SOME UNSOLVED PROBLEMS
By th e tim e yo u han progressed in a per u sal of the m an ual to th is page, several in te res ting ideas have n o do u bt come to m ind . One, pe r h ap s, is that all the prob lems on the
p reced ing pages have al re ad y been solved an d you r task was r eall y to solve them all over
again - a som ewhat u n profi ta ble occu pa tion. H owe ver, several p roblems for wh ich the
ans wers ar c no t known arc listed below. T hese prob lems are o nl y a few o f ve r y, ver y m an y.
T hey have be en selected for in clusion he r e on the basis of thei r sim plicity o f presentat ion .
(T he re ar c many other p roblems, some mor e interesti ng, n o dou b t , than the ones posed
here, t hat ca n no t be easily descr ibed to th e b egi n ner ill scicncc.) Also , b ecause of th eir
sim pl icity , we do have a loose sort o f ex planat ion for a few o f the problems in th is list. You
ma y even be aware of some of th ese expla n ations. Bu t th ey arc not solved in any real sense ;
th at is, for those for whi ch we han a h ypothe sis, the h ypothesis is doub ted b y at least some
o f those who h ave cond u cted tes ts in their la bo rator ies. H ence they arc, all of the m ,
unsol ved .
Later on , yo u m ay be the on e to conce ive o f an accepta b le exp lan at ion for a few o f
these. Let th is be you r cha llenge!
I. To 200 m l of bo ili ng water , ad d , with st irring, 0.5 g of each of the follow in g dyes:
Sudan red , su lfan il b lue, an ili n e yell ow. W hen the dyes ha ve d ispe rsed , ad d sm all swat ches
of co tt on , silk , woo l, an d acetate r ayon to the h ot liquid . Aft er a few minutes r em ove the
p ieces o f clo th and r inse in ta p water.
Wlry arc the pieces of clo th d yed di fferen t colors?
2. '\'ash an ar ti cle soiled with greasy and with no ngr easy d irt
solution .
W hy is th e ar ticle clean ed ?
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a soap or de terge n t
3. P u t a bo ut 50 0 n il of wa te r in a large beaker an d hea t it to boi ling. Cont inue to b oil
the wat er vigorously; note th at th e bub bles for m fro m fixe d spots o n the bo tt om, or sides,
o f t he beak er .
\Vhy do b ubbles form from particu lar spots when the water is b oi led vigoro usly?
4. Add 5 m l of a n . I-.N silver n it rat e solut ion to 5 uil of a O.I -N KBr solut ion. Filter
o ff the prec ipi tate wh ich is form ed am i cxp ose it to a strong li gh t.
\V h y d id th e silver br om ide darken ?
5. Clea n I ml of m ercu ry by sh ak ing it vigoro usly for on e m in u te in a test t ube con ta inin g 10 m l o f I-M n itri c acid . D iscard the acid an d wash the m er cury with dist ill ed water.
P ut the m cr cu r y 011 a clean watc h glass and ad d enough 5-N su lf u r ic acid to cove r the
m ercur y co m pletely. Ad d I 1111 o f O. I-.M po tassiu m permanganate solu tion to the acid an d
st ir ge n tly. (If the m crcury at th is po int is bro ken lip into seve ra l glob u les, collect it into
on c glob ulc .) \ Vith a steady hand , p ut the po int of a steel sewing n eed le u nder the surface
of thc aq ue ous so lu tion an d li ghtl y touch the side o f th e m er cury glob u le , a few de gre es
ab ove its "eq u ator." H ol d th e need le ste ady. R h yt hm ic act ion will co nt inue fo r several
seco nd s.
Wh y d ocs the m crcury pulsate?
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6. Prepare a collod ion bag sim ilar in size and shape to a test tube. H alf-fill the bag
with a sol u tion co nta in ing 0.1 g of po tato starch and 0.1 g of sod ium chloride per 100 ml .
Suspe nd the half-filled bag in a beaker o f d ist illed water. From t ime to t im e test the di stilled
water for the pr esen cc of CI- ions and for the p resen ce of sta rch.
' Vh y does the electrolyte d iffuse through the collod ion membrane, wherea s the sta rch
does not?
7. I n the hood , pass a little ph osp horo us t rihydr id e (or arsen ic tr ih ydride or antimon y
u -ihydri d e) in to a O. I-M solu tion of silver n itrate. A yello w p recipitate whic h turns black
in a few ho urs or less is formed.
' Vhat is the nature of the yellow precip itat e?
8. Mi x 2 g o f finel y d ivided P b aO ~ with 2 g of finel y d ivid ed clea n sa nd. Put 50 m l
of water and 50 m l of paraffin oil in a tall glass cylinder. (A grad uate will do , bu t the good
chem ist uses a grad uat e on ly for mea suring vo lumes, no t for the p urpose o u tl ined hcrc.)
Add the lead ox ide-sand mi x ture, and with the pal m of your han d over the mou th of the
cylinde r, shake vigorously for several m in ut es. T hen let the cylinde r a nd its co n te n ts sta nd
un d istur bed for a few min u tes.
' Vh y is the lead ox ide separated from the sand ?
Every che m istry class includes a few studeurs interested in subjects other than chemistry.
In recog ni tion of these nonchem ists, here arc a few p ro blems from ot her d iscipl ines.
Fro m geo log y: w har caused the deformat ion of the outer layers of the eart h an d th e
n msccluen t fo rmation of mo u n ta ins?
From a su bd ivision o f b iology, emb ryo logy : T he ne rve cells whi ch are d istr ibuted
throughout the bod y o f an an imal were o rigi na ll y, in the ver y yo u ng embr yo, all collected
together in one place. D ur ing th e su bsequen t gro wth o f th is em bryo, man y of these cells
left the site of their origi n and mi grated to remo te places in th e body, where they gr ew
into fu nct io ning cells.
What fac tors in it iated t his m igration? \\'h at di rected the m igr a tory cells to certa in
specific locat ion s? W hat was thei r mod e o f locom ot ion?
It is remar kable to realize t hat o nly lOO yea rs ago almost every q uestion listed in th is
ma n ua l as an exerci se for th c stude nt (ami many ot he rs, no t l isted , for wh ich the answers
are now fa irly well esta blished ) would have been p ut in t he list in th is part of th e m anual.
At some fut u re t ime t he an swers to the question s now listed here will be rea so na bly well
established and ot her quest ions not as ye t even co nce ived (!) will ta ke thei r place in a list
such as th is one.
Yo ur duty and pleasure, as a scien tist , will be to move q uest ions from the u nsolved li st
t he solved list (and occasiona lly back aga in ). Yo u will learn to note with awe th at for
e' "ery question re moved from the list o f un solved problem s two or three will arise to take
its place. A nd yct, for all this. o u r knowled ge of what is true gets closer and closer to T r u th ,
a nd th is is thc wonder of wonders.
to
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