Name: ______

Period: ______

Review for Unit 10: Solutions - KEY

Define and expand upon the following terms:

  • Solution: a solution is a homogeneous mixture of two or more substances, a solvent and a solute.
  • Solute: part of a solution; the substance that is dissolved.
  • Solvent: part of a solution; the substance doing the dissolving. (Water is considered “the universal solvent”)
  • Factors that affect the rate of dissolution: Increased temperature, agitation (stirring), and/or surface area increase the rate of dissolution
  • Polar: a property resulting from a difference in electronegativity
  • “Like dissolves like”: refers to polarity. Polar solvents dissolve polar solutes. Nonpolar solvents dissolve nonpolar solutes.
  • Molarity (concentration): a numerical value of concentration
  • Dilution: adding more solvent to a solution in order to decrease concentration
  • Unsaturated solution: a solution in which there is less solute than the maximum
  • What will happen if I add more solute to this type of solution? The solute will continue to dissolve and it will stay in a solution state
  • Saturated solution: a solution in which there is the maximum amount of solute
  • What will happen if I add more solute to this type of solution? Extra solute will just collect at the bottom of the container
  • Supersaturated: a solution that contains more solute than what is allowed under assumed “normal” circumstances; achieved by heating and dissolving solute
  • What will happen if I add more solute to this type of solution? If I add a “seed” to this solution, it will crystallize
  • Electrolyte: a substance that dissociates into ions and, in solution, is able to conduct electricity
  • What are common electrolytes? Ionic compounds, acids, metallic salts
  • Nonelectrolyte: a substance that does not dissociate into ions in solution, unable to conduct electricity in solution
  • What are common nonelectrolytes? Covalent compounds

The following are practice problems and/or practical application questions you should be able to answer. BE AWARE OF CONVERSIONS!

  1. What is the general formula to find molarity? M = moles of solute/L of solvent
  1. What is the general formula for figuring out a dilution? M1V1 = M2V2
  1. What is the molarity of 0.5 moles of sodium chloride is dissolved to make 0.05 liters of solution?
    (Answer: 10 M)

Givens:

moles of solute = 0.5 moles
liters of solution = 0.05 L

M = ?

Formula: M = moles of solute/L of solvent

  1. An aqueous solution is made from 0.315 mol of Na2Cr2O7. If the volume of the solution is 25.0 mL, what is the molarity of the solution? (Answer: 12.6 M)
    Givens:
    moles of solute = 0.315 moles
    liters of solution = 25 mL = 0.025 L (MUST CONVERT)

M = ?

Formula: M = moles of solute/L of solvent

  1. How many grams of iron (III) chloride, FeCl3, should be added to a 100.0 mL volumetric flask in order to prepare 0.050 M FeCl3? (Answer: 0.81 grams)

Givens:

liters of solution: 100.0 mL = 0.100 L
M = 0.050 M
moles of solute = ? … and I will have to concert my moles to grams using molar mass and dimensional analysis to obtain the answer!

Formula: M = moles of solute/L of solvent

  1. The label is missing from the stock solution of sodium hypochlorite. Consulting partial lab notes, you find that you originally prepared a 0.49 M solution of sodium hypochlorite by adding 67.0 mL of the stock solution to water to make a total volume of 0.55 L. What must the concentration have been of the stock solution? READ THIS ONE CAREFULLY!(Answer: 0.557 M)

M1 = ? (you do not know original molarity/stock solution)

M2= 0.49 M

V2 = 0.55 L (notice the words “total volume”)

*I added 67.0 mL to my original volume to obtain the 0.55 L. Notice also that these are in two different units. So let us convert 67.0 mL to 0.067 L (moving decimal places or via dimensional analysis). So my original volume was 0.55 L – 0.067 L = .483 L. This I will assign to V1.

V1= 0.483 L

M1V1 = M2V2

  1. How many mL of stock NH3 is needed to make 100.0mL of 1.00M NH3? Your stock solution is 14.8M. (Answer: 6.76 mL)

V2 = 100 mL (no need to convert since my answer needs to be in mL anyway)
M2 = 1.00 M
M1 = 14.8M

V1 = ?

Formula: M1V1 = M2V2

  1. Solubility: the maximum amount of solute that may be dissolved in a solvent
  1. List some factors that affect solubility. Polarity (CHECK SOLUBILITY RULES IN STAAR CHART)
  1. Which salt is least soluble at 10 degrees Celsius? KClO3
  2. How many grams of KCl can be dissolved at 80 degrees Celsius? 50 grams
  1. Which compound shows the least amount of change in solubility as temperature increases? NaCl
  1. At 60 degrees Celsius, 72 grams of NH4Cl is dissolved in 100 grams of water. Is this solution saturated or unsaturated? I look at my chart at this particular temperature, and see that 55 g of NH4Clcan be dissolved in 100 grams of water (maximum). I have dissolved more than that maximum, so my solution is saturated.
  1. At 60 degrees Celsius, 72 grams of NH4Cl is dissolved in 100 grams of water. How much solute would collect at the bottom of the beaker? Once again, I see 55 g of this solute can be dissolved in 100 grams. 72 grams is greater than this maximum. Therefore, 17 grams will settle to the bottom of the beaker.