If 15g of NaOh is dissolved in 285 g of water, calculate the following. Assume the density of the solution is 1.06 g/cc.
a) Calculate the moles of NaOH in the solution? My answer is 15gNaOH/40g NaOH= .0375 mole NaOH
b) Waht is the mass % w/w of the solution? My answer is 15g NaOH/ 300g sol NaOH * 100 = 5%
c) What is the molarity of the dolution?
My anser is 0.375 mol NaOH/ 0.283L= 0.13M NaOH
Kindly please correct my answers. Thanks
pls can anybody check my answers
a.
I think 15/40 = 0.375 mols. You must have just made a typo because you have 0.375 in part c.
b. good work here. Many students forget to add the 15 and 285 and divide by 285.
c. That looks ok to me.
a) To calculate the moles of NaOH in the solution, you correctly used the formula:
moles = mass / molar mass
The molar mass of NaOH is 40 g/mol, so the calculation should be:
moles = 15 g NaOH / 40 g/mol = 0.375 mol NaOH
So your answer of 0.375 mole NaOH is correct.
b) To calculate the mass % w/w of the solution, you used the formula:
mass % w/w = (mass of solute / mass of solution) * 100
The mass of NaOH is still 15 g, but the mass of the solution is the sum of the masses of NaOH and water, which is given as 285 g. However, it's important to note that the density of the solution is given as 1.06 g/cc. This means that the volume of the solution can be calculated as:
volume = mass / density
volume = 285 g / 1.06 g/cc = 268.87 cc (rounded to two decimal places)
Now we can calculate the mass % w/w:
mass % w/w = (15 g NaOH / (15 g NaOH + 268.87 cc solution)) * 100
mass % w/w = 5.29% (rounded to two decimal places)
So your answer of 5% is close, but it should be 5.29%.
c) To calculate the molarity of the solution, you used the formula:
molarity = moles of solute / volume of solution (in liters)
You have correctly determined the moles of NaOH as 0.375 mol. However, you used 0.283 L as the volume of the solution, which is incorrect.
To determine the volume of the solution in liters, we need to convert the given density from g/cc to g/mL, then divide the mass of the solution by the density to get the volume in mL, and finally convert mL to L:
volume = (mass of solution / density) / 1000
volume = (285 g / 1.06 g/cc) / 1000 = 0.26887 L (rounded to five decimal places)
Now we can calculate the molarity:
molarity = 0.375 mol NaOH / 0.26887 L = 1.396 M NaOH (rounded to three decimal places)
So your answer of 0.13 M NaOH is incorrect. The correct molarity is 1.396 M NaOH.