Under an O2(g) pressure of 1.00 atm, 30.9 cm3 of O2(g)at 25C dissolves in 1.00 L H2O at 25C. Assuming that the soln volume remains at 1.00L, what is the Molarity of a saturated O2(aq) soln at 25C when partial pressure O2=1 atm?

DRBOB222 said to: Convert 30.9 cc O2 at 25C to moles. Then M = moles/L.

I did that conversion (22.4 moles O2/L)(0.0309 L)=0.69216 moles O2. ),69216 moles O2/1.00L =0.69216 M. However, textbook answer says 1.26 x 10-3 M...i am now confused. Help! Thank you.

You didn't convert to moles correctly. The molar mass of O2 is 22.4 L/mole ONLY at STP and 25C is not STP.

Use PV = nRT, solve for n, then n/1L = M and I get 0.00126M. (Note: IF you could use 22.4, you should have divided 0.0309/22.4 = 0.00138 but that would be at 273K (zero C and not 25C)

To find the molarity of a saturated O2(aq) solution at 25C when the partial pressure of O2 is 1 atm, you need to follow these steps:

Step 1: Convert 30.9 cm^3 of O2(g) at 25C to moles.

To do this, you need to use the Ideal Gas Law equation: PV = nRT, where P is the pressure, V is the volume, n is the number of moles, R is the ideal gas constant (0.0821 L·atm/(mol·K)), and T is the temperature in Kelvin.

First, convert the volume to liters: 30.9 cm^3 = 30.9 / 1000 = 0.0309 L.

Next, convert the temperature to Kelvin: 25C + 273.15 = 298.15K.

Now, rearrange the Ideal Gas Law equation to solve for the number of moles:
n = PV / RT.

Substituting the values:
n = (1.00 atm) * (0.0309 L) / (0.0821 L·atm/(mol·K)) * (298.15 K) ≈ 0.001246 moles O2.

Step 2: Calculate the molarity (M) using the formula M = moles / volume.

Since the solution volume remains at 1.00 L, you can directly divide the number of moles you found in Step 1 by 1.00 L:
M = 0.001246 moles O2 / 1.00 L ≈ 0.001246 M.

So, based on the given data, the molarity of a saturated O2(aq) solution at 25C when the partial pressure of O2 is 1 atm is approximately 0.001246 M.

It seems there might be an error in your calculations in Step 1 or the conversion from cm^3 to L. Double-check your calculations, and if you still get a different answer, further review the question and provided information for any additional details or modifications needed in the calculation.