Chemistry Homework: Calculations of Molarity, Freezing/Boiling Points

This document contains solutions for two chemistry assignments. Assignment 22 focuses on molarity calculations, including determining molarity, calculating moles and mass, and understanding the effect of evaporation on solution concentration. It also covers solubility rules, net ionic equations, and the behavior of electrolytes. Assignment 23 explores colligative properties, specifically freezing point depression and boiling point elevation. It includes calculations for freezing point depression using molality and the freezing point constant of water, as well as an explanation of how impurities affect boiling points. The assignment also touches on the role of salt in lowering the freezing point of ice cream. References are provided for further reading on these topics.

Assignment 22
1. Molarity is given by moles of solute divided by volume of solution
Molarity =moles of the solute/volume of the solution
3.5 moles / 5L = 0.7M
2. First calculate the number of moles which is given by molarity multiplied by the volume
of the solution
1.50x0.500 =0.75 moles
Mass is given by molecular mass of KF multiplied by the number of moles, therefore
mass will be 0.75x58.0967032 =43.5g
3. First calculate the number of moles of hydrochloric acid which is given by
6Mx225ml=1350 moles
To get the final volume you divide the number of moles by the final molarity is given by
1350/1.5 =900ml
4. Allowing the solution to undergo evaporation makes it more concentrated since the
solvent evaporates leaving the solute behind. Evaporating will reduce the solvent and
increase the solubility of the solute as temperature increases.
5. Chlorides of all metals are soluble in water except silver and it will be in solid form while
all salts of sodium are soluble in water thus sodium chloride will be in aqueous form thus
the equation will be
NaNO3 (aq) +AgCl (s)
6. We say the solution is saturated-saturated means no more solute can be dissolved in the
solvent. It is understood that saturation of the solution has been achieved when any
additional substance that is added results in a solid precipitate or is let off as a gas.
7. Sodium chloride (NaCl) dissociates to form one sodium ion and one chloride ion while
magnesium bromide (MgBr2) dissociates to form 2 magnesium ions and one bromide ion
and calcium nitrate dissociates to form one calcium ion and 2 nitrate ions
8. The net ionic equation is a chemical equation for a reaction which lists only those species
participating in the reaction leaving out the spectator ions thus choice b represents the net
ionic equation.

9. The solubility of solids increases as temperature increases, the increase in kinetic energy
that comes with higher temperatures allows the solvent molecules to more effectively
break apart the solute molecules that are held together by intermolecular attractions.
10. This property is called cohesion. Water molecules gets attracted to water molecules
leading to stickiness.
11. Electrolytes are salts or molecules that ionize completely in solution. As a result, electrolyte
solutions readily conduct electricity. Nonelectrolytes do not dissociate into ions in solution. CH4
is non electrolyte because it’s a gases do not ionize.
Assignment 23
1. C6H12O6 will affect the freezing point most because its mass will be paramount, the
content of impurities will be greater compare to the other substances.
2. Molarity is given by moles of solute divide by the volume in liters
Molarity =3.25/0.25=13M
3. Freezing point difference will be X-0 degrees Celsius
Molal concentration multiply by the constant freezing point of water which is 1.86 will
be 1.86x5.7=10.602 thus the freezing point of sucrose will be 10.602-0=10.602
4. Boiling point will increase due to addition of solute which will be an impurity, impurities
raises the boiling point. This occurs because the presence of impurities decreases the
number of water molecules available to become vaporized during boiling.
5. Salt lowers the freezing point of the ice cream allowing the mixture to get colder, salt
helps to melt ice and prevents refreezing. It is a sweetened frozen food eaten as a snack
flavored with a sweetener such as sugar.
References
Zhou, E., Mirzadeh, M., Pellenq, R., & Bazant, M. (2019). Theory of freezing point depression
and materials damage by nano-fluidic salt trapping. Bulletin of the American Physical Society.
Robertson, B. (2017). Q: Why Do You Add Salt When Making Homemade Ice Cream?. Science
and Children, 55(4), 68-71.