experimental chemistry part 1
TRANSCRIPT
Describe methods of separations and purification for the components of the following types of mixtures:
(i) solid-solid(ii) solid-liquid(iii) liquid-liquid (miscible and immiscible)
Done by: Chew Yun Jin (3)3H/2011
1.2 Methods of
purification and analysisa)
Techniques to be covered for separations and purification include:(i) Use of suitable solvent, filtration and crystallization
or evaporation(ii) Sublimation(iii) Distillation and fractional distillation(iv) Use of a separating funnel(v) Paper chromatography
Separating a Solid from Solid. . .
H o w d o w e u s e f i l t r a t i o n t o
s e p a r a t e t w o s o l i d s ?
A m i x t u r e o f t w o s o l i d s c a n a l s o
b e s e p a r a t e d b y f i l t r a t i o n i f o n e
o f t h e m a r e s o l u b l e i n a s o l v e n t
b u t t h e o t h e r i s n o t . F o r
e x a m p l e , a m i x t u r e o f s a l t a n d
s a n d c a n b e s e p a r a t e d b y
f i l t r a t i o n u s i n g w a t e r a s t h e
s o l v e n t . S a l t i s s o l u b l e i n w a t e r
Filtration
I t i s u s e d t o
s e p a r a t e o n e
s o l u b l e s o l i d a n d
a n o t h e r s o l i d .
E x p e r i me n t 3T o s e p a r a t e a m i x t u r e o f c o m m o n t a b l e s a l t
a n d s a n d
P r o c e d u r e :
1) P o u r s o m e d i s t i l l e d w a t e r i n t o t h e
m i x t u r e o f c o m m o n t a b l e s a l t a n d s a n d .
S t i r a n d w a r m t h e m i x t u r e .
2) P o u r t h e w a r m m i x t u r e i n t o a f i l t e r
f u n n e l l i n e d w i t h f i l t e r p a p e r . C o l l e c t
t h e f i l t r a t e i n a c o n i c a l f l a s k (F i g . 3.14).
3) Wa s h t h e r e s i d u e w i t h a l i t t l e d i s t i l l e d
w a t e r t o r e m o v e a l l t h e s a l t s o l u t i o n
f r o m i t . T h e r e s i d u e i s s a n d .
4) P o u r t h e f i l t r a t e i n t o a n e v a p o r a t i n g
d i s h a n d e v a p o r a t e t h e f i l t r a t e t o
d r y n e s s (F i g . 3.15). T h e w h i t e s o l i d l e f t i n
t h e e v a p o r a t i n g d i s h i s s a l t .
A n o t h e r E x a m p l e :
T o s e p a r a t e s a l t a n d
c h a l k p o w d e r
-D i s s o l v e t h e m i x t u r e u s i n g
d i s t i l l e d w a t e r .
-T h e s a l t w i l l d i s s o l v e i n
w a t e r w h i l e
t h e s a n d w i l l r e m a i n i n t h e
b e a k e r .
-T h e f i l t e r p a p e r o n l y a l l o w s
t h e
s o l u t i o n t o p a s s t h r o u g h .
-T h e c h a l k p o w d e r w i l l b e
-C o l l e c t t h e
f i l t r a t e a n d p l a c e
i t
i n t o a n
e v a p o r a t i n g d i s h .
-E v a p o r a t e t h e
w a t e r / s o l v e n t
u n t i l
t h e s o l u t i o n i s
s a t u r a t e d . (D o n o t
h e a t t o d r y n e s s )
-C o o l t h e s o l u t i o n
a n d c r y s t a l s w i l l
a p p e a r .
C r y s t a
l l i z a t
i o n
Separating a Solid from a Liquid. . .DecantingThe simplest way to separate the water from the
pebbles is to just pour the water away. This
method is called decanting (Fig 3.10) We use
decanting to separate a dense, insoluble solid
from a liquid. Decanting is carried out everyday
during many activities. For example during
cooking, water is poured off various cooked foods
by decanting.
FiltrationTo separate sand from water, we use a method known as filtration. In general, we use filtration to separate small solid particles from liquid. Examples of small solid particles include sand, clay, dust particles and precipitates (small solid particles produced in a liquid by chemical reactions)
How can we remove a precipitate from a reaction mixture by filtration?
A white precipitate of lead (II) sulfate is produced when we add sodium sulfate
A s o l i d c a n b e s e p a r a t e d f r o m a l i q u i d b y
f i l t r a t i o n b e c a u s e t h e f i l t e r p a p e r a c t s
a s a s i e v e . A l i q u i d c a n p a s s t h r o u g h t h e
p o r e s (s m a l l h o l e s ) o f t h e f i l t e r p a p e r b u t
a s o l i d c a n n o t d o s o .
U p o n f i l t r a t i o n , t h e s o l i d t h a t r e m a i n s o n
t h e f i l t e r p a p e r i s c a l l e d t h e r e s i d u e . T h e
l i q u i d o r s o l u t i o n t h a t p a s s e s t h r o u g h t h e
f i l t e r p a p e r i s c a l l e d t h e f i l t r a t e .
Evaporation to Dryness and Crystallization
When a solid is insoluble in water, the easiest way to separate it from a liquid is by filtration. However, many substances, like common salt, dissolve in water to form solutions. To separate such substances, we evaporate water from the solution. This separation technique is called evaporation to dryness. Fro example, when we evaporate salt solution to dryness, we recover solid salt. This method can be used to recover salt from seawater.
However, many substances decompose when they are heated strongly. For example, sugar will decompose to give water and carbon when it is heated strongly. Most crystals, such as copper (II) sulfate crystals, give off water to become powders when heated. For such substances, evaporation to dryness is nota good method of purification. Also, when all the water is removed during evaporation, any soluble impurities present will be left on the crystals.
The best method of obtaining a pure solid sample solution is called crystallization.
How do we purify by crystallization?In crystallization, water is removed by heating the solution. Heating is stopped at the stage when a hot saturated solution is formed. If the resulting solution is allowed to cool to room temperature, the dissolved solid will be formed as pure crystals.
How do we test for a saturated solution?A clean glass rod can be used to test whether a solution is saturated. It is dipped into the solution and removed. There will be a small amount of solution on the rod. If small crystals form on the rod as the solution cools, the solution is saturated. The solution is at its saturation point or crystallization point.
Example: Obtaining copper (II) sulfate crystals from copper (II) sulfate solutionFlowchart below shows the steps involved.
Copper (II) sulfate solution
Saturated copper (II) sulfate solution
Heat until the solution is saturated
Copper (II) sulfate crystals + solution (contains soluble
impurities)
Allow solution to cool
Copper (II) sulfate solution
Filter the mixture
1)Chemistry Matters (Marshall Cavendish)
textbook
2) www.chemcompass.pbworks.com
3) www.google.com
Done by:
Chew Yun Jin (3)3H/2011