solubility/diffusion/ separating mixtures Flashcards
Explain how you know that a solid is soluble in a solvent in terms of forces of attraction
- If new attractive forces formed between solute and solvent
- are strong enough to overcome the old ones between the solute
Explain the 6 major steps in an experiment of investigating solubility of a solute in solvent
- measure basin
- heat boiling tube and allow solute to dissolve until no more solute can dissolve
- pour solution into evaporating basin and weigh basin now
- heat solution to evaporate all water until heated to a constant mass
- measure the solute and the basin
- calculate mass of solute/mass of solvent x 100
If you have s solution of 148g dissolved in water at 80 degrees, and it cools down to room temperature 20 degrees which now has a mass of 86g, what will happen. (3)
- Solubility decreases
- 62 grams will come out as crystals.
- It precipitates.
What is the maximum mass of a substance that will dissolve in 50 grams of water if at 40 degreees it dissolves 40 grams
20grams
Because 40/20
Why is diffusion through a liquid slower than diffusion through a gas
Because particles move much slower
- and are more closely packed so there is less space for particles to move
In diffusion experiment of ammonia and hydrochloride acid, why is the white ring further away from the ammonia
Because ammonia particles are lighter and so travel faster
Why does adding more water to potassium manganate make it paler
Because the particles are now more widely spread out
Why does diffusion happen quickly in gases
Because the particles have are more widely spread so have more space AND are able to move quicker
If the solute is white then why is the solution colorless
Because the particles break apart
- and spread out through the water
Why is dilution slow in liquids
Because the particles are more closely packed AND because they move slower
Explain how diffusion happens in liquids with the example of potassium manganate and water
Potassium manganate and water particles are moving randomly so their particles are able to slide over each other
Particles can therefore easily mix
Concentration of particles are now evenly spread
In paper chromatography where is the original spot placed
Placed on the baseline
Is calcium carbonate (chalk) soluble in water
No
Is calcium carbonate (chalk) soluble in water
No
If you want to separate pure water from sea water what technique would you use
Simple distillation
If you want to separate pure water from sea water what technique would you use
Simple distillation
Is copper sulfate soluble or insoluble in water(it is a salt)
Soluble
Is copper sulfate soluble or insoluble in water(it is a salt)
Soluble
What is the meaning of aqueous
The solvent is water
What are two reasons we put a lid on chromatography
To avoid evaporation
To avoid toxic fumes from escaping
How do you know if a substance is aqueous or a liquid
Aqueous if a precipitate, water, or ions are involved
What is a precipitate
The insoluble solid that forms from a liquid solution
How can you obtain a pure dry sample of crystals from a solution (4)
1) heat to evaporate water
2) leave to crystallize
3) filter to remove access liquid
4) dry with kitchen paper
Why do crystals form when a hot saturated solution is cooled
Because of the temperature decrease, the solubility decreases
Describe what you should do as soon as you place the spots on the chromatogram
- Place paper in beaker, solvent level should be below
- seal the container
- wait until the solvent reaches the top of the paper
Why would you leave a solid in a warm place to dry
To increase the rate of evaporation
What do the glass rods in the fractionating column do?
Provides a large surface area which condenses the gases that rise
3 main Steps in fractional distillation if you have three liquids to separate
1) first liquid with lowest boiling point evaporates and condenses
2) other liquids may evaporate by chance but will condense back into flask
3) temperature will be altered for substance of the second lowest boiling point
If they ask you to draw the different dyes in a chromatography experiment , what must you include in your diagram
Labels
What separation method would you use to separate water FROM a solution of copper sulfate and water
Simple distillation
Because solvent form solute
Why would you mix sodium chloride and heat it when trying to dissolve
1) to dissolve sodium chloride
2) More quickly
Name one reason that crystallization is better than evaportaion
Upon heating, Bunsen burner could cause the solute to thermally decompose in evaportion,
But crystallization uses a water bath which is much more gentle
A student is making hydrated copper sulfate crystals
1)He first heats sulfuric acid
2)He then adds copper oxide to the sulfuric acid until the copper oxide is in excess
3)then he filters the mixture
Explain why he filters the mixture in step three
To remove the excess copper oxide
remeber that the copper oxide will stick to the filter paper and the copper sulphate solution will pass through
A liquid solution of copper sulfate is cooled to form hydrated copper sulfate crystals.
Explain why crystals form when the hot saturated solution is cooled (2)
1) solubility decreases in cooler temperatures
2) so an ionic lattice is formed
After a student has placed the dots of food coloring on the chromatography paper, explain three more things she needs to do in order to complete the experiment
1) move paper into the solvent so that solvent level is slightly below the spots
2) place a lid on it and wait for the solvent level to reach the top of the paper
3) leave to dry
Explain how the diffusion of potassium manganate (VII) occurs with water
Crystals diffuse from high concentration to low concentration
Because there are gaps between the particles, and because particles in a liquid are able to slide over each other
So they can thus easily mix with each other
Give formula for RF value
Distance travelled by solute/ distance travelled by solvent
State the names of three experiments that can be used to show diffusion
Potassium magnate (VII) in water
Ammonia gas and hydrogen chloride gas
Bromine gas and air
In the ammonia and hydrogen chloride gas experiment to demonstrate diffusion, state the solution that each cotton wool is soaked in
Ammonium
Hydrochloric acid
Explain the diffusion between bromine gas and air
Bromine gas is able to diffuse from high concentration to low concentration
Because of the random movement of particles of a gas, and because there are large gaps between them
Give the equation for finding solubility
Solubility = (mass of solute/mass of solvent) x100
As temperature increases,
Describe what happens to the solubility of a gas
And what happens to the solubility of a solid
Solubility of a gas decreases
Solubility of a solid increases
Explain the experiment to investigate the solubility at different temperatures
1)heat a boiling tube and add in excess solute to it until solution become saturated
2)allow it to cool to ensure that all the excess has sunk to the bottom
3)weigh an empty evaporating basin
4)add to it only the solution, making sure no solid is added to it
5)weigh the basin with the soltuion
6)heat until all the water has evaporated, and then weight just the absinthe and the dry crystals
7)reheat and resign, which is called heating to a constant mass to ensure that all the water has been evaporated
8)repeat for different temperatures
9)to find solubility, find the mass of solute dissolved and the solvent it took
During fractional distillation, what happens if some of the other liquids with high boiling points also start to evaporate whilst the ones with the lowest boiling point is already evaporating
Because the column is coolest near the top,
Once they reach the top, These liquids with high boiling points will reach a temperature lower than their boiling point, so will begin to condense back into a liquid and will drop back down into the flask
Why does the RF value have no units
Because it’s a ratio
A substance has RF value of 0.8
Another has a Rf value of 0.2
Explain their solubilities
0.8 has RF Closer to 1 so more soluble
0.2 has RF closer to 0 so less soluble
In paper chromatography, state three things u mist do to ensure reliable results
Make sure pencil line is above solvent so that the inks don’t automatically get washed away
Make sure u draw in pencil, because it’s insoluble so won’t dissolve in solvent
Place a lid on it to stop it from evaporating
In paper chromatography, from the results, how do u know if a substance is pure or impure
Pure substance will produce only one spot
Impure substances will produce more than one spot
Paper chromatography is used to separate….
Soluble mixtures
Miscible means
When two liquids can be mixed with each other
When temperature increases, why does solubility…, for a solid
Increase
This is because the solvent molecules have more kinetic energy
So can more efficiently break apart the solute molecules which are held together by intermolecular forces of attraction
What is rock salt made up of
Sand and salt
