# 7.5 Practice problems

- What is the molarity of a solution where 5 moles of Na
_{2}CO_{3}is dissolved in 2.5 l of water? - What is the molarity of 5 g of NaOH in 750 ml of solution? (The molecular weight of NaOH is 40 g mol
^{–1}.) - How many moles of H
_{2}SO_{4}are in 10 l of a 2 M solution? - What weight (in g) of Na
_{2}CO_{3}is needed to make 750 ml of a 100 mM solution? (The molecular weight of Na_{2}CO_{3}is 106 g mol^{–1}.) - 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}.) - 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}.) - Convert 50 mg of calcium carbonate, CaCO
_{3}, into moles. (The molecular weight of CaCO_{3}is 100.1 g mol^{–1}.) - 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}? - 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.)
- You want to prepare 300 ml of a 60% (w/v) solution of sucrose. How much sucrose do you need to weigh out?
- 2 l of an aqueous solution of KCl contains 45 g of KCl. What is the weight/volume percentage concentration of this solution?
- A solution is made by adding 30 ml of benzene to 95 ml of toluene. What is the percent by volume of benzene?
- How much ampicillin do you need to weigh out to make 150 ml of solution containing 50 µg ml
^{–1}ampicillin? - If 0.025 g of Pb(NO
_{3})_{2}is dissolved in 0.1 l of H_{2}O, what is the concentration of the resulting solution, in parts per million? - 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?
- 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.