Unit 8: Solutions
How can you tell when a solution is supersaturated?
You will see cloudiness or a white precipitate at the saturation temperature.
What is a Calorie (Cal)?
a unit of food energy
What is a calorie (cal)?
a unit of heat energy
When the energy of the reactants is less than the energy of the products, the process _________.
absorbs heat
Most solutions are...
aqueous
How are you going to do on this test.
awesome.
Which of the following is an exothermic process? a. C2H5OH (s) ® C2H5OH (l) b. H2O (g) ® H2O (l) c. CH3OH (l) ® CH3OH (g) d. CO2 (s) ® CO2 (g)
b. H2O (g) ® H2O (l)
An exothermic process ______ bonds.
breaks bonds
What does c represent in q=mc(delta T)?
c represents the specific heat in J/g degrees C
Which of the following processes is endothermic? a. a popsicle melting b. water boiling c. both are endothermic d. neither are endothermic
c. both are endothermic
When wax is freezing the: a. temperature remains constant b. enthalpy decreases c. entropy decreases d. all of the above
c. entropy decreases
Delta H is...
change in heat (enthalpy)
Examine the equation below, and determine which statement describing the equation is TRUE. 2 K(s) + 2 H2 (l) ® 2 KOH(aq) + H2(g) + 393 kJ a. this is an endothermic reaction b. 393 kJ of energy is being absorbed c. the reactants have more energy than the products d. the reactants have less energy than the products
d. the reactants have less energy than the products
Examine the process below. Which of the following statements about the process is TRUE? H2O (s) ® H2O (l) DHfus = 334 kJ/kg a. this is a chemical change b. entropy is increasing c. the substance is undergoing solidification d. the substance is releasing 334 kJ of energy
d. the substance is releasing 334 kJ of energy
What does delta T represent in q=mc(delta T)?
delta T represents the change in temperature, T final- T initial
What calculations represents the Boiling Point Elevation/Freezing Point Depression concept?
delta T= Kmi
What do dissolved ioninc compounds form?
electrolytes
As you move to the right along the heating curve, the changes are
endothermic
If a value that results from the equation q=mcdeltaT is positive, the reaction is...
endothermic
Absorbed energy is _____.
endothermic, it is written as the reactant
What is kinetic energy?
energy of motion
If a value that results from the equation q=mcdeltaT is negative, the reaction is...
exothermic
Combustion is a _____ process.
exothermic process
Released energy is _____.
exothermic, it is written as the product
A form of energy that flows from a warmer to a cooler object is?
heat
What does i represent within the colligative property equation?
i represents the Van't Hoff factor.
If 2 liquids cannot dissolve they are...
imminscible
What is a catalyst that slows down, or inhibits, reaction rates?
inhibitor
If a solid of gas cannot dissolve it is called...
insoluble
What does m represent in q=mc(delta T)?
m represents the mass of the substance in grams
What does m represent within the colligative property equation?
m represents the molality of the solution.
If 2 liquids dissolve in each other they are...
miscible
When temperature increases, the motion of the molecules ____________.
motion increases
Nonpolar solvents will dissolve ________ solutes.
nonpolar
Polar solvents will dissolve _____ solutes.
polar
What does q represent in q=mc(delta T)?
q represents the heat lost or gained in Joules
What are the calculations used to determine the heat lost or gained in Joules?
q=mc(delta T)
If a solid or gas can dissolve it is called...
soluble
The substance that is being dissolved is the...
solute
The substance that does the dissolving is the...
solvent
What is energy?
the ability to do work or produce heat, it can be absorbed or released
What is solution classification based on?
the amount of solute added to the solvent
What does the heat of fusion equal?
the heat of fusion equals 334 J/g
What does the heat of vaporization equal?
the heat of vap = 2260 J/g
The measure of kinetic energy of particles in a substance is?
the temperature
Using the heat equation q=m · c · ∆T, calculate c for the aluminum for trial 1and then againfor trial 2. (Use 4.184 J/goC for the specific heat of water).
#1 - sovle for q (q=mcdeltaT) #2 - plug in and splve for c
Give two possible explanations for this (Which component (the Al orwater) experienced a greater change in temperature (∆T))
#1 Water had a greater specific heat so it experiences a lower change in temp for the same change in energy #2 Water also had more PE due to the IMF so it takes longer for it to heat compares to a metal like Al
What is the heat released by 0.85 moles of Iron that cools from 63oC to 25oC. (specific heat capacity of iron is 0.499 J/g degree C)
-809 Joules
What volume of 12M HCI solution will hold 3.0 mol HCI?
0.250 L
What will the Van't Hoff factor be for covalent compounds?
1
1 mL equals
1 cm^3
1000 cal = ____ kcal (kilocalorie)
1 kcal
How many Calories of energy are in 432 J?
1) Divide 432J by 4.184 Joules 2) Put 1 cal on top of 4.184 and then divide by 1000 cal 3) 1000 cal = 1 Cal Final answer - 0.103 Cal
A calorimeter contains 195 g of water at 20.4°C (start). A 37.8 g sample of an unknown metal is heated to 133°C (start) and placed into the water in the calorimeter. Heat flows from the metal to the water until both reach a final temperature of 24.6°C (final). What is the specific heat of the metal?
1) Find temperature values 24.6-20.4=4.2 degrees H20 24.6-133= -108.4 degrees metal 2)use Q=mcdeltaT (-mcdeltaT= mcdeltaT) -(37.8g)(x)(-108.4)=(195g)(4.184)(4.2) 3) C=0.836 J/g degrees c FILL IN TABLE SET UP LIKE THIS substance a water Q= m= c= Delta T=
A solution of salt water raised the boiling point of water from 100 degrees Celsius to 102.5 degrees Celsius. What is the molality of the solution? Assume the Kb of water is 0.51°C/m.
1) Find the change in temperature by subtracting (102.5-100) = 2.5 2) Solve for molality (2.5 degrees C)=(0.51C/m)(2)(m) 3) Answer - 2.5 m
If you use 3.68mol of sucrose (C12H22O12) and dissolve this into 2.50kgof water, what will be the change in the freezing point of your solution. Assume the Kfof water is -1.86°C/m.
1) Find the m of the solution by doing the following (3.68 mol/2.50 kg) which would give you 1.47 mol/kg. 2) Multiply the given values with the molality 3) Final answer: Delta T = -2.73 degrees C
What are the three components of the collision theory?
1) Reactant particles must collide in the same vessel 2) Reactant particles must collide with proper orientation 3) Reactant particles must collide with enough energy to break the activation energy barrier
What is the boiling point of water?
100 degrees C
I Cal = ____cal
1000 cal
How many calories are in a 105 Calorie banana?
105,000 cal
A sample of iron metal (0.449) with a mass of 25.0 g is heated to a temperature of 120.°C and placed in a calorimeter of water at 23.0°C. The final temperature of the water and the iron is 33.0°C. Assuming no heat loss, what mass of water was in the calorimeter?
23.3g
1 cal = ____J
4.184 J
What is the specific heat capacity of water?
4.184 J/gC
A 4.57 gram nugget of gold is at a temperature of 32oC. When 35 Joules of heat are added, the temperature increases. What is the final temperature? (gold SHC - 0.129J/g degree c) (must use x-32)
91 degree C
What is a solution?
A homogeneous mixture combined physically and looks the same throughout.
What is solubility?
A measure of the amount of solute that will dissolve in a given amount of solvent - usually water.
What is the definition of temperature?
A measure of the kinetic energy of particles.
What does nonpolar mean?
A molecule that is symmetrical, has no dipole moments, or they cancel.
What is a catalyst?
A substance added to a chemical reaction that speeds up the rate of a reaction
Explain why all reactions have activation energy, using your knowledge of collision theory.
ACCORDING TO THE COLLISION THEORY, ALL REACTIONS MUST HAVE A COLLISION. COLLISIONS MUST OCCUR WITH SUFFICIENT ENERGY. NO CHEMICAL PROCESS CAN TAKE PLACE WITHOUT HAVING AT LEAST A LITTLE ENERGY TO GET THINGS STARTED.
Explain how adding a solute (like a salt) to a solvent (like water) influences the solutions vapor pressure.
Adding a solute to a solvent interferes with the movement of the solute particles. The solvent isn't able to escape the solution as a gas as easily therefore lowers the vapor pressure.
What are 4 factors that affect solubility?
Agitation, Temperature, Surface Area/particle size, and Pressure
How does agitation speed up dissociation?
Allows for the solvent (in this case water) to surround the entire solute. It can then pull it apart.
Independent vs Dependent variable
An independent variable is the variable that is changed or controlled in a experiment to test its effects on the dependent variable. A dependent variable is being tested and measured in a scientific experiment.
What does a supersaturated solution cause?
An unstable solution in which extra solute precipitates out of the solution.
Explain the relationship between temperature and the solubility of a gas.
As temperature increases, the solubility decreases. The relationship is inversely proportional. This is because the gas particles increase in energy with higher temperatures and will escape the solution.
Explain the relationship between temperature and the solubility of a solids
As temperature increases, the solubility increases as well. The relationship is directly proportional.
In the case of the dissolving of Ca3(PO4)2, why does PO4 stay together?
Because PO4 its a polyatomic covalent compound.
Why are electrolytes called electrolytes?
Because their aqueous solutions can conduct an electric current.
How is polarity determined?
By the dipole moments and electronegativity difference. The shape also contributes.
How would the compound Ca3(PO4)2 dissolve?
Ca2+ PO4^3- Ca2+ PO4^3- Ca2+
How can collisions be manipulated?
Collision theory directly correlates to reaction rates which is how fast of slow a reaction will happen. There are four factors that can be altered that will alter the rate of a reaction. All four of these directly relate to the amount of collisions.
What does unsaturated mean?
Contains less than the max amount of the dissolved solute particles.
What does saturated mean?
Contains the max amount of the dissolved solute particles.
What does supersaturated mean?
Contains the more dissolves solute than normally possible.
During periods within the heating curve of water where energy is constant, what is taking place?
Energy is going into disrupting IMF, trying to break those forces.
True or False- An aqueous solution is made more concentrated by adding more water to a solute.
False (because the number of moles doesn't change but the volume of the solution increases.
True or False : Increasing the concentration of a substance increases the kinetic energy of the particles that make up that substance.
False (replace concentration with temperature)
True or False : Factors that influence the rate of chemical reactions include catalysts, temperature, and the reactivity, concentration, and surface are of the reactants
False, reactivity should be taken out
Which will dissolve faster in a glass of water, a cube of sugar or a package of granulated sugar? (both have same mass)
Granulated sugar will dissolve faster as it has greater surface area allowing the solvent molecules more access to the solute particles which allows for solvation and dissociation to happen at a faster rate.
How does temperature affect solubility?
Heating a solution increases collisions of solid solutes and solvent, increasing the amount dissolved and the rate of dissolving. Temp increase allows this to happen faster because the amount of movement is increasing.
What do solubility curves show?
How much solute dissolves in a given volume of a solvent at a given temperature.
How do solutions form?
In 2 steps, solvation and dissociation.
Calculate the energy needed to increase the temperature of 40g of H20 from -15 degrees to 108 degrees. USE Q=mc delta T
In order to solve this, you must calculate Q=mc delta T for each change in the graph. 1) For the first increase within the graph (when water is solid) - (40g)(2.02J/g oC)(0--15) = 1212 2) Q=m(delta)Hfusion - (40g)(334J/g) =13360 3) Q=mc delta - (40g)(4.184J/g)(100-0) = 16736 4) Q=m(delta)Hvap - (40g) (2260J/g) = 90400 5) Q=mc delta - (40g) (2.03J/g) (108-100) = 649.6 6) 122357.6 J final answer
Explain how Temperature affects the rate of reaction?
Increase in temperature increases the kinetic energy of the particles. Increases frequency of collisions because particles are bouncing around more. Increases frequency of the collisions with proper orientation. Because particles are moving faster, they are more likely to achieve enough energy to overcome the Ea barrier.
Explain how Surface Area affects the rate of reaction?
Increasing the amount of surface area exposed for the reaction increases the amount of surface area available to collide. More particles present leads to increased frequency of collisions. More frequent collisions lead to higher probability of collisions with proper orientation.
How does an exothermic graph look like?
Initially, there is a middle level of energy, then activation energy is added to the max. After this, a large amount of energy is released. More energy is released then the reaction began with.
Do electrolytes have a greater effect on colligative properties in covalent compounds or ionic compounds?
Ionic compounds
How do covalent compounds dissolve in a solution?
Ionic compounds dissolve but do not dissociate. This forms an non electrolyte solution.
How do ionic compounds dissolve in a solution?
Ionic solutes will dissociate into ions within the solution. This will form an electrolyte solution. (ex. NaCl will break up into +Na and -Cl)
Explain how a Catalyst affects the rate of reaction?
It lowers activation energy, the do NOT make more of a product. Catalysts are NOT used up of consumed in a reaction so they can be used over and over again, very cost efficient. Catalysts form an activated complex of lower energy than a reaction without a catalyst.
What does the collision theory state?
It states how reacting particles (atoms and molecules) must interact to start a chemical reaction.
What will the Van't Hoff factor be for ionic compounds?
It will be however many molecules the compound splits into.
How does KCI dissolve in water as it is heated?
It will disassociate into 2 ions per formula unit.
What would be the effect on your calculation if you measured the temperature using the Kelvin scale?
It would not change the specific heat because the change in 1 degree C is equal to the change in 1 degree K.
What is the SI unit for heat?
Joule (J)
What does K represent within the colligative property equation?
K represents the molal freezing/ boiling point constant (its given).
What are some requirements in making a graph?
Key, label both axis, title (y vs x) and appropriate scale.
What is density?
Mass of solution over volume of solution. (g/mL)
Explain how Concentration affects the rate of reaction?
Molarity (mol/L) is typically how concentration is expressed. Increasing the concentration increases the number of particles present in a reaction. More particles present leads to increased frequency of collisions. More frequent collisions lead to higher probability of collisions with proper orientation.
How does surface area/ particle size affect solubility?
More surface area allows for greater contact between solute and solvent therefore faster solvation and dissociation.
How do you prepare a solution from a solid sample?
Obtain a volumetric flask of the desired size and wash with water. Fill flash half way with DI water. Measure out the solid with a weigh boat and scale and add the specific amount into the flask. Use the squirt bottle if residue is on sides of flask. Cap off flask and invert it to mix. Add the remaining DI water to the line and invert again.
What does Lead (II) nitrate dissociate into?
Pb 2+ NO3-
What is the formula for Lead (II) nitrate?
Pb(No3)2
What are colligative properties?
Physical properties that are either observed or measured that are influenced by the number/amount of solute particles but NOT the identity of those particles.
During the point at the graph between solid state and liquid state, what is the formula used?
Q=m(delta)Hfusion
During the point at the graph between the liquid state an the gas state, what is the formula used?
Q=m(delta)Hvap
What does polar mean?
Regions of opposite charges that are asymmetrical.
What is solvation?
Solvation is the process in which solvent particles completely surround solute particles.
How do you dilute a stock solution?
Solve M1 V1= M2 V2. Obtain volumetric flask and clean it with water. Using a beaker, transfer the desired amount of stock solution to a beaker. Fill volumetric flask halfway with D1 water and use a volumetric pipette and pipett your solution and transfer. Cap off flask and invert it. Add D1 water until it reaches the desired mark.
How does an endothermic graph look like?
Starts with a small amount of energy. Large amounts of AE is added, leaving the amount of energy absorbed by the reaction being greater than the initial amount of energy.
How does agitation affect solubility?
Stirring the solution increases the collisions between the solute and the solvent so that solvation and dissociation occurs faster.
What is potential energy?
Stored energy in an object that has the potential to do work. Chemical P.E. is associated with the composition of the substance.
What are the 4 factors that affect the rate of reaction?
Surface Area, Concentration, Temperature, Catalyst
Explain the difference between high and low activation energies and how this affects the reaction?
THE HIGHER THE ACTIVATION ENERGY, THE MORE ENERGY THE PARTICLES WILL NEED WHEN THEY COLLIDE. IF THE ACTIVATION IS LOW, REACTIONS TEND TO OCCUR FASTER THEN HIGHER ACTIVATION ENERGY.
Describe how the activation energy affects the overall rate of the chemical reaction?
THE HIGHER THE ACTIVATION ENERGY,THE MORE ENERGY IS REQUIRED DURING THE COLLISION FOR THE REACTION TO OCCUR.
What is the result of ionic solutions breaking apart and always producing MORE than one ion?
That makes the number of solute particles increase.
Which component (the Al orwater) experienced a greater change in temperature (∆T) ?
The Al experienced a greater change in temp.
As a phase change is taking place, what is happening with the kinetic energy?
The KE is increasing.
As a phase change is taking place, what is happening with the potential energy?
The PE remains constant.
If all three requirements in the collision theory are met what takes place within the reaction?
The activated complex forms where all of the reactant particles stick together. (this complex is a temporary and unstable structure).
Explain how the addition of a solute to a solvent affects the vapor pressure of the solvent.
The addition of a solute will lower the vapor pressure of a solvent. The solute particles interfere with the solvent particles which lessens the amount of solvent that evaporates. Less molecules evaporating = less vapors = lower vapor pressure.
What is specific heat?
The amount of energy required to raise 1 gram of substance by 1 degree Celcius.
What is Boiling Point (Elevation)? (Longer Explanation)
The boiling point elevates with the addition of a solute to the solvent. For a substance to boil, atmospheric pressure pushing down must equal vapor pressure pushing up. Solute particles interfere with the solvent at the surface so it will take more energy to get the solvent particles to push their way to evaporate meaning you have to heat the solution to a higher temperature.
What happens to the boiling point of water when you add a solute? Describe the difference in the boiling point of water upon the addition of 0.5 moles of C5H12O6 versus 0.5 moles of KCI?
The boiling point of water would increase with the addition of a solute. The 0.5 moles of KCI would have a greater impact as it will dissociate into 2 ions per formula unit versus the C6H12O6 which does not dissolve into anything more than individual molecules.
A chemist heated a sample of steel wool in a burner flame exposed to oxygen in the air. He also heated a sample of steel wool in a container of nearly 100% oxygen. The steel wool sample in the container reacted faster than the other sample. Explain why.
The concentration of O2 was increased in the container allowing for more collisions between the steel wool and the O2 molecules.
What does delta T represent within the colligative property equation?
The delta T represents a change in temperature.
What is proper orientation?
The direction/orientation the particles must collide.
What is kinetic energy?
The energy associated with movement.
What is Freezing Point (Depression)? (Longer Explanation)
The freezing point decreases with the addition of solute to solvent. Solute particles are mixed in with the solvent particles interfering with the ability of solvent particles to get close enough together to solidify. Meaning the temperature has to drop a lot for the solvent to push the solute out of the way in order to solidify.
In any chemical reaction, energy can neither be created or destroyed. This is the law of ________.
The law of conservation of energy
What is % by mass?
The mass of solute per mass of solution times 100.
If you forgot to tare the scale, what would be the effect on the calculation?
The mass of the Al would be greater so the calculated specific heat would be lower.
What is the definition of activation energy?
The minimum amount of energy required for a reaction to occur.
What is molarity?
The moles of solute per L of solution.
What is molality?
The moles of solute per kg of solvent.
What is mole fraction?
The number of moles of solute per moles of solution.
What does the Van't Hoff factor state?
The number of particles produced per molecule/ formula unit.
What is the definition of the colligative property: Boiling Point (Elevation)?
The point at which the vapor pressure (pushing up) equals the atmospheric pressure (pushing down), this equal but opposite force results in the solvent boiling, heat is only needed to get vapor pressure up high enough to equal the downward push of atmospheric pressure.
What is dissociation?
The process in which the solute particles are pulled apart by the solvent. Dissociation depends on the forces between the atoms (between positive and negative ions).
If there is low AE, at what rate is the reaction rate?
The reaction rate is fast.
If there is a high AE, at what rate is the reaction rate?
The reaction rate is slow.
How does the number of solute particles affect these properties?
The solute particles INTERFERE with the solvent particles. The more solute particles that are in the solution, the more colligative properties are affected.
What is a calorimetry?
The study of heat flow and heat measurement
What is the activated complex also referred to?
The transition phase because its the phase of breaking old bonds and forming new ones.
How does NaCl affect H2O in a solution?
The water attaches to the salt. The particles wont be colliding just as H2O some particles will be trapped by NaCl and will need to pass through. The water won't vaporize as quickly resulting in a longer amount of time to boil the water, the longer it takes for the water to boil the less time it takes for it took cook.
What are the components of a calorimeter?
Thermometer, Lid, Insulation, Water, Stand, Heat Source
Explain why calcium chloride spread on icy roads would be more effective at melting ice than sodium chloride.
This is a colligative property which is dependent among the number of solute particles. Ionic compounds dissociate into ions which increases their effectiveness at lowering freezing points. CaCl2 would dissociate to 3 ions per formula unit versus 2 ions per formula unit for NaCl. Greater number of ions has a greater effect.
What is a calorimeter used for?
To determine the energy change associated with a chemical or physical reaction. This is reliant upon the relationship between heat transfer and temperature change
True or False : A heterogeneous catalyst exists in a different physical state than the reaction it catalyzes
True
What is Vapor Pressure (Lowering)? (Longer explanation)
Vapor pressure decreases with the addition of the solute to the solvent. There are solute particles interfering with the solvent at the surface of the solution. Less of the solvent will then be able to evaporate and push upwards because the solute is at the surface too. Since less solvent is evaporating, the vapor pressure drops because there is not gas pushing upwards.
Use collision theory to explain why reactions should occur more slowly at lower temperatures
WHEN TEMPERATURE IS DECREASED THERE ARE FEWER COLLISIONS AND LESS ENERGY.
Why does it take longer to cook pasta properly in boiling water in Denver (the "mile high city") than it does in New York City?
Water boils at a lower temperature in Denver. Places at higher elevation have lower atmospheric pressure so it would take less time to boil the water, but the temperature would also be lower.
Why is water called the universal solvent?
Water is a polar covalent molecule.
Explain this example of proper orientation NO3 + CO → NO2 + CO2
When NO3 and CO react together, they must collide with sufficient energy and with the nitrogen atom in NO3 colliding with the carbon atom in CO. In other words - the nitrogen and carbon atoms must "bump" together. (Think in terms of the two like charges must repel, one pos and one neg for the reaction to take place)
What is the definition of endothermic?
When energy is absorbed in a reaction. (+Delta H)
What is the definition of exothermic?
When energy is released. ( - Delta H)
What is the definition of the colligative property: Vapor Pressure (Lowering)?
When pressure is exerted in a closed container by the solvent particles as they evaporate form a liquid into a gas, the evaporated gas then rises and pushes on the container top creating upward pressure (aka vapor pressure).
What is the definition of the colligative property: Freezing Point (Depression)?
When you have a low temperature, you have low kinetic energy. Freezing happens when energy is low enough for particles to stay close together.
