0.1586 g of NaCl + KCl mixture. 22.90 mL of 0.1000 M AgNO3

0.1586 g of NaCl + KCl mixture. 22.90 mL of 0.1000 M AgNO3

 

 

A mixture contains only sodium chloride and potassium chloride. A 0.1586 g sample of the mixture was dissolved in water. It took 22.90 mL of 0.1000 M AgNO3 to completely precipitate all the chloride present. What is the composition (by mass percent) of the mixture?

 

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AgNO3(aq) → Ag^+(aq) + NO3^-(aq)

AgNO3 : Ag^+ = 1 : 1 계수비(= 몰수비) 이므로,

0.1000 M AgNO3 용액 22.90 mL에 들어있는 Ag^+의 몰수를 계산하면,

(0.1000 mol/L) × 0.02290 L = 0.002290 mol Ag^+

 

 

Ag^+(aq) + Cl^-(aq) → AgCl(s)

Ag^+ : Cl^- = 1 : 1 계수비(= 몰수비) 이므로,

0.002290 mol Ag^+ = 0.002290 mol Cl^-

 

 

NaCl의 mol수 = x, KCl의 mol수 = y 라 두면,

x + y = 0.002290 mol

x = 0.002290 – y

 

 

NaCl의 몰질량 = 58.44 g/mol 이고,

KCl의 몰질량 = 74.55 g/mol 이므로,

58.44x + 74.55y = 0.1586 g

 

 

58.44(0.002290 – y) + 74.55y = 0.1586

58.44(0.002290) - 58.44y + 74.55y = 0.1586

16.11y = 0.1586 – 58.44(0.002290)

y = (0.1586 – 58.44(0.002290)) / 16.11 = 0.001538 mol KCl

 

 

KCl의 질량 백분율을 계산하면,

(0.001538 mol × 74.55 g/mol) / 0.1586 g × 100 = 72.29% KCl

 

NaCl의 질량 백분율 = 100 – 72.29 = 27.71% NaCl