Question

1. What is the molarity of a solution that contains 18.7 g of KCl (MW=74.5) in 500 mL of water?
   
2. 25 g of NaOH (MW = 40) is added to 0.5 L of water. What is the molarity of this solution if an additional 0.25 L of water is added to this solution?
   
3. How many grams of H₂SO₄ (MW = 98) are in 750 mL of 3 N H₂SO₄?
   
4. What is the normality of a solution that contains 280 g of NaOH (MW=40) in 2000 mL of solution?
   
5. A serum potassium is 19.5 mg/100 mL. This value is equal to how many mEq/L (MW = 39)?

You are given a series of 5 tubes, each of which contains 5 mL of saline. To the first tube is added 1 mL of serum, and a serial dilution using 1 mL is carried out in the remaining tubes.

6. What is the dilution in the first tube?
7. What is the final dilution in the third tube
8. The third tube was run, and the triglyceride concentration was 3 mg/dL. Give the triglyceride concentration in the 1^st tube:
9. What is the concentration of the original specimen?
10. What result do you report out?

Answer 1

What is the molarity of a solution that contains 18.7 g of KCl (MW=74.5) in 500 mL of water?

Mass of KCl = 18.7 g

Moles of KCl =   18.7 g /74.5 g/mol =  0.2510 Mole s

Molarity = Moles of solute / liters of solvent

Molarity of KCl =  0.2510 Mole / 0.5 L = 0.502 M

25 g of NaOH (MW = 40) is added to 0.5 L of water. What is the molarity of this solution ?

Mass of NaOH = 25 g

Moles of NaOH =   18.7 g /40 g/mol =  0.624 Mole s

Molarity = Moles of solute / liters of solvent

Molarity of NaOH =  0.624 Mole / 0.5 L = 1.25 M  

if an additional 0.25 L of water is added to this solution

Molarity of NaOH after addition of 0.25 L water =  0.624 Mole / 0.75 L = 0.833 M  

How many grams of H2SO4 (MW = 98) are in 750 mL of 3 N H2SO4?

Normality of H2SO4 = 3 N

Molarity of H2SO4 = 1.5 M

Moles of H2SO4 = 1.5 x 750 /1000 = 0.1125 moles

Mass of H2SO4 = 0.1125 mol x 98 g/mol = 11.025 g

What is the normality of a solution that contains 280 g of NaOH (MW=40) in 2000 mL of solution?

Mass of NaOH = 280 g

Volume of solution = 2000 ml

Normality of NaOH = 280 g x 1000 ml / (2000 mlx 40g/mol) = 3.5 N