a). Let\'s pretend for a moment that you didnt forget about a teapot on the hot

Question

a). Let's pretend for a moment that you didnt forget about a teapot on the hot stove and actually used hot water to make tea before it all boiled away. If you dissolve 4 g of sugar in your hot tea (made form 296 grams of hot water), what would be the boiling point of your tea solution? The boiling point constant for water is 0.512 Celisus/m and sugar has a molar mass of 342.3 g/mol.

b). In a rush you left your tea outside in the cold winter. At what temperature would your tea freeze?

c). If you used a thermomter that showed 20 degrees celsius as the maximum temp and -10 degrees celsius as the minimum, would you be able to reliably measure the freezing point depression of tea? EXPLAIN

Explanation / Answer

. Let's pretend for a moment that you didnt forget about a teapot on the hot stove and actually used hot water to make tea before it all boiled away. If you dissolve 4 g of sugar in your hot tea (made form 296 grams of hot water), what would be the boiling point of your tea solution? The boiling point constant for water is 0.512 Celisus/m and sugar has a molar mass of 342.3 g/mol.

Boiling point elevation= i*kb*m, m= molality= moles of solute/ kg of solvent, moles = mass/molar mas= 4/342.3 =0.011686 moles, mass of water = 296 gm, 1000gm= 1kg, mass of water in kg= 296/1000=0.296Kg, m= 0.011686/0.296=0.0394m, i= Van't Hoff factor=1 for sugar ( since it is not an electrolyte), Kb= boiling point constant, boiling point elevation = 1* 0.0394*0.512 =0.020 and boiling point of solution = boiling point of water+ boiling point elevation =100+0.020= 100.020 deg,c,

Freezing point depression = i*kf*m, kf = freezing point constant = 1.82 deg.c/m, freezing point depression =1*1.82*0.0394 =0.072 deg,c, Freezing point of solution = Freezing point of water- freezing point depression = 0-0.072=-0.072 deg.c

since the thermometer reads +20 to -10 deg.c, the boiling elevation (0.020 deg.c and freezing point depresion

fall in the range, the thermometer can be used.

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