Concentrations of SolutionsConcentrations of Solutions

ConcentrationConcentration measures measures exactly how much solute is in a exactly how much solute is in a certain amount of solvent.certain amount of solvent.

Parts per Million (ppm or mg/L)Parts per Million (ppm or mg/L) Parts per Billion (ppb)Parts per Billion (ppb)

Acceptable lead levels in drinking water

[http://www.mwra.state.ma.us/mw2002ccrmain/assets/leadgraph.jpg]

Concentrations of SolutionsConcentrations of Solutions

If chlorine levels are 3.0 ppm in If chlorine levels are 3.0 ppm in drinking water what does this drinking water what does this mean in terms of grams of mean in terms of grams of water?water?

1 million H2O molec. 1 mole H2O

6.02 x 1023 molec.

1.66 x 10-18 moles H2O

1.66 x 10-18 moles H2O

= 2.988 x 10-17 g H2O

18.0 g H2O

1 mol H2O

Or…

3 chlorine atoms in every

0.000000000000000002988 g of water!

Concentrations of SolutionsConcentrations of Solutions

For larger concentrations, For larger concentrations, MolarityMolarity (M) can be used: (M) can be used:

solvent of Liters

solute Moles M

Concentrations of SolutionsConcentrations of Solutions

Example:Example: What is the molarity of a What is the molarity of a

solution where 10.0 g of Hsolution where 10.0 g of H22SOSO44

is mixed in 100.0 mL of water?is mixed in 100.0 mL of water?

= 0.102 mol

= 1.02 mol/L

10.0 g H2SO4 1 mol H2SO4

98.1 g H2SO4

0.102 mol

0.1000 L

Concentrations of SolutionsConcentrations of Solutions

When When only the massonly the mass of the of the solution can be measured, solution can be measured, molalitymolality (m) can be used: (m) can be used:

solvent of Kg

solute Moles m

Concentrations of SolutionsConcentrations of Solutions

Example:Example: What is the molality of a What is the molality of a

solution where 87.8 g of NaCl is solution where 87.8 g of NaCl is mixed with 150.0 g of ice mixed with 150.0 g of ice (H(H22O)?O)?

= 1.50 mol

= 10.0 mol/kg

87.8 g NaCl 1 mol NaCl

58.5 g NaCl

1.50 mol

0.150 kg