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Solving Real World Problems

Solving Real World Problems. WARM-UP : Chemists measure the acidity of a liquid by determining the concentration of the hydrogen ion (H + ) in the liquid. The acidity of a liquid on the pH scale is defined as: pH = -log [H + ] where [H + ] is the concentration of the hydrogen ion in mol/L.

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Solving Real World Problems

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  1. Solving Real World Problems WARM-UP: Chemists measure the acidity of a liquid by determining the concentration of the hydrogen ion (H+) in the liquid. The acidity of a liquid on the pH scale is defined as: pH = -log [H+] where [H+] is the concentration of the hydrogen ion in mol/L. ***TEST DATES*** Determine the pH of distilled water if it contains 10-7 mol/L of H+. 2. Determine the hydrogen ion concentration of a fruit juice with a pH of 3.10.

  2. Solving Real World Problems • Quantities that vary significantly are compared using a logarithmic scalesince a logarithmic scale is based on exponents. • Note: If N=10000, then log10 104 = 4 • Therefore, using a logarithmic scale, 10000 is represented as 4. • Logarithmic scales are applied to many real-life situations: • Chemistry (the pH scale) • Earthquakes (the Richter scale) • Sound intensity (the decibel scale)

  3. Example 1: Dropping a measured volume of liquid into a solution changes the pH value from 4.2 to 3.5. How many times as acidic is a solution with a pH value of 3.5 than a solution with a pH value of 4.2? Recall: pH = -log [H+] Therefore: pH2 – pH1 = ( - log [H+]2 ) – ( -log [H+]1 )

  4. Solving Real World Problems: Earthquakes The magnitude (strength) of an Earthquake is defined as: where I is the intensity of the earthquake being measured and S is the standard intensity.

  5. Example 2: Earthquake B measures 4.5 on the Richter Scale while Earthquake A measures 7.5. How many times stronger is Earthquake A than B?

  6. Example 3: Earthquake A measures 6.9 on the Richter Scale. Calculate the magnitude of an earthquake with twice the intensity.

  7. Solving Real World Problems: Sound The decibel scale is used to measure the intensity of sound. The starting point of the scale, zero decibels, represents a sound minutely below that which the human ear can hear. The formula used to compare sound is: where L is the intensity of the sound being sought, Lk is the intensity of the reference sound and y is the loudness in decibels.

  8. Example 4: A jet engine produces sound waves with a loudness of 100 dB. The ordinary household noise level is approximately 50 dB. How many times louder is the jet engine than an ordinary household noise?

  9. HOMEWORK!!! • Unit 6 Workbook • Complete the workbook! • Exercise 5 (Page 13) • MUST BE DONE BY TOMORROW’S CLASS!! • Use the Instructions on P.10-12 to help you

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