CH.12 and 13 Questions
What is the molal concentration of an aqueous calcium chloride solution that freezes at -2.43°C!
0.4 molal
How many kilograms of H20 must be added to 75.5 g of Ca(NO3)2 to form a 0.500 m solution?
0.920 kg
solution made from ethanol, C2H5OH, and water is 1.75m ethanol. How many grams of C2H5OH are contained per 250. g of water?
1.75 m = x mol ethanol / .250 kg water = .4375 mol C2H5OH x 46 g C2H5OH = = 20.125 g C2H5OH
How many moles of ions are contained in 1 L of a 1 M solution of KCI? of Mg(NO3),?
2 mol; 3 mol
2. How many grams of antifreeze, C, H, (OH),, would be required per 500. g of water to prevent the water from freezing at a temperature of -20.0°C?
333.7 g. Explanation: The depression in freezing point of water (ΔTf) due to adding a solute to it is given by: ΔTf = Kf.
3. What is a net ionic equation?
A net ionic equation shows only the chemical species that are involved in a reaction, while a complete ionic equation also includes the spectator ions.
a. What is a saturated solution? b. What visible evidence indicates that a solutionis saturated? c. What is an unsaturated solution?
A.) A solution in which the maximum amount of solvent has been dissolved B.)If more solute is added to the solution and the solute remains undissolved, then you know that solution is saturated. C.)An unsaturated solution is a chemical solution in which the solute concentration is lower than its equilibrium solubility.
A. Suppose you wanted to dissolve 106 g of Na2CO3 in enough H20 to make 6.00 L of solution. (1) What is the molar mass of Na2 CO? (2) What is the molarity of this solution? b. What is the molarity of a solution of 14.0 g NH4Br in enough H20 to make 150. mL of solution?
A2. 0.167 M B. 0.953 M
14. How does the presence of a nonvolatile solute each of the following properties of the solvent in which the solute is dissolved? a. vapor pressure b. freezing point c. boiling point d. osmotic pressure
Here, it asked how the non volatile substance affect the vapor pressure, freezing point, boiling point, and osmotic pressure of solvent. a. When non volatile substance is added to the solvent, the vapor pressure decreases due to the decrease of the entropy difference of both liquid and gas molecules in a solution. b. When non volatile substance is added to the solution, the freezing point is affected due to the decrease of vapor pressure, the temperature where the liquid freezes also decreases. c. If the non volatile substance is added to the solution, the boiling point will increase. The molecules in this solution can hardly transform from liquid to gas state. d. For the osmotic pressure, as the concentration of the solution increases, its osmotic pressure will increase as well.
6. What determines the strength of a solute as an electrolyte?
How well electrical current flows through a solution determines the strength of a solute as an electrolyte. Ionic compounds that dissolve readily in solvents will wholly separate into their ions. This is what allows electric current to flow through the solution.
Under what circumstances might we prefer toexpress solution concentrations in terms ofa. molarity?b. molality?
If you are making a solution by volume, use molarity(moles/liter). If you are weighing your ingredients, use molality (moles/1000g solvent).
a. What rule of thumb is useful for predictingwhether one substance will dissolve inanother? b. Describe what the rule means in terms of
In general, the rule means that polar substance dissolves in polar solvents while non-polar substances dissolve in non-polar solvents.
Given an unknown mixture consisting of two ormore substances, explain how we could determinewhether that mixture is a true solution, a colloid, or a suspension.
Pass the mixture through filter paper. The large particles in the suspension will filter out. Solution: homogeneous mixture of two or more substances in a single phase . Colloids: particles are intermediate in size between those in solutions and suspensions. To tell the difference between a solution and a colloid, shine a beam of light through the mixture, if it reflects then it is a colloid, if it doesn't then it is a solution
5. a. Define and distinguish between strong electrolytes and weak electrolytes. b. Give two examples of each type.
There are two types of electrolytes- strong and weak electrolytes. A strong electrolyte is an electrolyte that dissolves almost completely in water. An example of a strong electrolyte is Hydrogen Chloride (HCI) A weak electrolyte is an electrolyte that doesn't dissolve completely in water.
What is the Tyndall effect? Identify one example of this effect.
a) It is the scattering of light by colloids and suspensions. b) The visibility of a headlight beam on a foggy night.
What is solution equilibrium? What factors determine the point at which a given solute-solvent combination reachesequilibrium?
a) Solution Equilibrium is the physical state in which the opposing processes of dissolution and crystalization of a solute occur at equal rates. b) The time to reach the equilibrium value depended on the drop size, solute, solvent, and temperature combination.
13. The enthalpy of solution for AgNO, is +22.8 kJ/mo a. Write the equation that represents the dissolutic AgNO, in water. b. Is the dissolution process endothermic or exothermic? Is the crystallization process endothermic or exothermic? c. As AgNO, dissolves, what change occurs in the temperature of the solution? d. When the system is at equilibrium, how do the rates of dissolution and crystallization compare? e. If the solution is then heated, how will the rates of dissolution and crystallization be affected? Why? f. How will the increased temperature affect the amount of solute that can be dissolved? g. If the solution is allowed to reach equilibrium and is then cooled, how will the system be affected?
B. endothermic and exothermic because crystallization is inverted. c. The solution will get colder d.The rates of dissolution and crystallization will occur at the same rates e.The rate of dissolution will be increased and crystallization will decrease f.The amount that can dissolve will be increased. gThe rate of crystallization will increase to relieve stress and the dissolution will decease
4. a. What is ionization? b. Distinguish between ionization and dissociation.
The difference between ionization and dissociation : Ionization breaks ionic bonds, and dissociation breaks covalent bonds. Ionization breaks the ionic bond into its constituent ions while dissociation is breaking of bond into its simple constituent. Ionization is a irreversible process and dissociation is reversible process. The bond involves in the process of ionization is ionic bond and the bond involved in the process of dissociation is the covalent bond. The compound related to ionization is ionic compound and the compounds related with dissociation is covalent compound. Thus, The difference between ionization and dissociation : (A) Ionization breaks ionic bonds, and dissociation breaks covalent bonds.
a. What is meant by the solubility of asubstance? b. What condition(s) must be specified whenexpressing the solubility of a substance?
The solubility of a substance is the amount of that substance that is dissolved at solution equilibrium in a specific amount of solvent at a specified temperature. 2The temperature and pressure (for gases) must be specified
Write the equation for the dissolution of each of the following in water, and then indicate the total number of moles of solute ions formed. a. 0.50 mol strontium nitrate b. 0.50 mol sodium phosphate
We need to write a balanced equation for the dissolution of a) 0.50 molesof strontium nitrate Sr(NO3)2Sr(NO3)2 and b) 0.50 moles of sodium phosphate Na4PO4Na4PO4 and calculate the total number of moles of ions formed. a) Strontium nitrate is soluble in water and dissociates the following way: Sr(NO3)2(s)→Sr(aq)2+ +2NO3(aq) We can see that 1 mole of strontium nitrate produces 1 mole of strontium ions and 2 moles of nitrate ions, so the total number of moles of ions produced is 3 moles. We need to establish a ratio: nSr(NO3)2:nions=1:3 Now we can calculate the total moles of ions produced: Nions=3nSr(NO3)2= 3⋅0.5 mol=1.5 mol b) Sodium phosphate is soluble in water and dissociates the following way: Na3PO4(s)→3Na(aq)++PO4(aq)3− We can see that 1 mole of sodium phosphate produces 3 moles of sodium ions and 1 mole of phosphate ions, so the total number of moles of ions produced is 4 moles. We need to establish a ratio: nNa3PO4:nions=1:4 Now we can calculate the total moles of ions produced: nions=4nNa3PO4=4⋅0.5 mol=2 mol
Write the equation for the dissolution of each of the following ionic compounds in water. (Hint: See Sample Problem A.) a. KI c. MgCl2 b. NaNO3
We need to write a balanced equation for the dissolution of a) potassium iodide KIKI, b) Sodium nitrate NaNO3 c) magnesium chloride MgCl2 and d) sodium sulfate Na2SO4Na2SO4 A) a) Potassium iodide is soluble in water and dissolves the following way: KI(s)→K(aq)+ I(aq)− b) Sodium nitrate is soluble in water and dissolves the following way: NaNO3(s)→Na(aq)+ NO3(aq)− c) Magnesium chloride is soluble in water and dissolves the following way: MgCl2(s)→Mg(aq)2+ + 2Cl(aq)− D)Sodium sulfate is soluble in water and dissolves the following way: Na2SO4(s)→2Na(aq)+. + SO4(aq)2−
7. Distinguish between the use of the terms strong and weak and the use of the terms dilute and concentrated when describing electrolyte solutions.
When we are describing electrolyte solutions we can say that there are strong and weak electrolytes. These terms refer to the degree of ionization or dissociation of electrolytes. On the other hand, the terms dilute and concentrated refer to the amount of solute dissolved in the solution.
How does pressure affect the solubility of a gas in a liquid? b. What law is a statement of this relationship? C.If the pressure of a gas above a liquid is increased, what happens to the amount of the gas that will dissolve in the liquid, if all other conditions remain constant? d. Two bottles of soda are opened. One is a cold bottle, and the other is at room temperature. Which system will show more effervescence and why?
a. The solubility of a gas in a liquid is directly proportional to its pressure above the liquid .b. Henry's law c. If the pressure above the gas increases, the amount of gas that can dissolve will increase. d. There will be more bubbles released from the partially frozen one. The gas molecules have less kinetic energy in the colder bottle and gases dissolve better in liquids at lower temperatures. Therefore they take up less volume; it is more difficult for them to escape from the solvent.
Write a balanced equation for the dissolution of sodium carbonate, Na,CO, in water. Find the number of moles of each ion produced when 0.20 mol of sodium carbonate dissolves. Then, fir the total number of moles of ions.
in the presence of water H2O Na2CO3 (S) --> 2Na+ (aq)+ (CO3)2-( One mole of sodium carbonate produces two moles of Na+ ions Therefore 0.207 moles produces 0.414 moles of Na+ ions = 0.414 moles of Na+ ions Explanation: In water Na2CO3 --> 2Na+ (aq)+ (CO3)2-(aq) In a limited reaction, the carbonate ion reacts with the water molecules as follows (CO3)2-(aq) + H2O←→HCO3-(aq) + OH-(aq) sodium carbonate or soda ash dissolves in water to give 2 sodium cations and one carbonate anion
