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Science Flashcards

6 cards from real BMST practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A gas occupies 4.0 L at 300 K and 2.0 atm. If the pressure is increased to 3.0 atm while the temperature drops to 200 K, what is the new volume?

    Answer: 1.78 L

    Using the combined gas law: P₁V₁/T₁ = P₂V₂/T₂ → V₂ = (P₁V₁T₂)/(T₁P₂) = (2.0 × 4.0 × 200)/(300 × 3.0) = 1600/900 ≈ 1.78 L. Both the pressure increase and temperature decrease act to reduce the volume.

  2. Which of the following best explains why water has an anomalously high boiling point compared to other hydrides of Group 16 elements (H₂S, H₂Se, H₂Te)?

    Answer: Water molecules form strong hydrogen bonds due to oxygen's high electronegativity and lone pairs

    Oxygen's high electronegativity and its two lone pairs allow water to form extensive hydrogen bonding networks (each molecule can donate and accept two H-bonds). This strong intermolecular force requires significantly more thermal energy to overcome, giving water a boiling point far above the trend predicted by molecular mass alone.

  3. A 2 kg object moving at 6 m/s collides and sticks to a stationary 4 kg object. What percentage of the original kinetic energy is lost in this perfectly inelastic collision?

    Answer: 67%

    Initial KE = ½(2)(6²) = 36 J. By conservation of momentum: (2)(6) = (6)v → v = 2 m/s. Final KE = ½(6)(2²) = 12 J. Energy lost = 36 − 12 = 24 J. Percentage lost = 24/36 × 100 ≈ 67%. In a perfectly inelastic collision, energy loss equals m₂/(m₁+m₂) of original KE when target is stationary.

  4. Which process describes how the Sun generates energy, and which law explains why this process releases energy?

    Answer: Nuclear fusion of hydrogen into helium; E = mc² shows the mass defect converts to energy

    The Sun fuses hydrogen nuclei (protons) into helium-4 through the proton-proton chain. The helium-4 nucleus has slightly less mass than the four individual protons combined — this 'mass defect' is converted into energy per Einstein's E = mc². Each fusion reaction releases ~26.7 MeV. Fission (splitting heavy nuclei) is used in nuclear power plants, not stars like the Sun.

  5. A solution has a hydroxide ion concentration [OH⁻] of 1 × 10⁻³ mol/L at 25°C. What is its pH?

    Answer: 11

    At 25°C, Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴. With [OH⁻] = 1 × 10⁻³, pOH = −log(10⁻³) = 3. Since pH + pOH = 14, pH = 14 − 3 = 11. The solution is basic (alkaline). A common error is reporting pOH (3) as pH.

  6. During meiosis, crossing over (recombination) occurs between non-sister chromatids. What is the PRIMARY evolutionary significance of this event?

    Answer: It generates new combinations of alleles, increasing genetic variation in offspring

    Crossing over shuffles segments between homologous (non-sister) chromatids, creating recombinant chromosomes with novel allele combinations not present in either parent. This is a primary driver of genetic diversity in sexually reproducing populations, providing raw material for natural selection. Error correction is handled by DNA repair mechanisms, not crossing over.