Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
22 Cards in this Set
- Front
- Back
Purpose |
to find the molar mass of an unknown and become familiar with colligative properties |
|
Method |
Part a -measure cyclohexane, pour in test tube and place in an ice/salt/water bath, gently stir until crystals form -remove from bath and measure temp every 30 sec until we reach a temp between 12 to 15c. -plot data on graph and use inflection point to determine the freezing point Part b -weight the unknown and add to cyclohexane -place in ice/salt/water bath and gently stir with metal rod until slush appears -remove from bath and record temp every 30 seconds until a temp between 10 to 15c is reached -plot data on graph and determine the freezing point -use this information to determine the molar mas of the unknown substance |
|
what are solutions? |
homogeneous mixtures that contain two or more substances |
|
what are solvents? |
the major component solution |
|
what are solutes? |
the minor component in a solution |
|
what are colligative properties? |
they are independent of the nature of the solute, depend only on the concentration |
|
what are four colligative properties? |
1.vapor pressure lowering 2. boiling point elevation 3. freezing point depression 4. osmotic pressure |
|
what happens when vapor pressure = atmospheric pressure? |
the solvent boils at this temperature and the gaseous and liquid states are in dynamic equilibrium |
|
what have experiments found about the dissolution of non-volatile solutes in a solvent? |
it lowers the vapor pressure of solvent, raises the boiling point, and lowers the freezing point |
|
what does anti-freeze do concerning colligative properties? |
lowers the freezing point and raises the boiling point of coolant (water) |
|
what is salt used for concerning colligative properties? |
melts ice
|
|
what is the colligative property law? |
states that the freezing point and boiling point of a solution differ from those of the pure solvent by amounts that are directly proportional to them molal concentration of the solute |
|
what is the formula of the relationship for freezing point lowering and boiling point elevation? |
^T = Km ^T is the change in temperature K is the constant m is molality of solution |
|
what is supercooling? |
the lowering of temperature of a substance below the normal freezing point without making the substance into a solid, cooling slowly while rapidly stirring |
|
what is another name for temp/time graphs? |
cooling curves |
|
list the colligative properties and suggest a ratinoale for the choice of the word colligative to describe the properties. |
1. vapor pressure lowering 2. freezing point depression 3. boiling point elevation 4. osmotic pressure they are colligative because they are dependent on the concentration of the solute, not the identity |
|
distinguish between volatile and non-volatile |
volatile, high vapor pressure at room temperature (easily evaporates) non-volatile, low vapor pressure at room temperature (do not evaporate easily) |
|
what effect does the presence of a non-volatile solute have upon the vapor pressure? |
lowers vapor pressure |
|
what effect does the presence of a non-volatile solute have upon the freezing point? |
lowers the freezing point |
|
what effect does the presence of a non-volatile solute have upon the boiling point? |
raises the boiling point |
|
what do colligative properties depend on? |
number of particles present (concentration of solute) |
|
what do colligative properties not depend on? |
type of particles (solute) |