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A calorimeter contains 70.2gof water at 15.30C. If 143.7g of water at 36.50C is mixed with the common temperature is 28.70C. The water equivalent of the calorimeter is
(A) 15.6g
(B) 9.4g
(C) 6.3g
(D) 13.4g

Answer
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Hint:-
Use the equation heat H=mCΔT, m is mass of the substance, C is the specific heat and ΔT is the change in temperature. Water equivalent means the mass of water which can raise the same amount of temperature in this process.

Complete step by step solution:-
In this process the heat is transferred from hot to colder body.
Total heat transferred is common heat transferred in a calorimeter.
Heat is given by H=mCΔT
mCΔT=m1CΔT1+m2CΔT2
But Cis specific heat is common in all, everything is water in this problem.
Value of specific heat of water C=1calorie/gram
We can cancel out the specific heat.
mΔT=m1ΔT1+m2ΔT2
Calorimeter contain water m1=70.2g
Temperature of calorimeter T1=15.30C
Amount of water added is m2=143.7g
Temperature of added water T2=36.50C
Common temperature or the equilibrium temperature T=28.70C
Change in common temperature ΔT=28.70C00C=28.70C
Change in calorimeter temperature ΔT1=T1T=15.30C28.70C=13.40C
Change in added water temperature ΔT2=T2T=36.50C28.70C=7.80C
mΔT=m1ΔT1+m2ΔT2
Rearrange the equation
Water equivalent of calorimeter m
m=(m1ΔT1+m2ΔT2)ΔT
m=(70.2×(13.4))+(143×7.8)28.7
m=1120.86940.6828.7=180.1828.7=6.27804878g
But in the option there are only two significant figures, and there only one digit after decimal point.
6.27804878g Approximate to 6.3g
So the answer is (C) 6.3g

Note:- In this question we don’t need the value of Specific heat of water, it cancels outs in both sides of the equation. Calorimeter is the measuring device of heat produced in any kind of reaction which produces any kind of reaction and the material properties like heat capacity, etc.
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