Chopped-up Chapter chapter 15 (supershortened)
Chapter 15 Solutions
solutions are everywhere! air, brass, shampoo, Diet Coke, gasoline, cough syrup, etc. defined simply as a homogeneous mixture (chm a) substance in largest amt = solvent other substances = solute in aqueous solns water is solvent
15.1 solubility when an ionic cmpd dissolves, it conducts electricity ionic cmpds break up into their ions
as it dissolves, waters surround and rip away the helpless ions
notice which end of the water butts up against the cations & anions
water can also dissolve polar substances like ethanol here; why?
the H-bonding plays a big role here the more you look like water the more likely it will dissolve you
why do you think sucrose here dissolves so well?
why do you think sucrose here dissolves so well? H-bond attraction! (see all the OH s?)
not everything can dissolve in water if you have no polar handle on you, water doesn t recognize you like the long nonpolar hydrocarbon above
so to dissolve in water you have to be able to break the net, to interrupt the H-bonding; you have to fit in polar molecules and ionic cmpds can do that; nonpolar cannot like dissolves like is a good general phrase nonpolar solutes can dissolve into nonpolar solvents, too!
Hydrogen Carbon Oxygen Vitamin A is above, Vitamin C below. If you took too much of them both which ends up stored in your fat, which goes out with the pee pee? (Hint: Lots of CH s mean nonpolar, lots of OH s means polar.)
frinking frap time 1 Why offer this person oil or butter to clean his hands - and not water?
frinking frap time 2 Why does water fall in drops?
frinking frap time 3 Why does the water bead on the leaf?
frinking frap time 4 How can the buggie do that?
15.2 solution concentration there is a limit to how much you can dissolve; like sugar in iced tea when the limit is reached = saturated depends on T (think: iced T vs hot tea) can it still hold more solute? unsaturated! add more it will dissolve
what s happening here? why didn t c change afterwards once saturated, game over
after a certain time, the rate leaving equals the rate coming back
chemists also use concentrated and dilute - both really qualitative terms concentrated basically means there s a lot of stuff dissolved in there; dilute means not so much but neither tells us how much (quantitative)
15.3 factors affecting the rate of dissolution three big factors here on how fast something dissolves surface area stirring temperature
dissolving occurs at the surface of a solid, so the more surface exposed to a solvent, the faster it will dissolve like powdered sugar vs rock candy
frinking frap time which will dissolve faster, fine salt or rock salt? why???
stirring will increase the rate, too in slow motion the solute is dissolved in the solvent, but instead of hanging around and getting in the way, stirring gets the dissolved fellows out of the way this exposes new solute to new solvent
raising the T means speeding up the solvent molecules this lets them get their job done faster not only does it happen faster, but most solutes dissolve more completely at higher T s
what is the obvious pattern here? as the temp goes up, most solids are more soluble in water
but! the opposite is true for gases dissolved in water higher T or more stirring means they don t dissolve well that s why we don t heat up soda or aquariums, and why we don t stir (shake) soda
why do carbonated beverages do this? sol of gas also depends on pressure release the P and bye bye gases
can force more gas into liq w/ higher pres cans and glass bottles can keep gases under pres; not plastic
Lake Nyos (Cameroon, 1986) overturned CO 2 flowed down the hills covering villages and livestock 2000 people killed
Killer Lakes
walk away with...1 A solution is a homogeneous mixture of a solute dissolved in a solvent. Substances with similar polarities tend to dissolve each other to form a solution. Water is a very polar substance and tends to dissolve ionic solids or other polar substances.
walk away with...2 Various terms are used to describe solutions: saturated - contains the maximum possible dissolved solid unsaturated - not saturated supersaturated - contains more dissolved solid than should dissolve at a given temperature concentrated - contains a relatively large amount of solute dilute - contains a relatively small amount of solute
walk away with...3 The rate of dissolution is affected by surface area of a solute stirring temperature
15.5 molarity concentration with numbers! most commonly used unit is molarity
15.5 molarity molarity (M) = moles solute/l soln e.g. a 2.7M soln means there are 2.7 mol crud per litre of soln given that M = mol/l, you shd be able to solve for any one variable if I give you other two
M = mol/l example How many mols HCl are in 1.45 L of a 2.25 M soln? 2.25 M = mol 1.45 L 2.25 M 1.45 L = mol 3.26 = mol
M = mol/l example How many mols HCl are in 3.5 L of a 6.5 M soln? 6.5 M = mol 3.5 L 6.5 M 3.5 L = mol 23 = mol
M = mol/l example How many mols NaCl are in 2.5 L of a 1.5 M soln? 1.5 M = mol 2.5 L 1.5 M 2.5 L = mol 3.8 = mol
mass percent another way, an easy way, to do concentration is mass percent mass% = (mass solute/ mass solution) x 100
example A solution is made by mixing 1.00 g of ethanol with 100.0 g of water. What is the mass percent? mass% = (mass solute/mass solution) x 100 mass % = g ethanol/(g ethanol + g water) x 100 mass % = 1.00/(100.0 + 1.00) x 100 mass % = (1.00/101.0) x 100 mass % = 0.990% ethanol
example Cow s milk typically contains 4.5% by mass of lactose, a sugar. Calculate the mass of lactose present in 175 g of milk. mass% = (mass solute/mass solution) x 100 4.5% = (mass lactose/175 g milk) x 100 mass lactose = 7.9 g (alternate -> 4.5 is to 100 as x is to 175 cross multiple and divide
A 135-g sample of seawater is evaporated to dryness, leaving 4.73 g of solid residue (the salt in the seawater). What is the mass percent of solute present in the original seawater? mass % = g salt / g seawater solution x 100 mass % = 4.73/135 x 100 mass % =.0350 x 100 mass % = 3.50% salt
walk away with... Descriptions of solution concentration: mass% = mass solute/mass solution x 100 molarity (M) = moles solute/ L soln
15.10 the properties of solns: boiling point & freezing point when you add solute to water it boils at a higher T than 100 C! and freezes at less than 0 C! [BTW, it happens with all the solutes in all liquid solvents]
in boiling the stuff (solute) interferes with the water molecules ability to push out bubbles this makes the water need more energy to make the bubbles therefore, higher bp
they get in the way of building a solid, too so at normal fp, there are more leaving than coming back (thus, it melts) this means we have to lower the temp until rate leaving = coming back therefore, the fp is lower salt on ice will melt it
both the raising of bp and the lowering of fp is seen when we add antifreeze to water
walk away with... The properties of a solvent are affected by dissolving a solute! The boiling point of a solvent increases as the amount of dissolved solute increases. The melting point of a solvent decreases as the amount of dissolved solute increases.
49, 51 15eocs