AP Chemistry - Chapter 13 Deep Dive Review Packet

AP Chemistry – Chapter 13 Deep Dive Review Packet (With Beer-Lambert & Spectroscopy) Beer-Lambert Law (Beer's Law) • • • • • • • • A = εbc A = absorbance (unitless). ε = molar absorptivity (L/mol·cm). b = path length (cm). c = concentration (mol/L). Absorbance is directly proportional to concentration. If concentration doubles → absorbance doubles. Used to determine unknown concentration via calibration curve. Transmittance vs Absorbance • • • • • Transmittance (T) = I / I■. Percent transmittance = (I / I■) × 100%. A = -log(T). Lower transmittance → higher absorbance. AP loves converting %T → A. Spectroscopy Fundamentals • • • • • • Measures interaction between light and matter. Electrons absorb specific wavelengths to move to higher energy levels. Energy of light: E = hν. c = λν (speed of light equation). Shorter wavelength → higher energy. UV-Vis spectroscopy commonly tested on AP. How Spectrophotometers Work • • • • Light source → monochromator → sample → detector. Blank used to calibrate instrument. Calibration curve: absorbance vs concentration. Slope of line = εb. Worked Example – Beer’s Law • • • • • • A solution has absorbance 0.650. ε = 1.30 × 10^4 L/mol·cm. Path length = 1.00 cm. c = A / (εb). c = 0.650 / (1.30 × 10^4 × 1.00). c = 5.00 × 10^-5 M. Common AP Traps – Beer’s Law • • • • Forgetting to convert %T to absorbance. Forgetting log is base 10. Assuming linearity outside valid concentration range. Not using blank correctly. Connection to Solutions Chapter • • • • Spectroscopy used to determine concentration of solutions. Often combined with dilution calculations. Colligative properties depend on concentration determined experimentally. Spectroscopy data may be used in equilibrium or kinetics problems. AP Exam Strategy – Spectroscopy • • • • • Always identify what is proportional to what. If graph is linear → use slope to find ε. If graph curved → outside linear range. Units matter: check L/mol·cm and cm. Use scientific notation carefully.