Question 9.16: The cells of a tomato contain mostly an aqueous solution of ...
The cells of a tomato contain mostly an aqueous solution of sugar and other substances. If a typical tomato freezes at -2.5 °C, what is the concentration of dissolved particles in the tomato cells (in moles of particles per kg of water)?
ANALYSIS The freezing point decreases by 1.86 °C for each mole of solute dissolved in 1 kg of water. We can use the decrease in freezing point (2.5 °C) to find the amount of solute per kg of water.
BALLPARK ESTIMATE The freezing point will decrease by about 1.9 °C for every 1 mol of solute particles in 1 kg of water. To lower the freezing point by 2.5 °C therefore requires about 1.5 mol of particles per kg of water.
We can rearrange this expression to
(-2.5 \cancel{^\circ C}) \left(\frac{1 mol solute particles}{-1.86 \cancel{^\circ C} kg water} \right) = 1.3 \frac{mol solute particles}{kg water}BALLPARK CHECK: The calculated answer is relatively close to our estimate (1.5 mol/kg).