Question

How many moles of sodium chloride (NaCl) solute are in 155 grams of an 85.5 percent by mass solution?
1.19 mol NaCl
2.27 mol NaCl
7.75 mol NaCl
10.6 mol NaCl

4. How many grams of zinc metal will react completely with 8.2 liters of 3.5 M HCl? Show all of the work needed to solve this problem.

Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)

Answer 1

How many moles of sodium chloride (NaCl) solute are in 155 grams of an 85.5 percent by mass solution?


1) Calculate the mass of solute

% = [mass of solute / mass of solution] * 100 =>

mass of solute = [% / 100] * mass of solution = [85.5/100] * 155 g = 132.525 g

2) Pass to moles using the molar mass, MM, of NaCl

MM = 23 g/mol + 35.5 g/mol = 58.5 g/mol

n = mass (g) / MM = 132.525 / 58.5 = 2.27 mol
 
Answer: the second option of the list

4. How many grams of zinc metal will react completely with 8.2 liters of 3.5 M HCl? Show all of the work needed to solve this problem.

Zn (s) + 2 HCl (aq) ---> ZnCl2 (aq) + H2 (g)

From the molarity, calculate the number of mols of HCl

M = n/V => n = M*V = 3.5 mol/liter * 8.2 liter = 28.7 mol HCl

From the reaction: [1 mol Zn / 2 mol HCl] * 28.7 mol HCl = 14.35 mol Zn

Pass to mass, using the atomic mass of Zn

mass = n*atomic mass = 14.35 mol * 65.4 g/mol =  938.5 g Zn

Answer: 938.5 g.

Answer 2

3.0 L*3.5mol/ 1 L dillute solutio = 10.5 mol HCl

10.5mol*1 L stock solution/18.5 mol = .568L stock solution

3.0L - .568 L = 2.93 liters of water added

Measure .727 L of the 18.5 molar HCl stock solution, then add 2.93 of water to make 3.0 K of 3.5 M solution.