D425 Introduction to Chemistry - Set 1 - Part 1

Correct Answer: Evaporation process

Option c is correct because evaporation removes water as vapor while leaving dissolved salt crystals behind, effectively separating both components without chemical change.
Option a is incorrect because magnetic separation only works with magnetic materials like iron filings, not dissolved salts in solution.
Option b is incorrect because filtration separates solids from liquids but cannot separate dissolved substances like salt from water.
Option d is incorrect because sieving separates particles by size but cannot separate dissolved salt molecules from water.

Correct Answer: Physical change

Option b is correct because dissolving sugar involves physical dispersion of molecules without changing chemical composition or creating new substances.
Option a is incorrect because chemical reactions create new substances with different properties, while dissolved sugar retains its chemical identity.
Option c is incorrect because nuclear transformations involve changes to atomic nuclei, not the simple mixing of substances at molecular level.
Option d is incorrect because combustion requires oxygen and produces new substances through burning, unlike simple dissolution in liquid.

Correct Answer: Density differences

Option c is correct because oil has lower density than water, causing it to float, while detergent acts as surfactant bridging both.
Option a is incorrect because neither oil nor water exhibits magnetic properties that would cause separation or floating behavior in normal conditions.
Option b is incorrect because electrical conductivity doesn't determine whether substances float or sink relative to each other in mixtures.
Option d is incorrect because color variations are visual properties that don't influence physical positioning of liquids in gravitational field.

Correct Answer: Standardized units

Option b is correct because standardized units like seconds and Celsius ensure consistent communication and comparison of results globally.
Option a is incorrect because personal preference in measurement would lead to inconsistent data that cannot be compared or verified scientifically.
Option c is incorrect because equipment brand doesn't matter if measurements use same standardized units and proper calibration procedures.
Option d is incorrect because laboratory location is irrelevant when using standardized measurement systems that work identically everywhere on Earth.

Correct Answer: Electrons control bonding

Option b is correct because outer electrons participate in chemical bonds and reactions, determining how atoms interact with others.
Option a is incorrect because atomic mass primarily affects physical properties like density, not chemical reactivity or bonding behavior patterns.
Option c is incorrect because neutrons contribute to mass and stability but don't directly participate in chemical reactions or bonding.
Option d is incorrect because atomic size influences some properties but electron configuration is the primary determinant of chemical behavior.

Correct Answer: Electronegativity differences

Option b is correct because electronegativity differences determine electron transfer direction, with less electronegative atoms losing electrons to more electronegative ones.
Option a is incorrect because atomic mass doesn't determine electron transfer tendency or the direction of electron movement in bonding.
Option c is incorrect because nuclear size alone doesn't determine electron transfer, though it influences electronegativity and atomic properties.
Option d is incorrect because neutron count affects isotope mass and stability but doesn't influence electron transfer in chemical bonding.

Correct Answer: Similar nonmetals together

Option b is correct because nonmetals with similar electronegativity share electrons equally or nearly equally in covalent bonds.
Option a is incorrect because metals typically form metallic bonds with delocalized electrons rather than localized covalent bonds between atoms.
Option c is incorrect because metals and nonmetals usually form ionic bonds due to large electronegativity differences causing electron transfer.
Option d is incorrect because noble gases rarely form bonds due to their stable electron configurations and low chemical reactivity.

Correct Answer: Stoichiometric calculations possible

Option b is correct because moles provide a counting unit linking mass to particle numbers, enabling precise reaction calculations.
Option a is incorrect because the mole concept eliminates guesswork by providing exact mathematical relationships between mass and particle count.
Option c is incorrect because visual appearance cannot determine particle numbers or masses needed for quantitative chemical reaction predictions.
Option d is incorrect because while temperature affects reactions, the mole concept works independently of temperature for counting particles.

Correct Answer: Mass conservation law

Option b is correct because mass conservation requires equal numbers of each atom type before and after chemical reactions.
Option a is incorrect because while energy is conserved, balancing equations specifically addresses atom counts and mass, not energy changes.
Option c is incorrect because volume can change during reactions and isn't conserved, especially with gases or phase changes.
Option d is incorrect because color is a physical property that often changes in reactions and isn't a conservation principle.

Correct Answer: Coefficient ratios

Option b is correct because coefficients in balanced equations show mole ratios between reactants and products for calculations.
Option a is incorrect because subscripts indicate atoms per molecule and cannot be changed when balancing equations or calculating yields.
Option c is incorrect because element symbols identify substances but don't provide quantitative relationships needed for stoichiometric calculations.
Option d is incorrect because state symbols indicate physical states like solid or gas but don't show numerical relationships.

Correct Answer: Stirring and temperature

Option b is correct because stirring increases particle collisions while higher temperature provides more kinetic energy for dissolution.
Option a is incorrect because container shape doesn't affect dissolution rate, only the mixing pattern and surface area exposure.
Option c is incorrect because light exposure doesn't significantly affect dissolution of most substances under normal laboratory conditions.
Option d is incorrect because magnetic fields don't influence dissolution unless dealing with magnetic materials, which is extremely rare.

Correct Answer: Neutralization reaction

Option b is correct because acids and bases neutralize each other, typically producing salt and water as products.
Option a is incorrect because decomposition involves breaking down one compound into simpler substances, not combining acid with base.
Option c is incorrect because combustion requires oxygen and fuel producing carbon dioxide and water, not acid-base interaction.
Option d is incorrect because while neutralization combines substances, it specifically involves acid-base reaction producing characteristic products.

Correct Answer: Concentrations remain constant

Option b is correct because at equilibrium, formation and consumption rates balance, maintaining constant concentrations despite ongoing reactions.
Option a is incorrect because reactions continue in both directions at equilibrium, just at equal rates with no net change.
Option c is incorrect because products remain present at equilibrium in constant concentration determined by equilibrium constant value.
Option d is incorrect because reactants persist at equilibrium unless the equilibrium constant extremely favors products, which is rare.

Correct Answer: Speed increases significantly

Option b is correct because temperature directly relates to average kinetic energy, causing particles to move faster when heated.
Option a is incorrect because gas particles never stop moving completely, even at extremely low temperatures approaching absolute zero.
Option c is incorrect because individual gas particles don't change size with temperature, only their speed and kinetic energy.
Option d is incorrect because particle number remains constant in closed systems regardless of temperature changes or energy input.

Correct Answer: Similar electron configuration

Option d is correct because elements in same group have similar outer electron arrangements determining their chemical properties.
Option a is incorrect because atomic mass increases down a group but isn't same for elements in vertical columns.
Option b is incorrect because neutron numbers vary significantly within groups and don't determine chemical similarity or reactivity.
Option c is incorrect because proton count defines different elements, so same column elements must have different proton numbers.

Correct Answer: Molar mass

Option b is correct because molar mass provides the conversion factor between grams and moles for any substance.
Option a is incorrect because density relates mass to volume but doesn't directly convert between grams and moles.
Option c is incorrect because volume isn't needed for gram to mole conversions unless working with gases or solutions.
Option d is incorrect because temperature doesn't affect the gram to mole conversion ratio for a given substance.

Correct Answer: Aufbau principle

Option c is correct because the Aufbau principle states electrons fill lowest available energy orbitals first for stability.
Option a is incorrect because orbital filling follows energy levels and quantum rules, not alphabetical or arbitrary ordering systems.
Option b is incorrect because electron filling follows specific rules and energy considerations, not random placement in orbitals.
Option d is incorrect because orbital size isn't the determining factor; energy level determines the filling order sequence.

Correct Answer: Calculate theoretical yields

Option b is correct because comparing theoretical yields from each reactant's complete consumption identifies the limiting reactant.
Option a is incorrect because mass alone doesn't determine limiting reactant; mole ratios and stoichiometry are crucial factors.
Option c is incorrect because smallest mass doesn't necessarily limit; stoichiometric ratios determine which reactant runs out first.
Option d is incorrect because cost has no bearing on chemical limitations; only mole ratios and amounts determine limits.

Correct Answer: Electron pair repulsion

Option b is correct because electron pairs repel each other, arranging themselves to minimize repulsion and determine molecular shape.
Option a is incorrect because molecular geometry follows physical forces and electron interactions, not arbitrary alphabetical arrangements or naming.
Option c is incorrect because molecular shapes are highly predictable based on electron arrangements, not random three-dimensional orientations.
Option d is incorrect because gravitational forces are negligible at molecular scale compared to electromagnetic forces between electrons.

Correct Answer: Particles gain movement

Option b is correct because added energy allows particles to overcome some intermolecular forces and move more freely.
Option a is incorrect because molecules remain intact during phase changes; only their arrangement and movement patterns change.
Option c is incorrect because atoms retain their identity during physical changes like melting; no chemical change occurs.
Option d is incorrect because mass is conserved during phase changes; only density and volume may change significantly.