Week 2 Concetrations, units, molarity, normality, formality, molality, percentage solutions, ppm (parts per million) and ther aplications

Solution Homogenous mixture of 2 or more substances in single phase = 1 layer Component present in largest amt = solvent Other component(s) = solute Alloys, air are all solutions (solns)

Units of Concentration A solution is a homogeneous mixture of one substance (the solute) dissolved in another substance (the solvent). Concentration is a ratio of the amount of solute to the amount of solvent. A common task in a biotechnology lab is preparing solutions. What exactly is a solution? A solution is a mixture of what is dissolved (the solute) and the dissolving medium (the solvent). For example, if you are making koolaid the colored sugar is the solute and the pitcher of water is the solvent. The concentration of a solution is the ratio of the amount of solute to solvent. It is necessary to prepare solutions with the correct concentration or you can destroy months of hard work in a biotechnology lab.

Calculations The Mole Concept One Mole = 6.023 x 1023 The amount of substance which contains as many entities as there are atoms in 12 grams of 12C. One Mole = 6.023 x 1023 Avogadro’s Number 3

Units of Concentration A mole is the SI unit of number of particles and can be used as an expression of the molecular weight of a substance. So your next question is probably “what is a mole”? Well, it’s not the furry animal wearing sunglasses in the previous slide, it is actually the SI unit of number of particles. It is a chemistry term that can be used to calculate the formula weight of a substance. In fact formula weight is often called molar mass. The formula weight of an element is recorded on the periodic table. For example, the formula weight of sodium is 22.990 grams/mole. The formula weight of an element is expressed as grams/mole

Units of Concentration The molar mass of a compound can be calculated by adding the molar mass of the individual elements. To calculate the molar mass of a compound, you simply add the formula weights of the individual elements. So in this example you add the formula weight of sodium (22.990) with the formula weight of chlorine (35.453) to tell you that the molar mass of salt (NaCl) is 58.443 grams/mole. 22.99 + 35.45 = 58.44 g/mol

Making Solutions You just calculated the molar mass of sodium chloride to be 58.44 g/mol. You have to know the formula weight of a compound if you are going to prepare the correct concentration of a solution with that compound. The formula (grams = molarity x liters x molar mass) is used to tell you how much of a compound to use to make a solution with a specific concentration.

Making Solutions g = M x L x molar mass How many grams of NaCl would you need to prepare 200.0 mL of a 5 M solution? g = M x L x molar mass g = (5mol/L) (0.2L) (58.44g/mol) g = 58.44 g For example, if I wanted to make a 200 milliliters of sodium chloride with a concentration of 5 M, how much of the compound would I use? Remember that Molarity actually stands for moles per Liter. That means I’m going to have to convert 200 milliliters to liters. On our metric line, there were three places between milli and the base unit, so we will have to move our decimal three places to the left. That means 200 milliters is 0.2 L. Now we can plug our numbers into our formula. According to my formula, the number of grams I need will be 5M x 0.2L x 58.44 g/mol. After canceling units and multiplying these three numbers together, I get the answer 58.44g. My balance goes to 2 decimal places, that means that I will weigh out 58.44 grams of NaCl and add 0.2 L or 200 millilters of water. When making a stock solution, we usually dissolve the solid in about two-thirds volume of water. So that means we would dissolve our 58.44 g of NaCl in only about 150 mls of water and stir. When it is completely dissolved, we would transfer the solution to a graduated cylinder and bring it to the final volume of 200 milliliters.

Equivalent is also a unit of amount and it can be defined as, one equivalent is that amount which containing Avogadro number (6.0221415 × 1023) of reactive specie. Equivalent mass can be defined as molecular mass of the analyte divided by number of reacting units as

Calculate the number of equivalents for 8g mass of Na2CO3.

Formals Formal is also a unit of amount similar to mole but in case of crystalline ionic compounds like NaCl we are writing formula unit mass instead of molecular mass i.e. Formula mass of NaCl = 23 + 35.5 = 58.5amu

Molarity It is a unit of concentration and is denoted by “M”. It can be defined as the number of moles of solute dissolved per unit volume of solution

Problem Give the concentration (in M) of 0.0012 grams of NaCl in 545 mL of water MW of NaCl = 58.442 g/mol go back

Example: Prepare 0.1M NaOH solution of 250ml volume.

Normality It is also a unit of concentration and denoted by N. It can be defined as the number of equivalents of solute dissolved per unit volume of solution Example: 1.2. Prepare 0.1N H2SO4 solution of 250ml volume.

Example: Prepare 0.1N H2SO4 solution of 250ml volume.

Formality It is a unit of concentration and denoted by “F”. It can be defined as the number of formals of solute dissolved per unit volume of solution

Example: Prepare 0.1F NaCl solution of 250ml volume.

Molality It is also a unit of concentration and denoted by “m”. It can be defined as number of moles of solute dissolved per Kg of solvent.

Example: 1.4. Prepare 0.1m NaOH solution in 250g of solvent.

Percentage Solution (%) In order to prepare solutions of higher concentrations we use the units of percentage. There are three types of percentage Solution i.e. weight/volume, weight/ weight and volume/volume.