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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)**Proportions**1mg = 10mg 10 mL 100mL**Example 1: How could you make 300 mL of a solution that has**a concentration of 10g of NaCl in 100 mL total solution? 10 g = ? 100 mL 300 mL 300 mL x 10 g = ? 100 mL . 30 g = ?**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**6. A student adds 13.5 grams of KCl to volumetric flask**and fills it to the 1000mL mark. What is the weight per volume percent of the solution?**7. A student adds 45.6 grams of MgCl2 to volumetric flask**and fills it to the 1000mL mark. What is the weight per volume percent of the solution?**By rearranging the equation we can determine how much**chemical we needed to add to the desired volume to prepare a solution of the correct concentration. Grams of solute = Volume of solution x W/V %**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**8. How many grams of NaCl would be needed to prepare 250 ml**of a 5% solution of NaCl?**9. How many grams of Glucose would be needed to prepare 200**ml of a 2% solution of glucose?**10. How many grams of EDTA would be needed to prepare 475 ml**of a 15% solution of EDTA?**11. How many grams of Pb(NO3)2 would be needed to prepare**500 ml of a 5% solution of Pb(NO3)2?**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%**12. A student adds 10.0 ml of ethanol to 100mL volumetric**flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?**13. A student adds 3.5 ml of isopropanol to 50mL volumetric**flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?**14. A student adds 1.5 ml of methanol to 100mL volumetric**flask and fills it to the mark. What is the percent per volume (v/v) concentration of the solution?**By rearranging the equation we can determine the volume the**chemical solution we needed to add to the desired volume to have a solution of the correct concentration. Volume of solute = Volume of solution x Volume %**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**15. How many milliliters of ethanol would you need to make**20.0 mL of a 10% by volume solution of ethanol in water? volume of solute = Volume of solution x Volume /volume %**16. How many milliliters of isopropyl alcohol would you need**to make 100 mL of a 75% by volume solution of isopropyl alcohol in water? volume of solute = Volume of solution x Volume /volume %**17. How many milliliters of methanol would you need to make**1L of a 90% by volume solution of methanol in water? volume of solute = Volume of solution x Volume /volume %**18. How many milliliters of bleach would you need to make 1L**of a 20% by volume solution of bleach water? volume of solute = Volume of solution x Volume /volume %**19. How many milliliters of SDS solution would you need to**make 1L of a .1 % by volume solution of SDS buffer? volume of solute = Volume of solution x Volume /volume %**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**20. What is the weight percent of sucrose in a solution made**by dissolving 29.89 g of sucrose in 1000 g of water?**21. What is the weight percent of NaCl in a solution made by**dissolving 123.5 g of NaCl in 898 g of water?**By rearranging the equation we can determine the mass of the**chemical we needed to make the solution of the correct concentration. Grams of solute = Gram of solution x Weight/Weight %**Example 7: How much NaCl would you need to prepare 400 g of**a 2.50% solution of sodium chloride? Grams of solute = Gram of solution x Weight/Weight % Grams of solute = 400 g x 2.50 % Grams of solute = 10.0 g salt**22. How much KCl would you need to prepare 300g of a 25%**solution of KCl? Grams of solute = Gram of solution x Weight/Weight %**23. How much AgNO3 would you need to prepare 150 g of a 3.0%**solution of Ag NO3? Grams of solute = Gram of solution x Weight/Weight %**24. How much resin would you need to prepare 200 g of a 75%**solution of resin in acetone? Grams of solute = Gram of solution x Weight/Weight %