Laboratory Solutions. In the laboratory, we will be using different concentration of chemical solutions. Each protocol will require different solutions in varying concentrations. Revised 9/06/2006. Concentration.

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Laboratory Solutions

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Laboratory Solutions In the laboratory, we will be using different concentration of chemical solutions. Each protocol will require different solutions in varying concentrations. Revised 9/06/2006

Concentration • The amount of a particular substance in a stated volume (or sometimes mass) of a solution or mixture. • Ratio where the numerator is the amount of the material of interest and the denominator is the volume or mass of the entire mixture.

Concentrations • weight per volume • Percents • Molarity

Weight per Volume • The simplest way to represent concentration of a solution is as the mass in grams per unit of volume. Weight = mass of solute volume volume of solution

2g NaCl 1L • Means that 2 g of NaCl is dissolved in enough liquid so that the total volume is 1L.

Solute • The substance that is being dissolved • NaCl

Solvent • The liquid in which the solute is dissolved. • Water

Amount vs. Concentration • Amount is how much substance is present. • Concentration is ratio with a numerator (amount) and a denominator (usually volume)

Question • Your mother gives you 250mg of acetaminophen and a cup containing 500ml of water. What is the concentration of the solution if you dissolve the Tylenol in the water?

Question 2. If a solution requires a concentration of 3g of NaCl in 250 mL total volume, how much NaCl is required to make 100mL?

Question 3. How many milligrams of NaCl are present in 50 mL of a solution that has a concentration of 2mg/mL NaCl?

Question • If the concentration of MgSO4 in a solution is 25 g/L, how much magnesium sulfate is present in 100mL of this solution?

Question • If a solution requires .005 g of Tris base per Liter, how much Tris Base is required to make 10-3 Liters of this solution?

Percentage Concentrations When concentration is expressed in terms of percent, the numerator is the amount of solute and the denominator is 100 units of total solution. • weight/volume percent • volume percent • weight percent

Weight/Volume Percent Weight/Volume % = grams of solute x 100 volume of solution A weight per volume percent concentration is the weight of the solute in grams per 100 mL of solution. It can be abbreviated as w/v.

Example 2A student adds 20.0 grams of NaCl to volumetric flask and fills it to the 100mL mark. What is the weight per volume (w/v) percent concentration of the solution? Weight % = grams of solute x 100 volume of solution Weight % = 20.0 grams x 100 100mL of solution Weight % = 20% NaCl solution

Example 3How many grams of NaCl would be needed to prepare 500 ml of a 5% solution of NaCl? Grams of solute = Volume of solution x Weight % Grams of solute = 500mL x 5% Grams of solute = 500mL x 5g/100mL Grams of solute = 25 g of NaCl

Volume/Volume Percent volume % = volume of solute x 100 volume of solution Volume % = mL of solute x 100 100 mL of solution In a percent by volume expression, both the amount of solute and the total solution are expressed in volume units. It can be abbreviated as v/v.

Example 4A student adds 20.0 ml of ethanol to volumetric flask and fills it to the 1L mark. What is the percent volume (v/v) concentration of the solution? Volume % = volume of solute x 100 volume of solution Volume % = 20.0 mL of solute x 100 1000mL of solution Volume % = 2%

Example 5How many milliliters of ethanol would you need to make 10.0 mL of a 10% by volume solution of ethanol in water? volume of solute = Volume of solution x Volume /volume % volume of solute = 10.0 ml x 10% volume of solute = 1.0 ml ethanol

Weight Percent Weight % = weight of solute weight of solution x 100 In a Weight (mass) Percent the numerator is the mass of solute and the denominator is mass of total solution.

Example 6: What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water? Determine total weight of solution: 4.6 g glucose + 145.2 g water 149.8 g solution Calculate Weight % glucose = 4.6 g glucose x 100 = 3.1% glucose 149.8 g solution