7.5 Practice problems

1. What is the molarity of a solution where 5 moles of Na₂CO₃ is dissolved in 2.5 l of water?
2. What is the molarity of 5 g of NaOH in 750 ml of solution? (The molecular weight of NaOH is 40 g mol^–1.)
3. How many moles of H₂SO₄ are in 10 l of a 2 M solution?
4. What weight (in g) of Na₂CO₃ is needed to make 750 ml of a 100 mM solution? (The molecular weight of Na₂CO₃ is 106 g mol^–1.)
5. A patient has a cholesterol count of 97 mg/dl. What is the molarity of cholesterol in this patient’s blood? (The molecular weight of cholesterol is 386.64 g mol^–1.)
6. What is the mass of HCl present in 90 ml of a 3 M solution? (The molecular weight of HCl is 36.46 g mol^–1.)
7. Convert 50 mg of calcium carbonate, CaCO₃, into moles. (The molecular weight of CaCO₃ is 100.1 g mol^–1.)
8. You are given a 5 µM solution of a protein (molecular weight = 27,000 g mol^–1). What is the concentration in mg ml^–1?
9. You lyophilise 1 ml of a 50 nM solution of a 60 kDa protein dissolved in water. What is the expected weight of the dried protein? (Come back to this one if you find it difficult.)
10. You want to prepare 300 ml of a 60% (w/v) solution of sucrose. How much sucrose do you need to weigh out?
11. 2 l of an aqueous solution of KCl contains 45 g of KCl. What is the weight/volume percentage concentration of this solution?
12. A solution is made by adding 30 ml of benzene to 95 ml of toluene. What is the percent by volume of benzene?
13. How much ampicillin do you need to weigh out to make 150 ml of solution containing 50 µg ml^–1 ampicillin?
14. If 0.025 g of Pb(NO₃)₂ is dissolved in 0.1 l of H₂O, what is the concentration of the resulting solution, in parts per million?
15. A 600 g sample of stream water has a concentration of 130 ppb dissolved nitrates. What is the mass of dissolved nitrates in this sample?
16. What is the total mass of solute in 1 l of water at a concentration of 5 ppm?

Solution to Practice Problem 7.2.

Solution to Practice Problem 7.9.

Solution to Practice Problem 7.11.