ACIDS AND BASES
esretsting
t
c
ri es inte
e
m
urat produc
t
Test 2
t
enrmeric thses.
l
l
e
of
c ith tu ith ba
x
ml) l.
e
5
(
w
w
o
oon
coh
heorther testspecially
t
asp ing al
e
o
t
Anere is an anges, e , mix one ml) rubb
OR.
.
jar up (60
CAT nd
I
w
s
D
o
s
l
a /4 c
yel
IC IN or a
e gl
1
ight RMER indicat
r
In th eric in
b
TU
rns
he
turm
it tu ISON – sing t
l
i
t
u
n
! PO not
re u
ixtu RNING u are n.
m
he r: WA en yo hildre
ve t
c
h
ach
ly
Lea l the ja on w small
of e direct
e
e
d
l
i
l
b
m
p
e
e
o
c
La
m
r
sa
tan
p th ay f
Kee it aw
th a h subs ic
i
w
p
er
ers
eac
kee
r filt Label he turm r
ith
o
s
ew
t.
el
f t e you in
g
s
o
n
w
e
t
o
a
e
ch
littl
er t
. Us
n to
own
dish se the rite
pap ou pla sfer a stance as sh
or
d
e
t
e
h
n
,
r
t
u
y
w
a
b
s
a
i
t
,
a
a
r
u
Do tance per. T the s do th
nce
ect
bec
dic
s
n
exp acids ( substa
i
n
sub the pa ator to traw to
a
er ses madeilter
ou c w with r each
on indic king s n.
h
Y
.
t
o
ges
ello
). Fo
no nd ba lso be offee f is n
drin lustrati
a
han vious y yellow .
l
c
i
r
e
t s a can a ip a c ntil it per o ut
the
a
olou ess ob lready r base
c
e
r
l
a
sa
k fo
id o
Cr acid lution per. Dution uilter pa tely. C m
Loo s and lution i an ac
e
for eric soator paric sol e wet f omplet 1.25 c
bas eric so her it is
c
a
e
t
u
h
m ic
turm n whe
Tur ind turm ace t it dry f abo ips in is
w
do
into o the d. Pl d let ips o e str per red
int rate n an o str re th ic pa into
r
t
tu
sa lat pa er in d sto rme ges .
u
n
f
t
p
a
a pa m Dry chan ases
Save a bit of your turmeric indicator to play a
the 7.5 c ag. and ith b
blood-red trick on your friends.
by stic b ellow tact w
pla ght y con
bri en in
Mix one or two teaspoons (5 – 10 ml)
wh
Turmeric is a s
of baking soda with water in a glass.
pice
Then carefully and slowly pour a little
used by chefs
to a
of the turmeric indicator down the
flavour to currie dd
s and
inside of the glass.
H ur ch
colo
Acids and Bases
In the March issue of EasyScience we discussed acids and
bases and how you can test for them using red cabbage as indicator. Here is another quick and easy way to test whether a liquid
is an acid or a base. The colour changes are especially interesting. Watch out – this indicator can stain your hands and clothes!
eed:
n
l
l
i
w
You
or
els
er tow
p
a
p
White filters
coffee
Using a drinking straw as a medicine dropper
d:
e
e
n
l
il
You w
lid
with a
r
a
j
s
s
A gla
s
Label
om
hol (fr
o
c
l
a
ing
Rubb armacy)
h
the p
If you do not have a pipette or medicine dropper to transfer a solution drop by drop, you can use a drinking straw.
Put one end of the straw into the solution. Put your finger
over the other end and lift the straw out of the solution.
Release the solution by removing your finger from the end
of the straw. Caution: Don’t drink from this straw!
If you take too much liquid into the straw it will all run out
when you open the top end of the straw.
raw
ing st
k
n
i
r
Ad
ric
Turme
els
r tow
e
p
a
p
White e filters
fe
f
o
want to
or c
stance you
b
u
s
h
o
c
t
a
e
Label the
es
p of
stanc tap
Place a dro r towel or coffee filter.
b
✎
u
s
ape
Liquid e vinegar, ,
test on a p
e paper.
e
k
i
c
l
i
irectly on th
,
d
u
t
j
e
c
n
n
ta
tes
s
o
b
su
and
r, lem
your thumb
n
e
e
wate of tartar ,
tw
e
b
r
t sample.
of turmeric
cream ed in wate
n each tes
Pinch a bit
o
h
c
✎
in
p
a
lv
Drop
disso ent, milk
forefinger.
nge. The
g
colour cha
r
a
e
r
fo
h
tc
det
a
W
hen it is
ys yellow w ses,
e)
ta
s
r
c
ri
o
e
t
c
i
s
rm
r
tu
s. With ba
Turme e grocery
ped on acid e of red
p
h
t
ro
d
m
(fro
e a rang
k
you will se
eboo
t
id or base
o
n
ce
rs. Write ac
u
n
lo
o
e
c
i
c
s
of each
Your n
e the name
id
s
e
b
sted.
e
you have te
and p
substance
Test 3
A blood-red trick
Tur meric
Baking soda is a base, so you should see a reddish colour change.
The yellow alcohol-turmeric solution will float on top of the baking
soda solution, because it is less dense. Where the two solutions
meet, you should see a blood-red colour change.
Test 1
Show this to your friends!
Now, add an acid like vinegar and see what happens. The solution
foams and the colour turns to pale yellow!
Chart for universal indicator papers:
Hydrochloric acid
Vinegar
22
The word “acid” comes from the
Latin word “Acidus” which means “sour”.
Most acids have a sour taste. Some acids
are poisons, some can cause serious skin
burns, and thers are quite harmless. Some are
good to eat, like oranges. Our own bodies make
acids to digest food. Bases are substances
that are the opposite of acids. Some bases are
very reactive and corrosive, such as lime and
caustic soda. When an acid and base are
mixed in the right quantities, they neutralise each other (cancel each
other out).
MiniMag
Tap Water
Household cleaner
Liquid soap
to give mustard
a deep
yellow colour. C
hefs
also use it to c
olour
rice. You can bu
y it in a
grocery store.
EasyScience
is produced by the South
African Agency for Science and
Technology Advancement (SAASTA), an
operational unit of the National Research
Foundation. SAASTA’s mission is to
promote the public understanding, appreciation
and engagement
with science and
technology among
all South Africans.
Visit the website:
www.saasta.ac.za
for more
information.
23
Enzymes
✽ Enzymes are special catalysts in our
bodies which allow changes such as a kind of
burning to take place very gently.
✽ Digestive enzymes convert food to simpler substances,
but many other enzymes work in the opposite way, linking
simple substances together to form the more complex ones
needed to build up tissue.
✽ Enzymes themselves are made of protein.
✽ Enzymes work best at a particular temperature,
which is one of the reasons why our bodies are
kept at a constant temperature.
Do biological washing powders work?
You will need:
Have you heard or seen advertisements for washing powders that claim the
powders contain enzymes that can remove specific stains? People have
been experimenting with ways to use the power of enzymes to clean clothing
for a long time; in fact, the first patent was in 1913. Are the claims of the
manufacturers true? Let’s see ...
Our bodies use food to give us energy. Some foods like proteins, such as gelatine
and starch, need to be broken down before our bodies can use them. The units, or molecules
that make up proteins and starches are large, but they again are made up of smaller units.
This breaking down of the larger units into smaller ones is called digestion. Our bodies use
enzymes to burn the foods (or digest them) for energy.
The enzymes which help in digestion are specialists. An enzyme which digests protein will
not digest starch, nor will a starch-digesting enzyme break down proteins.
To see how an enzyme can break down proteins, and at the same time see if the claims
of manufacturers of washing powders are true, try the following two experiments:
✓ Read the instructions on the packets carefully and pre-
d:
e
e
n
ill
GELATINE
w
u
o
Y
uy
can b
pare two dishes of clear jelly, one of gelatine, and the
AGAR
r (you nce
a
g
A
e
d
i
n
c
a
s
other of agar.
e
t
et
Gelatin m specialis acher to g
e
o
t
r
f
✓ On each jelly, put a small pinch of an ordinary powder
r
e
agar
tanc
k you
, or as el-like subs
detergent, and of a so-called biological washing powder.
s
p
o
h
g
s
It is a
d)
✓ The biological powder is supposed to contain an enzyme
some. om seawee
r
f
which 'removes difficult stains like egg, gravy and blood'.
made
dishes
lastic
These contain proteins.
p
ll
a
Two sm
✓ If this is a true claim, we would expect to find the gelatine (a
protein) dissolved away under the 'biological' washing powder,
but not under the ordinary powder.
der
g pow
in
h
s
a
✓ The agar (not a protein) should not be dissolved by either. The
inary w
An ord
jelly might soften a little for many reasons, but do not be misled by
this. Look for a great hole in the jelly.
wder
ing po
h
s
a
w
ical
✓ Try this experiment and see what you find. If there is a hole in the
biolog
A
gelatine under the biological washing powder, but not one under the
ordinary washing powder, then the claims of the manufacturer are true.
Hole
GELATINE
Ordinary
washing powder
Biological
washing powder
ting
cipes floa .
e
r
d
n
a
s
p”
me
many na ut let’s call it “goo
b
There are
,
r this stuff
around fo
1
/4 cup corn starch and
3 1/2 teaspoons water
AGAR
Food colouring
Two glasses
Bowl
Two eggs
Biological washing
powder
Ordinary washing
powder
Fun Fact
A bee sting is acidic, so it
can be treated with alkalines
such as bicarbonate of soda,
while a wasp’s sting is
alkaline and can betreated
with acids such as vinegar.
24
Boil two standard eggs together, and push two
teaspoons into the yolks so that there is some
yolk left on the spoons. You may now eat the rest
of the eggs!
Dissolve equal amounts of ordinary and 'biological'
detergents in two separate glasses of water, and leave a yolk-stained
spoon in each glass. After some time you will see that the spoon
in the ordinary detergent still has yolk on, but the yolk on the
other spoon has been digested by the 'biological'
detergent. This will happen if the 'biological'
detergent really contains enzymes that
break down the proteins in egg yolk.
Biological washing powder - no egg yolk
Ordinary washing powder - egg yolk
Catalyst
A catalyst is something
that allows or encourages
a chemical reaction to take
place, while it remains
unchanged itself.
wl and
in the bo fingers.
h
rc
ta
s
ur
orn
ll with yo
Put the c
e
w
ix
M
water.
get the
add the
ment to
ri
ixture
e
p
x
e
uch the m mack your
ave to
h
to
y
u
a
o
y
m
n
You
ou s
Whe
. When y e a solid. Pick
ncy right.
consiste ld be like a liquid
your
sist lik
hould re ant, you can give
shou
s
it
,
re
y
tl
tu
n
ix
e
g
the m
you w
ring.
wn on it, hat happens. If
od colou
fo
f
o
s
hand do
w
p
and see
a few dro
some up zap by adding
me
goop so
tes of
called sta a
re
a
e
s
as. The
there is
quid or g en states when
li
,
d
li
o
s
on
e
e
. Goop is
es can b
nge betw
Substanc stances can cha ange in pressure u smack it
ub
or a ch
hen yo
matter. S
ently
perature lid and liquid. W
m
te
e goop g
in
th
e
o
h
g
s
c
n
u
n
a
e
to
h
e
c
ou
tw
. When y
erline be
the bord it acts like a solid
),
(pressure liquid.
a
e
it acts lik
ning?
e
p
p
a
h
What’s
25