   # In some regions of the southwest United States, the water is very hard. For example, in Las Cruces, New Mexico, the tap water contains about 560 μ g of dissolved solids per milliliter. Reverse osmosis units are marketed in this area to soften water. A typical unit exerts a pressure of 8.0 atm and can produce 45 L water per day. a. Assuming all of the dissolved solids are MgCO 3 and assuming a temperature of 27°C, what total volume of water must be processed to produce 45 L pure water? b. Would the same system work for purifying seawater? (Assume seawater is 0.60 M NaCl.) ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243

#### Solutions

Chapter
Section ### Chemistry: An Atoms First Approach

2nd Edition
Steven S. Zumdahl + 1 other
Publisher: Cengage Learning
ISBN: 9781305079243
Chapter 10, Problem 129CP
Textbook Problem
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## In some regions of the southwest United States, the water is very hard. For example, in Las Cruces, New Mexico, the tap water contains about 560 μg of dissolved solids per milliliter. Reverse osmosis units are marketed in this area to soften water. A typical unit exerts a pressure of 8.0 atm and can produce 45 L water per day.a. Assuming all of the dissolved solids are MgCO3 and assuming a temperature of 27°C, what total volume of water must be processed to produce 45 L pure water?b. Would the same system work for purifying seawater? (Assume seawater is 0.60 M NaCl.)

a)

Interpretation Introduction

Interpretation: The total volume of water has to be calculated and to predict if the same system would work for purifying seawater

Concept Introduction:

Colligative properties of a substance include the depression in the freezing point, elevation of boiling-point and osmotic pressure. These are dependant only on the number present and not based on the solute particles present in an ideal solution.

The osmotic pressure can be given by the equation,

Π=MRT

Here,Π=OsmoticpressureM=MolarityofsolutionR=GaslawconstantT=Temperature

### Explanation of Solution

Record the given info

Temperature = 27°C

Volume of Water = 45L

Osmotic pressure = 8.0atm

Mass of dissolved solids = 560μg

To calculate the moles of Magnesium chloride

Molar mass of Magnesium chloride = 84.32g

Assume MgCO3(s) does not dissociate, the concentration of solute in water,

Moles of MgCO3 = 560μgmL=560mgL=560×10-3gL×1molMgCO384.32g

= 6.6×10-3molK-1

Moles of MgCO3 = 6.6×10-3molK-1

To calculate the molarity of MgCO3

M=ΠRT=8

b)

Interpretation Introduction

Interpretation: The total volume of water has to be calculated and to predict if the same system would work for purifying seawater

Concept Introduction:

Colligative properties of a substance include the depression in the freezing point, elevation of boiling-point and osmotic pressure. These are dependant only on the number present and not based on the solute particles present in an ideal solution.

The osmotic pressure can be given by the equation,

Π=MRT

Here,Π=OsmoticpressureM=MolarityofsolutionR=GaslawconstantT=Temperature

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