Concentrations of Solutions

The Amount of a Solute In qualitative terms, solutions can be concentrated, dilute, or somewhere in between. There are a number of common ways that solution concentrations are measured: % by mass or volume parts per million or parts per billion mass per unit volume (g/L)

% by Mass or Volume Bleach is 6% NaClO by mass Vinegar is 5% CH3COOH by volume Hydrogen Peroxide is 3% H2O2 by volume These are relatively concentrated solutions – they contain a lot of solute.

Calculating % Solutions This way of representing solution concentration is easy and convenient The % composition formula is all that is needed

Dilute Solution Concentration For environmental toxins, hormones, and other substances dissolved in small amounts, the term parts per million (ppm) is often used.

Arsenic is toxic in very small amounts. Because it is in the same family as phosphorus, it interferes with ATP metabolism, nucleic acid synthesis, and a number of other processes. The EPA considers drinking water containing arsenic above 0.010 ppm to be unfit to drink. Currently 56 million people in 25 states drink water with concentrations of As above this level!

Given tap water at the 0.010 ppm limit, how much arsenic would be in a 1 kg sample of tap water? A sample of well water contains 0.005 grams in 3500 g of tap water. Is this water fit to drink?

Dioxin is a non-polar compound that is highly toxic Dioxin is a non-polar compound that is highly toxic. The EPA has set a limit of 0.000005 ppm in drinking water. A sample of water contains 1 mg of dioxin in 10 kg of solution. Is the water safe to drink?

Problems with Mass-Concentration Units When comparing solutions of different substances: 5% acetic acid vs. 5% sodium hypochlorite 10 ppm lead vs. 10 ppm copper 3 g/L of NaCl vs. 3 g/L KCl The numbers look the same, but the concentrations are not the same! Concentration is a function of the molar mass of the substance.

Molarity Molarity is a unit of solution concentration that considers the number of physical solute entities in a solution. It is a more complex unit than the others, but much more useful in making comparisons.

What is the molarity of 500 ml of a solution containing 30 What is the molarity of 500 ml of a solution containing 30.0 g of NH4Cl?

How many moles of Na2CO3 are contained in 1.2 L of a 2.2 M solution?

How many grams of CuSO4 are required to make 2 L of a 0.30 M solution?

A student wishes to make a 0 A student wishes to make a 0.5 M solution of NaOH using 20 grams of solute. How much water does she need?  

Water from the Great Salt Lake has salt concentrations that are up to eight times more concentrated than sea water. Given a maximum concentration of 24 g/L, what is the molarity of the lake?

Formula Mass of Solute (amu) Final volume of solution Moles of solute Mass of solute Final volume of solution molarity   NH3 2 250 ml HNO3 63 g 0.5 M H2SO4 49 g 5 liters MgCl2 1 2 M AlPO4 244 g 0.5 liter C6H12O6 45 g CH3COOH 4000 cm3 KI 498 g 1 M Na2Cr2O7 3 9 M B(OH)3 4 12 liters ??? 294 g 2 liters 1.5 M

Formula Mass of Solute (amu) Final volume of solution Moles of solute Mass of solute Final volume of solution molarity   NH3 17 2 34  250 ml 8M  HNO3 63 1 63 g 2 L  0.5 M H2SO4 98  0.5 49 g 5 liters 0.1 M  MgCl2 95.2  95.2 0.5 L  2 M AlPO4 122  2  244 g 0.5 liter 4 M  C6H12O6 180  0.25 45 g 0.125 L  CH3COOH 60   120 g 4000 cm3 0.5 M  KI 166  3 498 g 3.0 L 1 M Na2Cr2O7 0.33 L  9 M B(OH)3 4 12 liters 0.33 M  ??? 3  294 g 2 liters 1.5 M

Molarity Worksheet What is the concentration, in moles per liter, when 0.89 moles of NaCl is added to 500 ml of water?

What is the concentration, in (M) when 34 What is the concentration, in (M) when 34.6 grams of NaCl is added to 1500 ml of water?

How many moles of KNO3 are needed to make 600 ml of a 1.3 M solution?

How many grams of KNO3 are needed to make 0. 75 liters of a 2 How many grams of KNO3 are needed to make 0.75 liters of a 2.0 M solution?

72 moles of KClO3 is used to make a 0. 60 M solution 0.72 moles of KClO3 is used to make a 0.60 M solution. What is the volume?

72. 0 grams of KClO3 is used to make a 1 72.0 grams of KClO3 is used to make a 1.25 moles/liter solution of potassium chlorate. What is the volume?

Lab 13 Making a Salt Solution and Studying its Properties Objective: To make aqueous solutions of a ionic and a covalent compound, and compare their properties to pure water.

Procedure Make 20 ml (0.020 L) of a 1 M solution of sodium chloride. Show the following: Your calculation for the number of moles of sodium chloride needed. Your calculation for the molar mass of sodium chloride. Your calculation the number of grams of sodium chloride needed to make the solution. Make your solution in the beaker, put it aside.

Turn on the conductivity meter. Place it in your solution Turn on the conductivity meter. Place it in your solution. Write your results below. Fill a plastic pipette with distilled water. Place drops of water on top of a clean penny. Be sure to hold the pipet vertically. Do not touch the penny or the accumulating water. Count the number of drops you can add before the water flows off the penny. Record the total Repeat the experiment two more times.

Using a fresh pipette, repeat the penny experiment with your 1 M salt solution. Get some prepared 1 M Sucrose (C12H22O11) solution, and test its conductivity. Write your results below: Then perform the same penny experiment three times, as on the front page. Make a data table of your results from the three experiments in the space below.

Conclusions On a separate sheet of paper, write several paragraphs describing the results of your experiments, trying to explain any differences between the water and two solutions based on what you have learned in class thus far. On the same sheet of paper, draw a picture of a sodium ion, a chloride ion, surrounded by at least six water molecules.