Molarity, Solution Stoichiometry, and Dilutions

When you make a dilution, which of these values remains constant?

• The molarity (M)

• The total moles of solute

• The volume (V)

• The concentration

How do we make a dilution?

• Add more solute

• Remove solute

• Remove solvent

• Add more solvent

Solution A: 10g of Na₂SO₄ dissolved in 200mL of water
Solution B: 20g of Na₂SO₄ dissolved in 400mL of water

• The concentration of the solutions are the same
• Solution A is more concentrated than Solution B
• Solution A is more dilute than Solution B
• Not enough information

How many moles of NaCl are present in 125 mL of solution with a molarity of 8.59 M?

• 1074 mol
• 0.069 mol
• 1.07 mol
• 62.7 mol

What is the molarity of 4 grams of NaCl in 3800 mL of solution?  The molar mass of NaCl is 58.44 g/mol.

• 0.018 M
• 0.0011 M
• 1.052 M
• 0.062 M

How many grams of calcium hydroxide are needed to produce 500. mL of 1.66 M Ca(OH)₂ solution?  The molar mass of Ca(OH)₂ is 74.093 g/mol.

• 38.7 g
• 61.5 g
• 94.0 g
• 19.7 g

How many grams of solute are dissolved in 125.0 mL of 5.000 M NaCl?

• 0.625 g NaCl
• 56.3 g NaCl
• 36.53 g NaCl
• 0.625 mol NaCl

18.26 mL of a 1.50 M hydrochloric acid reacts with magnesium hydroxide. Calculate the moles of magnesium hydroxide needed for the reaction.
Mg(OH)_2(s)  +  2 HCl_(aq)  -->  2 H₂O_(l) + MgCl_2(aq)       

• 0.0274 moles Mg(OH)₂
• 0.0137 moles Mg(OH)₂
• 0.799 moles Mg(OH)₂
• 1.07 moles Mg(OH)₂

HCl_(aq) + NaOH_(aq) --> H₂O_(l) + NaCl_(aq)
25 mL of 1M HCl is required to react completely with with 20. mL of NaOH solution. What is the concentration of the NaOH solution?
Hint: determine first the moles of HCl that react.

• 0.8 M
• 1 M
• 1.25 M
• 1.5 M

Ca(OH)_2(aq) + 2 HCl_(aq) --> CaCl_2(aq) + 2 H₂O_(l)
A 50.0 mL sample of 1.0 M Ca(OH)₂ is required to react completely with 50.0 mL of HCl solution. Calculate the molarity of the HCl solution.
Hint: determine first the number of moles of Ca(OH)₂ that react.

• 1.0 M
• 0.50 M
• 2.0 M 
• 4.0 M