Chapter 2 - Separating Techniques

Question 1

How to separate solid from solid?

Answer 1

Magnetic attraction and sublimation

Question 1

What is a residue?

Answer 1

Solid that remains on filter during filtration

Question 2

How to separate an insoluble solid from liquid? What materials are needed?

Answer 2

Filtration using conical flask and filter paper

Question 3

What is a filtrate?

Answer 3

Liquid or solution that passes through filter paper

Question 4

What is “evaporation to dryness”?

Answer 4

Allowing liquid to evaporate completely with solid left in evaporating dish

Question 5

How do we separate a soluble solid from a solid-liquid mixture? (3)

Answer 5

Evaporation,evaporation to dryness and crystallisation.

Question 7

When do we use crystallisation?

Answer 7

Only used for substance which will decompose on heating.

Question 7

What is a saturated solution?

Answer 7

A saturated solution contains the maximum amount of dissolved solute(solid) at a given temperature.

Question 8

How do we form crystals by crystallisation?

Answer 8

Water is removed by heating the solution but not to dryness. Heating is stopped when a hot saturated solution is formed. Allow it to cool in room temperature and the solid will form pure crystals.

Question 9

How to test for a saturated solution?

Answer 9

A clean glass rod is dipped into the solution and removed. If the small amount of solution on the rod form crystals, the solution is saturated and is at its saturation or crystallisation point.

Question 10

How do we separate immiscible(do not dissolve in each other) liquids?

Answer 10

We use a separating funnel with a burette-like thing at the bottom. We allow the liquid at the bottom to drip into a beaker before changing to a new beaker and allowing the next liquid to drip.

Question 11

How does sublimation work?

Answer 11

It is the process where it converts solid into gas directly, skipping the liquid stage. It is done by heating the mixture and allowing the sublimes to solidify on the inverted cold filter funnel

Question 12

How do we separate a pure liquid from a solution?

Answer 12

Simple and fractional distillation

Question 13

What is simple distillation? And what are its steps?

Answer 13

Solution boils in the distillation flask with boiling chips to ensure smooth boiling. The water vapor rises and enters the liebig condenser, which is where is it is cooled and condensed into water. Pure water is then collected in the receiver.

Question 14

What are the 5 things to note when setting up a distillation apparatus?

Answer 14

1. Boiling chips (smooth boiling)
2. Bulb of thermometer to be beside side arm, not dipped in the solution to ensure that it measures the boiling point
3. The condenser should slope downwards
4. Cold water is allowed to enter the water jacket from the BOTTOM and leave from the TOP. It has to be completely filled.
5. If distillate is volatile(vaporises easily), receiver can be surrounded ny ice so it remains in liquid state.

Question 15

What is fractional distillation?

Answer 15

It is a separating method of two liquids that are miscible(mix very well)

Question 16

What is the difference between simple and fractional distillation?

Answer 16

Simple distillation is for immiscible mixtures and fractional distillation is for miscible mixtures (only liquids)

Question 17

How does fractional distillation work?

Answer 17

The mixture first boils in the round bottom flask. The liquid of lower boiling point will evaporate first and condense first. The liquid of higher boiling point will evaporate later.

Question 18

How doe the temperature change as a solution of e.g. Ethanol and water undergoes fractional distillation?

Answer 18

The temperature increases as it is heated. At 78C, ethanol distils over. The temperature remains constant until ethanol has distilled out of the flask. The temperature then increases to 100C and water distills over. The temperature remains unchanged as water is being distilled.

Question 19

What is chromatography?

Answer 19

It is the method of separating two or more components(spots) that dissolve in the same solvent

Question 20

How does chromatography work?

Answer 20

The start line will be drawn by a pencil (will not dissolve) on a chromatography paper, above the solvent. A spot of food colouring is applied on the start line. It will rise as the solvent rises and stop when it reaches its maximum. The longer it goes, the more soluble it is.

Question 21

What is the Rf value?(retention factor)

Answer 21

It is the ratio/fraction between the distance travelled by the substance and the distance travelled by the solvent. (2dp)
It does not change as long as it is carried out under the same temperature and solvent.

Question 22

How do we interpret the results of a chromatogram?

Answer 22

If there is only 1 dye, the food coloring is pure. If there are 2 or more, it is not pure.

Question 23

What if the solvent rose and surpassed the solvent front?

Answer 23

The Rf value will remain the same but the spot will be slightly raised as well. The positions depend on how long the experiment ran.

Question 24

How do we identify colorless substances?

Answer 24

We apply a locating agent on a chromatogram like Ninhydrin or Iodine.

Question 25

What are the uses of chromatography?

Answer 25

It can identify proteins and their amino acids, detect drug abuse, check for harmful substances and find out dyes in certain things.

Question 26

How would the boiling and melting point change when impurities are added into water?

Answer 26

The boiling point would increase slightly while the melting point would decrease slightly.

Question 27

List 3 examples of solids that sublimes.

Answer 27

Iodine, ammonium chloride and dry ice(CO2)