Chem Lab Final ALL VERSIONS 2025 | LATEST AND ACCURATE REAL EXAM QUESTIONS WITH DETAILED ANSWERS | VERIFIED FOR GUARANTEED PASS | LATEST UPDATE

What are the different colors caused by that we can see in the flame test? A. Heating of metal atoms B. Presence of carbon dioxide C. Electrons falling back into their original shell D. Increase in temperature of the flame Correct answer: C Rationale: The different flame colors occur because electrons absorb energy, get excited to a higher shell, and emit specific light wavelengths when falling back to their original shell. Chlorine is part of the Halogens, or salt formers. How many valence electrons does sodium have when forming an ionic bond with chlorine? A. 1 B. 7 C. 0 D. 8 Correct answer: D Rationale: Sodium transfers its 1 valence electron to chlorine, completing chlorine’s octet, making both ions have 8 valence electrons in their outer shell. Based on their periodic table location, what do cesium and chlorine react to form? A. CsCl B. CsO C. Cl₂ D. ClCs₂ Correct answer: A Rationale: Cesium is an alkali metal and chlorine is a halogen; they combine in a 1:1 ratio to form CsCl through ionic bonding. Which group of elements have a full octet of electrons? A. Alkali metals B. Halogens C. Transition metals D. Noble gases Correct answer: D Rationale: Noble gases have full valence shells (8 electrons), making them chemically stable and unreactive. What is a likely oxidation state of chlorine? A. +2 B. +1 C. -1 D. 0 Correct answer: C Rationale: Chlorine typically gains 1 electron in reactions, resulting in a -1 oxidation state. What is the reason for an increasing atomic radius within a group? A. Increase in proton number B. Decrease in shielding effect C. Increase in number of electron shells D. Decrease in electron repulsion Correct answer: C Rationale: As you move down a group, atoms gain more electron shells, increasing atomic radius. What is the reason for a decreasing atomic radius across a period? A. Increase in electron shells B. Decrease in nuclear charge C. Increase in number of protons D. More isotopes Correct answer: C Rationale: More protons attract electrons more strongly, pulling the electron cloud closer and reducing atomic size. When moving from left to right across a period, ionization energy increases. What causes this trend? A. Increase in atomic radius B. Decrease of atomic radius C. Increase in shielding D. Decrease in electron affinity Correct answer: B Rationale: A smaller atomic radius means electrons are held more tightly, requiring more energy to remove one. What does the atomic number represent? A. Number of neutrons B. Number of energy levels C. Number of electrons in the outer shell D. Number of protons Correct answer: D Rationale: Atomic number equals the number of protons, which defines the element. What does the green color on the periodic table represent? A. Transition metals B. Metalloids C. Non-metals D. Halogens Correct answer: C Rationale: In many periodic table color codes, green indicates non-metals, which include elements like oxygen and nitrogen. Elements in the same group as krypton have what in common? A. Same atomic mass B. Same number of energy levels C. Same number of valence electrons D. Same melting point Correct answer: C Rationale: Elements in the same group have the same number of valence electrons, determining their chemical properties. Which element has the lowest electronegativity? A. Chlorine B. Hydrogen C. Francium D. Oxygen Correct answer: C Rationale: Francium, an alkali metal, has the lowest tendency to attract electrons due to its large size and low nuclear charge. Which equation is needed to find the number of moles of NH₄Cl solution? A. m = n × M B. n = C × V C. V = M × n D. n = M / m Correct answer: B Rationale: The formula n = C × V relates moles (n) to concentration (C) and volume (V). How do you convert from moles (n) to mass (m)? A. m = V / n B. m = n / M C. m = n × M D. m = M / V Correct answer: C Rationale: To find mass, multiply the number of moles by the molar mass: m = n × M. What is the first step before weighing with a balance? A. Place the substance directly B. Close the balance C. Tare the balance with the dish on D. Calibrate the scale Correct answer: C Rationale: Taring ensures that only the substance's weight is measured, excluding the container. Why is the volumetric flask the right choice? A. Easy to carry B. Mixes gas solutions better C. Ideal for precise volume measurement and mixing D. Wide neck for fast pouring Correct answer: C Rationale: Volumetric flasks are used for preparing precise concentrations due to their narrow neck and calibration mark. How accurate is the concentration of the solution right after preparation? A. Very accurate B. Slightly accurate C. Highly precise D. Really inaccurate Correct answer: D Rationale: Until all the solute dissolves completely and the volume is correctly adjusted, the concentration is uncertain. What should you do if you add too much solvent when filling the volumetric flask? A. Remove the excess B. Heat to evaporate C. Start over D. Stir and record Correct answer: C Rationale: Once you exceed the calibration line, the solution’s concentration is altered and must be restarted. How do we count atoms and molecules if they’re too small to see? A. By using microscopes B. By volume C. By mass D. By color Correct answer: C Rationale: Counting is done using mass and molar relationships, such as using grams and moles. Where do you find the most particles among sand grains, water molecules, and iron atoms? A. In water B. In iron C. In sand D. Roughly the same amount in all Correct answer: D Rationale: At the molecular level, a similar number of particles can be present in equal masses of different substances. Why is demineralized water important? A. It tastes better B. It evaporates faster C. It contains no impurities D. It doesn’t contain minerals Correct answer: D Rationale: Demineralized water lacks ions that could interfere with chemical reactions or measurements. How can we ensure all chloride ions precipitate during gravimetric analysis? A. By heating the solution B. By using pure water C. By having excess silver ions D. By stirring more Correct answer: C Rationale: Excess silver ions guarantee that all chloride reacts to form a precipitate. How many moles of AgNO₃ should there be relative to alkaline earth metal chloride? A. Half as many B. Equal C. Twice as many D. Four times as many Correct answer: C Rationale: Each XCl₂ reacts with 2 moles of AgNO₃, so twice the amount is needed stoichiometrically. How many moles of AgNO₃ should be used to ensure excess for any of the three compounds? A. 0.050 mol B. 0.075 mol C. 0.100 mol D. 0.200 mol Correct answer: C Rationale: 0.100 mol is a safe excess amount regardless of the identity of the unknown compound. What is the molar ratio between AgNO₃ and AgCl formed? A. 1:2 B. 1:1 C. 2:1 D. 1:3 Correct answer: B Rationale: One mole of AgNO₃ yields one mole of AgCl in a typical precipitation reaction. Which compound is most likely formed if the experimental yield exceeds 90%? A. BaCl₂ B. CaCl₂ C. MgCl₂ D. SrCl₂ Correct answer: C Rationale: A high yield suggests MgCl₂, which forms a predictable precipitate under standard lab conditions. Which of the following is NOT a valid reason for a yield below 100%? A. Loss during transfer B. Side reactions C. Impure reactants D. Product not completely dry Correct answer: D Rationale: Incomplete drying affects mass, but it would falsely increase the yield, not