edited by
J. DUDLEY HERRON Purdue Un~vers~ty West Lafavene. Indiana 47907
Defined?"
Purdue Uniuersity West Lafayette, Indiana 47907 In the December issue of This Journal [54,758 (1977)] we asked whether chemists agree on the meaning of terms and followed with a short quiz i n ionization and dissociation. The resnonse was not overwhelming - hut sufficient to raise interesting questions. Most responses were from faculty and graduate students a t Purdue. (I copied the quiz and placed i t in mailboxes.) I t should not be assumed that these responses are representative of all chemists or even those at Purdue. The response rate was simply too small to justify generalization to any population. Resoonses are shown in Tables 1-4 and discussed below. First, there seems to he general agreement concerning two items in the ouiz. 96% of Purdue eraduate students. 87% of university fackty and chemists in ion-teaching positions, and 73% of undergraduate chemistry students who responded would describe the following process as ionization.
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Most others would describe the vrocess as oxidation and this is clearly an acceptable name. Agreement was just as high on the last item of the quiz
2 H(g)
94% of the faculty and chemists in non-teaching positions, 87% of the graduate students and 61% of all others who responded would call this a dissociation. The only other terms used by university chemists, graduate students, or secondary school teachers were atomization and bond dissociation, both of which appear to he descriptive and unlikely to he confused with other chemical processes. A few undergraduate students gave responses which are clearly inappropriate. Table 3.
Response frequency for Three Undergraduate Classes. N = Aae Term Used
ltem
Ionization
Dissociation
Oxidation
1 2 3 4 5 6 7 6 9
34 (0.73) 33 (0.67) 26 (0.53) 18 (0.37) 19 (0.39) lE(0.37) 19 (0.39) 23 (0.47) 3
3 3 5 S(0.16) 30 (0.61) 30(0.61) 30 (0.61) 15 (0.31) 31 (0.63)
1 1 (0.22)
Table 4.
Reduction
Other
1
1 1
12 (0.24) 17 (0.35) 13 (0.27)
6 (0.12)
1
1
1
10 (0.20) 1 1 (0.22)
1
Responses Frequencies tor Secondary School Teachers. N = 10' Term Used
Hem
Table 1.
-
Item 9: Hdg)
Response to "Are Chemical Terms Well
lonization
Dissociation
Oxidation
Reduction
Other
Response Frequencies tor Purdue Graduate Students. N = 511s Term Used
ltem
ionization
1 2 3 4 5 6 7 8
51 (0.96)' 31 (0.58) 31 (0.56) 21 (0.40) 10 (019) 10 (0.19) 9 (0.17)
9
Dissociation
Oxidation
Reduction
Omer
lO(0.19)
10 (0.19)
2 1
5 (0.09) 30(0.57) 40 (0.75) 39 (0.74) 8(0.15) 46 (0.87)
20 (0.38) 18 (0.34)
4
3
3 14 (0.26) 13 (0.25) 4 25 (0.47) 7 (0.13)
Responw Frequencies for Unlverslty Faculty and Chemists in Non-Teaching Positions. Purdue Facultv = 18: Other University Faculty = 7; Other ~hemlsts= 6; Total N = 31"
Table 2.
Ionization
Dissociation
Oxidation
Data were summarized separately fw ~urduegraduate &dents able 1) but were o r o u. ~ rRes~onre . from vnlverslN combinad la othar . . faculN outside of Purdue and from chemists in non-teachingpoaifms war law and appeared to be similar to responses hom faculty members from omer Purdue laculhl, mese dam were pooled as Table 2. ~ h r e s u n f ~ e ~ l i iPent e s re~pmses Com h i r undergsduate clauen. One contribution was a class of 17 In ohyeical Chemistry. BSecOndwasaclassof 16 in inawnic chemistrv. and themlrd . . was simply identifiedas an undergraduate class. Although there were soma obvious dliferencer in response from the three groups. lf was decided to p w l these data as undergraduate rhdents Table 3). Response horn sscondw school t e a m was much t w low resoonses mat omiina wim snv omer lo .imtiw. analvsis . but sYnioIenllv dillwent from group appeared questionable. These responses are shown as Table 4.
.
m
Term Used ltem
Notes lor Tables
Reduction
.
.
Other P T l m ~ ~ l e n t r lIn e sead mblerepeaentthanmber oftimeraterm war vredmdesaibe the process denoted by the quiz item, Therefore me sum acmrr a row of me table will n m l l y produce the N (total number of respondents)for that table. m e n this is not the case. It ISbecause some respondents len mat item blmk or indicated mattwo terms are aqmlly appropriate responses. aNumbe~sin parenmeees represents me proportionof renpondsnta(N) who gave mat response. Thus, me sum of pmponms may be slightly more than one asiightly lessman one. (See prevlour notel Due to the low number of respondents in Table 4 no propwtlons w-e cabulaled. In addition. when hnumber of responses in a given category was -11 me propation was not calcumted.
Volume 55, Number 6.June 1978 / 393
'l'hcre was less agreement on other Items in the quiz w d this was expectrd. Older dictionaries or encvcloual~asot rhemistrv commonly restrict the use of ionizatibn to dissociation of solute into ions. Under this notion, items 5 . 6 . and 7 on the quiz would be described as ionization but items 2, 3 and 4 would not. This restricted meaning of the term is clearly out of step with the majority of faculty and graduate students who responded to this survey. It is also contrary to the definition of ionization found in more recent reference hooks. For example, "The Encyclopedia of Chemistrv (3rd ed.)" describes ionization as "the process by which a ne&l or an uncharged atom or molecule acquires a charge, thus becoming an ion" ( I ) . This would include processes which occur in solution as well as thoae that occur in gas phase. Even though ionization in the gas phase normally results in formation of positive ions, the reference cited makes clear that ionization may be used to refer to changes that produce negative ions as well. In spite of this, it is evident from the quiz results that there is some reluctance to call such processes ionization. ~
~~~
a
-
Item 2: Cl(g) + le- C1-(g) Although over half of the students descrihed this process as iamizafion, less than hall'(3OouJuf facultv and chemists in non-teaching positions did so. For the latte; group, reduction was almost as popular (32%)-and miaht have been more popular had the quiz suggested this as term to use. There were many answers in the "other" category. Among faculty, "electron capture" and "electron attachment" were popular and among graduate students, "electron affinity" was often used. This latter term is interesting because electron affinity is usually defined as the energy associated with the process rather than the name for the process itself. Response patterns for
a
-
Item 3: Fe2+(g) Fe3+(g)+ l e c md
-
Item 4: F-(g) F(g) + leme very similar to the patterns found for item 2 with graduate t u d ~ n & n n duniiergrabuate; more willing to call the processes onization thun were the university tacnlry. chemists in noneachinl: pusit ions and secon(iilry schwl teachers. The latter :rmlps preferred t o (IeirriOt. the process as oxidation, an ap~ropriateterm. In view of arguments previously made ahout the difficulty ,f seeing that a loss of electrons corresponds to again in oxilation number ( 2 , 3 ) ,it is of interest that four graduate stulents. one undergraduate and one secondarv school teacher nade this common mistake. They described;tem 4 as reducion. None of the universitv facultv. or other chemists made he same slip. There is hope yet! Responses to items 3 and 4 are of interest in light of the lefinition that ionization is "the process by which a neutral r an uncharged atom or molecule acquires a charge . . ." emphasis added). Obviously neither of the processes fits this efinition. Still, in the case of item 3 it is easy to understand he identification of this process as ionization since the process i associated with the third ionization potential of iron. Jnsification for calling item 4 ionization is less clear, however, ince there is no ionization potential associated with this irocess. I assume that those who named this Drocess ionization -end to equate "loss of an electron" with ionization. In "The Encvclouedia ~ - -~~" . of Chemistrv (3rd ed.)." , , the disnwion under Ions, gaseous begins, "~(emists tend to think of mization as exclusively a solution phenomenon . . Aparently this is not so. When we look at the responsesto those ~
."
items on the quiz that describe solution processes, ionization was not the most popular term. The items are Item 5: HCNg)
(Hz01
Hf(aq) + C1-(aq)
Item 6: NaCl(s) +Na+(aq)+ C1-(aq)
-
(Hz01
Item 1:HAc(aq) H+(aq)+ Ac-(aq) Taking all responses into account, the most popular term for these items was dissociation but there were a number of other responses. Among the terms used were solvation, dissolution, hydration, hydrolysis, dissociation and hydration, dissociation and dissolution, dissolution and ionization, ionization and dissociation. solvation and dissociation.. and will-base reactiun. Most of these terms appear to be suitable. An exceotion miehr be the use of hvdrol\~iisto describe items 5 and 6. Perhaps; quiz on hydration andhydrolysis would & he instructive. The rather low proportion of respondents willing to call item 6 an ionization is of some interest. The reasonine is clear. We believe that a crystal of salt contains ions and t i a t these merely come apart under the action of the solvent. What makes the response interesting is that this process would be called ionization under the definition given in many dictionaries and encyclopedias of chemistry. Indeed, this exact process is often given as an example of ionization. For example, in "The Condensed Chemical Distionary" (4) we read that "[ionization] occurs spontaneously in many salts when dissolved in water or melted. Thus, solium chloride yields positive sodium ions and negative chloride ions.. . " Item 8 [SOdg) HzOfl) 2H+(aq) + SOa2-(aq)]certainly involves more than one simple process and few respondents were content to call it either ionization or dissociation. Probably fewer would have done so had the quiz not specifically focused on these terms. Most of the terms used to describe items 5-7 were used for 8 as well but the most popular terms were hvdrolvsis . - and solvation. Several res~ondentseave no name for the process. ~
+
~~~
-
-
Discussion If it was not clear before, it is clear now that chemists do not all agree on the meaning of ionization. Does this matter? Prohahlv not for the exnerienced chemist. Understanding ~~-~ chemistry as she does, the meaning is usually clear in context However, this may not he true to beginners. When we become so casual in our use of words that they mean different things to different people, it makes it more difficult to communicate an already difficult subject. We complain that our students don't understand what we are saying but how can they if what is meant depends on who says
.".
it?
Some may object that virtually all words have different meanings in different contexts and this is certainlv true to some extent. However, in other walks of life we go out of our way to make this clear. We explain in what sense we use a word. Do we do this when we teach chemistry? I fear that in science we oversell the "exact" nature of our discipline-implying to others that things are more precise than they are. Perhaps using words like ionization, valence, dissociation, and "strong" in different ways would not be so bad if we made more effort to explain to students that the terms are used tomean different things. At least the student would be forewarned and not quite so confused when his second semester college lecturer uses a term in a wav" that is diiferrnt thnn usrd 1); the first semester prof who used the term differently thun it was taught in high school! Literature Cited
High School Forum is a monthly feature presenting short articles Finterest and use to hieh schwl teachers in their work. Contributions ) Hieh School ~orum~from high school teachers are esoeeiallv soritrd. &mr teachrr.may feel ihat they huv~morrq~~esti~m.it~r ask tun ilnawrrs lo g i v e These arc also i w w d Srnd twlr c@ea uf ,dl m~ributlonstc, the ~ , l u m neditor. 394 1 J o U r ~of l Chemical Education
11975).
(41 Hawley, G.G., "The Condensed ChemicalDictianary: 1SthEd.J. New Yark van^,,^. trand. 1971.
