(a) if we mix 2.00L of 3.00M (NH 4 ) 2 CO 3 , 4.00L of 1.50M (NH 4 ) 2 CO 3 solu
ID: 510778 • Letter: #
Question
(a) if we mix 2.00L of 3.00M (NH4)2CO3, 4.00L of 1.50M (NH4)2CO3 solutions and 4.00L of water, Calculate the final concentration. Assume there is no volume contraction upon mixing. [Hint: the water contributes to the final volume, but NOT to the total moles].
(b) If the final solution in (a) is set aside and allowed to evaporate until the volume of the solution is 5.00L, what will be the molarity of the solution after evaporation?
(c) Calculate the (m/v)% of the solution in (b).
(d) If the density of 5.00L of ammonium carbonate solution is 1.05g/mL in (b), determine the %(m/m) in this case.
Explanation / Answer
Ans. #A. Moles of (NH4)2CO3 in solution 1 = Molarity x Volume in liters
= 3.00 M x 2.0 L
= (3.00 mol/ L) x 2.0 L ; [1 M = 1 mol/ L]
= 6.0 mol
Moles of (NH4)2CO3 in solution 2 = 1.50 M x 4.0 L = 12.0 mol
Total volume of mixed solution = Volume of solution 1 + Volume of solution 2
= 2.00 L + 4.00 L = 6.00 L
Total moles of (NH4)2CO3 in mixed solution = moles of (NH4)2CO3 in (sol. 1+ 2)
= 6.0 mol + 6.0 mol = 12.0 mol
Now, Final [(NH4)2CO3] = Total moles of (NH4)2CO3 / Total mixed volume
= 12.0 mol/ 6.00 L
= 2.0 mol/ L
= 2.0 M
#B. Evaporation causes the loss of water only, but there is no loss of (NH4)2CO3.
Therefore, final volume becomes 5.0 L and total moles remain the same as 12.0 mol
Final [(NH4)2CO3] after evaporation = Moles of (NH4)2CO3 / Remaining volume
= 12.0 mol / 5.0 L
= 2.4 mol/ L
= 2.4 M
Ans. #C. Mass of (NH4)2CO3 in solution B = No. of moles x molar mass
= 12.0 mol x (96.0862 g/ mol)
= 1153.03 g
Volume of solution = 5.0 L
So,
% (m / V) = (Mass of (NH4)2CO3 in g / Volume of solution in mL) x 100
= (1153.03 g / 5000 mL) x 100
= 23.06 %
Ans. #D. Mass of solution b = Volume of solution b x its density
= 5000 mL x (1.05 g/ mL)
= 5250.0 g
Mass of (NH4)2CO3 in solution b = 1153.03 g ; [see #C]
Now,
% (m / V) = (Mass of (NH4)2CO3 in g / Mass of solution in g) x 100
= (1153.03 g / 5250.0 g) x 100
= 21.96 %
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