The second laboratory exam covers experiments 7 (hydrates), 9 (Properties of solutions), 10 (Composition of potassium chlorate), 11 (Double replacement reactions), and 12 (Single replacement reactions).  To prepare for the exam, the first thing you should do is to go back and read the write-ups in your lab manual. Don’t just read the answer sheets – read the introductory material to each lab too!

You’re responsible for these experiments:

• Experiment 7: p 61-66
• Experiment 9: p 83-92
• Experiment 10: p 93-98
• Experiment 11: p 99-104
• Experiment 12: p 105-108

The lab exam should take you approximately an hour. Since I will not time it, you’re free to take as much time as you need up until the end of the lab period. The exam will not cover experiments 2, 3, 4, 5, and 6 directly, but you are responsible for basic concepts covered in those labs (like significant figures).

There will be several types of question on this exam – multiple choice, fill in the blank, short (a sentence or so) answer, and some “complete and balance this chemical equation” or “balance the chemical equation”. Bring your calculator to lab with you on the day of the exam, since you will need it for calculations.

Specifics

Overall: Know how to write names and/or formulas of chemical compounds. You won’t be asked a naming question specifically, but if you’re asked a question about (for example) calcium bromide, you should know that the question asks about CaBr₂. Be able to write and balance chemical equations. When performing a calculation, be able to write the answer with the correct number of significant figures. Know the signs of a chemical reaction; how can we tell if a chemical reaction has occurred? You should review chapters 6 and 7 in your textbook to help you with this material.

Experiment 7: For the hydrates lab, you should first know what a hydrate is (a salt with water molecules bound in its crystals). You should know what happens when you heat a hydrate – anhydrous salt is formed and water is released. What does cobalt chloride test paper do? What happened when we added water to anhydrous copper (II) sulfate? How did we determine the mass of water in our unknown hydrate samples? Why is mass lost when we heat a hydrate in the crucible? Be able to calculate the mass of water in a hydrate from appropriate data.

Experiment 9: You should know the terminology of solutions: solution, solute, solvent. You should know that a solution is not just any mixture, but one that is homogeneous (uniformly dispersed). You should know the terms miscible and immiscible (are oil and water miscible or immiscible?) What is the difference is between a dilute and a concentrated solution? What is the difference between a saturated and an unsaturated solution? How do the temperature and the size of solute particles affect the rate of dissolving? Be able to calculate solubility of a compound in mass percent or g solute/100 g solution units given the appropriate data. Be able to perform simple calculations using the solubility (see the questions at the end of the experiment).

Experiment 10: This experiment dealt with a decomposition reaction. Be able to define and identify a decomposition reaction. What is the major hazard of working with potassium chlorate, KClO₃? Be able to calculate the mass percent of an element in a compound given appropriate experimental data (see the percent O₂ calculation) or given a compound’s chemical formula (see Chapter 8 in your lecture textbook). What was the reaction used to determine whether chloride ions were present in the residue?

Experiment 11: This experiment dealt with double replacement reactions: AB + CD –> AD + CB. Be able to define, identify, and write the products of double replacement reactions. Know the three types of compounds that can be formed by double replacements (precipitates, gases, or slightly ionized compounds like water). You will be required to write and balance double replacement reactions and to identify precipitates if formed. You will be given copies of the solubility chart and the periodic table. Using these, you should be able to properly write the formulas of chemical compounds. Use chapter 7 in your textbook to practice with double replacement reactions before taking the lab test..

Experiment 12: This experiment dealt with single replacement reactions: A + BC –> AC + B. You should be able to define and identify a single replacement reaction. You should know what an activity series is, and how to use it to decide whether one element will replace another in a compound. (You do not have to memorize the order of the elements in the activity series!) You should be able to write or identify the products of a simple single replacement reaction. You should be able to tell me whether an element is more or less active than another based on whether is can displace another element. For example, “The reaction 2Ag(s) + Cu(NO₃)₂(aq) –> 2AgNO₃(aq) + Cu(s) does not proceed. Which is more active, copper or silver?” [The answer to this one is copper, because it is not displaced by the silver.] Your class notes have more information on this type of reaction.