Question

phase 3:
diffusion rate in a semisolid
complete the following steps:
1 add one crystal to agar dish using tweezers
2 wait 15 minutes
3 measure the diffusion spot diameter. record in lab data
4 calculate average diffusion rate from time zero in mm/h. record in lab data

Explanation:

Read the diffusion spot diameters

Using the Diffusion Measurement and Lab Data Recording knowledge points

• Top Petri Dish (Purple Dye):
• Left edge of the purple circle is at \(7.0\text{ cm}\).
• Right edge of the purple circle is at \(17.0\text{ cm}\).
• Diameter \(D_{\text{purple}} = 17.0\text{ cm} - 7.0\text{ cm} = 10.0\text{ cm} = 100\text{ mm}\).

• Bottom Petri Dish (Red/Brown Dye):
• Left edge of the red circle is at \(0.5\text{ cm}\).
• Right edge of the red circle is at \(1.5\text{ cm}\).
• Diameter \(D_{\text{red}} = 1.5\text{ cm} - 0.5\text{ cm} = 1.0\text{ cm} = 10\text{ mm}\).

Calculate the average diffusion rates

Using the Diffusion Rate Calculation knowledge point

• Elapsed Time: \(15\text{ minutes} = 0.25\text{ hours}\).

• Purple Dye Rate:

$$ \text{Rate}_{\text{purple}} = \frac{100\text{ mm}}{0.25\text{ h}} = 400\text{ mm/h} $$

• Red Dye Rate:

$$ \text{Rate}_{\text{red}} = \frac{10\text{ mm}}{0.25\text{ h}} = 40\text{ mm/h} $$

Answer:

Dye Color	Diffusion Spot Diameter (mm)	Average Diffusion Rate (mm/h)
Red/Brown	\(10\)	\(40\)