts gradually to a constant equilibrium value.

Question 21Organic chemistry and macromolecules

A hydrocarbon has the molecular formula C6H10. How many degrees of unsaturation (total rings plus pi bonds) does it have?

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

Explanation

Degrees of unsaturation for a hydrocarbon CxHy can be found from (2x+2-y)/2. For C6H10, this gives (2x6+2-10)/2 = (14-10)/2 = 2, meaning the molecule contains a combination of two rings and/or pi bonds, such as one ring plus one double bond, two double bonds, or a triple bond alone.

Question 22Organic chemistry and macromolecules

Proteins are polymers built from which class of monomer units, linked together by peptide bonds?

  1. Amino acids Correct answer.
  2. Monosaccharides
  3. Nucleotides
  4. Fatty acids

Explanation

Proteins are polypeptide chains formed by linking amino acid monomers through peptide bonds between the carboxyl group of one amino acid and the amino group of the next. The specific sequence of the 20 common amino acids determines a protein's identity and ultimately its three-dimensional structure and function.

Question 23Organic chemistry and macromolecules

What is the name of the bond formed between the carboxyl group of one amino acid and the amino group of the next, releasing a molecule of water?

  1. A peptide bond Correct answer.
  2. A glycosidic bond
  3. An ester bond
  4. An ionic bond

Explanation

A peptide bond is an amide linkage formed in a condensation reaction between the -COOH group of one amino acid and the -NH2 group of another, releasing water. Chains of amino acids joined by peptide bonds make up polypeptides and proteins.

Question 24Organic chemistry and macromolecules

At its isoelectric point, an amino acid exists predominantly in which form?

  1. A zwitterion, with both a protonated amino group and a deprotonated carboxyl group but no overall net charge Correct answer.
  2. A fully protonated cation, with both groups positively charged
  3. A fully deprotonated anion, with both groups negatively charged
  4. A completely neutral molecule with neither group ionized

Explanation

At the isoelectric point, an amino acid's amino group is protonated (-NH3+) and its carboxyl group is deprotonated (-COO-), giving the molecule both a positive and a negative site that exactly balance to a net charge of zero. This dipolar, internally charged but overall neutral form is called a zwitterion.

Question 25Organic chemistry and macromolecules

The folding of a polypeptide chain into regular, repeating patterns such as the alpha-helix or beta-sheet, stabilized mainly by hydrogen bonds along the peptide backbone, describes which level of protein structure?

  1. Secondary structure Correct answer.
  2. Primary structure
  3. Tertiary structure
  4. Quaternary structure

Explanation

Secondary structure refers to the local, regularly repeating folding patterns of a polypeptide backbone, such as the alpha-helix and beta-sheet, held together by hydrogen bonds between backbone carbonyl oxygens and amide hydrogens. This is distinct from the underlying amino acid sequence and from the overall three-dimensional folding of the whole chain.

Question 26Organic chemistry and macromolecules

Heating a protein or exposing it to extreme pH commonly causes denaturation. What does this process typically do to the protein?

  1. Disrupts secondary and tertiary structure (such as hydrogen bonds) without breaking the peptide bonds of the primary sequence Correct answer.
  2. Breaks the peptide bonds and hydrolyzes the protein completely into free amino acids
  3. Has no measurable effect on the protein's structure or function
  4. Changes the underlying amino acid sequence of the protein

Explanation

Denaturation disrupts the weaker interactions that maintain a protein's folded shape, such as hydrogen bonds, ionic interactions, and hydrophobic interactions, causing the protein to unfold and typically lose its biological function. The strong covalent peptide bonds that define the primary amino acid sequence remain intact even though the protein's overall shape is lost.

Question 27Organic chemistry and macromolecules

Triglycerides (fats) are formed by a condensation (ester-forming) reaction between glycerol and which other molecules?

  1. Fatty acids Correct answer.
  2. Amino acids
  3. Monosaccharides
  4. Phosphate groups

Explanation

A triglyceride forms when glycerol, a three-carbon molecule with three hydroxyl groups, reacts with three fatty acid molecules in ester-forming condensation reactions, releasing three molecules of water. The resulting three ester linkages join the fatty acid chains to the glycerol backbone.

Question 28Organic chemistry and macromolecules

Polyethylene is produced by joining many ethene (ethylene) monomers into a long chain without losing any atoms in the process. This is an example of...

  1. Addition polymerization Correct answer.
  2. Condensation polymerization
  3. Hydrolysis polymerization
  4. Substitution polymerization

Explanation

In addition polymerization, monomers containing a double bond, such as ethene, open up their pi bonds and link directly to one another with no atoms lost, building a long saturated chain. This differs from condensation polymerization, where monomers join while releasing a small molecule, typically water, at each linkage.

Question 29Physical chemistry, amounts and reactions

What is the oxidation number of sulfur in the sulfate ion, SO4^2-?

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

Explanation

Each oxygen in the ion is assigned an oxidation number of -2, giving a total of 4 x (-2) = -8 from the four oxygens. Since the overall ion charge is -2, sulfur must contribute +6 so that +6 + (-8) = -2, matching the overall charge.

Question 30Physical chemistry, amounts and reactions

In a redox reaction, oxidation is defined as...

  1. Loss of electrons Correct answer.
  2. Gain of electrons
  3. Loss of protons
  4. Gain of protons

Explanation

Oxidation is defined as the loss of electrons by a species, which corresponds to an increase in that species' oxidation number. The complementary process, reduction, is the gain of electrons and a decrease in oxidation number; together these two processes always occur simultaneously in a redox reaction.

Question 31Physical chemistry, amounts and reactions

How many electrons are transferred when a single aluminum atom (Al) is oxidized to Al^3+?

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

Explanation

Aluminum starts as a neutral atom (oxidation number 0) and is oxidized to Al^3+ (oxidation number +3), a change of three units. This corresponds to the loss of exactly 3 electrons per aluminum atom, matching the half-reaction Al -> Al^3+ + 3e-.

Question 32Physical chemistry, amounts and reactions

In a galvanic (voltaic) cell, at which electrode does oxidation occur?

  1. The anode Correct answer.
  2. The cathode
  3. The salt bridge
  4. The external wire connecting the two half-cells

Explanation

By definition, oxidation always occurs at the anode in any electrochemical cell, whether galvanic or electrolytic. In a galvanic cell, the anode is the negative terminal, where electrons are released into the external circuit as the anode material is oxidized.

Question 33Physical chemistry, amounts and reactions

Given standard reduction potentials Cu2+/Cu = +0.34 V and Zn2+/Zn = -0.76 V, what is the standard cell potential (E° cell) for a galvanic cell in which zinc is oxidized and Cu2+ is reduced?

  1. +1.10 V Correct answer.
  2. +0.42 V
  3. -1.10 V
  4. +1.42 V

Explanation

E°cell = E°cathode - E°anode, where the cathode is the reduction half-reaction (Cu2+/Cu, +0.34 V) and the anode is the oxidation half-reaction (Zn2+/Zn, -0.76 V). This gives E°cell = 0.34 - (-0.76) = 1.10 V, a positive value indicating a spontaneous reaction as written.

Question 34Physical chemistry, amounts and reactions

Based on standard reduction potentials (Li = -3.04 V, Zn = -0.76 V, Cu = +0.34 V, Ag = +0.80 V), which metal is the strongest reducing agent?

  1. Lithium (Li) Correct answer.
  2. Zinc (Zn)
  3. Copper (Cu)
  4. Silver (Ag)

Explanation

The metal with the most negative standard reduction potential is the one most easily oxidized, which makes it the strongest reducing agent. Lithium has by far the most negative reduction potential (-3.04 V) of the four listed, so it is oxidized most readily and is the strongest reducing agent.

Question 35Physical chemistry, amounts and reactions

Using the simplified Nernst equation E = E° - (0.059/n)log(Q) at 25 degrees Celsius, what is the cell potential for a Zn-Cu cell (E° = 1.10 V, n = 2) when Q = 100 (so log Q = 2)?

  1. About 1.04 V Correct answer.
  2. 1.10 V (unchanged)
  3. About 1.16 V
  4. About 0.98 V

Explanation

Substituting into the Nernst equation gives E = 1.10 - (0.059/2) x 2 = 1.10 - 0.059 = 1.041 V, which rounds to approximately 1.04 V. Because Q is greater than 1 here, the cell potential is slightly lower than the standard value, consistent with the Nernst correction reducing the driving force as the reaction proceeds away from standard conditions.

Question 36Physical chemistry, amounts and reactions

A concentration cell is built using the same metal and ion in both half-cells, but at different concentrations. Why does this cell generate a voltage?

  1. The system has a spontaneous tendency to move toward equal concentrations, which drives electron flow through the external circuit Correct answer.
  2. Two different metals are used, creating a large electrode potential difference
  3. Standard conditions (1 mol/L) are maintained in both half-cells at all times
  4. One half-cell contains no ions of the metal at all

Explanation

Even with identical electrodes and ions, a concentration difference between the two half-cells creates a driving force, described by the Nernst equation, for the system to move toward equilibrium by equalizing the concentrations. This drives oxidation in the more dilute half-cell and reduction in the more concentrated half-cell, generating a measurable voltage that would be zero if both concentrations were equal.

Question 37Physical chemistry, amounts and reactions

Electrolysis is a process that uses electrical energy from an external source to drive a...

  1. Non-spontaneous redox reaction Correct answer.
  2. Spontaneous redox reaction
  3. Reaction that would occur without any energy input at all
  4. Purely physical change with no chemical reaction involved

Explanation

Electrolysis forces a redox reaction to occur that would not happen on its own (a non-spontaneous reaction) by supplying electrical energy from an external power source. This is the opposite situation from a galvanic cell, which generates electrical energy from a spontaneous redox reaction.

Question 38Physical chemistry, amounts and reactions

How many moles of electrons are required to electroplate 0.10 mol of Cu2+ ions into solid copper metal, according to Cu2+ + 2e- -> Cu?

  1. 0.20 mol Correct answer.
  2. 0.10 mol
  3. 0.05 mol
  4. 0.40 mol

Explanation

The half-reaction shows that each Cu2+ ion requires 2 electrons to be reduced to solid copper. For 0.10 mol of Cu2+, the moles of electrons needed are therefore 0.10 mol x 2 = 0.20 mol.

Question 39Physical chemistry, amounts and reactions

Using Faraday's constant (F is approximately 96,500 C per mole of electrons), how much electric charge is needed to supply 0.20 mol of electrons during electrolysis?

  1. 19,300 C Correct answer.
  2. 96,500 C
  3. 9,650 C
  4. 48,250 C

Explanation

The total charge is found by multiplying the moles of electrons by Faraday's constant: Q = n x F = 0.20 mol x 96,500 C/mol = 19,300 C.

Question 40Physical chemistry, amounts and reactions

In an electrolytic cell (a cell driven by an external power source), the cathode is...

  1. The electrode connected to the negative terminal of the power source, where reduction occurs Correct answer.
  2. Always positively charged, regardless of how the cell is set up
  3. The electrode where oxidation takes place
  4. Not connected to the external circuit at all

Explanation

In an electrolytic cell, the external power source pushes electrons into the cathode, which is connected to its negative terminal, driving reduction at that electrode. This is different from a galvanic cell, where the cathode is spontaneously positive; the labels anode and cathode are always defined by which half-reaction (oxidation or reduction) occurs there, not by a fixed charge sign.

Question 41Physical chemistry, amounts and reactions

A rechargeable battery (accumulator), such as a lead-acid battery, differs from a non-rechargeable (primary) battery because its electrode reactions...

  1. Can be reversed by applying an external electrical current, regenerating the original reactants Correct answer.
  2. Never involve any redox chemistry at all
  3. Use only inert electrodes that never react chemically
  4. Produce no electrical current under any conditions

Explanation

In a rechargeable battery, the discharge (spontaneous, galvanic) reaction can be driven backward by applying an external current during charging, essentially running the cell as an electrolytic cell to regenerate the original reactants. A primary (non-rechargeable) battery's reaction products cannot practically be converted back once the reactants are consumed.

Question 42Physical chemistry, amounts and reactions

A hydrogen-oxygen fuel cell generates electrical energy by...

  1. Continuously reacting hydrogen and oxygen fuel supplied from outside the cell, producing water Correct answer.
  2. Consuming a fixed internal supply of metal electrodes that eventually runs out
  3. Using only physical (non-chemical) processes to store and release charge
  4. Converting electrical energy into hydrogen and oxygen gas

Explanation

A fuel cell is continuously supplied with fuel (hydrogen) and an oxidant (oxygen) from external tanks, and it produces electrical energy through the redox reaction between them, generating water as the main product. Unlike a typical battery, the fuel cell itself does not store the reactants internally; it keeps generating power as long as fuel and oxidant continue to be supplied.

Question 43Physical chemistry, amounts and reactions

Rusting of iron is an electrochemical process. In this process, iron metal is...

  1. Oxidized to Fe2+ or Fe3+, while dissolved oxygen is reduced in the presence of water Correct answer.
  2. Reduced by atmospheric oxygen
  3. Unaffected by the presence of water at the metal surface
  4. Dissolved through a purely physical process with no electron transfer at all

Explanation

In rusting, iron metal loses electrons and is oxidized to iron ions (Fe2+, later further oxidized to Fe3+ in hydrated iron oxide), while dissolved oxygen at the metal surface is reduced, typically in a reaction that also involves water. This coupled oxidation-reduction process is why rusting is classified as an electrochemical (corrosion) reaction rather than a simple physical change.

Question 44Physical chemistry, amounts and reactions

Attaching a block of zinc metal to a steel ship hull to prevent rusting is an application of which corrosion-prevention strategy?

  1. Cathodic protection using a sacrificial anode Correct answer.
  2. Directly increasing the iron's own standard reduction potential
  3. Insulating the hull completely from all contact with water
  4. A purely mechanical barrier coating with no electrochemical component

Explanation

Zinc has a more negative standard reduction potential than iron, so it is oxidized preferentially, acting as a sacrificial anode that is consumed instead of the iron hull. Because the iron is thereby forced to act as the protected cathode, this technique is known as cathodic protection.

Question 45Physical chemistry, amounts and reactions

In the reaction Zn + Cu2+ -> Zn2+ + Cu, which species is reduced?

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

Explanation

Cu2+ gains two electrons to become neutral Cu metal, which is a decrease in oxidation number (from +2 to 0) and therefore a reduction. Meanwhile, Zn loses two electrons to become Zn2+, which is the paired oxidation half-reaction.

Question 46Physical chemistry, amounts and reactions

To balance the redox reaction Fe2+ + MnO4- -> Fe3+ + Mn2+ (in acidic solution) for electron transfer, given that Mn goes from +7 to +2 (a 5-electron change) and Fe goes from +2 to +3 (a 1-electron change), how many Fe2+ ions must react per MnO4- ion?

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

Explanation

Each MnO4- ion gains 5 electrons as manganese is reduced from +7 to +2, while each Fe2+ ion loses only 1 electron as it is oxidized to Fe3+. To balance the total electrons lost and gained, 5 Fe2+ ions must react for every 1 MnO4- ion, matching the well-known permanganate titration stoichiometry.

Question 47Physical chemistry, amounts and reactions

A reaction between a metal and a metal ion, written in a particular direction, is spontaneous when the calculated standard cell potential (E° cell) is...

  1. Positive Correct answer.
  2. Negative
  3. Exactly zero
  4. Unrelated to whether the reaction is spontaneous

Explanation

A positive E°cell indicates that the reaction as written is thermodynamically favorable (spontaneous) under standard conditions, which is directly linked to a negative standard Gibbs free energy change (ΔG° = -nFE°cell). A negative E°cell instead indicates that the reverse reaction is the spontaneous one.

Question 48Physical chemistry, amounts and reactions

In the reaction Cu + 2Ag+ -> Cu2+ + 2Ag, how many moles of Ag+ are reduced when 0.05 mol of Cu is oxidized to Cu2+?

  1. 0.10 mol Correct answer.
  2. 0.05 mol
  3. 0.025 mol
  4. 0.20 mol

Explanation

The balanced equation shows that each mole of Cu reacts with 2 moles of Ag+. For 0.05 mol of Cu oxidized, the moles of Ag+ reduced are therefore 0.05 mol x 2 = 0.10 mol.

Question 49Physical chemistry, amounts and reactions

According to the Brønsted-Lowry theory, an acid is defined as a substance that...

  1. Donates a proton (H+) to another substance Correct answer.
  2. Accepts a proton (H+) from another substance
  3. Donates a pair of electrons to form a new bond
  4. Accepts a pair of electrons to form a new bond

Explanation

The Brønsted-Lowry theory defines an acid as a proton donor and a base as a proton acceptor. This definition focuses on proton transfer between substances, rather than on electron-pair donation or acceptance, which instead describes the Lewis acid-base theory.

Question 50Physical chemistry, amounts and reactions

What is the conjugate base formed when water (H2O) donates a proton?

  1. OH- (hydroxide ion) Correct answer.
  2. H3O+ (hydronium ion)
  3. O2- (oxide ion)
  4. H2O2 (hydrogen peroxide)

Explanation

When water acts as a Brønsted-Lowry acid and donates one proton (H+), it loses one hydrogen, leaving the hydroxide ion, OH-. The conjugate base of any acid always has one fewer proton and one more unit of negative charge than the original acid.