C HAPTER 7 S OLUTIONS 7.5 Molarity and Dilution 1

M OLARITY (M) Molarity (M) is a concentration term for solutions. gives the moles of solute in 1 L of solution. moles of solute liter of solution 2

P REPARING A 1.0 M OLAR S OLUTION A 1.00 M NaCl solution is prepared by weighing out 58.5 g of NaCl (1.00 mole) and adding water to make 1.00 liter of solution. 3

C ALCULATION OF M OLARITY What is the molarity of L of NaOH solution if it contains 6.00 g of NaOH? STEP 1: Given 6.00 g of NaOH in L of solution Need molarity (mole/L) STEP 2: Plan g NaOH mole NaOH molarity 4

E XAMPLE What is the molarity of 325 mL of a solution containing 46.8 g of NaHCO 3 ? 1) M 2) 1.44 M 3) 1.71 M 5

E XAMPLE What is the molarity of 225 mL of a KNO 3 solution containing 34.8 g of KNO 3 ? 1)0.344 M 2)1.53 M 3)15.5 M 6

M OLARITY C ONVERSION F ACTORS The units of molarity are used as conversion factors in calculations with solutions. MolarityEquality 3.5 M HCl1 L = 3.5 moles of HCl Written as Conversion Factors 3.5 moles HCl and 1 L 1 L3.5 moles HCl 7

C ALCULATIONS U SING M OLARITY How many grams of KCl are needed to prepare 125 mL of a M KCl solution? STEP 1: Given 125 mL (0.125 L) of M KCl Need g of KCl STEP 2: Plan L KCl moles KCl g KCl 8

E XAMPLE How many grams of AlCl 3 are needed to prepare 125 mL of a M solution? 1) 20.0 g of AlCl 3 2) 16.7 g of AlCl 3 3) 2.50 g of AlCl 3 9

EXAMPLE How many milliliters of 2.00 M HNO 3 contain 24.0 g of HNO 3 ? 1) 12.0 mL 2) 83.3 mL 3) 190. mL 10

D ILUTION In a dilution water is added. volume increases. concentration decreases. 11

C OMPARING I NITIAL AND D ILUTED S OLUTIONS In the initial and diluted solution, the moles of solute are the same. the concentrations and volumes are related by the following equations: For percent concentration: C 1 V 1 = C 2 V 2 initial diluted For molarity: M 1 V 1 = M 2 V 2 initial diluted 12

D ILUTION C ALCULATIONS WITH P ERCENT What volume of a 2.00% (m/v) HCl solution can be prepared by diluting 25.0 mL of 14.0% (m/v) HCl solution? Prepare a table: C 1 = 14.0% (m/v) V 1 = 25.0 mL C 2 = 2.00% (m/v) V 2 = ? Solve dilution equation for unknown and enter values: C 1 V 1 = C 2 V 2 V 2 = 13

EXAMPLE What is the percent (% m/v) of a solution prepared by diluting 10.0 mL of 9.00% NaOH to 60.0 mL? 14

D ILUTION C ALCULATIONS WITH M OLARITY What is the molarity (M) of a solution prepared by diluting L of M HNO 3 to L? Prepare a table: M 1 = M V 1 = L M 2 = ? V 2 = L Solve dilution equation for unknown and enter values: M 1 V 1 = M 2 V 2 M 2 = 15

EXAMPLE What is the final volume (mL) of 15.0 mL of a 1.80 M KOH diluted to give a M solution? 1) 27.0 mL 2) 60.0 mL 3) 90.0 mL 16

7.6 M OLARITY IN C HEMICAL R EACTIONS In a chemical reaction, the volume and molarity of a solution are used to determine the moles of a reactant or product. molarity ( mole ) x volume (L) = moles 1 L if molarity (mole/L) and moles are given, the volume (L) can be determined. moles x 1 L = volume (L) moles 17

U SING M OLARITY OF R EACTANTS How many mL of 3.00 M HCl are needed to completely react with 4.85 g of CaCO 3 ? 2 HCl( aq ) + CaCO 3 ( s ) CaCl 2 ( aq ) + CO 2 ( g ) + H 2 O( l ) STEP 1: Given 3.00 M HCl; 4.85 g of CaCO 3 Need volume in mL STEP 2: Plan g CaCO 3 mole CaCO 3 mole HCl mL HCl 18

EXAMPLE If 22.8 mL of M MgCl 2 is needed to completely react 15.0 mL of AgNO 3 solution, what is the molarity of the AgNO 3 solution? MgCl 2 ( aq ) + 2AgNO 3 ( aq ) 2AgCl( s ) + Mg(NO 3 ) 2 ( aq) 1) M 2) M 3) M 19

EXAMPLE How many liters of H 2 gas at STP are produced when Zn reacts with 125 mL of 6.00 M HCl? Zn( s ) + 2HCl( aq ) ZnCl 2 ( aq ) + H 2 ( g) 1) 4.20 L of H 2 2) 8.40 L of H 2 3) 16.8 L of H 2 20

SOL7.7 P ROPERTIES OF S OLUTIONS UTIONS Solutions contain small particles (ions or molecules). are transparent. do not separate. cannot be filtered. 21

C7.7 P ROPERTIES OF S OLUTIONS OLLOIDS Colloids have medium-size particles. cannot be filtered. can be separated by semipermeable membranes. 22

EXAMPLES OF COLLOIDS Examples of colloids include fog whipped cream milk cheese blood plasma pearls 23

7.7 P ROPERTIES OF S OLUTIONS SUSPENSIONS Suspensions have very large particles. settle out. can be filtered. must be stirred to stay suspended. Examples include: blood platelets, muddy water, and calamine lotion. 24

S OLUTIONS, C OLLOIDS, AND S USPENSIONS 25 Copyright © 2009 by Pearson Education, Inc.

EXAMPLENING CHECK A mixture that has solute particles that do not settle out, but are too large to pass through a semipermeable membrane is called a 1) solution. 2) colloid. 3) suspension. 26

OSMOSIS In osmosis, water (solvent) flows from the lower solute concentration into the higher solute concentration. the level of the solution with the higher solute concentration rises. the concentrations of the two solutions become equal with time. 27

OSMOSIS Suppose a semipermeable membrane separates a 4% starch solution from a 10% starch solution. Starch is a colloid and cannot pass through the membrane, but water can. What happens? semipermeable membrane 28 4% starch10% starch H2OH2O

WATER FLOW EQUALIZES The 10% starch solution is diluted by the flow of water out of the 4% and its volume increases. The 4% solution loses water and its volume decreases. Eventually, the water flow between the two becomes equal. 29 7% starch H 2 O

OSMOTIC PRESSURE Osmotic pressure is produced by the solute particles dissolved in a solution. equal to the pressure that would prevent the flow of additional water into the more concentrated solution. greater as the number of dissolved particles in the solution increases. 30

EXAMPLECHECK A semipermeable membrane separates a 10% sucrose solution A from a 5% sucrose solution B. If sucrose is a colloid, fill in the blanks in the statements below. 1. Solution ____ has the greater osmotic pressure. 2. Water initially flows from ___ into ___. 3. The level of solution ____will be lower. 31

OSMOTIC PRESSURE OF THE BLOOD Red blood cells have cell walls that are semipermeable membranes. maintain an osmotic pressure that cannot change or damage occurs. must maintain an equal flow of water between the red blood cell and its surrounding environment. 32

ISOTONIC SOLUTIONS An isotonic solution exerts the same osmotic pressure as red blood cells. is known as a “physiological solution.” of 5.0% glucose or 0.90% NaCl is used medically because each has a solute concentration equal to the osmotic pressure equal to red blood cells. 33 H2O H2O

HYPOTONIC SOLUTIONS A hypotonic solution has a lower osmotic pressure than red blood cells. has a lower concentration than physiological solutions. causes water to flow into red blood cells. causes hemolysis: RBCs swell and may burst. 34 H2OH2O

HYPERTONIC SOLUTIONS A hypertonic solution has a higher osmotic pressure than RBCs. has a higher concentration than physiological solutions. causes water to flow out of RBCs. cause crenation: RBCs shrink in size. 35 H2OH2O

DIALYSIS In dialysis, solvent and small solute particles pass through an artificial membrane. large particles are retained inside. waste particles such as urea from blood are removed using hemodialysis (artificial kidney). 36

EXAMPLES Indicate if each of the following solutions is 1) isotonic, 2) hypotonic, or 3) hypertonic. A.____ 2% NaCl solution B.____ 1% glucose solution C.____ 0.5% NaCl solution D.____ 5% glucose solution 37

EXAMPLES When placed in each of the following, indicate if a red blood cell will 1) not change, 2) hemolyze, or 3) crenate. A.____ 5% glucose solution B.____ 1% glucose solution C.____ 0.5% NaCl solution D.____ 2% NaCl solution 38

EXAMPLES Each of the following mixtures is placed in a dialyzing bag and immersed in pure water. Which substance, if any, will be found in the water outside the bag? A. 10% KCl solution B. 5% starch solution C. 5% NaCl and 5% starch solutions 39