Why should the washing solvent be cold in the suction filtration step?

Based on the melting point of your impure solid, you look at the given samples and believe you havecompound A. Compound A is recrystallized using a mixed solvent system of ethanol and water. You add1 ml of hot ethanol to your sample and it doesn’t completely dissolve. You continue to add hot ethanolbut there isn’t any change. Some solid remains. What should you do next?

Determine a procedure to accurately create a 1.5•10^-6 mg Fe/mL solution using a 0.0500 mg Fe/mL standard solution and only having access to 100.0 mL volumetric flasks and 1.00, 2.00, 3.00, 4.00, 5.00 and 10.00 mL volumetric pipets. (You may have it make more than one solution by dilution to accomplish this)