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The TX PACT 740 exam has 125 questions and runs 3 hours 45 minutes.
These 10 free TX PACT 740 questions are organized by exam domain, so you can see how each part of the TX PACT: Chemistry: Grades 7-12 (740) blueprint is tested. Reveal the answer and explanation under each question.
During a laboratory activity, a dilute acid solution splashes onto a student's forearm. Which action should the teacher direct the student to take FIRST?
Correct answer: A - Flush the affected area with large amounts of running water
A student measures the density of an aluminum sample four times and records 2.44, 2.46, 2.45, and 2.45 g/cm³. The accepted density of aluminum is 2.70 g/cm³. Which conclusion is BEST supported by these data?
Correct answer: B - The measurements are precise but not accurate, indicating systematic error
A student states that the kinetic molecular theory will eventually become a scientific law once enough evidence supports it. Which statement BEST corrects this misconception?
Correct answer: C - Theories explain phenomena and never become laws, which describe patterns
A student investigates how temperature affects the rate at which an antacid tablet dissolves. The student uses 100 mL of water at 20 °C, 40 °C, and 60 °C, but crushes the tablet before adding it to the 60 °C sample only. Which flaw MOST seriously undermines the student's conclusion about temperature?
Correct answer: A - Surface area was not held constant across the trials
An orbital diagram for the 2p sublevel of a nitrogen atom shows two electrons paired in the first orbital, one electron in the second orbital, and the third orbital empty. Which principle or rule does this diagram violate?
Correct answer: B - Hund's rule, which governs how equal-energy orbitals are occupied
Boron occurs naturally as two isotopes: boron-10 (mass 10.01 amu, 19.9% abundance) and boron-11 (mass 11.01 amu, 80.1% abundance). What is the average atomic mass of boron?
Correct answer: C - 10.81 amu
On a heating curve for water, a horizontal plateau occurs at 100 °C even though heat continues to be added at a constant rate. Which statement BEST describes what happens to the water during this plateau?
Correct answer: C - Hydrogen bonds between molecules are overcome as potential energy rises
A 96 g sample of a radioisotope decays until only 6 g of the original isotope remains. If the half-life of the isotope is 8 days, how much time has elapsed?
Correct answer: C - 32 days
A reaction has ΔH = +58 kJ/mol and ΔS = +176 J/(mol·K). Under which conditions is this reaction spontaneous?
Correct answer: D - Only at temperatures above approximately 330 K
Carbon dioxide (CO₂) and water (H₂O) both contain polar covalent bonds, yet CO₂ is a nonpolar molecule while H₂O is polar. Which factor BEST accounts for this difference?
Correct answer: A - The bond dipoles in CO₂ cancel because the molecule is linear
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