Chemistry

Question 1

what is an isotope?

Answer 1

different atomic forms of the same element, which have the same number of protons but a different number of neutrons

Question 2

What is ionic bonding?

Answer 2

when atoms lose or gain electrons to form charged particles (ions) which are then strongly attracted to one another

Question 3

what are the groups on the periodic table that are most likely to form ions?

Answer 3

1,2,6 and 7

Question 4

what are covalent bonds?

Answer 4

the sharing of electrons

Question 5

what are the two types of covalent substances?

Answer 5

simple molecular and giant covalent

Question 6

what are the properties of a simple molecular substance?

Answer 6

weak attraction, low melting point/boiling point, usually gas or liquids, don’t conduct electricity

Question 7

what are the properties of a giant covalent structure?

Answer 7

strong bonds, very high melting/boiling points, don’t conduct electricity (not even when molten)

Question 8

what are the properties of giant metallic structures?

Answer 8

delocalised electrons, good conductors of heat and electricity, strong forces of electrostatic attraction, can be bent and shaped.

Question 9

what are smart materials?

Answer 9

materials that behave differently depending on the conditions. Nitinol is a ‘shape memory alloy’, when cool it can be bent and when heated it goes back to a remembered shape.

Question 10

what are nano-particles?

Answer 10

tiny particles that are 1-100 nanometres across and contain roughly a few hundred atoms

Question 11

what are fullerenes?

Answer 11

nano-particles of carbon shaped like hollow balls or closed tubes. The carbon atoms are arranged in a hexagonal ring

Question 12

what’s a thermosoftening polymer?

Answer 12

polymers that dont have cross-linking between chains. Easy to overcome forces between the chains so it’s easy to melt the plastic. When it cools it hardens into a new shape and can be remoulded numerous times.

Question 13

what’s a thermosetting polymer?

Answer 13

have cross-links. Hold their chains together in a solid structure. The polymer doesn’t soften when heated. They’re strong, hard and rigid.

Question 14

how is low density polythene made and what is it?

Answer 14

made by heating ethene to about 200C under high pressure. Flexible and is used for bags and bottles

Question 15

how is high density polythene made and what is it?

Answer 15

made at lower temperature and high pressure (with catalyst). It’s more rigid and is used for water tanks and drainpipes.

Question 16

what is the relative formula mass?

Answer 16

Mr, all the relative atomic masses of a compound added together

Question 17

What’s a mole?

Answer 17

one mole of a substance is equal to its Mr(relative formula mass) in grams

Question 18

how do you work out the number of moles in a substance?

Answer 18

No. of moles = mass in g (of element of compound) / Mr(of element or compound)

Question 19

how do you calculate the percentage mass of an element or compound?

Answer 19

Percentage mass = Ar (relative atomic mass) x No. of atoms (of that element) / Mr (of whole compound) x 100

Question 20

How do you work out the empirical formula of a compound?

Answer 20

1) list all the elements in the compound
2) underneath, write their experimental masses or percentages
3) divide each mass or percentage by the Ar for that element
4) turn the numbers you get into a nice ratio
5) get the ratio into its simplest form

Question 21

what are the three important steps when calculating masses in reactions?

Answer 21

1) write out the balanced equation
2) work out the Mr - just for the two bits you want
3) Apply the rule: divide to get one, then multiply to get all

Question 22

How do you workout percentage yield?

Answer 22

percentage yield = actual yield (g) / predicted yield (g) x 100

Question 23

How do you separate artificial colours?

Answer 23

using chromatography