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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.

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)

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 )

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.

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?

Example 3:

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

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.

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?

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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