Question

Question #13

Calculate number of moles of Potassium hydrogen phosphate needed to obtain a pink color with phenothalein. (hint equivalence point) when 15.30

ml of a 0.0100 M NaOH solution added?

Question #14

A piece of copper of mass 20.0 g at 100oC is placed in a Styrofoam cup calorimeter containing 50.7 g of water at 22oC. Calculate the final temperature of the water. Assume that the water gains all the energy lost by the copper. The specific heat capacity of copper is 0.38 J g-1 oC-1.

Answer 1

13.

moles of potasium hydrogen = moles of NaOH at equivalence point

so moles of NaOH = molarity*volume = 0.01*0.0153 = 0.000153 moles

14.

Step 1 -

qlost by copper = qgained by water + qgained by calorimeter

q copper = q water + 0 (as the calorimeter is not gaining any heat) given in question

heat capacity of water = 4.184 J g-1 °C-1

2) Therefore:

(20.0 g) (100 °C - x) (0.38 J g-1 K-1) = (50.7 g) (x - 22.0 °C) (4.184 J g-1 °C-1)

Step 2 = calculate the x

760 - 7.6x = 212.12x - 4666.83

219.72x = 5426.83

x = 24.69 degree celcius

ANswers
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