Topic: How to write a ionic compound formula
July 19, 2019 / By Kaylie Question:
Which of the following is a salt,and which of the following is a strong electrolyte?
Huldah | 1 day ago
Strong electrolytes come in two general categories: strong acids and soluble salts. It may help to remember that relatively few compounds are strong electrolytes. However, these compounds are also very common. Consequently, if the compound does not look familiar, it is probably not a strong electrolyte. The rules for strong electrolytes assume the solvent is water. Since there are few compounds that form ions in solvents other than water, you may assume that any substance dissolved in a solvent other than water is a nonelectrolyte.
Since there are only seven strong acids, the easiest way to identify strong acids is to learn the list. If it is not on the list, it is not a strong acid.
For a substance to fall in the category of “soluble salt” it must meet the criteria of both soluble and salt. Recall that “salt” is another name for an ionic compound, normally formed by a metal and an nonmetal. (Ammonium ion, NH4+ , combined with another nonmetal or polyatomic ion is also a salt.) To determine whether the salt is soluble, you should learn the solubility rules. Since most salts are insoluble, it is easier to learn the few that are soluble, and if it is not one you have learned, it must be insoluble.
Strong acids: HCl, HBr, HI, HNO3, HClO4, HClO3, H2SO4
Solubility rules from Table 5.4 (in the book):
All compounds containing alkali metal ions, ammonium (NH4+), nitrate (NO3–), or acetate (CH3CO2– or C2H3O2–) ions are soluble.
All compounds containing halide ions except salt of Ag+, Cu+, Hg22+, or Pb2+ are soluble.
All compounds containing sulfate (SO42–) ion except salts of Ba2+, Ca2+, Hg2+, Pb2+, and Sr2+ are soluble.
Ba(OH)2, Ca(OH)2, and Sr(OH)2 are soluble.
When determining the ions formed by strong electrolytes in water, remember these tips:
There are normally only two ions per compound, and you will probably recognize at least one of them.
The cation is written first in the formula. For strong acids, the cation is H+.
Polyatomic ions must not be broken up! (See Table 4.1 for list.)
Subscripts become stoichiometric coefficients.
Stoichiometric coefficients are not part of the formula.
Ions without charges are wrong.
>> Example 1
Are the following compounds strong electrolytes? If so, what ions do they form in water?
a. NaNO3 b. CO2 c. HF d. MgO e. FeCl3
NaNO3 is a strong electrolyte. Ions: Na+ and NO3–
Logic: It is a salt with the metal, sodium, and nonmetal, polyatomic anion, nitrate. Compounds containing either sodium or nitrate would be soluble (rule 1), so this certainly is. Sodium, as a group IA, alkali metal, always has a +1 charge; nitrate is a common polyatomic ion with a formula that should already be memorized.
CO2 is not a strong electrolyte; therefore it does not form ions in water.
Logic: It is a molecular compound of two nonmetals and not one of the strong acids.
HF is not a strong electrolyte.
Logic: Since hydrogen is the first element, it is an acid. However, it is not on the list of strong acids; therefore it is not a strong electrolyte.
MgO is not a strong electrolyte.
Logic: It is a salt of magnesium metal and oxide. However, neither element appears on the solubility rules. By default, that makes it insoluble. To be a strong electrolyte it must both be a salt and be soluble.
FeCl3 is a strong electrolyte. In water it will make Fe3+ and 3 Cl–.
Logic: It is a salt of iron and chloride. According to solubility rule 2, chlorides (group VIIA or 17, the halogens) are normally soluble. The exceptions do NOT include iron, so this compound is soluble. Iron is a transition metal, so its charge depends on how it is combined. Chloride, however, always has a charge of –1. Since there are three and the entire compound has a net charge of zero, iron must have a charge of +3.
>> Example 2
Which of the following are strong electrolytes? For each strong electrolyte, what are the ions it makes in solution?
a. HNO3 b. PbBr2 c. K2CO3 d. Na e. Ba(OH)2
HNO3 is a strong electrolyte. Ions = H+ and NO3–
It is on the list of strong acids.
PbBr2 is not a strong electrolyte.
Bromide is a halide, which is usually soluble, but Pb2+ is one of the exceptions.
K2CO3 is a strong electrolyte. Ions = two ions of K+ and one ion of CO32–
Potassium is in group 1, is always soluble, and always has a +1 charge. Carbonate is a familiar polyatomic. If you forgot its charge, the two K+'s were a hint!
Na is not a strong electrolyte.
It is not a strong acid. It is not a salt. It is sodium salts that are always soluble, this is sodium metal.
Ba(OH)2 is a strong electrolyte. Ions = Ba2+ and two ions of OH–
Rule 4, it is one of the soluble hydroxides.
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B. Calculating Molarity or Molality of Ions of Strong Electrolytes
First, you need to recognize that a solution is a strong electrolyte. Relatively few substances fit this category, but those that do are com
There is something you should understand about your question. Even if it is answered, you will likely not see a pattern. The reason for this is that all questions like this are answered in the laboratory and not necessarily by any pattern. If there is a pattern it is very short and there are exceptions.
Acids have H as the metal.
Bases have OH as their none metal
Salts are a combination of Acids and Bases.
Electrolytes like water.
Organics are made of Carbon Hydrogen and Oxygen. Most do not like water.
HF should be a strolng Acid, but it is not. More magic from the lab.
A. Strong Acids that are good electrolytes
B. Strong Bases that are good electrolytes
C. Other Strong Electrolytes
It's a good idea to look at what's left. NH3 in water forms NH4OH which is a base. It is a strong electrolyte in the form that is in water, but that is not how you are presented with it.
HF is not as strong an electrolyte as the first two.
CaSO4 is a salt but a hopeless electrolyte. This is a very important fact for anyone who has to take Calcium supplements. Most Calcium compounds cannot stand being in water -- sort of the dirty old chemicals of the chemical world. Too much calcium and it collects on joints and it can be very painful.
The others are organic compounds. The second last one is a sugar. The third last one I'm not sure.