This section describes a technique used in generating 36 computer graded quizzes, each with three variables: x, y, z

Working in the background all second quarter is a quick basic program which solves the problems on 36 quizzes (4 different versions, each, of the 9 mole quizzes). An example of such a quiz might be:

Given the reaction of x grams of CyHz and given the equation: CyHz + O2 => CO2 + H2O

(the teacher pencils in the values of x, y, and z, which appear as blanks on the quiz)

1. How many grams of oxygen react?

2. How many moles of water are formed?

3. How many grams of water are formed?

4. How many grams of carbon dioxide are formed?

5. How many moles of oxygen molecules react?

Step 1: Balance the equation in terms of the variables y and z.

CyHz + (Y+Z/4) O2 => Y CO2 + (Z/2) H2O

Step 2: Determine the mole and gram ratios for the reaction

CyHz (Y+Z/4) O2 Y CO2 (Z/2) H2O

mole ratio 1 (Y+Z/4) Y Z/2

mass ratio 12Y +Z 32(Y+Z/4) 44Y 9Z

Step 3: Insert x grams of CyHz for the actual mass of CyHz. Set up the appropriate ratios to determine the actual moles and actual masses reacted for all of the reactants and products.

CyHz (Y+Z/4) O2 Y CO2 (Z/2) H2O

mole ratio 1 (Y+Z/4) Y Z/2

mass ratio 12Y +Z 32(Y+Z/4) 44Y 9Z

actual moles X/(12Y + Z) (Y+Z/4)[X/(12Y + Z)] YX/(12Y + Z) (Z/2)X/(12Y + Z)

actual mass X 32{(Y+Z/4)[X/(12Y + Z)]} 44[YX/(12Y + Z)] 18[(Z/2)X/(12Y + Z)]

Step 4: making the substitutions A = X/(12+Z) and B = Y + Z/4, the above table greatly simplifies:

CyHz (Y+Z/4) O2 Y CO2 (Z/2) H2O

mole ratio 1 (Y+Z/4) Y Z/2

mass ratio 12Y +Z 32(Y+Z/4) 44Y 9Z

actual moles A BA YA AZ/2

actual mass X 32BA 44YA 9AZ

Step 5: The answers to the quiz questions above are

1. 32*B*A

2. A*Z/2

3. 9*A*Z

4. 44*Y*A

5. B*A

Step 6: Write the program:

INPUT “Enter x, y, z”; X: INPUT Y: INPUT Z: A = X/(12+Z) : B = Y + Z/4: PRINT “1.”, 32*B*A : PRINT “2″, A*Z/2 : PRINT “3.” 9*A*Z : PRINT “4.” 44*Y*A : PRINT “5.” B*A

Unfortunately, I wrote this on the fly and didn’t bother to uncompile my quick basic program or test this one out so I hope no careless mistakes or typos crept into this. One day soon I will get around to testing this after which I will remove this message.

Step 7: Repeat steps 1-6 for the other 35 quizzes and link them with a menu.

Step 8: Give the student a quiz after penciling in the values of x, y, z.

Step 9: When the student submits the quiz, select the quiz number from the menu, enter the values of x, y, and z, which you penciled into the quiz, and the program will instantly output the answers. Naturally, a statement telling the computer to return to the menu (sorry, I used goto 10, since my menu is at 10; even though line numbers are from the age of the dinosaurs) after hitting enter (INPUT W) will ready the computer for the next quiz to be graded.

In this manner, one program will take care of grading individualized quizzes for the entire quarter. Unless you are preoccupied with other classroom matters, you will be able to give virtually instantaneous feedback to your students.

An example of a quiz sheet which is given to the student upon request follows:

Quiz 2 Mass Ratio Quiz:

Given the hydrate Na2SO4· 10H2O and given that x =___ :

1. Write the balanced equation for its decomposition into anhydrate and water.

2. Write the theoretical gram ratio

3. How many grams of Na2SO4 are in x grams of Na2SO4· 10H2O?

4. How many grams of water are in x grams of Na2SO4· 10H2O?

5. How many grams of Na2SO4· 10H2O are needed to contain x grams of Na2SO4?

Quiz 6 Per Cent Composition Quiz

Given the molecule: C__ H__ O__ : and given that x =__ :

.

1. What is the per cent of C in the molecule?

2. What is the per cent of O in the molecule?

3. How many grams of C are in x grams of the molecule?

4. How many grams of the H are in x grams of the molecule?

5. How many grams of the molecule contain x grams of O?

Quiz 10 Mole Quiz:

Given ___ moles of C__ H__ :

:1. How many moles of carbon atoms are there?

2. How many moles of hydrogen atoms are there?

3. How many hydrogen atoms are there?

4. How many carbon atoms are there?

5. How many molecules are there?

Quiz 14 Moles and Mass

Given ___ grams of C___ H___ :

:1. How many moles of carbon atoms are there?

2. How many molecules are there?

3. How many grams of hydrogen atoms are there?

4. How many hydrogen atoms are there?

5. How many grams of carbon atoms are there?

As quizzes are taken, they are torn off and the remainder of the quiz sheet is used for other students.

You may be confused by the fact that the quiz numbers jump by 4. This is because there are four different versions of each quiz. So quizzes 1, 2, 3, and 4 each are versions of the first mole quiz, while quizzes 5, 6, 7, and 8 are each versions of the second mole quiz.

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