edited by: RON
DELORENZO
Middle Georgia Coiiege Cochran, Georgia31014
Significance, Concentration Calculations, Weak and Strong Acids
Calculate their total income if Mr. Jones works 7.5 hours and Mrs. Jones works 4 hours.
H. van Lubeck
Weak and Strong Acids
SchalengemeenschapNoord u.d Pekpleln 2 Amsterdam-the Netherlands
The ability of solutions of weak acids, unlike strong acids, to deliver more protons when the protons present are removed, can be illustrated by a financial analogy. Consider two persons, A and B, each possessing $200. A has $200 in his wallet and represents a strong acid. B has $40 in his wallet and the remaining in his hank account. B, of course, represents the weak acid. After spending all the money in their wallets, B still has some remaining money in his bank account; A obviously has not. This is analogous to a situation in which hoth solutions have the same molarity. If, on the other hand, A and B hoth have $200 in their wallets and B still has some money in his account, B is richer (greater molarity), hut hoth are equal in available cash (equal pH).
Significance
Many students have trouble in determining significance when numbers are added. For example, when 2 ml (0.002 1) hydrochloric acid solution is added to 1.0 l of water, the resulting volume, to the correct number of significant figures, of course, is 1.0 1. Alot of students will answer 1.0021 (1002ml). However, in daily life they would deal with the concept of significance in age-basically the same prohlem-in the correct way. T o the question "how old were you yesterday and how old are you today?" most students (unless a birthday occurs on the day the question is asked) will give the same answer. (I've never had a bright student say, perhaps justifiably, that his 17th birthday should be celebrated on the day he becomes 16 years and 6 months!) Concentration Calculations
Concentration problems (concentration: moles per liter) can often he clarified with an earnings analogy (earnings: dollars per hour). Consider the following problem: what is the total amount of moles of sucrose if 0.200 1 of 0.100 M sucrose solution is mixed with 0.350 1of 0.300 M sucrose solution? Students who have difficulty with this problem may have no difficulty with the following analogous problem: Mr. and Mrs. Jones hoth work. Mr. Jones earns $8.30per hour, his wife $6.80 per hour.
Conclusion
These analogies are certainly not the only ones that can be used to make students understand the scientific problems dealt with in this article. Especially a concentration problem offers several other possibilities. ..
has its own limitations. analogies designed to help students understand some of the difficult concepts frequently encountered in chemistry. Contributions that will produce a greater appreciation and knowledge of political, religious. economic, historical. and scientific aspects of life are encouraged.
Volume 60 Number 3
March 1983
189
