Question

A student wants to determine the specific heat of NaCl. He weighs out 50 g of NaCl at 10 ºC and adds it to 100. mL of water at 30 ºC. The final temperature of the solution is 24.5 ºC. The student calculates that the specific heat of NaCl is 3.17 J/gK, but the instructor tells him that value is not correct. Why is this answer incorrect?

Answer 1

q_{lost of water}    = q_{gain of NaCl}

mC_waterT = mC_NaClT

T of water = 5.5⁰C

T of NaCl = 14.5⁰C

m of water = 100 g

m of NaCl = 50 g

C_water  = 4.186J/g⁰C

100 x 4.186 x 5.5 = 50 x C_NaCl x 14.5

2302.3 = 725 C_NaCl

C_NaCl   = 2302.3 / 725

C_NaCl = 3.17 J/g⁰C

therotically it is correct only

but some heat may absorb by vessel we taken the solution. so we should consider the heat absorbed by vessel also. it depends on type of vessel we used.

if total heat is transferred ti NaCl only given value is correct. but it is not posible because some heat absorbed by vessel also.