Mole and Avogadro Number

Part 2: Calibrating a Dropper

1. The number of drops in 1 mL water (drops used to move from the 1.00 mL to 2.00 mL mark):

Trial 1: 23 drops

Trial 2: 22 drops

2. The number of drops on average per one milliliter: 22.5

Part 3: Calculating the Number of Molecules

1. The diameter of the circle formed (cm): 1 cm

Calculations

1. Calculate the surface area of the circle formed (πd2/4):

Surface area = .785 cm2

2. Calculate the number of molecules on the top layer. We must convert the surface area in centimeters squared to nanometers squared and then multiple that by the surface area of a sodium stearate molecule.

Convert the surface area of the circle formed (#1) to molecules per layer using the matrix below:

Answer = 4.76*10^14 molecules/top layer

3. Calculate the concentration of grams of sodium stearate per milliliter of diluted solution. To do this, multiply the concentration of sodium stearate in the dishwashing liquid by the dilution of the solution (1.50 mL dishwashing liquid per 100 mL solution).

Answer = 1.5 *10^-4 g/mL

4. Calculate the number of moles of sodium stearate in a single layer. To do this, first take the number of drops used to achieve the monolayer (1 drop) and convert it to mL using the calibrated number of drops per mL. Then multiply the number of grams of sodium stearate per milliliter of solution. Finally, convert to moles through the molar mass of sodium stearate. HINT: The molar mass of sodium stearate is 296.5 g/mole.

Answer = 1.06*10^7 moles/top layer

5. Finally, we can calculate Avogadro’s number through the comparison of molecules of sodium stearate in the top single layer to the moles of sodium stearate in the monolayer.

Answer = 4.5*10^21 molecules/mole

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