Ksp_Lab_2 - Chemistry Double Displacement Precipitation

Background Information: Chemical reactions involve the rearrangement of elements to form new compounds. According to the law of conservation of matter, (nothing can be created or destroyed), the products we end up with must have the same number of atoms as the reactants we started with.

Background Information: Double displacement reactions occur when the positive ion of one compound displaces the positive ion of another compound. This “swap” of chemical bonding partners produces two new compounds that are different from the reactants at the start. Usually in double displacement reactions, a precipitate forms. Acid – base reactions are examples of double displacement reactions.

Background Information: General formula for double displacement reactions: AB + CD → CB + AD (the positive ion or cation (A) is displaced by (C); A and C “swap” places) For example: Antacid + stomach acid yields precipitate + water Magnesium hydroxide + hydrochloric acid → magnesium chloride + water Mg(OH) HCl → MgCl H 2 O

Objective: To determine the compounds produced from some double displacement reactions.

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. A clear plastic page cover with a table of circles (first slide of this PowerPoint) is at your Lab station with 2 drops of liquid in each circle. All the drops in a row are of the labeled ionic compound shown to the left. Make sure the tip of the dropper bottle does not touch the 2 drops of solution already on the plastic.

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. At the Lab station you will find dropper bottles filled with the ionic compounds that are listed at the top of the table.

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. Using the dropper bottle with the same chemical formula label as is at the top of the column, carefully drop 2 drops of the solution onto the two drops already on the top circle in that column on the plastic sheet. Continue placing 2 drops into each circle of the column until you reach the bottom circle.

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. Exchange dropper bottles for the next ionic compound listed at the top of the table and go down the column, placing 2 drops into each solution. Continue this for all the columns.

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. Record the results (if there was a precipitation, color and type of precipitation if present, etc.).

Procedure: Please be careful: Some of the chemicals are toxic and carcinogenic so handle them with care. Clean up by carefully placing a paper towel on top of the drops of chemicals so that they soak into the paper towel. You may have to use more than one paper towel. Once the liquid is soaked up, carefully roll up the plastic, paper, and paper toweling and carefully deposit it in the trash can.

Lab Report: For each of the reactions you will need to write out: 1.The Dissociation Equations for both of the initial ionic compounds. (you will have to look up on the internet what ions each ionic compound dissociates into)

Lab Report: For each of the reactions you will need to write out: 2. Which of the two ionic compounds, formed from each double replacement reaction, has the smallest Ksp. (Again you will have to look this up on the internet) 3. Write out the dissociation equation for this new ionic compound.

Lab Report: For each of the reactions you will need to write out: 4. Write down the Ksp value for this new ionic compound. (you will probably have to find it on the internet) 5. Write out the complete Ksp expression for this new ionic compound.

Lab Report: For the grade for the lab, each student will be in charge of a column or row, and he or she will get their grade from the results that are handed in for that column (be sure to label what column or row you did with your name).

AgNO 3 Pb(NO 3 ) 2 CuSO 4 KI NaCl HCl Na 2 CO 3 Stir this one gently with a toothpick