chem 22 jan

Question 1

When would you use chromatography?

Answer 1

When separating two substances which are soluble in the same solvent

Question 1

What would you call a solution where you cannot dissolve any more solute?

What about one in which you can?

Answer 1

Saturated and Unsaturated

Question 2

What is the difference between a mixture and a compound?

Answer 2

• A mixture is made up of substances which are not joined by chemical bonds, whereas in a compound they are joined together.
• In a mixture, the components do not take on new properties, whereas they do take on new properties in a compound.

Question 3

Define filtration

Answer 3

A process used to separate a solid, insoluble solute from a solvent

Question 4

Give two ways in which you can increase the solubility of a substance?

Answer 4

increasing the temperature- (as this would provide energy to the solute particles, allowing them to move and create space. this would allow more solvent to disperse throughout the solution)

and stirring the solution

Question 5

Which type of separating technique would you use to separate sea water but keep the water?

Answer 5

distillation

Question 6

What is the advantage of distillation over evaporation for separating a mixture?

Answer 6

In distillation the solvent is kept, whereas in evaporation this will be lost as a gas

Question 7

Why are mixtures easy to separate?

Answer 7

Because the substances in the mixture are not chemically joined

Question 8

what happens when a substance dissolves?

Answer 8

The solvent particles surround the solute particles.

Question 9

what are mixtures

Answer 9

mixtures consist of substances that are not chemically joined together. These substances can be both compounds and elements.

Question 10

what are the two types of mixtures and what are their properties?

Answer 10

heterogeneous mixtures- separate substances are visible.

homogeneous mixtures- unable to distinguish between different substances.

Question 11

what is a pure substance

Answer 11

A pure substance contains only one substance- it is not mixed with anything else. All its particles are of the same type.

Question 12

How can you identify pure substances?

Answer 12

-If you heat up both pure and impure substances uThe melting/boiling points of pure substances are one exact temperature. However, in impure substances, the melting/boiling points are within a range of temps

This is bc there are substances which each have different melting/boiling points.

Question 13

solute

Answer 13

The substance that is dissolved in the solvent

Question 14

solvent

Answer 14

the substance (usually liquid) which the solute is dissolved in.

Question 15

solution

Answer 15

The resulting mixture of the solvent and solute.

Question 16

insoluble

Answer 16

if a solute cannot dissolve in the solvent, it is insoluble.

Question 17

soluble

Answer 17

if a solute can dissolve in the solvent, it is soluble

Question 18

saturated

Answer 18

when the solvent is so concentrated to the point where no more solute can be dissolved in it.

Question 19

concentrated

Answer 19

A concentrated solution is one that has a relatively large amount of dissolved solute in a given volume of solvent.

Question 20

why do solutions become saturated

Answer 20

due to how packed the particles have become, there is no space for more particles to be allowed in.

Question 21

how does temperature affect solubility?

Answer 21

When a solvent is at a high temperature, the particles in it obtain more energy allowing them to disperse and move further apart which increases solubility.

Question 22

immiscible

Answer 22

when two substances cant form a homogeneous mixture

Question 23

apparatus for filtration

Answer 23

conical flask, filter funnel, filter paper.

note that filtrate is the liquid left after solute is filtered out and residue is the solute that is left in the filter paper.

Question 24

what is evaporation used for

Answer 24

to separate soluble solid from a solution. You will be left with the soluble solid.

Question 25

apparatus for evaporation

Answer 25

evaporating basin, tripod, heat proof mat, bunsen burner

Question 26

what is distillation used for?

Answer 26

the method of distillation is used to separate solvent from solute, while maintaining both substances.

Question 27

what is the method of distillation

Answer 27

-assemble apparatus
-pour the mixture into the round bottom flask. Ensure it is not more than half full
-heat the mixture in the flask. As it comes to a boil, water vapour will escape and pass through the neck of the flask and into the condenser where it will condense.
- the water (liquid) will be collected in the flask.

Question 28

when is fractional distillation used?

Answer 28

It is used when the mixture that is to be separated consists of two liquids. The process depends on the two different boiling points of the liquids.

Question 29

distillation apparatus

Answer 29

-round bottom flask, bunsen burner, distillation column (fractional), condenser, receiver flask, clamp

Question 30

fractional distillation method

Answer 30

-Arrange the fractional distillation apparatus. This includes a distillation flask, a fractionating column on top of it, a condenser, a thermometer, and a collection flask.

-pour the mixture into a round bottom flask

-attach the fractionating column.

-Heat the flask with the temperature of the lowest boiling point among the liquids in the mixture.

-as the mixture comes to a boil, the liquid with that boiling point will evaporate and condense first.

-The thermometer will measure the heat so that we know which liquid has evaporated.

-Increase the temp according to the boiling point of the next liquid. The liquid left will then evaporate and condense. It will then collect in another reciever flask.

Question 31

what is retention factor?

Answer 31

retention factor (rf) is:
the distance travelled by dye or other solute/ distance travelled by solvent.

note that rf is always less than one bc it is always a smaller number divided by a larger number

this is used to obtain a certain number e.g 0.5 which tells us what the unknown substance is.

Question 32

explain why in chromatography some substances travel further up the paper than others

Answer 32

due to different solubility. A solvent that dissolves a particular substance well will carry that substance further.