Facts on ECM and separation techniques

Question 1

What effect do impurities have on melting and boiling points? (heating/cooling curves)

Answer 1

• Has a range of state changes
• causes the substance to start melting from a lower temperature(the greater amount of impurity, the lower the melting point)
• also raises the boiling point for the greater amount of impurity

Question 2

How to calculate the Rf value?

Answer 2

Distance travelled by compound/ Distance travelled by the solvent
-note that Rf value should always be < 1

Question 3

What does it mean when solvent a travels more than solvent b? (chromatography)

Answer 3

It means that component A is more soluble than component b

Question 4

Why do we stop the distillation from fully evaporating? (distillation)

Answer 4

Should forever avoid evaporation to dryness as the glass flask used for evaporating would crack under the heat

Question 5

What to do with the crystals obtained? (crystallisation)

Answer 5

rinse the crystals under some cold water and never add water into the solution as it would cause dilution of liquid. After that, dry by squeezing between sheets of filter paper

Question 6

How are crystals made? (crystallisation)

Answer 6

• Crystals can only be formed with the water of crystallisation
• Without this said water, a powdery substance will form, signalling that crystallisation has failed

Question 7

What happens when the component cannot be seen? (chromatography)

Answer 7

Spray a locating agent on the component, such that the component will react to the locating agent causing us to see the liquid

Question 8

What are boiling chips for?(fractional distillation)

Answer 8

To ensure smooth boiling

Question 9

How do u know the liquid has finally distilled finish? (fractional distillation)

Answer 9

When an increase of temperature could be observed and the liquid stopped boiling

Question 10

What are elements?

Answer 10

Substances that only has the same type of particle(atom)

Question 11

What are compounds?

Answer 11

• Substances that same type of particle(molecule) which are made up of two OR more atoms
• that are chemically bonded
• these particles are also in a fixed ratio

Question 12

What are mixtures?

Answer 12

Substances that consisted of two or more different molecules or atoms that are not chemically bonded.

Question 13

What are pure/mixtures?

Answer 13

Pure is 1 type of substance while mixtures is 2 or more diff substance

Question 14

What is element/compound?

Answer 14

Element has 1 type of atom only while compounds has 2 or more diff types of atoms that are chemically bonded

Question 15

What is atoms/molecule?

Answer 15

Atoms are single entity while molecules are chemically(covalently) bonded

Question 16

What are the units for temperature?

Answer 16

Degrees Celcius

-remember to correct to 1d.p

Question 17

Keywords?

Answer 17

• Deposits(when smth is forming)
• Efficient(easy and fast)
• Condense(…)
• miscible/immisible(mixable/nonmixable)
• homogeneous solution(remains the same throughout)`

Question 18

Why shouldn’t you be immersing the thermometer in the liquid?

Answer 18

This is such that the thermometer would measure the temperature of the distillate and not the liquid

Question 19

What about evaporation and boiling?

Answer 19

Evaporation occurs at any temperature while boiling only occurs at the boiling point of the solution.