Dilutions Solution A Solution B Solution C 500 g of solute in 100 mL of solvent Solution B 100 g of solute in 100 mL of solvent Solution C 1 g of solute in 100 mL of solvent Dilutions

C11-4-16 CONCENTRATION AND DILUTION OUTCOME QUESTION(S): C11-4-16 CONCENTRATION AND DILUTION Differentiate among the various representations of concentration, and solve concentration problems. Solve problems involving the dilutions and combinations of common solutions. Include: stock solutions Vocabulary & Concepts 

Labs buy highly concentrated solutions to save storage space – stock solutions. Dilution: adding more solvent to small volume of stock without adding more solute. moles from the stock = moles in the dilution nstock = ndilution Dilution is just “watering it down” – the moles don’t change

Stock Prepared Dilution nstock = ndilution The moles taken in the sample of stock are all the moles present in the diluted solution

Remember how to find moles… nstock = ndilution n M = V Remember how to find moles… creates C1V1 = C2V2 M1V1 = M2V2 Where: C1 is the initial (stock) concentration (molarity) V1 is the initial (stock) volume taken C2 is the concentration (molarity) of the dilution V2 is the final volume of the dilution

Try to make a rough estimate of the If 500.0 mL of water is added to 300.0 mL of a 0.100 mol/L solution of NaCl, what is the new concentration? C1 V1 = C2 V2 Try to make a rough estimate of the answer… V2 = 300.0 + 500.0 = 800.0 mL 1 L = 0.800 L 1000 mL (0.100) (0.300) = 0.0375 M (0.800)

It’s a good habit to always convert to litres What is the concentration of the stock solution if 50.0 mL of the stock is diluted to make 220.0 mL of a 0.400 M solution? C1 V1 = C2 V2 (0.400 M) (0.220 L) 1.76 mol/L C1 = (0.0500 L) It’s a good habit to always convert to litres

How much water must be added to 25. 0 mL of a 1 How much water must be added to 25.0 mL of a 1.00 M stock solution of NaOH to make a 0.100 M solution? C1 V1 = C2 V2 Look at the two concentrations… estimate the answer (1.00) (0.0250) = 0.250 L (0.100) 0.250 L – 0.0250 L = 0.225 L 225 mL of water must be added to make a final volume of 250 mL

Making A Dilution: 1. Calculate the volume of stock needed. 2. Transfer measured stock to a second volumetric flask. 3. Add more solvent to dilute to the correct final volume. 4. Mix.

Don’t try to memorize this… Mixing Solutions: Same solute but different concentrations Sometimes called “marrying” solutions Total moles CFinal = Total volume mol1 mol2 = (C1V1 + C2V2 + …) CFinal (V1 + V2 + …) total volume Don’t try to memorize this… understand it

450. 0 mL of a 0. 150 M NaCl solution is mixed with 125 mL of a 0 450.0 mL of a 0.150 M NaCl solution is mixed with 125 mL of a 0.220 M NaCl solution. Total moles CFinal = Total volume mol1 mol2 = (0.150)(0.450) + (0.220)(0.125) CF (0.450 + 0.125) total volume CF = 0.165 M

C11-4-16 CONCENTRATION AND DILUTION CAN YOU / HAVE YOU? C11-4-16 CONCENTRATION AND DILUTION Differentiate among the various representations of concentration, and solve concentration problems. Solve problems involving the dilutions and combinations of common solutions. Include: stock solutions Vocabulary & Concepts