Elements, Compounds/ Mixtures, Separation techniques

Question 1

Element

Answer 1

An element is a substance that cannot be broken down into simpler substances by chemical method

Question 2

Compound

Answer 2

A compound is a pure substance that contains two or more different elements chemically combined, in a fixed ratio

Question 3

Mixture

Answer 3

A mixture consists of two or more substances that are not chemically combined

Question 4

Colloid

Answer 4

A colloid is a substance microscopically dispersed evenly throughout another substance.

Question 5

Atom

Answer 5

An atom is the smallest unit of an element that has the properties of that element

Question 6

Molecule

Answer 6

A molecule is made of two or more atoms chemically combined together

Question 7

Soluble

Answer 7

A soluble substance is a substance that can dissolve in a solvent

Question 8

Filtrate

Answer 8

Substance that is able to pass through the filter paper

Question 9

Residue

Answer 9

Substance that is unable to pass thru the filter paper

Question 10

Solute

Answer 10

The substance that is being dissolved

Question 11

Solvent

Answer 11

The substance that dissolves others

Question 12

Miscible

Answer 12

Soluble in one another

Question 13

Immiscible

Answer 13

Insoluble in one another

Question 14

Properties of elements

Answer 14

• Composition: Made up of only one type of atoms or molecules
• Melting and boiling point: Fixed
• Properties: Has its own set of properties
  -cannot be separated

Question 15

Elements can be broadly classified as?

Answer 15

Metals, non metals and metalloids

Question 16

Elements=> Metals

Answer 16

• Appearance: Shiny
• Melting and boiling points: High (except for mercury)
• Physical state at r.t.p: Solids at room temperature
• Thermal conductivity: Good
• Malleability: Malleable (can be hammered into different shapes with our breaking)

Question 17

Elements=> Non-metals

Answer 17

• Appearance: Dull
• Melting and boiling points: Low
• Physical state at r.t.p: Mostly liquids or gases at room temperature
• Thermal conductivity: poor
  Malleability: Brittle (break or shatter when hammered)

Question 18

What is a pure substance?

Answer 18

A pure substance is a single substance that is not contaminated with other substances

Question 19

Properties of a pure substance

Answer 19

A pure substance has a fixed melting point and boiling point at room temperature and pressure that is not similar to any other substance

Question 20

How do we check if a substance is pure?

Answer 20

1. Check that it has a fixed melting point or boiling point
2. Use chromatography paper: There should only be one spot one the chromatogram

Question 21

Filtration

Answer 21

The bigger solid particles are unable to pass through the small pores of filter paper

Question 22

Similarities between evaporation to dryness and crystallisation

Answer 22

• both are to obtain the dissolved solid from the solution

Question 23

Difference between evaporation to dryness and crystallisation

Answer 23

• Evaporation to dryness: Dissolved solid is thermally stable and does not decompose on strong heating
• Crystallisation: Dissolved solid is not thermally stable and decomposes on strong heating
  
  • many crystals give off water to form powders when heated strongly. As such, evaporation to dryness cannot be used to obtain crystals

Question 24

Process of Evaporation to dryness

Answer 24

1. Heat the solution until all the liquid has been evaporated
2. The solid left behind is the dissolved solid

Question 25

Process of crystallisation

Answer 25

1. Heat the solution until saturated* * Dip a clean glass rod into the solution. If crystals form one the rod upon cooling, then the solution is saturated. 2. Cool the solution for crystallisation to occur 3. Filter the mixture and collect the crystals as residue 4. Wash crystals with cold distilled water and dry crystals with filter paper

Question 26

What is a saturated solution?

Answer 26

A solution is saturated when it contains the maximum amount of solute that can dissolve in a fixed amount of solvent at a specific temperature

Question 27

Aim of chromatography

Answer 27

- to identify the component present in a sample - to identify the number of components in a sample - to determine whether the sample is pure

Question 28

Process of chromatography

Answer 28

1. Draw a line using a pencil, about 2cm from the bottom of chromatography paper to indicate the starting position of the sample. This is called the START LINE 2. The chromatography is dipped into the solvent. The mixture dissolves in the solvent and moves up the paper and the mixture gets separated 3. The furthest point reached by the solvent is called the SOLVENT FRONT

Question 29

How does chromatography work?

Answer 29

Different substances have different solubilities in the chosen solvent The more soluble substances dissolve more readily in the solvent and travel further up the chromatography paper compared to less soluble substances

Question 30

How to calculate RF value?

Answer 30

Distance travelled by solute/ Distance travelled by solvent

Question 31

Simple distillation

Answer 31

- To obtain a pure solvent from a solution - This method requires a significant difference in the boiling points between the solute and solvent that make up the solution

Question 32

How does simple distillation work?

Answer 32

-The water gains heat and boils to form water vapour. - The water vapour rises and enters the condenser. - The water vapour will condense into water droplets. - The water droplets flow out into beaker and is collected (distillate)

Question 33

Fractional distillation

Answer 33

To separate miscible liquids with different boiling points. The difference in boiling points of the liquids being separate is less significant (compared to simple distillation)

Question 34

Miscible meaning

Answer 34

Miscible: Able to dissolve in one another and will not form separate layers.

Question 35

Metalloids

Answer 35

Appearance: Shiny Physical state at room temperature: solids Electrical + thermal conductivity: between metals and non metals Malleability: brittle

Question 36

Factors affecting rate of dissolving of a solute?

Answer 36

Temperature of a solvent Rate of stirring Size of solute particles

Question 37

Impurities cause the substance to? (Melting and boiling points)

Answer 37

Melting point: decreased Boiling point: increased