Lab # 2

Solutions

Part 1

Solution

• Saline water solution is an example of chemical solutions and that can be made by dissolving a table of salt (NaCl) in a cup of water (H2O)

Solution

• Solutions are mixtures of ( ions – atoms – two

molecules or more ).

• Types of Solutions:

homogeneous solution & heterogeneous solution .

• Consists of Solutions : Solvent (higher amount) such as water – oils.

solute (lower amount) such as sugars – sodium chloride - gas.

Solution

• In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent

• A common example for liquid solution is when a salt or sugar which are solid substances, dissolved in water .

• Gases may dissolve in liquids, for example, carbon dioxide or oxygen in water.

• Liquids may dissolve in other liquids like ethanol and water preform alcoholic beverages.

• Gases can combine with other gases to form mixtures, rather than solutions for instant oxygen dissolved in nitrogen in the air.

Solution

• All Solutions are characterized by interactions between the solvent phase and solute molecules.

• Under such a definition, gases typically cannot function as solvents, since in the gas phase interactions between molecules are minimal due to the large distances between the molecules. This lack of interaction is the reason gases can expand freely and the presence of these interactions is the reason liquids do not expand.

Solutions

• If both solute and solvent exist in equal quantities (such as in a 50% ethanol, 50% water solution), the concepts of "solute" and "solvent" become less relevant,

• but the substance that is more often used as a solvent is normally designated as the solvent (in this example, water).

Unit definition

• Milligram= mg = 1/1ooo of a g. or 0.001g• gram= g• kilogram= kg = 1000 g• mole = 6.023 x 1023 molecules• molarity = moles per liter• molar = M = term used to discuss the molarity of

solutions (e.g., 2.5 M means 2.5 moles of solute dissolved In one liter)

• mill molar = 1/1000 of a mole• mill molar = mM = term used to discuss the molarity

concentration of one on one-thousandth of a mole per (e.g., a 20 mM solution contains 20/1000 = 0.02 moles per liter)

Percentage Solutions• In biology percentage solutions are often preferred to molar

ones. • A 1% solution would have 1 g of solute dissolved in a final

volume of 100 ml of solvent . • This would be labeled as a weight/volume [w/v] percentage

solution. • For w/w, both solvent and solute would need to be weighed

in the required ratios.• For v/v, both solvent and solute would need to be volumed in

the required ratios. • Volume would accordingly be measured using a

measuring cylinder, volumetric flask, pipette or similare equipments.

• Labels should show what the percentage relationships are (w/v, w/w or v/v).

Concentration units

• Percent Concentration . • Molar Concentration.

• Normal Concentration.

Percent Concentration

• The amount of solute / g in 100 g from solution. • Example: prepare solution of sodium chloride 10% .• Water = 90g• Sodium chloride = 10g. (w /w).• Types of percent concentration (w /w). (v /v). (v /w). (w /v).

Percentage Solutions

• The molarity of a percentage solution (w/v) can be calculated using the molar mass of the solute used.

Molar Concentration or molarity (m)

A molar solution is one that contains one mole of solute per litre of solution.

Mole = compound mass (g) / atomic mass1mM (millimolar) = 103 moles1M (micromolar) = 106 moles1nM (nanomolar) = 1m mole =109 molesMolar Concentration= the amount ( mole) /

volume of solution (liter)

Molar Concentration

• The phrase may be prefixed with a number to denote other concentrations.

• For example, a five molar solution of aqueous hydrochloric acid (written as "5M HCl (aq)") means there are 5 moles of HCl per litre of solution.

• If the solvent is not mentioned (such as "5M NaOH"), it is safe to assume that the solvent is water or the one most commonly used with that solute.

Molar Concentration

• For work with aqueous solutions, concentrations expressed in terms of molarity are most useful when performing stoichiometric calculations since easily measured volumes correspond directly to moles of chemical substances involved.

Molar Concentration or Molarity (m)

Example: prepare solution of Nacl 5% molar Compound mass (g) = volume of solution (liter)

x Mole x Molar ConcentrationCompound mass (g) = 1x 58.5 x 5 = 292.5gNacl 5% molar = 292.5g Nacl + 1 liter water

How about preparing a 1% Nacl molar solution in half liter?

Molar Concentration or Molarity (m)

Compound mass (g) = 0.50x 58.5 x 1 = 29.25g

Nacl 5% molar = 29.25g Nacl + 500 milliliter water

Preparation

• The most common way to prepare a solution of known molarity is:

• decide which volume to prepare and make sure a clean volumetric flask is available.

• calculate the number of moles of solute needed in this volume.

• weigh off the right amount of solute.

• put (all) the solute in the volumetric flask (use funnel).

• add a bit of solvent to dissolve the solute.

Preparation

• (If any powder sticks to the funnel, rinse it into the flask)

• continue to add solvent, homogenizing and dissolving as you go.

• fill the volumetric flask up to (and not over!) the calibration line.

• homogenize thoroughly, applying heat if necessary.

• label the flask with a clear label that does not fade or wash off.

• cool solution to room temperature, and verify volume.

• store, ensuring neither solvent nor solute can evaporate by providing a barrier such as a stopper.