Question

passage #104
directions: the solubility curve for several common salts is shown in the graph. use the graph to answer any questions that follow
solubility of common salts
graph of solubility vs. temperature for nano₃, kno₃, kcl, k₂cr₂o₇, nacl

• which action would allow 40 g of k₂cr₂o₇ to completely dissolve in 100 g of water?

a. heating the solution to 60°c
b. heating the solution to 40°c
c. cooling the solution to 20°c
d. cooling the solution to 0°c

Explanation:

Step1: Analyze solubility curve of \(K_2Cr_2O_7\)

The solubility curve for \(K_2Cr_2O_7\) is the solid line (from the key). We need to see how temperature affects its solubility to determine when 40 g can dissolve.

Step2: Check solubility at different temps

• At \(0^\circ C\): Solubility of \(K_2Cr_2O_7\) is low (below 10 g/100g water? Wait, no, looking at the curve, \(K_2Cr_2O_7\) has a solubility that increases with temp. Wait, the question is about dissolving 40 g. Wait, maybe I misread. Wait, the curve: let's check the \(K_2Cr_2O_7\) line. At higher temps, solubility increases. Wait, the options: heating or cooling. Wait, the correct action to dissolve more (or allow 40 g to dissolve) would be heating, because solubility of \(K_2Cr_2O_7\) increases with temperature. Wait, let's check the curve again. The \(K_2Cr_2O_7\) line (solid line) at 60°C: what's its solubility? Wait, maybe the original question is about dissolving 40 g. Wait, maybe I made a mistake. Wait, the key: \(K_2Cr_2O_7\) is the solid line. Let's see the options:

Option A: Heating to 60°C. As temperature increases, solubility of \(K_2Cr_2O_7\) increases (since the line is upward sloping). So heating would increase solubility, allowing more solute to dissolve. Other options: cooling would decrease solubility, so less would dissolve. So heating to 60°C (option A) would allow 40 g to dissolve.

Answer:

A. heating the solution to \(60^\circ\text{C}\)