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12.
(b) We want to dispense 12 suppositories
each weighing 2gm and containing 400mg of tannic
acid,
Amount
of coca butter = 2 gm x 12
=
24 gm
Amount
of tannic acid = 0.4 gm x 12
=
4.8 gm.
Displacement
value of tannic acid is 0.9, therefore
=
4.8/0.9 = 5.33 gm of base will displace
4.8
gm tannic acid = 5.33 gm cocabutter
Amount
of coca butter = 24 gm - 5.33 gm
=
18.67 gm
13. (c) Median or
Mode is generally expressed as a middle value
of experiment, if number of values are even, then
average of middle values should be considered.
To find median or mode of experiment data, one
should first arrange the data in ascending or
descending order.
In
our example,
105,
115, 118, 120, 135, 140, 175, 190
=
(120 + 135)/2 = 127.50
14. (a) The concentration
of reactant M is half in a reaction that is third
order in kinetic,
dx/dt
= k (a-x) (b-x) (c-x)
=
k (a-x)3 where a=b=c
=
k (M)3
now
M = M/2
=
k (M/2)3
=
1 /8 k (M)3
15.
(b) 0.025 min-1
For
the first order kinetic,
K
= 2.303/t x log Co/C
=
2.303/90 x log 500/50
= 2.303/90 x log 10
= 0.025 min-1
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