I don't understand how I didn't answer the question:
Both NaCl and CaCl2 are used to melt ice in winter. Describe the
chemistry involved in both and explain how it is different for the two
chemicals.
¨ Write Equations
¨ suggested ideas/terms to consider: acidity, redox, solubility,
exothermic, endothermic (this is not an exhaustive list)
¨Think beyond the initial reaction if applicable
¨Remember, there is C02 in air
Research paper
Both NaCl and CaCl2 are used to melt ice in winter. Describe the chemistry involved in both and explain how it is different.
NaCl and CaCl2 are Salts. Salts are defined as any chemical compound formed from the reaction of an acid with a base, with all or part of the hydrogen of the acid replaced by a metal or other cation. Strong bases/acids are those that completely ionized in water. While Weak bases/acids partly ionize in water. HCl Is a strong base, while NaOH is a Strong base. The product of these two molecules is NaCl, a nuetral molecule. CaCl2 is nuetral also.
Ca(OH)2 ( strong base) + HCl (strong acid) -> CaCl2
Acid + Base --> Salt + Water
Ice nomally has a film of water around it. The the surrounding water warms up the ice because kenetic energy is transfered to the ice. The then water cools because of lost of energy. At the same time some of the water particles freeze, but because it is harder to take energy from an object than to give it energy, the rate of melting is faster than freezing. Eventually the ice melting and water cooling reaches dynamic equilibrium, the point where the melting rate and the freezing rate are in equilibrium. This happens when the water temperature reaches 0 degrees celcius. Adding salt disrupts the equilibrium, and increases the conductivity.
Water, which the Hydrogen has a greater pull on the electrons causign it to be polar, breaks down salt into ions. Electricity is defined as a form of energy resulting from the existence of charged particles. Ions are charged particles, and ions make water more conductive (Water is already conductive because is self ionizing) As the concentration of these ions in water increases, they begin to form into their original compounds again. The formation of ions, and the formation of molecules lead to a decrease in the rate at which ions enter the solution. Eventually it reaches an equilibrium, called a saturated solution. The amount of salt that must be added to a given volume of solvent to form a saturated solution is called the solubility of the salt.
The dissolved salt doesn't attatch easily to the ice; thus the rate of freezing goes down. The rate of melting is unaffected, so the melting rate is higher than the freezing rate. Then, the water begins to cool, slowing down the melting process. Eventually they reach dynamic equilibrium, but at a lower freezing point. In essence, salt melts ice because adding salt lowers the freezing point of the water.
The equations for salts turning into ions.
NaCl(s) + H2O --> Na+(aq) + Cl-(aq)
CaCl2 (s) -> Ca+2 (aq) + 2 Cl - (aq).
equilibrium constant expression for solubility
Kc= [Na+] [Cl-]/ [NaCl]
Kc= [Ca 2+] [Cl -] [Cl -]/ [CaCl2]
Kc is the equilibrium constant expression for solubility. The [NaCl] term represents the number of moles of NaCl per a liter. The [Na+] and [Cl-] terms represent the concentrations of the ions in moles per liter. The NaCl concentration can be calculated from its density and the molar mass. The Ksp -the solubility product- expression for a salt is the product of the concentrations of the ions. The solubility product of a salt can be calculated from its solubility
the solubility product
Ksp= [Na+] [Cl-]
Ksp= [Ca 2+] [Cl -] [Cl -]
The Difference between Cacl2 and NaCl
CaCl2 is better to use than NaCl because when water flows over the concrete, the Calcium leeches out of the concrete becoming brittle. The higher the calcium content in the water, the less this occurs.
Freezing point depression occurs when the freezing point of a liquid is lowered by adding another compound to it. .Sodium chloride can only melt ice only down to about -9°C (15°F), while Calcium chloride can reach -29°C (-20°F). .
Calcium Chloride also melts the ice faster because adding to ice creates an exothermic reaction. An exothermic reaction is one that gives off heat.
Calcium Chloride absorbs moisture from the atmosphere as opposed to relying on the little water that snow has to offer.