L1 Elements, Compounds & Mixtures

Question 1

What are the eight properties of matter?

Answer 1

Electrical conductivity, Heat conductivity, Density, Melting point, Boiling point, Refractive Index, Malleability & Ductility

Question 2

What are Intensive (Intrinsic) properties (of matter)?

- Give an example

Answer 2

Properties that depend on the identity of the substance and can, therefore, be used to identify the substance.
e.g. density, colour, boiling point

Question 3

What are Extensive (Extrinsic) properties (of matter)?

- Give an example

Answer 3

Properties that depend on the amount of matter present

e.g. mass, volume, weight

Question 4

What are physical properties?

Answer 4

Properties observed by examining a sample of a pure substance - arise from molecular structure and strength of intermolecular interaction.

Question 5

What are chemical properties?

Answer 5

Properties observed in the course of a chemical reaction - arise from the distribution of e- around the nucleus (especially valence e-).

Question 6

What is an element?

Answer 6

The simplest form of matter that has a unique set of properties.
- It cannot be split into 2 or more simpler substances by chemical means.

Question 7

What is a compound?

Answer 7

A substance that contains two or more elements chemically bonded in a fixed proportion.

Question 8

What are the two properties of atoms?

Answer 8

1. Mass - Relative Atomic Mass (Ar/RAM) = the mass of one atom of an element divided by the mass of 1/12 of an atom of Carbon-12
2. Valency (combining power) = the ability of one element to combine with other atoms to form chemical bonds

Question 9

What properties do Pure Substances have?

Answer 9

• Fixed composition
• Chemical & physical properties that don’t vary
• Cannot be broken down into simpler substances by physical methods
• Can only be changed in identity & properties by chemical methods

Question 10

What is a mixture?

- What properties do they have?

Answer 10

= a physical blend of two or more pure substances.
Properties:
- Variable composition
- The components retain their individual characteristic properties
- Separable into pure substances by physical methods
- Can be heterogenous OR homogenous

Question 11

What’s a homogenous mixture?

Answer 11

A mixture in a single-phase - same properties throughout the mixture with a uniform appearance.
e.g. a solution

Question 12

What is a heterogeneous mixture?

Answer 12

A mixture with multiple phases - variable properties with a non-uniform appearance (often opaque).
e.g. granite

Question 13

What is a colloid?

Answer 13

A visually homogenous mixture that is microscopically heterogeneous.
e.g. milk - emulsion - cloudy

Question 14

What is a solution?

Answer 14

A type of homogenous mixture formed when one substance (solute) dissolves into another (solvent).
= The BEST mixed of all mixtures.

Question 15

How does the separation of mixtures work?

- Give examples and how they work.

Answer 15

Mixtures are separated by using their differences in physical properties.

e. g.
- Filtration = selects components by particle size (solid/liquid)
- Crystallisation = select components by solubility (solid from solution)
- Extraction = selects components by solubility (solid or liquid from solution)
- Distillation = selects components by boiling point (liquid/liquid)
- Magnestisation = selects magnetic metal from other components
- Chromatgraphy = selects components by affinity to a stationary phase

Question 16

What are the different types of chromatography?

- How do they work, practical uses?

Answer 16

• Water/variable solvents (e.g. alcohol) = capillary action - separation depends on how strongly parts of the mixture interact with the stationary/mobile phase - Rf value
• HPLC (high-pressure liquid chromatography) = retention time = identifier
• Uses: drug testing, blood samples, retention time in body (how long it takes the body to metabolise chemicals)