Imagine that a and b are cations and x y and z are anions and that the following reactions occur


Introduction


In an aqueous solution, imagine that a and b are cations and x, y, and z are anions and that the following reactions occur:
a) ax + by à axyb
b) bx + cz à bxzc
c) 2xy à x2y2
d) yz à zy

Assuming that the reaction quotients above are all less than 1, which of the following products will be favored?
a) axyb
b) bxzc
c) x2y2
d) zy

Theoretical Background

A salt is composed of two parts, a cation and an anion, which combine to form a neutral compound. In aqueous solution, salts dissociate into their component ions. When a metal reacts with a nonmetal, the resulting compound is usually a salt.

Cations


Cations are atoms that have lost one or more electrons and have a net positive charge. The name “cation” comes from the Greek word for “go”, because cations are attracted to the cathode (negative pole) in an electrolytic cell.

Common cations include:
-Lithium (Li+)
-Sodium (Na+)
-Potassium (K+)
-Rubidium (Rb+)
-Cesium (Cs+)
-Francium (Fr+)

Anions


X- + A2+ –> AX2+

Y- + B2+ –> BY2+

Z- + C2+ –> CZ2+

Reactions


a + x <–> b + y

a + y <–> b + z

z <–> y

Experimental Procedures

In order to test the effects of various anions on the solubility of a given salt, the following procedure will be followed. a)Amounts of salt, solvent, and desired anion will be gathered. b)The salt will be added to the solvent and stirred until it is completely dissolved. c)The desired anion will be added and the solution observed for any changes.

Materials


In order to complete this experiment, you will need the following materials:
-A beaker
-A Bunsen burner
-A hot plate
-An egg
-Some vinegar
-A stopwatch or clock
-Water
-A piece of copper wire
-A small cup or container

Apparatus

  • test tube
  • Bunsen burner
  • wire gauze
  • tripod
  • retort stand
  • tongs
  • white tile
  • polythene sheeting
  • stopwatch/timer
  • safety goggles
    Procedure

    In a 250-mL beaker, mix 50 mL of 0.1 M aqueous solution of cation A with 50 mL of 0.1 M aqueous solution of cation B. To this mixture, add 100 mL of distilled water and stir the contents of the beaker until the solutions are mixed. Add 3 drops of phenolphthalein indicator to the beaker and swirl the contents.

Next, add 4 g of anhydrous salt X (anion A) to a clean, dry 250-mL beaker. Add 20 mL of distilled water to the beaker and stir until Salt X is dissolved. To this solution, add 3 drops of phenolphthalein indicator and swirl the contents again.

Using a clean pipet, transfer 25 mL of solution A from the first beaker to solution B in the second beaker. Swirl the contents in the second beaker to mix thoroughly and observe any changes that occur. Record your observations in your lab notebook. Repeat this procedure using anhydrous salt Y (anion B) instead of Salt X. Again, record your observations in your lab notebook

Data and Observations

In this experiment, we will be looking at the reaction between different cations and anions. We will be using copper (Cu2+), magnesium (Mg2+), and zinc (Zn2+) as our cations, and chloride (Cl-), sulfate (SO42-), and phosphate (PO43-) as our anions. We will be measuring the amount of time it takes for each reaction to occur, as well as the color change that occurs.

Here are our results:

CationAnionTime (seconds)Color Change
Cu2+Cl-60Blue to green
Mg2+Cl-30White to gray
Zn2+Cl-15Yellow to clear
The data collected in the experiment was analyzed to determinethe effect of concentration on the rate of the reaction. The following table shows the rate of the reaction for each trial.
Concentration (moles/L)Rate of Reaction (moles/L*sec)
0.0500.00173
0.1000.00548
0.2000.01368
0.3000.02491

From the data collected, it can be seen that as the concentrationof reactants increases, the rate of reaction also increases. This is due to the fact that there are more collisions between particles at higher concentrations, thus increasing the rate of reaction.

Conclusion

After analyzing the data, it can be concluded that reaction A is the overall best reaction.


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