A solution is made by dissolving 0.100 mol of NaCl in 5.35 mol of water. What is the mass % of NaCl?
So far, I have determined molecular weight of NaCl (58.44 g/mol) multiplied by 0.100 mol = 5.844g NaCl, and mw of H2O (18 g/mol) = 96g H20.
I thought mass solute/mass solution (5.8/102 = .057 or 5.7%) but my homework program says incorrect. Am I doing this problem wrong?
Well, solving homework problems can sometimes feel like trying to solve a Rubik's cube blindfolded. But don't worry, I'm here to clown around and help you out!
Let's go through the problem together. You're on the right track with calculating the mass of NaCl and water. The mass of NaCl is indeed 5.844g, and the mass of water is 96g.
To find the mass percent of NaCl in the solution, you can use the formula:
(mass of NaCl / total mass of solution) * 100
Substituting the values we have:
(5.844g / (5.844g + 96g)) * 100 = 5.744%
So the mass percent of NaCl in the solution is approximately 5.744%.
If your homework program is still saying it's incorrect, maybe it's just not in the mood for jokes. But don't sweat it, and give it another try!
You have correctly determined the molecular weights of NaCl and H2O. However, the calculation for the mass % of NaCl is incorrect. The mass % of NaCl in the solution can be calculated by dividing the mass of NaCl by the total mass of the solution and multiplying by 100.
To find the total mass of the solution, you need to account for the mass of both NaCl and water. The mass of NaCl can be calculated by multiplying the number of moles (0.100 mol) by the molecular weight (58.44 g/mol), which gives you 5.844 g.
The mass of water can be calculated by multiplying the number of moles (5.35 mol) by the molecular weight of water (18 g/mol), which gives you 96.3 g.
Now, add the mass of NaCl (5.844 g) to the mass of water (96.3 g) to get the total mass of the solution, which is 102.144 g.
To calculate the mass % of NaCl, divide the mass of NaCl by the total mass of the solution and multiply by 100:
(5.844 g / 102.144 g) * 100% = 5.72%
So, the correct mass % of NaCl in the solution is approximately 5.72%.
To find the mass % of NaCl in the solution, you need to divide the mass of NaCl by the total mass of the solution and then multiply by 100.
First, calculate the mass of NaCl:
Mass of NaCl = moles of NaCl * molar mass of NaCl
You have correctly determined the moles of NaCl as 0.100 mol. Multiplying it by the molar mass of NaCl (58.44 g/mol), the mass of NaCl is:
Mass of NaCl = 0.100 mol * 58.44 g/mol = 5.844 g
Next, calculate the mass of water:
Mass of water = moles of water * molar mass of water
You have 5.35 mol of water. Multiplying it by the molar mass of water (18 g/mol), the mass of water is:
Mass of water = 5.35 mol * 18 g/mol = 96.30 g
Now, calculate the total mass of the solution:
Total mass of solution = mass of NaCl + mass of water
Total mass of solution = 5.844 g + 96.30 g = 102.144 g
Finally, calculate the mass % of NaCl:
Mass % of NaCl = (mass of NaCl / total mass of solution) * 100
Mass % of NaCl = (5.844 g / 102.144 g) * 100 ≈ 5.71%
Your calculation of 5.7% is very close, but it seems you rounded unnecessarily. Keep the answer in decimal form and round it at the end to avoid any rounding errors. Hence, the mass % of NaCl in the solution is approximately 5.71%.
I think one problem may be that you are reporting only to two significant figures and you are allowed three.
I agree with 5.844 g NaCl. For water I have 5.35 x 18.015 = 96.38 g.
Total mass = 96.38 + 5.844 = 102.22 and
(5.844/102.22)*100 = 5.7168 which rounds to 5.72 mass percent. The other thing I do when I work these problems is (or don't do) is to round between calculations; i.e., I leave the number in the calculator with all of those dangling numbers and wait until I finish the calculation to round to the correct number of s.f.