13. Solid sodium reacts violently with water, producing heat, hydrogen gas, and sodium hydroxide. How many molecules of hydrogen gas are formed when 48.7 g of sodium are added to water?
2Na + 2H2O = 2NaOH + H2
So far I have this much figured out:
Mass to moles for Na: 48.7g Na x 1mol / 22.990g = 2.118mol Na
...2.118mol Na....(I need help with this part!!)
1.06mol x 6.02*10^23 atoms / 1 mol = 6.38 x 10^23 molecules of hydrogen gas are formed.
That middle part is really throwing me off. I'm seeing people doing this: 2.12/2 x 24 =25.44dm^3 H = 1.06mol
But I really dont understand where the 24 is coming from?? I understand the math behind it, but I'm confused as to how these people are getting that when working through the problem. Thank you!!
let's do this one step at a time.
1. Write and balance the equation. You've done that.
2Na + 2H2O = 2NaOH + H2
2. Convert g Na to mols. You've done that. 48.7/22.99 = 2.12 mols.
3. Now you want to convert mols Na (what you have)to mols H2(what you want). You do that with the coefficients in the balanced equation.
2.12 mols Na x (1 mol H2/2 mol Na) = 1.06 mols H2 produced.
4. Now you convert mols H2 to molecules. You know that 1 mol of anything contains 6.02E23 of those anythings; therefore, 1.06 mols H2 x (6.02E23 moleculers/1 mol H2) = ?
My notes. There is no need to convert mols H2 to liters before converting to molecules. Doing that brings up that pesky 22.4L(U.S.) or 24 (U.K.). It is worth noting that 1 mole of a gas occupies 22.4 L IF the gas is at STP. At NTP it occupies 24 L which is probably the source of that 24. Unfortunately some people use 20 C as normal T and others like to use 25 C. Finally there is SATP (24.8 L). Also i should note that "normal pressure) is almost always 1 atm in the U. S. but 100 kPa is usually seen in the definitions. The good news in this problem is that none of that matters if you go directly from mols to number of molecules.
maybe the H2 is hot when it comes off, so it occupies more space. Do you have some thermal information?
Yeah the question states that when the solid sodium reacts violently with water, it produces /heat/, hydrogen gas, and sodium hydroxide. I never learned anything about how to write heat into an equation, could you explain it to me?
@Steve? Still there, buddy? Can anyone else help me, I'm struggling.
Awesome! Thank you so much! My answer was 6.38 x 10^23 molecules
Never mind. I figured it out.
The H2 stuff looks ok.
the 24 also confuses me. 1 mole of any gas at STP is 22.4 liters, not 24. I suspect a typo (the missing 2)
I have the same problem to figure out, but mine gave this equation: Na + H20 -> H2 + NaOH
So I was just wondering what I should do since mine aren't the exact same.
To determine the number of molecules of hydrogen gas formed when 48.7 g of sodium reacts with water, you are on the right track by converting the mass of sodium into moles using the molar mass of sodium (22.990 g/mol). You correctly calculated that 48.7 g of sodium is equal to 2.118 mol of sodium.
Now, using the balanced chemical equation 2Na + 2H2O = 2NaOH + H2, we can see that 2 moles of sodium react to produce 1 mole of hydrogen gas. Thus, the ratio of moles of hydrogen gas to moles of sodium is 1:2.
To find the number of moles of hydrogen gas, multiply the number of moles of sodium by the mole ratio:
2.118 mol Na * (1 mol H2 / 2 mol Na) = 1.059 mol H2
Since you are looking for the number of molecules of hydrogen gas formed, you can use Avogadro's number (6.02 x 10^23 molecules/mol) to convert moles to molecules:
1.059 mol H2 * (6.02 x 10^23 molecules/mol) = 6.38 x 10^23 molecules of hydrogen gas
Now, let's discuss the part that is confusing you. The calculation you mentioned, 2.12/2 x 24 = 25.44 dm^3 H2 = 1.06 mol, is the conversion between moles of hydrogen gas and the volume of hydrogen gas at standard temperature and pressure (STP). This conversion is based on the ideal gas law, which relates the number of moles of gas to its volume (in liters) at STP.
The number 24 in the equation represents the molar volume of an ideal gas at STP, which is approximately 24 liters/mol. This value is derived from the ideal gas law equation PV = nRT, where P is pressure (at STP, it is 1 atmosphere), V is volume, n is the number of moles of gas, R is the ideal gas constant, and T is temperature (at STP, it is 273 K).
So, by using the equation 2.12/2 x 24, you are calculating the volume in liters of the hydrogen gas produced based on the number of moles of sodium used. However, this calculation is not necessary to answer the original question about the number of molecules of hydrogen gas formed.
I hope this explanation helps clarify the confusion. Let me know if you have any further questions!