Which of the following salts will give highest pH in water?
A
KCl
B
NaCl
C
Na2CO3
D
CuSO4
Explanation
Na2CO3 is salt of
strong base, NaOH and weak acid, H2CO3 hence
the pH value of the solution will be high.
3
NEET 2013 (Karnataka)
MCQ (Single Correct Answer)
The dissociation constant of weak acid is 1 $$ \times $$ 10$$-$$4. In order to prepare a buffer solution with a pH = 5, the [Salt]/[Acid] ratio should be
The values of Ksp of CaCO3 and CaC2O4 are 4.7 $$ \times $$ 10$$-$$9 and 1.3 $$ \times $$ $$-$$9 respectively at 25oC. If the mixture of these two is washed with water, what is the concentration of Ca2+ ions in water ?
A
5.831 $$ \times $$ 10$$-$$5 M
B
6.856 $$ \times $$ 10$$-$$5 M
C
3.606 $$ \times $$ 10$$-$$5 M
D
7.746 $$ \times $$ 10$$-$$5 M
Explanation
CaCO3
$$ \to $$
Ca2+
+
CO32-
x
x
CaC2O4
$$ \to $$
Ca2+
+
C2O42-
y
y
[Ca2+] = x + y
Now, Ksp (CaCO3) = [Ca2+] [CO32-]
or 4.7 × 10–9 = (x + y)x .......(1)
similarly, Ksp (CaC2O4) = [Ca2+] [C2O42–]
or 1.3 × 10–9 = (x + y)y .......(2)
Dividing equation (1) and (2), we get
$${x \over y} = 3.6$$
$$ \therefore $$ x = 3.6y
Putting in equation (2) we get
y(3.6y + y) = 1.3 × 10–9
$$ \Rightarrow $$ y = 1.68 $$ \times $$ 10-5
and x = 3.6 $$ \times $$ 1.68 $$ \times $$ 10-5 = 6.048 $$ \times $$ 10-5