11. Table 1. Specific Heats of Various Metals (3 pts for a, 3 pts for b) Element

Question

11. Table 1. Specific Heats of Various Metals (3 pts for a, 3 pts for b) Element Aluminum Tin Magnesium Lead Zinc 0.9012 0.2167 0.4686 0.1289 0.3883 In a coffee cup calorimeter, you place 15.0 mL of distilled water and measure the starting temperature to be 25°C. You then place 2.44 g of an unknown metal (initially heated up to 99.8°C) into the distilled water andinsulate the calorimeter. After equilibrium, the final temperature of the water and the unknown metal is 26.1. What is the specific heat (in J/g °C) of the unknown metal? The specific heat of water is 4.184 J/g °C. Assume that no heat is transferred to the calorimeter. Show your starting equations, all of your calculations, and box in your final answer a. b. Which of the metals in Table 1 is most likely your unknown?

Explanation / Answer

Coffee cup calorimeter

a. Using relation,

q = mCpdT

for water,

density of water = 1 g/ml

m = 15 ml/1 g/ml = 15 g

Cp = 4.184 J/g.oC

dT = 26.1 - 25 = 1.1 oC

So,

q = 15 x 4.184 x 1.1 = 69.036 J

Heat gained by water = heat lost by unknown metal

So,

for metal,

m = 2.44 g

Cp = ?

dT = 99.8 - 26.1 = 73.7 oC

So,

2.44 x Cp x 73.7 = 69.036

specific heat of uknown metal (Cp) = 0.384 J/g.oC

b. Most likely the metal is Zinc which has the cosest specifc heat value to the calculated one here.

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