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Triss [41]
3 years ago
11

. Calculate the molality of each of the following solutions: (a) 0.710 kg of sodium carbonate (washing soda), Na2CO3, in 10.0 kg

of water—a saturated solution at 0°C (b) 125 g of NH4NO3 in 275 g of water—a mixture used to make an instant ice pack (c) 25 g of Cl2 in 125 g of dichloromethane, CH2Cl2 (d) 0.372 g of histamine, C5H9N, in 125 g of chloroform, CHCl3
Chemistry
1 answer:
Step2247 [10]3 years ago
4 0

Answer:

a)0.67 molal

b) 5.67 molal

c) 2.82 molal

d) 0.0268 molal

Explanation:

Step 1: Data given

Molality = moles solute / mass solvent

(a) 0.710 kg of sodium carbonate (washing soda), Na2CO3, in 10.0 kg of water—a saturated solution at 0°C

Calculate moles of Na2CO3 =  710 grams / 105.99 g/mol = 6.70 moles

Molality = 6.70 moles / 10 kg = 0.67 molal

(b) 125 g of NH4NO3 in 275 g of water—a mixture used to make an instant ice pack

Calculate moles of NH4NO3 = 125 grams / 80.04 g/mol = 1.56 moles

molality = 1.56 moles / 0.275 kg = 5.67 molal

(c) 25 g of Cl2 in 125 g of dichloromethane, CH2Cl2

Calculate moles Cl2 = 25 grams / 70.9 g/mol= 0.353 moles

Molality = 0.353 moles / 0.125 kg = 2.82 molal

0.372 g of histamine, C5H9N, in 125 g of chloroform, CHCl3

Calculate moles histamine = 0.372 grams / 111.15 g/moles = 0.00335 moles

Calculate molality = 0.00335 moles / 0.125 kg = 0.0268 molal

NOTE: histamine is C5H9N3 not C5H9N

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Answer:

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Explanation:

Hello there!

In this case, since this a problem in which we need to calculate the total heat of the described process, it turns out convenient to calculate it in three steps; the first one, associated to the heating of the liquid water from 40 °C to 100 °C, next the vaporization of liquid water to steam at constant 100 °C and finally the heating of steam from 100 °C to 115 °C. In such a way, we calculate each heat as shown below:

Q_1=45g*4.18\frac{J}{g\°C}*(100\°C-40\°C)=11286J\\\\Q_2=45g* 2260 \frac{J}{g} =101700J\\\\Q_3=45*2.02\frac{J}{g\°C}*(115\°C-100\°C)=1363.5J

Thus, the total energy turns out to be:

Q_T=11286J+101700J+1363.5J\\\\Q_T=114349.5J

Best regards!

5 0
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