Reading the Precipitate Labs and some of the Bonding HW’s I realize that some of you are a bit in the dark about a few important details in chemistry. Read and learn, or at your own peril, guess your best on the Regents exam questions (not a good plan).
When table salt, sodium chloride goes into water something happens. It’s NOT a chemical reaction at all. It creates a mixture between the salt and the water. You know this is not a reaction as there are not two more reactants, nor is there something with new properties and a new formula as a “product”.
The sodium chloride dissolves (and ionizes) into the water as shown from Table I. The ions become AQ, they become LOOSE and MOBILE.
Salt and water mix to become salty water.
The solution is homogeneous, the same throughout. In the water the solid salt breaks into smaller and smaller (invisible) pieces, then, they break apart into LOOSE MOBILE IONS.
The salt disappears into solution, and although it ionizes (AKA dissociates into ions), if the water gets evaporated, the salt reforms as good old fashioned NaCl again. Easy when you are just mixed, not possible if it were a reaction.
When an ionic compound (metal cation/nonmetal anion couple) go into water they often will dissolve like this, first invisible, then into loose mobile ions. Sometimes the salt is so strongly bonded that the water can’t ionize it, and it stays “stuck” together and does NOT ionize. How do you know when that happens?
Look in Table F, the table that tells you IF an ion forms AQ or S in water. AQ means it dissolves into solution. S means it stays solid.
If an ionic compound is AQ in water, it will become LOOSE MOBILE IONS, and that solution will conduct electricity.
Ionic solutions have LOOSE MOBILE IONS, they conduct electricity. Water does not conduct electricity.
Ionic compounds that do not dissolve into water (like AgCl, or CaCO3 say) fall to the bottom of the water as they are denser than the water, and they do NOT release any ions into solution. They are STUCK together. There are NO IONS in solution, it’s not even a solution really. It cannot conduct electricity either.
When you put table sugar into water, sugar is C12H22O11(S) and it is NOT ionic. It dissolves and becomes AQ in water, but it has LOOSE MOBILE (NEUTRAL) MOLECULES, not ions. It does not conduct electricity.
Electrolytes are ionic compounds that can become AQ in water. The solids (NaCl(S), or CuSO4(S) say) cannot conduct, they do not have loose mobile ions. They are still called electrolytes because they can become AQ, they will have LOOSE MOBILE IONS in solution, and they WILL conduct electricity as AQ solutions.
Skip this one!
Sugar water has no ions, it cannot possibly conduct electricity. Water does not conduct, loose mobile ions do.
NaCl is an electrolyte because it CAN become AQ, and as NaCl(AQ), it can conduct electricity.
AgCl is NOT an electrolyte. It is ionic, but is does not form AQ with water, so no ions in solution, and no conduction of electricity either.
KNO3 is an electrolyte. As a solid the ions are locked up, so the solid does
NOT conduct electricity, but when it goes into water we get K+1(AQ) cations
and NO3-1(AQ) anions. Loose mobile ions in solution conduct electricity.
Mg(OH)2(S) is ionic but it’s not an electrolyte, it does not form an AQ solution in water, it has no loose mobile ions, it cannot conduct electricity.
A chemical reaction is when Reactants become Products. New formulas come about, as do products with different properties than before. And it is more or less IRREVERSIBLE. There are atom to atom ratios (or molecules to molecules ratios). In a mixture, like dissolving salt, or sugar, into water, you end up with either a weak mixture (a dilute or less concentrated solution) or a strong mixture (a concentrated or even saturated solution). With mixtures, no new formulas form, just mixing up your stuff. Mixtures do not have real formulas, any amount of stuff can mix with any amount of different stuff.
