SOLUTIONS

• Solutions : Homogeneous mixture of two or more substances. Consist of

a solute and a solvent.

• Properties of a solution

• Solutions have variable composition

• Solutions are always clear ( transparent to light)

• Solutions are homogeneous

• Solutions do not settle out

• Solutions can be separated by physical means

• Solutions pass through filter paper

SOLUBILITY (FORMATION) OF SOLUTIONS

• Ionic substances (NaCl) will dissolve in polar

solvents (H2O)

• The positive hydrogen atoms of water attract the

negative Cl- ions.

• The negative oxygen atoms of water attract the

positive Na+ ions.

• This results in hydration (solvation) of the Na+

and Cl- ions.

NaCl dissolves in water because it is ionic (polar)

Nonpolar compounds like Cl2 and oil do not

dissolve in polar solvents like water.

Like dissolves like.

Factors affecting solubilities.

* Temperature.

Solubility of solid solutes generally increases with increase in

temperature. However there are exceptions,

e.g. Ce(SO4)3 solubility decreases.

NaCl little change.

Gases become less soluble with incr. in temperature, e.g. SO2.

* Pressure.

Solids and liquids are unaffected by change in pressure.

For gases solubility in liquid increases with increase in partial

pressure above the liquid. (Henry’s Law)

e.g. Soda Can.

IONIZATION.Some solutes ionize in solution.

Ionization results in the formation of ions or

electrolytes. (Biologically referred to as minerals)

Electrolytes are substances whose water solution

conducts electricity. They dissociate into ions when

placed in water (ionisation). Ions are charged and the

net charge is zero.

Nonelectrolytes do not conduct electricity.

Conductivity.

When electrolytes are placed in solution they dissociate into ions.

The ions are attracted to oppositely charged electrodes, i.e. cations

attracted to cathode (- electrode) and anions attracted to anode (+

electrode). This can result flow of electricity.

ELECTROLYTES

Strong electrolytes: ionize completely in solution

e.g. NaCl → Na+ + Cl -

Weak electrolytes: ionize partially in solution.

e.g. Acetic acid (vinegar)

CH3COOH H+ + CH3COO-

EQUIVALENTS

UNIT USED TO EXPRESS THE AMOUNT OF EACH ION IN SOLUTION.

Amount of ion in solution (e.g. body fluids) determined by equivalent (Eq).

This is the amount of each ion (positive or negative ion) in 1 mole of

solution.

Relates the amount of an ion to its charge.

e.g. NaCl → Na+ + Cl-

1 mole of Na+ ions has 1 equivalent (Eq) of positive charges

1 mole of Cl- ions has 1 equivalent of negative charges.

MgO → Mg2+ + O2-

1 mole of Mg2+ ions has 2 equivalent (Eq) of positive charges

1 mole of O2- ions has 2 equivalent of negative charges

NB: Number of positive ions always equal number negative ions in neutral

solution.

How many equivalents (Eq) are present in each of the

following?

a. 0.5 mol K+

b. 0.75 mol Ca2+

c. 0.5 mol PO43-

MILLIEQUIVALENTS (mEq)

1 Eq = 1000 mEq

Used to determine concentration of ions in the body.

e.g. How many mEq of the Calcium ion are there in 0.4 g of

CaBr2.

e.g. The blood Magnessium level for a patient was found to

be 16.0 mEq/L. How many moles of magnessium ion are

in 0.4 0 L of blood?

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Concentration UnitsWeight/Volume Percent Concentration

• The concentration of a solution tells how much solute is dissolved in a given amount of solution.

• Weight/volume percent concentration, (w/v)%, is the number of grams of solute dissolved in 100 mL of solution.

Weight/volumepercent concentration

Weight/volumepercent concentration

(w/v)% = volume of solution (mL) x 100%mass of solute (g)

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Concentration UnitsWeight/Volume Percent Concentration

For example, vinegar contains 5 g of acetic acid in100 mL of solution, so the (w/v)% concentration is

5 g acetic acid100 mL vinegar solution

x 100% = 5% (w/v)

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Concentration UnitsVolume/Volume Percent Concentration

Volume/volumepercent concentration

Volume/volumepercent concentration

(v/v)% = volume of solution (mL) x 100%

For example, if a bottle of rubbing alcohol contains70 mL of 2-propanol in 100 mL of solution, then the (v/v)% concentration is

70 mL 2-propanol100 mL rubbing alcohol x 100% = 70% (v/v)

volume of solute (mL)

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Concentration UnitsUsing a Percent Concentration as a Conversion

FactorSample Problem

7.6A saline solution used in intravenous drips contains0.92% (w/v) NaCl in water. How many grams of NaClare contained in 250 mL of this solution?

Step [1]

Identify the known quantities and the desired quantity.

0.92% (w/v) NaCl solution250 mL

known quantities

? g NaCl

desired quantity

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Concentration UnitsUsing a Percent Concentration as a Conversion

FactorStep [2]

Write out the conversion factors.

100 mL solution0.92 g NaCl

or 0.92 g NaCl100 mL solution

Choose this one to cancel mL.Step [3] Solve the problem.

250 mL x0.92 g NaCl

100 mL solution= 2.3 g NaCl

Answer

Milliliters cancel.

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Concentration UnitsParts Per Million

When a solution contains a very small concentrationof solute, it is often expressed in parts per million.

Parts per millionParts per million

mass of solute (g)mass of solution (g)

x 106

or

volume of solute (mL)volume of solution (mL)

x 106

ppm =

ppm =

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Concentration UnitsMolarity

Molarity is the number of moles of solute per liter ofsolution, abbreviated as M.

moles of solute (mol) liter of solution (L)

moles of solute (mol) liter of solution (L)

Molarity = M =

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Concentration UnitsMolarity

HOW TO Calculate Molarity from a Given Number of Grams of Solute

Example

Calculate the molarity of a solution made from 20.0 g of NaOH in 250 mL of solution.

Step [1]

Identify the known quantities and the desiredquantity.

20.0 g NaOH250 mL solution

known quantities

? M (mol/L)

desired quantity

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Concentration UnitsMolarity

HOW TO Calculate Molarity from a Given Number of Grams of Solute

Step [2]

Convert the number of grams of solute to the number of moles. Convert the volume to liters if necessary.

• Use the molar mass to convert grams of NaOH to moles of NaOH (molar mass 40.0 g/mol).

20.0 g NaOH x 1 mol40.00 g NaOH

= 0.500 mol NaOH

Grams cancel.

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Concentration UnitsMolarity

HOW TO Calculate Molarity from a Given Number of Grams of Solute

• Convert milliliters of solution to liters of solution using a mL–L conversion factor.

250 mL solution x 1 L1000 mL

= 0.25 L solution

Milliliters cancel.

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Concentration UnitsMolarity

HOW TO Calculate Molarity from a Given Number of Grams of Solute

Step [3]

Divide the number of moles of solute by thenumber of liters of solution to obtain themolarity.

moles of solute (mol) 0.500 mol NaOH V (L) 0.25 L solution

= 2.0 M

Answer

=M =

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DilutionDilution is the addition of solvent to decrease theconcentration of solute. The solution volume changes,but the amount of solute is constant.

moles of solute (mol) = molarity (M) x volume (V)

initial values final values

M1V1 = M2V2

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Dilution

Sample Problem 7.13

How many milliliters of a 4.0% (w/v) solution must be used to prepare 250 mL of a 0.080% (w/v) solution?

Step [1]

Identify the known quantities and the desired quantity.

C1V1 = C2V2

initial values final values

? V(L)

desired quantity

C1 = 4.0% (w/v) C2 = 0.080% (w/v)V2 = 250 mL

known quantities

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Dilution

Step [2]

Write the equation and rearrange it to isolate the desired quantity, V1, on one side.

C1V1 = C2V2

Step [3] Solve the problem.

V1 = (0.080%)(250 mL) 4.0%

= 5.0 mL dopamine solution

Answer

V1 = C2V2

C1

Solve for V1 by dividing both sides by C1.

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Osmosis

• The membrane that surrounds living cells is a semipermeable membrane.

• Semipermeable membranes allow water and small molecules to pass across, but ions and large molecules cannot.

• Osmosis is the passage of water across a semipermeable membrane from a solution of low solute concentration to a solution of higher solute concentration.• Osmotic pressure is the pressure that prevents the flow of additional solvent into a solution on one side of a semipermeable membrane.

Osmosis and Biological Membranes

• Isotonic solutions.

• Two solutions with the same solute concentration/osmotic pressure

are said to be isotonic.

• A 0.92% m/v sodium chloride solution is called a physiologic saline

solution. It is isotonic with blood, i.e. has the same salt

concentration as blood.

• Hypotonic solutions.

• A solution that contains a lower solute concentration compared to

another is said to be hypotonic.

• Causes hemolysis ( bursting of red blood cells)

• Hypertonic solutions.

• Hypertonic solutions contain a higher solute concentration

compared to another.

• Causes plasmolysis/crenation (shrinking of the red blood cells)

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isotonicsolution

hypotonicsolution

hypertonicsolution

Hemolysis (burst)

Crenation (shrink)