Chem Class- November 30, 2009

Mid-term Exams are over and done with, and now we're continuing from where we left off:

CONCENTRATION:

Solution: A homogeneous mixture

Solute: The one present in smaller amount

Solvent: The one present in greater amount

Concentration = amount of solute/amount of solvent (the larger one is on the bottom)

Some units for concentration are g/ml, g/l, mg/L, mg/mL...

The most common (and useful) unitls are mol/L. This is also known as Molarity and Molar Concentration.

It's a good thing to note that the above only works for aqueous solutions and not for gases.

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Exercises:
Caclulate the molar concentration of 2.8 mol of HNO3 in 4.0 L of solution:

[HNO3] = 2.8 mol/4.0 L = 0.70 M

Brackets mean concentration of HNO3...

What volume of 2.40 M HCl can be made from 100.0 g of HCl?

Moles of HCl= 100.0 g x 1 mol/36.5 g = 2.74 mol

2.74 mol/2.40 mol/L = 1.14 L (V= mol/M)

How many grams of CaCl2 are contained in 225 mL of 0.0350 M CaCl2 solution?

0.0350 mol/L x 0.224 L = 7.88 x 10 to the power of -3 mol (Moles of CaCl2)

7.88 x 10 to the power of -3 mol x 111.1g/1 mol = 0.875 g (Mass of CaCl2)