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Solutions Chapter 14

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solution Homogeneous mixture of 2 or more substances in a single physical state –particles in a solution are very small –particles in a solution are evenly distributed –particles in a solution will not separate

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solute The substance that is dissolved examples: sugar, salt

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solvent Substance that does the dissolving –example: water, ethanol Aqueous solutions-use water as solvent

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Like dissolves like A solute will dissolve best in a solvent with similar intermolecular forces. If the intermolecular forces are too different the solute will not dissolve in that solvent.

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Calculating the strength of a solution Often the strength of a solution can be expressed in terms of percent.

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Percent Solutions can be calculated 2 ways. % by volume This compares the volume of solute to the total volume of solution. % by mass This compares the mass of solute to the total mass of solution.

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Volume Percent Volume of solute present in a total volume of solution. Volume Percent (v/v) = volume of solute / volume of solution x 100%

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Calculating volume percent A solution is prepared by dissolving 36 ml of ethanol in water to a final volume of 150 ml what is the solution’s volume percent? % (v/v) ethanol = 36 ml ethanol / 150 ml total x 100% Volume Percent ethanol = 24 %

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Volume percent If 15.0ml of acetone is diluted to 500ml with water what is the % (v/v) of the prepared solution? % (v/v) = 15.0ml / 500ml x 100% % v/v = 3.0% acetone

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Mass percent Way to describe solutions composition mass of solute present in given mass of solution mass percent = mass of solute mass of solution grams of solute grams of solute + grams of solvent X 100

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Mass percent A solution is prepared by dissolving 1.0g of sodium chloride in 48 g of water. The solution has a mass of 49 g, and there is 1.0g of solute (NaCl) present. Find the mass percent of solute.

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Mass Percent A solution is prepared by mixing 1.00g of ethanol, C 2 H 5 OH, with 100.0 g of water. Calculate the mass percent of ethanol in this solution.

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Solubility The extent to which a solute will dissolve –expressed in grams of solute per 100g of solvent –‘likes dissolve likes’

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Not every substance dissolves in every other substance –soluble- capable of being dissolved salt –insoluble- does not dissolve in another oil does not dissolve in water

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Solubility & liquids Miscible- two liquids that dissolve in each other completely immiscible- liquids that are insoluble in one another –oil & vinegar

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The compositions of the solvent and solute will determine if the substance will dissolve –stirring –temperature –surface area of the dissolving particles

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A solution is prepared by mixing 2.8 g of sodium chloride with 100 g of water. What is the mass percent of NaCl? What is the volume percent alcohol when you add sufficient water to 700mL of isopropyl alcohol to obtain 1000mL of solution?

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saturated solution contains the maximum amount of solute for a given quantity of solvent –no more solute will dissolve

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unsaturated solution contains less solute than a saturated solution –could use more

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Supersaturated solution Solution contains more solute than it can ‘hold’ –too much

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Dilute solution- contains a small amount of solute Concentrated solution- contains large amount of solute

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Solubility Table salt: at room temperature, 37.7 g can be dissolved in 100 ml of H 2 O Sugar: at room temperature, 200 g can be dissolved in 100 ml of H 2 O

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Solubility Curve

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Solubility curve Determines solubility of substances at specific temperatures with raising temperature solids increase in solubility with increase in temperature gases decrease in solubility ex: fish die

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saturated unsaturated supersaturated temperature Solute (g) per 100 g H 2 O on the line- saturated (can not hold anymore) above the line- supersaturated (holding more than it can) below the line- unsaturated (can hold more solute)

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92 g of NaNO 3 are added to 100ml of water at 25°C and mixed. What type of solution is it? 80 g of NaNO 3 are added to 100ml of water at 25°C and mixed. What type of solution is it?

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What is the solubility of NaNO 3 in 100g of H 2 O at 20°C? What is the solubility of NaNO 3 in 200g of H 2 O at 20°C?

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Concentration of solutions Concentration of a solution is the amount of solute in a given amount of solvent most common measurements of concentration are: –molarity –(mole fraction)

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Concentration of solutions Concentration of a solution is the amount of solute in a given amount of solvent most common measurements of concentration are: –molarity –(mole fraction) – not discussed in this class

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Molarity Number of moles of solute per volume of solution in liters moles of solute molarity (M) = liters of solution mol L

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Molarity Calculate the molarity of a solution prepared by dissolving 11.5g of solid NaOH in enough water to make 1.50 L of solution. Given: –mass of solute = 11.5 g NaOH –vol of solution = 1.50 L molarity is moles of solute per liters of solution

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Molarity Convert mass of solute to moles (using molar mass of NaOH). Then we can divide by volume molar mass of solute = 40.0 g 11.5 g NaOH x 1 mol NaOH 40.0 g NaOH 0.288 mol NaOH 1.50 L solution = 0.288 mol NaOH = 0.192 M NaOH

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Molarity Calculate the molarity of a solution prepared by dissolving 1.56 g of gaseous HCl into enough water to make 26.8 mL of solution. Given: mass of solute (HCl) = 1.56 g volume of solution = 26.8 mL

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Molarity Molarity is moles per liters we have to change 1.56 g HCl to moles HCl and then change 26.8 mL to liters molar mass of HCl = 36.5 g 1.56 g HCl x 1 mol HCl 36.5 g HCl = 0.0427 mol HCl = 4.27 x 10 -2 mol HCl

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Molarity Change the volume from mL to liters 1 L = 1000 mL 26.8 mL x 1 L 1000 mL = 0.0268 L = 2.68 x 10 -2 L

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molarity Finally, divide the moles of solute by the liters of solution molarity = 4.27 x 10 -2 mol HCl 2.68 x 10 -2 L = 1.59 M HCl

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molarity Calculate the molarity of a solution prepared by dissolving 1.00 g of ethanol, C 2 H 5 OH, in enough water to give a final volume of 101mL. Molarity = moles of solute/ L of solution Moles of ethanol MM ethanol = 46.08 g/mol 1.00 g ethanol / 46.08 g/mol= 0.0217 mol

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Solution volume = 101 ml convert to liters 101 ml / 1000ml per liter = 0.101 L Molarity (M) = moles / L M = 0.0217 moles / 0.101 L Molarity = 0.215 M ethanol

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molarity One saline solution contains 0.90 g NaCl in exactly 1.0 L of solution. What is the molarity of the solution? Calculate the moles of NaCl MM NaCl = 58.44 g / mol

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0.90 g NaCl / 58.44 g / mol = 0.015 moles Volume = 1.0 L Molarity = 0.015 moles / 1.0 L Molarity = 0.015 M NaCl

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molarity A solution has a volume of 250 mL and contains 7.0 x 10 ⁻¹ mol NaCl. What is its molarity? Convert volume to liters 250 ml / 1000 ml per L = 0.25 L M = 7.0 x 10 ⁻ ¹ / 0.25 L Molarity of NaCl = 2.8 M

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Finding moles to calculate grams How many grams of solute is needed to prepare 300. ml of 3.2 M KCl solution? Use the molarity relationship the find the number of mol. moles = L x M Convert volume to L 300. ml x (1 L/1000ml) = 0.300 L Calculate mol moles = 0.300 L x 3.2M = 0.96 mol Convert mol to grams 0.96 mol KCl x (74.5g/mol) = 72 g

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Finding volume How many liters of 0.442 M MgS can be made with 27.3 g of MgS? MM of MgS = 56 g/mol. Use the relationship L = mol / M Convert g to mol 27.3g x (1 mol/56 g) = 0.488 mol Calculate liters L = 0.488 mol/ 0.442 M = 1.10 L

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dilution Diluting a solution: –reduces the number of moles of solute per unit volume –the total number of moles of solute in solution does not change

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Diluting solutions M 1 V 1 = M 2 V 2 M 1 = molarity of stock solution (initial) V 1 = volume of stock solution (initial) M 2 = molarity of dilute solution V 2 = volume of dilute solution

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M 1 V 1 = M 2 V 2 How many milliliters of aqueous 2.00M MgSO 4 solution must be diluted with water to prepare 100.00 mL of aqueous 0.400M MgSO 4 ? M 1 = 2.00M MgSO 4 M 2 = 0.400M MgSO 4 V 2 = 100.00 mL MgSO 4 V 1 = ?

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M 1 V 1 = M 2 V 2 Solve for V 1 V 1 = M 2 x V 2 M 1 0.400M x 100.00 mL 2.00M = 20.0 mL

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M 1 V 1 = M 2 V 2 How many milliliters of a solution of 4.00M KI are needed to prepare 0.250 L of 0.760M KI? Mı=4.00M Vı=? M2=0.760M V2=0.250 L

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V1=M2xV2/M1 V1=(0.760M)(0.250 L)/4.00M V1=0.0475 L

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If 0.250 L of a 5.00 M HBr solution is diluted to 2.00 L with water what will the resulting concentration be? M1= 5.00 M V1= 0.250 L M2 = ? V2= 2.00 L M2 = M1 x V1 / V2 M2 = (5.00M)(0.250L) / (2.00 L) M2 = 0.625M

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