solutions homogeneous mixtures - solute & solvent
TRANSCRIPT
SolutionsHomogeneous Mixtures - Solute & Solvent
Objectives
Identify various types of solutions
Define solubility and the factors that affect it
Correctly use the terms unsaturated, saturated and supersaturated
Understand how to read a solubility graph
Express concentration in terms of molarity
Calculate the molarity of diluted solutions
Types of Solutions
Type Example Solvent Solute
Gas
Gas in Gas Air N2 O2
Liquid
Gas in
Liquid
Carbonated
H2OH2O CO2
Liquid in
LiquidVinegar H2O Acetic Acid
Solid in
LiquidOcean Water H2O NaCl
Solid
Liquid in
Solid
Dental
AmalgamAg Hg
Solid in
SolidSteel Fe C
Solvent and Solute
Solvent is the substance in the mixture in the greatest amount
Solute is the substance in the mixture in the lesser amount
Solvation
Process of surrounding solute particles with solvent particles
Solvation of ionic compound produces electrolyte (ions in solution - can conduct electricity)
Solvation of molecular compounds does not produce electrolyte
Which of the following would be a non-electrolyte?
HCl (hydrochloric acid)
NaOH (sodium hydroxide)
CaCl2 (calcium chloride)
C12H22O11 (sucrose)
Solubility
Situation: you add more and more sugar to your iced tea - sugar crystals start to collect at bottom of glass
Only a limited amount of solute can dissolve in a certain amount of solvent at a given set of conditions
Solubility
Solubility = maximum amount of solvent that will dissolve in a given amount of solvent at a specific temperature and pressure
Factors that affect Solubility
Temperature
Pressure
Agitation
Breakage into small particles
Solubility Graph - Solids
Most solids are more soluble as temperature of solution increases
Greater kinetic energy of solvent helps surround solute particles
Solubility Graph - Gases
Most gases are less soluble as temperature of solution increases
Greater kinetic energy helps gases escape intermolecular forces attracting them to solvent particles
Question
Given the following solubility curve for a particular solute in water, do you think the solute is a gas or a solid?
Saturated Solution
Saturated solution contains the maximum amount of dissolved solute for given solvent amount at particular temperature and pressure
Same rate of precipitation (solid coming out of solution) as dissolution (solid going into solution)
Unsaturated Solution
Less than the maximum amount of solvent in a solution at particular temperature and pressure
More solute can dissolve and stay in solution
Supersaturated Solution
More than the maximum amount of solvent in a solution at particular temperature and pressure
Can be made by dissolving solute in hot solvent and slowly cooling
Slight disturbance will cause crystallization
Watch video
Question
You have a glass of water with salt dissolved in it.
You add more salt, and it easily dissolves in the water.
Is the solution unsaturated, saturated or supersaturated?
Concentration
How much solute is dissolved in a solution
Qualitative expression: dilute, concentrated
Need quantitative way to express concentration
Expressing Concentration
Various quantitative concentration ratios: percent by mass, percent by volume, mole fraction, molality, molarity
We will focus on molarity - this is the most commonly used to express concentration of solute in liquid solution
Molarity
Ratio of moles of solute to liters of solution
Indicated by M
.85 mol solute in 1 liter of solution = 0.85 M
0.85 M read as “0.85 molar”
M = moles/liter
Question
What is molarity of aqueous solution containing 40.0 g of glucose (C6H12O6) in 1.5 liter of solution?
First - convert grams of glucose into moles
molar mass of glucose = 180 g/mol
Molarity Problem Continued
1mol/180 g (40 g) = 0.2 moles
0.2 mole/ 1.5 L = 0.133 M
Problems
What is molarity of bleach solution containing 9.5 g of NaOCl per liter of bleach?
Calculate the molarity of 1.60 L of a solution containing 1.55 g of dissolved KBr.
Preparing Molar Solutions
You want to make a 1 L of a 1.5 molar solution of sucrose (C12H22O11 - molar mass = 342 g/mol). How much sugar do you need?
First - figure out how many grams of sucrose you need -
1.5 moles (342 g/mol) = 513 g
Add 513 g of sucrose to volumetric flask. Add water until 1 liter mark reached.
Amount of water will be less than 1 L. Why?
Diluting Solutions
In labs, we use concentrated solutions of standard molarities called stock solutions
For example, concentrated HCl is 12 M
You want to have 1 liter of a 1.5 M solution of HCl - What do you do?
Preparing Dilutions
M1V1 = M2V2
You want 1 L of 1.5 M HCl
Figure out how much water you need to add:
Solve for V1 - this is how much concentrated solution you need
V1 = M2V2/M1
V1 = ((1.5 mol/L)(1 L))/(12 mol/L)
V1 = 0.125 L concentrated HCl - mix with DI water to dilute to 1 L
Questions - Write these down and work on them
What volume, in mL of 2.00 M CaCl2 stock solution would you use to make 0.50 L of 0.300M CaCl2 solution?
What volume of a 3.00 M KI stock solution would you use to make 0.300 L of a 1.25 M KI solution?
How many mL of a 5.0 stock solution would you need to prepare 100 mL of 0.25 M H2SO4?
If you dilute 20.0 mL of a 3.5M solution to make 100 mL of solution, what is the molarity of the dilute solution?