A student generates H2(g) over water using the reaction between zinc and hydrochloric acid
Zn(s)+ 2HCl(aq)---> ZnCl2(aq)+ H2(g)
Data:
Mass of vial and zinc 15.5082
mass of vial 15.3972
mass of zinc 0.111
final burette reading 45.30mL
barometric pressure: Patm 100.6kPa
temperature of trapped gas 24.3C
vapour pressure of water at 24.3 C: PH2O 3.004kPa
diff in solution lvls inside and outside burette 162mm H2O
I got 95.968 kPa of H2 since you said im allowed 4 sigfig i used 95.97 does that seem right?
and for the second part i got 297.5K im really not sure what am doing here the formulas i was trying to use were
atm = H2+ H2O+ lvldiff
H2= atm- lvldiff-H2O
Let's see. I said we should take
100.6 kPa - vp H2O - water diff or
100.6 - 3.004 - 1.5876 = 96.008 kPa which rounds to 96.00 to 4 s.f. How does that stack up with the formula you are using.
atm = H2 + H2O + |v| or
H2 = atm - H2O - |v| or
H2 = 100.6 - 3.004 - 1.5876 = 96.008 and it rounds to 96.00 kPa. (I didn't use a formula; I just reasoned it out but I'm glad to see that reasoning and the formula gets the same thing. Check your math. I don't believe 95.968 kPa is correct.
how would you calculate the temperature of H2 in kelvin? and the moles that H2 produced? do you know a formula for that? could you please explain it to me thanks for all your help so far i've understood everything thanks to you.
Your post says temperature of trapped gas is 24.3 C. In kelvin, that is 273.15+24.3 = 297.45. I would round that to 297.4; however, when I'm doing calculations, I can make "rounding" errors; therefore, I leave all of the numbers in my calculator and go to the next calculation. I also carry one more place than I'm allowed to avoid rounding errors, then round at the very end of all calculations.You can calculate moles H2 from PV = nRT. You know P now, you know V(must be in liters), you know R (it's 8.314 if you use P in kPa) and you know T in kelvin. Solve for n.
I did all my questions but there is this last one i don't get. Calculate the number of moles of zinc that must have reacted( assume that Zn is limiting and the yield of H2 gas is 100%) how do you do this? could you help me with this last one please?
moles Zn = grams Zn/atomic mass Zn
To determine the pressure of the hydrogen gas (H2) generated during the reaction, you need to take into account the different components contributing to the total pressure. Let's break it down step by step:
Step 1: Calculate the partial pressure of water vapor (PH2O) at the given temperature.
- Given: temperature of trapped gas (T) = 24.3°C
- Look up the vapor pressure of water at the given temperature from a reference table or use an online calculator.
- PH2O = 3.004 kPa
Step 2: Calculate the total pressure inside the burette.
- Given: final burette reading = 45.30 mL
- Convert the burette reading from milliliters (mL) to liters (L) by dividing by 1000.
- Burette reading = 0.04530 L
- The total pressure inside the burette is determined by the difference in solution levels inside and outside the burette, converted to pressure using the height of a water column (162 mm H2O).
- Total pressure inside the burette = atmospheric pressure (Patm) + pressure due to the difference in solution levels (converted to kPa using the density of water, g/cm³).
Step 3: Calculate the pressure of hydrogen gas (PH2).
- The pressure of hydrogen gas can be determined by subtracting the partial pressure of water vapor from the total pressure inside the burette.
- PH2 = Total pressure inside the burette - PH2O
Now let's calculate the values:
Step 1: From the data, we have:
- PH2O = 3.004 kPa
Step 2:
- Convert the height of the water column (162 mm H2O) to kPa using the density of water: 1 mm H2O = 0.098 kPa.
- Convert the mass of the displaced water (lvldiff) to volume using the formula: volume = mass/density.
- Subtract the converted lvldiff from the atmospheric pressure to get the total pressure inside the burette.
- Atmospheric pressure (Patm) = 100.6 kPa
- Lvldiff converted to kPa = 162 mm H2O x 0.098 kPa/mm H2O
- Total pressure inside the burette = Patm - lvldiff converted to kPa
Step 3:
- Calculate the pressure of hydrogen gas (PH2) by subtracting the partial pressure of water vapor from the total pressure inside the burette.
- PH2 = Total pressure inside the burette - PH2O
After calculating PH2, you should have the correct pressure for hydrogen gas. Similarly, you can apply the same methodology to calculate the correct temperature if needed.