Chemistry-C2-2a

Question 1

What do the mass number and atomic number represent?

Answer 1

Mass number: Total number of protons and neutrons.

Atomic number: Number of protons.

Question 2

Draw a table showing the relative masses of the three types of particle in an atom.

Answer 2

Particle - Mass

Proton - 1
Neutron - 1
Electron - Very small

Question 3

What is a compound?

Answer 3

Compounds are formed when atoms of two or more elements are chemically combined together. For example, Carbon Dioxide is a compound formed from the chemical reaction between Carbon and Oxygen.

Question 4

Define the term isotope.

Answer 4

Isotopes are the different of the same element, which have the same number of protons but a different number of neutrons.

Question 5

Describe the process of ionic bonding.

Answer 5

In ionic bonding, atoms lose or gain electrons to form charged particles (called ions) which are then strongly attracted to one another (because of the attraction of opposite charges, + and -).

Question 6

Describe the structure of a crystal of sodium chloride.

Answer 6

A single crystal of sodium chloride (salt) is one giant ionic lattice, which is why salt crystals tend to be a cuboid in shape.

Question 7

List the main properties of ionic compounds.

Answer 7

• They all have high melting points and high boiling points due to the strong attraction between the ions.
• It takes a large amount of energy to overcome this attraction.
• When ionic compounds melt, the ions are free to move and they’ll carry electric current.
• They do dissolve easily in water in water though.
• The ions separate and are all free to move in the situation, so they’ll carry electric current.

Question 8

What type of ion do elements from the following groups form?

a) Group 1
b) Group 7

Answer 8

Group 1-Positive ions

Group 7-Negative ions

Question 9

What is covalent bonding?

Answer 9

Covalent bonding is where the atoms share electrons with each other so they’ve got full outer shells.

Question 10

What are the two types covalent substances? Give three examples of each.

Answer 10

Simple molecular substances:

• Chlorine
• Oxygen
• Water

Giant covalent structures (called Macromolecules):

• Diamond
• Silicon Dioxide (Silica)
• Graphite

Question 11

List three properties of metals and explain how metallic bonding causes these properties.

Answer 11

• Hard
• Good conductors of heat and electricity
• High density
• High tensile strength
• High melting and boiling points

Question 12

Explain why alloys are harder than pure metals.

Answer 12

Different elements have different sized atoms. So when another metal is mixed with a pure metal, the new metal atoms will distort the layers of metal atoms, making it more difficult for them to slide over each other. So alloys are harder.

Question 13

Give an example of a “smart” material and describe how it behaves.

Answer 13

Example: Nitinol (a ‘shape memory’ alloy)
Behavior: it is a metal alloy, but when it’s cool you can bend it and twist it like rubber. Bend it too far, and it stays bent. But if you heat it above a certain temperature, it goes back to the ‘remembered’ shape.
Uses: Glasses frames co they can be molded to fit the patient, and dental braces so they continually pull the teeth together with the warm temperature of the mouth.

Question 14

What are nanoparticles?

Answer 14

Nanoparticles are really tiny particles.

Question 15

Give two different applications of nanoparticles.

Answer 15

Used in:

• New cosmetics, eg. sun tan cream and deodorant.
• Tiny electric circuits for computer chips.

Question 16

Explain the difference between thermosoftening and thermosetting polymers.

Answer 16

Themrmosoftening polymers don’t have cross-linking between chains. The forces between the chains are really easy to overcome, so it’s easy to melt the plastic. When it cools, the polymer hardens into a new shape. You can melt these plastics and remould them as many times as you like.
Thermosetting polymers have crosslinks. These hold the chains together in a solid structure. The polymer doesn’t soften when heated. Thermosetting polymers are strong, hard and rigid… They are a tough material.

Question 17

Define relative atomic mass.

Answer 17

How heavy different atoms are compared with the mass of an atom of carbon-12. (Ar)

Question 18

Define relative formula mass.

Answer 18

All the relative atomic masses added together. (Mr)

Question 19

What is the link between moles and relative formula mass?

Answer 19

The relative formula mass (Ar or Mr) of a substance in grams is known as one mole of that substance.

Formula:
number of moles=mass in grams (of element or compound)/Mr (of element or compound)

Question 20

What is an empirical formula?

Answer 20

An empirical formula is the only method of finding out the formula of a compound.

Formula:
mass/Ar * number to make them the divisible by the same number / another number to make them the same

Method:

1) List all the elements in the compound (There’s usually only two or three)
2) Underneath them, write their experimental masses or percentages.
3) Divide each mass or percentage by the Ar for that particular element.
4) Turn the numbers you get into a nice simple ratio by multiplying and/or dividing them by well chosen numbers.
5) Get the ratio in its simplest form, and that tells you the empirical formula of the compound.

Example:
Find the empirical formula of the iron oxide produced when 44.8g of iron reacts with 19.2g of oxygen. (Ar for iron=56; Ar for oxygen=16).
1) Fe
   O
2) 44.8
    19.2
3) 44.8/56=0.8
    19.2/16=1.2
4) 0.8*10=8/4=2
    1.2*10=12/4=3
5) Simplest formula is 2 atoms of Fe and 3 atoms of O ... Fe2O3

Question 21

Describe two factors that can reduce the percentage yield of a reaction.

Answer 21

• Other unexpected reactions can happen which use up reactants.
• A filtered liquid will almost always lose some products of the experiment, causing them to be separated from the reaction mixture.

Question 22

Explain how paper chromatography can be used to analyse the dyes used in a brown sweet.

Answer 22

A food colouring may contain one or a mixture of dyes. This is how you can tell:

1) Extract the colour from a food sample (in this case a brown sweet) by placing it in a small cup with a few drops of solvent (can be water, ethanol, salt water).
2) Put spots on the coloured solution in a pencil baseline on filter paper. (Don’t use because it doesn’t work right).
3) Roll up the sheet and put it in a beaker with some solvent - but keep the baseline above the level of the solvent.
4) The solvent seeps up the paper, taking the dyes with it. Different dyes form spots in different places.
5) Watch out though - a chromatogram with four spots means at least four dyes, not exactly four dyes. There could be five dyes, with two of them making a spot in the same place. It can’t be three dyes though, because one dye can’t split into two dyes.

Question 23

Briefly describe how gas chromatography works.

Answer 23

Gas chromatography can separate out a mixture of compounds and help you identify the substance present.