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Can White Make Yellow?-
Double Displacement Reactions in Solutions and Solids
Principle(s) Investigated: double displacement reactions, solubility rules, precipitation, polarity
HS-PS1-2. Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
HS-PS1-3. Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles.
Materials:
solid lead nitrate
solid potassium iodide
0.1 M lead nitrate solution
0.1 M potassium iodide solution
4 50mL beakers
test tube
analytical balance
you can get these materials from: http://www.flinnsci.com
Procedure:
Making the 0.1 M solutions:
1. weigh out
1.656 g solid lead nitrate
0.830 g solid potassium iodide
2. measure 50 mL water in 2 beakers
3. add lead nitrate to one beaker
4. add potassium iodide to the other beaker
Demonstration:
1. label one beaker (A) for lead nitrate and another beaker (B) for potassium iodide
2. pour 5 mL of lead nitrate solution into beaker A and 5 mL of potassium iodide solution into beaker B for pairs of students
3. weigh 2 g of both solid lead nitrate and potassium iodide and pour one of the compounds into a test tube
4. pour the other solid compound into the test tube, cover with a stopper and start to shake vigorously for a few minutes
5. ask the students while shaking the test tube what they predict to happen when the solutions combine and what they predict the solids will do. enter their answers into the quick write.
6. tell the students to carefully pour solution B into solution A and observe the reaction while continuing to shake the test tube
7. stop shaking the test tube once the solid has turned a bright yellow
8. enter answers to if this is what they expected for the solutions and solids into the quick write
Student prior knowledge: chemical bonding and how compounds form, names and formulas of ionic compounds, polarity, states of matter, mole stoichiometry to make solutions
Explanation:
There are four states of matter- solid, liquids, gases, and plasma. These states are composed of molecules and the molecules composed of ions (charged particles).
Solid molecules move very little, they vibrate. Liquid molecules slide around each other and move more freely so reactions can occur faster and completely. Gases have the most freedom and react quickly with other molecules. Plasma is made of ionized particles and occur at extremely high temperatures.
Why the liquids precipitated a solid:
Solutions are created by dissolving a salt in water. The dissolved molecule produces ions by the polarity of water molecules. The potassium and lead are positively charged are therefore are surrounded by the negative side of water while the nitrate and iodide are negatively charged and surrounded by the positively charged side of water.
Solubility rules give a list of which bonds are weaker than the bonding by water. In the reaction between potassium iodide and lead nitrate, the attraction between the lead and iodide ions are stronger than water and therefore react to form lead iodide. K+ and NO3- are stable in solution as mentioned by the solubility rules.
2KI(aq) + Pb(NO3)2(aq) <--> PbI2(s) +2K+(aq) + NO3-(aq)
A way to think about double displacement is that the ions switch partners.
AB + CD <--> AD + BC
Why the solids went through a chemical change:
The solid reacted because of the violent shaking of the test tube. If the solids were left in the test tube without being shaken, the reaction would take place because of the small vibrations of the molecules but it would take a much longer time than when energy is put into the reaction.
Questions & Answers:
1. What is something non-scientific that switches partners to create something new?
By: CHARLENE CHUA
Yesterday, MediaCorp announced that DJ The Flying Dutchman (FD) would be leaving radio station Class 95FM’s The Morning Express after having hosted the show for the last 10 years with co-presenter Glenn Ong.
FD, whose real name is Mark van Cuylenburg, will make a direct swap with Joe Augustin, who currently hosts The Gold Breakfast Show on Gold 90.5FM with Vernetta Lopez.
2. What is a way to remember the different between ionic and covalent bonds?
3. How can one remember that water is a polar molecule?
4. Are double displacement reactions always done with two solutions or two solids?
Double displacement reactions are commonly seen with two solutions especially in the lab for observation purposes. Some are accomplished by a solid and liquid but the two chemicals reacting must be able to switch partners.
Applications to Everyday Life:
Gastric acid and bicarbonate are naturally made in the stomach. The acid is made to break down food while the bicarbonate is made to neutralize the acid if it becomes to strong.
HCl + NaHCO3 <--> NaCl + H2CO3
the carbonic acid then breaks down into carbon dioxide and water
CO2 + H2O
Using an antacid for a heartburn:
2HCl + CaCO3 <--> CaCl2 + H2CO3
Precipitation of trace metals out of waste water is a common practice to reuse the water.
INTECH Determination of Trace Metals in Waste Water and Their Removal Processes by: Asli Baysal, Nil Ozbek and Suleyman Akman
"Precipitation is the most common method for removing toxic heavy metals up to parts per million (ppm) levels from water. Since some metal salts are insoluble in water and which get precipitated when correct anion is added. Although the process is cost effective its efficiency is affected by low pH and the presence of other salts (ions)."
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