Question

Would your calculated percent NaNo2 by mass by larger than, smaller than or unchanged from the correct value as a result of the following mistakes? Show your reasoning or calculations when appropriate.

A) You neglected to open the stopcock on your buret prior to the evolution of nitrogen gas.

B) Your measured temperature was erroneously recorded 5 degrees C higher than actual temperature.

C) You neglected to correct for the vapor pressure of water in your calculations.

Answer 1

A)

If you neglected to open the stopcock on your burette prior to the evolution of nitrogen gas, your calculated percent NaNo₂ by mass by smaller than correct value.

Nitrogen gas will tend to completely pop out when a large volume of liquid is being dispensed from the burette. Because the N₂ occupies a significant volume in and of itself, if it came out of the tip during the course of dispensing, the actual volume delivered would be less than the volume reported. So the mass of NaNO₂ smaller than correct value.

B)

If measured temperature was erroneously recorded 5⁰ C higher than actual temperature, calculated percent NaNo₂ by mass by unchanged from the correct value.

Increasing or decreasing temperature doesn't affect mass

C) You neglected to correct for the vapor pressure of water in your calculations. your calculated percent NaNo2 by mass by larger than the correct value

Explanation- The answer would be too high because the higher pressure would result larger moles.

In equation is PV = nRT

P is pressure, V = volume, n = moles of gas, R = gas constant, and T being temperature

Now use 1 atm and 1.2 atm to show the effect of not subtracting the vapor pressure

(1.2atm)(5liters) = n (.08206)(273K)

n = .268 moles of gas

With pressure subtracted you would get this

(1atm)(5liters) = n (.80206)(273K)

n = .223 moles of gas