Chemical Reactions Test

Below is a solutions guide to the optional review for tomorrow's test on chemical reactions. Come and see me tomorrow morning if you have any questions.

Quiz Reminder

Tomorrow will be a quiz covering the following topics listed below.

• Balancing chemical reactions and classifying types of chemical reactions. You will not need to write chemical compound formulas from names and then balance the reaction. You have your "Balancing Chemical Reactions" worksheet to study from.
• Using a solubility table. You will be given a name of a compound or a compound formula and then be asked to determine if the ionic compound is soluble (aqueous) or not soluble (solid).
• Using an activity series table. You will be given balanced single replacement reactions and then asked if the reactions could happen based upon the activities of the single element and its like element in the compound.

You will be able to use your owm periodic table and you will be supplied with a new solubility table / activity series table. The quiz grade will be going is the "Assessment" category of your grade.

Balancing Chemical Reactions

For those of you experiencing a little difficulty on the balancing chemical reactions worksheet, I have some advice for a possible sticking point.

Elements combine in whole number, that we know to be true. Thus, we need to have the smallest whole number ratio of the coefficients used to balance the equation. To balance an equation initially, you may use a fraction, but then you must modify the coefficients to make them whole numbers. Below is an example.

Reaction: C3H6O2 + O2 --> CO2 + H2O

Hint: Wait to balance oxygen last since placing a coefficient in front of elemental oxygen (O2) will not change any other elements.

Initial balancing: C3H6O2 + ?O2 --> 3CO2 + 3H2O

The carbons and hydrogens have been balanced. All that is left are the oxygens. There are a total of 9 oxygens of the product side (right of the arrow). Notice that 2 oxygens exist in the compound on the reactant side. Thus, to balance out the oxygens, an equation can be set up.

2 + x = 9 --> x = 7 --> Seven oxygens are required to balance the reaction, so this dictates that we use a coefficient in front of oxygen (O2) that will produce 7 oxygens. This will cause a coefficient of 3.5 to be used. This is not a whole number, but we can deal with that later.

Almost balanced: C3H6O2 + 3.5O2 --> 3CO2 + 3H2O

Having a fraction as a coefficient is not allowed, thus we must convert 3.5 to a whole number. To accomplish this, we will multiply 3.5 by 2. Just like in algebra, if something is done to one number, we must do the same thing to all of the numbers. Thus, all coefficients will be multiplied by 2. Doing this keeps the equation balanced.

Almost, nearly balanced: 2(C3H6O2 + 3.5O2 --> 3CO2 + 3H2O)

BALANCED!! 2C3H6O2 + 7O2 --> 6CO2 + 6H2O

Make sure that you check all of the elements on each side of the reaction to ensure that is has been balanced correctly.

Chemical Compound Remedial Work

If you would like more practice for the writing chemical compound formulas and chemical compound names quiz that will be given on Wednesday, November 3rd, 2010, a remedial quiz has been posted as a .pdf file on the Events Calendar on the class web-page. You can take the quiz and then check your results against the key for the quiz that has been given below. To mimick the quiz conditions as closely as possible, give yourself only 15 minutes to complete the quiz.