Question

2. Calculate the molar concentration for each for each of the following solutions. (a) 1.50 g NaCl in 100.0 mL of solution (b) 1.50 g K2Cr2O7 in 100.0 mL

Answer 1

i) Molar mass of NaCl = 22.99 + 35.45 = 58.44 g / mol

We know that, no. of moles = Mass / Molar mass

$\therefore$ No. of moles of NaCl = 1.50 g / 58.44 g / mol = 0.02566 mol

[NaCl] calculated by using formula [NaCl ] = No. of moles of NaCl / volume of solution in L

$\therefore$ [ NaCl ]= 0.02566 mol / 0.1000 L = 0.257 M

ANSWER : [ NaCl ] = 0.257 M

ii ) Molar Mass of K ₂Cr ₂O ₇ = ( 2 $\times$ 39.10 ) + ( 2 $\times$ 52.00 ) + ( 7 $\times$ 16.00 ) = 294.20 g/ mol

We know that, no. of moles = Mass / Molar mass

$\therefore$ No. of moles of K₂Cr₂O₇ = 1.50 g / 294.20 g/mol = 0.005098 mol

$\therefore$ [ K₂Cr₂O₇ ] = No. of moles of K₂Cr₂O₇ / volume of solution in L

= 0.005098 mol / 0.1000 L

= 0.05098

= 0.0510 M   

ANSWER : [ K₂Cr₂O₇ ] = 0.0510 M