Acids and Bases UPCAT Reviewer: Lesson and Practice

TEACHER ABI UPCAT SCIENCE

Acids and Bases

Translate between particle behavior, pH evidence, and reaction quantities without confusing strength and concentration.

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Acid–base questions connect proton transfer, concentration, and a logarithmic scale

A Brønsted–Lowry acid donates H+; a base accepts H+. At 25°C, pH+pOH=14. Each pH unit represents a tenfold change in hydrogen-ion concentration.

pH=−log[H⁺]pOH=−log[OH⁻]At 25°C: pH+pOH=14

Strength versus concentration

Strength is degree of ionization; concentration is amount of solute per volume.

Use evidence carefully

Indicators give ranges, conductivity reflects mobile ions, and pH alone does not identify a substance or guarantee safety.

DO IT FAST

Classify → compare powers of ten → use the reaction ratio

Problem: Compare pH 3 and pH 5.

Recognize: pH is logarithmic; the difference is 2 units.

Do it fast: 10²=100, so the pH 3 solution has 100 times greater [H⁺].

Why it works

This sequence handles conceptual, logarithmic, and neutralization questions without treating pH as an ordinary linear scale.

WORKED EXAMPLES

Five forms you should recognize

1. pH from concentration

[H+]=10⁻⁴ M gives pH 4.

2. Tenfold change

A one-unit pH decrease means ten times greater [H+].

3. Neutralization

H+ and OH− form water; remaining ions form a salt.

4. Strength

A weak acid partially ionizes; it can still be concentrated.

5. Buffer

A weak acid/conjugate base pair resists large pH changes.

COMMON TRAPS

Check before you commit

• Treating pH as linear
• Calling every concentrated acid strong
• Assuming neutralization removes all ions
• Confusing endpoint and exact equivalence
• Forgetting solution volumes in titration
• Using pH alone to judge safety

FIVE-FORM SKILL CHECK

Do you need the lesson-or just practice?

One original question in each form recommends your next step. It does not yet verify mastery.

CHOOSE YOUR PRACTICE

Work at the level you need.

Foundations

Build the core procedure with immediate explanations.

Core Practice

Use mixed forms with less scaffolding.

UPCAT-Style Transfer

Apply the competency in unfamiliar representations.

FRESH MASTERY CHECK

Ready to verify this competency?

A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.

QUICK ANSWERS

Acids and Bases FAQ

Is pH 2 twice as acidic as pH 4?

No. Its hydrogen-ion concentration is about 100 times greater.

Are weak acids harmless?

No. “Weak” describes ionization equilibrium, not concentration or safety.

RELATED COMPETENCIES

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SolutionsChemical ReactionsEquilibrium

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Chemical Bonding UPCAT Reviewer: Lesson and Practice

TEACHER ABI UPCAT SCIENCE

Chemical Bonding

Infer bonding from electron behavior and observable properties.

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Connect electron behavior to structure, then connect structure to properties

Ionic bonding: electron transfer produces oppositely charged ions held in a lattice. Covalent bonding: atoms share electron pairs; the result may be separate molecules or a continuous network. Metallic bonding: delocalized electrons move through a lattice of metal particles.

Need the quick foundation?

Valence electrons are the outer electrons involved in bonding. Bond type is a model for what happens to these electrons. Observable properties—conductivity, melting point, brittleness, malleability, and solubility—provide evidence for the model.

Do not classify from one clue alone. For example, both ionic and network covalent solids can have high melting points.

Use composition

Metal + nonmetal often suggests ionic; nonmetal + nonmetal often suggests covalent. This predicts the likely bond type but is not the only evidence.

Use properties

Ask what particles carry charge, whether they can move, and how strongly the particles are held together.

DO IT FAST

Read every property as evidence about particles

Problem: A brittle high-melting solid conducts electricity when molten but not when solid.

Recognize each clue:

• High melting point: strong attractions hold charged particles in a rigid lattice, so much energy is needed to separate them.
• Brittle: when lattice layers shift, ions with the same charge can line up, repel, and split the crystal.
• No conduction as a solid: ions are charged, but they are locked in fixed positions.
• Conduction when molten: melting frees the ions to move and carry electric charge.

Do it fast: All four clues fit an ionic compound. Do not rely on “high melting point” alone; use the entire pattern.

Why it works

A formula gives an initial prediction, while physical properties reveal whether the material actually contains fixed ions, mobile electrons, or separate molecules.

WORKED EXAMPLES

Five forms you should recognize

1. Why NaCl is ionic

Sodium loses one valence electron to form Na⁺; chlorine gains it to form Cl⁻. Opposite charges attract throughout a crystal lattice.

2. Why molten salt conducts

Solid salt already contains charged ions, but they are locked in place. Melting frees the ions to move and carry charge.

3. Why water is polar

Each O–H bond is polar. Because H₂O is bent, the two bond dipoles do not cancel, leaving a net molecular dipole.

4. Why CO₂ is nonpolar

Its C=O bonds are polar, but the molecule is linear and symmetric. Equal, opposite dipoles cancel.

5. Why boiling points differ

Boiling separates molecules rather than breaking their internal covalent bonds. Stronger intermolecular attractions therefore require a higher temperature.

COMMON TRAPS

Check before you commit

• Calling every polar bond ionic
• Saying electrons are shared in ionic bonding
• Expecting solid salts to conduct
• Confusing bonds with intermolecular forces
• Counting all electrons as valence electrons
• Using one property as absolute proof

FIVE-FORM SKILL CHECK

Do you need the lesson-or just practice?

One original question in each form recommends your next step. It does not yet verify mastery.

CHOOSE YOUR PRACTICE

Work at the level you need.

Foundations

Build the core procedure with immediate explanations.

Core Practice

Use mixed forms with less scaffolding.

UPCAT-Style Transfer

Apply the competency in unfamiliar representations.

FRESH MASTERY CHECK

Ready to verify this competency?

A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.

QUICK ANSWERS

Chemical Bonding FAQ

Why does solid NaCl not conduct if it contains charged ions?

Its ions are locked in the crystal lattice. Charge can flow only when the ions become mobile, such as after melting or dissolving in water.

Why are many ionic solids brittle?

A force can shift lattice layers so that like charges face one another. Their repulsion can split the crystal.

Are all metal–nonmetal compounds perfectly ionic?

Bonding exists on a continuum, but introductory classification uses dominant character.

Why do metals bend without shattering?

Metallic bonding is nondirectional, allowing layers to shift while attraction through delocalized electrons remains.

RELATED COMPETENCIES

Continue your science review.

Periodic TrendsAtomic StructureChemical Reactions

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Stoichiometric Mole Ratios UPCAT Reviewer: Lesson and Practice

TEACHER ABI UPCAT SCIENCE

Stoichiometric Mole Ratios

Turn balanced coefficients into conversion factors without guessing proportions.

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Balance, convert to moles, apply the ratio, then convert to the requested unit

Balanced coefficients represent particle and mole relationships—not gram relationships. A complete setup follows the units:

given unit → moles of given substance× coefficient ratio (wanted/given)→ requested unit

When two reactants are supplied, calculate how much product each could make. The smaller result identifies the limiting reactant.

Balance first

Never take a mole ratio from an unbalanced equation.

Units guide the setup

Arrange the conversion factor so the starting unit cancels.

DO IT FAST

Given × wanted/given

Write the given moles, then multiply by a coefficient fraction with the wanted substance on top and the given substance below.

Why it works

The balanced coefficients describe proportional amounts, so the conversion factor equals one reaction-scale relationship.

WORKED EXAMPLES

Five forms you should recognize

1. Mole ratio

For N₂+3H₂→2NH₃:

6 mol H₂ × 2 mol NH₃ / 3 mol H₂ = 4 mol NH₃

2. Mass to mass

For 2H₂+O₂→2H₂O, 4 g H₂ is 2 mol H₂. The 2:2 ratio gives 2 mol H₂O, or 36 g.

3. Limiting reactant

For N₂+3H₂→2NH₃, 2 mol N₂ need 6 mol H₂. If only 3 mol H₂ are present, H₂ limits production to 2 mol NH₃.

4. Excess reactant

For 2H₂+O₂→2H₂O, 2 mol O₂ consume 4 mol H₂. Starting with 5 mol H₂ leaves 1 mol.

5. Percent yield

If theory predicts 25 g but the experiment obtains 20 g:

percent yield=20/25×100%=80%

COMMON TRAPS

Check before you commit

• Using subscripts as mole ratios
• Using an unbalanced equation
• Putting the conversion factor upside down
• Treating coefficients as gram ratios
• Skipping the grams-to-moles step
• Rounding too early

FIVE-FORM SKILL CHECK

Do you need the lesson-or just practice?

One original question in each form recommends your next step. It does not yet verify mastery.

CHOOSE YOUR PRACTICE

Work at the level you need.

Foundations

Build the core procedure with immediate explanations.

Core Practice

Use mixed forms with less scaffolding.

UPCAT-Style Transfer

Apply the competency in unfamiliar representations.

FRESH MASTERY CHECK

Ready to verify this competency?

A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.

QUICK ANSWERS

Stoichiometric Mole Ratios FAQ

Do coefficients give volume ratios?

For gases at the same temperature and pressure, coefficients can also represent volume ratios.

When do I use molar mass?

Use it when converting between grams and moles, not for a pure mole-to-mole conversion.

RELATED COMPETENCIES

Continue your science review.

Balancing EquationsMole ConceptLimiting Reactants

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Periodic Trends UPCAT Reviewer: Lesson and Practice

TEACHER ABI UPCAT SCIENCE

Periodic Trends

Use direction and cause—not three unrelated arrows—to compare elements.

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Position predicts general patterns

Atomic radius increases down and left. Ionization energy and electronegativity generally increase up and right.

Across a period, nuclear charge increases while electrons enter the same principal energy level. Down a group, new energy levels and shielding place valence electrons farther from the nucleus.

Atomic radius

Generally increases down a group and toward the left.

Ionization energy and electronegativity

Generally increase up a group and toward the right.

DO IT FAST

Radius runs down-left; attraction runs up-right

If atoms hold or attract electrons strongly, think up-right. If the electron cloud is physically larger, think down-left.

Why it works

Smaller, less-shielded atoms generally exert a stronger attraction on valence or bonding electrons.

WORKED EXAMPLES

Five forms you should recognize

1. Na vs Cl

Na is larger; Cl generally has higher ionization energy and electronegativity.

2. Li vs K

K is larger; Li has higher ionization energy.

3. F vs Cl

F is more electronegative because it is higher in the group.

4. Across a period

Effective nuclear charge rises without adding a new principal shell, so radius generally falls.

5. Down a group

Additional shells increase distance and shielding, so radius rises.

COMMON TRAPS

Check before you commit

• Reversing the radius arrow
• Using atomic mass alone
• Forgetting that trends are general patterns
• Assuming more protons always means a larger atom
• Combining across-period and down-group reasoning incorrectly
• Ignoring shielding

FIVE-FORM SKILL CHECK

Do you need the lesson-or just practice?

One original question in each form recommends your next step. It does not yet verify mastery.

CHOOSE YOUR PRACTICE

Work at the level you need.

Foundations

Build the core procedure with immediate explanations.

Core Practice

Use mixed forms with less scaffolding.

UPCAT-Style Transfer

Apply the competency in unfamiliar representations.

FRESH MASTERY CHECK

Ready to verify this competency?

A score of 5/5 verifies mastery. An unsuccessful attempt loads a different five-form bank.

QUICK ANSWERS

Periodic Trends FAQ

Are there exceptions?

Yes. Electron configuration creates exceptions, especially in detailed ionization-energy comparisons.

Why exclude noble-gas electronegativity in basic comparisons?

Many introductory scales do not assign conventional values because noble gases rarely form bonds.

RELATED COMPETENCIES

Continue your science review.

Atomic StructureElectron ConfigurationChemical Bonding

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