Question

 

How many grams of Co(NO3)2 ·6H2O are needed to prepare 100.00 mL of 0.15 M solution of Co(NO3)2 ?

If 2.00 mL of the 0.15 M Co(NO3)2 solution is diluted to 10.00 mL with water, what is the resulting Co(NO3)2 concentration?

Answer 1

1)

volume , V = 100 mL= 0.1 L

we have below equation to be used:

number of mol,

n = Molarity * Volume

= 0.15*0.1

= 1.5*10^-2 mol

this is also number of mol of Co(NO3)2

Molar mass of Co(NO3)2.6H2O = 1*MM(Co) + 2*MM(N) + 12*MM(O) + 12*MM(H)

= 1*58.93 + 2*14.01 + 12*16.0 + 12*1.008

= 291.046 g/mol

we have below equation to be used:

mass of Co(NO3)2.6H2O,

m = number of mol * molar mass

= 1.5*10^-2 mol * 291.046 g/mol

= 4.366 g

Answer: 4.366 g

2)

use dilution formula

M1*V1 = M2*V2

Here:

M1 is molarity of solution before dilution

M2 is molarity of solution after dilution

V1 is volume of solution before dilution

V2 is volume of solution after dilution

we have:

M1 = 0.15 M

V1 = 2.0 mL

V2 = 10.0 mL

we have below equation to be used:

M1*V1 = M2*V2

M2 = (M1*V1)/V2

M2 = (0.15*2)/10

M2 = 0.0300 M

Answer: 0.0300 M