Part (i) asks What can be Observed? Notice we start with aqueous forms of two compounds, which means initially we have two clear solutions. (These compounds also happen to be colorless, but you wouldn't necessarily know that.) Also, note that both compound names include a metal with, in one case, a nonmetal (chloride) and in the other, a polyatomic anion (nitrate). These are therefore both ionic compounds.
In mixing together two aqueous solutions, most likely we are looking for formation of a precipitate, i.e., a solid that forms from the solution. This can occur if either of the products of a double replacement reaction, where the positive ion from one compound combines with the anion from the other compound and vice versa, is insoluble. To determine this, we figure out what the possible products would be, and use a solubility table to find out if either is insoluble. In this case, silver chloride will be found to be insoluble.
Thus silver chloride will precipitate, and the observation would be that when the two clear solutions are mixed, the mixture becomes cloudy and a solid gradually settles to the bottom of the container.
ii) The correct equation begins with the formulas. Finding formulas for ionic compounds requires finding the charges of all ions, and writing a formula that includes the smallest whole-number ratio that makes the formula electrically neutral (total positive and negative charges are equal). You may have had to memorize that zinc forms the Zn+2 ion and silver forms Ag+; you can also find this information in many places, including ptable.com. From the Periodic Table you can infer that chloride has a charge of -1, and a table of polyatomic ions shows that nitrate also has a charge of -1. Thus the formulas are ZnCl2, AgNO3, Zn(NO3)2, and AgCl.
Write these as an equation and be sure to balance it:
ZnCl2(aq) + 2 AgNO3(aq) --> Zn(NO3)2(aq) + 2 AgCl(s)
Here the (aq) state label is used for all aqueous compounds, including zinc nitrate since it is soluble. Silver chloride is insoluble and forms a solid, so it is labeled (s). Soluble (aqueous) compounds are assumed to be ionized in water, so we can write the ionic equation being careful with coefficients on the individual ions
Zn^(+2)(aq) + 2 Cl^(-)(aq) + 2 Ag^(+)(aq) + 2 NO_(3)^(-)(aq) -gt Zn^(+2)(aq) + 2 NO_(3)^(-)(aq) + 2 AgCl(s)
Note all ions are labeled (aq), and the solid silver chloride is written as the compound.
We can also write the net ionic equation by eliminating the spectator ions, those that appear on both sides:
Ag^(+)(aq) + Cl^(-)(aq) -> AgCl(s)
Since there were two of every remaining species, it is correct to somplify all of the coefficients to 1 (no coefficient). This equation leaves out the information of what compounds were actually mixed together, but has the advantage of clearly showing that silver and chloride ions join together to form solid silver chloride.
Zinc chloride is an ionic chemical salt with the formula ZnCl2. It is composed of the zinc cation (Zn++) and two chloride anions (Cl-). Silver nitrate is also an ionic chemical salt with the formula AgNO3. It is composed of a silver cation (Ag+) and a nitrate anion (NO3-). Both chemicals are soluble in water, and when mixed together you need to know that the silver and chloride anions will react to form silver chloride (AgCl), a chemical that is a white solid and is largely insoluble in water. So the answer to part one is that two clear aqueous solutions will be mixed together to make a cloudy mixture with a fine white solid suspended in the water. To answer the second part, let's look at the complete ionic equation below:
Zn_(aq)^(2+) + 2Cl_(aq)^(-) + 2Ag_(aq)^(+) + 2NO3_(aq)^(-) -> 2AgCl_(s) + Zn_(aq)^(2+) + 2NO3_(aq)^(-)
This shows that the zinc chloride and silver nitrate will form solid silver chloride and zinc nitrate, which is completely soluble in water and will remain as ions. The net ionic equation eliminates the unused spectator ions and is shown below:
2Cl_(aq)^(-) + 2Ag_(aq)^(+) -> 2AgCl_(s)
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