Question

question 5
10 pts
to make 100 g of a 5% (by mass, m/m%) aqueous sucrose solution one must dissolve:
95 g sucrose in 5 g of water.
5 g sucrose in 95 g of water.
5 g sucrose in 1 l of water.
5 g sucrose in 100 g of water.
question 6
10 pts
true or false? to make a 70% (v/v%) solution of isopropanol in water one could mix 70 ml of isopropanol and 100 ml of water.
true
false

Explanation:

Question 5

Step1: Recall mass percent formula

The formula for mass percent (\(m/m\%\)) is \(m/m\%=\frac{\text{mass of solute}}{\text{mass of solution}}\times100\). The solution mass is 100 g, and \(m/m\% = 5\%\).

Step2: Calculate solute mass

Let the mass of sucrose (solute) be \(m\). Then \(5=\frac{m}{100}\times100\), so \(m = 5\) g. The mass of water (solvent) is \(100 - 5=95\) g.

Volume percent (\(v/v\%\)) is \(\frac{\text{volume of solute}}{\text{volume of solution}}\times100\). If we mix 70 mL isopropanol (solute) and 100 mL water (solvent), the total solution volume is not 100 mL (it's \(70 + 100=170\) mL). For a 70% (\(v/v\%\)) solution, \(\frac{70}{\text{solution volume}}\times100 = 70\) implies solution volume should be 100 mL, so solvent volume should be \(100 - 70 = 30\) mL, not 100 mL. Thus the statement is false.

Answer:

5 g sucrose in 95 g of water.

Question 6