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 These are relatively concentrated solutions – they contain a lot of solute.

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 salt?