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Chemistry > Bonding And Reactions > Flashcards

Bonding And Reactions Flashcards

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0
Q

What is relative formula mass? (Mr)

A

All relative atomic masses added together.

E.g find the relative formula mass for calciumto prison two years later for calcium carbonate, CaCO3 using given data.
Ca=40 C=12 O=16
40+12+(16x3)=100
Mr for CaCO3= 100

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1
Q

What is relative atomic mass? A r

A

Just the mass number of the element (the bigger number).

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2
Q

How do you calculate % mass of an element in a compound?

A

% mass of an element in a compound =

Ar x no. of atoms (of that element)
divided by X100
Mr (of whole compound)

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3
Q

How do you find the empirical formula?

A
  1. List all the elements in the compound
  2. Underneath them white their experimental masses or percentages
  3. Divide each percentage by the Ar for that particular element
  4. Turn the numbers you get into a simple ratio by multiplying and/or dividing them by well chosen numbers
  5. Get the ratio into the simplistic form, and that tells you the empirical formula of the compound.

E.g

  1. Fe O
  2. 44.8 19.2
  3. 44.8/56= 0.8 19.2/16=1.2
    1. 12 (x10)
      2. 3
  5. Simplistic formula is 2 atoms of Fe to 3 ato,s of 0
    so. .. Fe2O3
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4
Q

How do you calculate masses of reactants?

A
  1. Write out the balanced equation
  2. Work out Mr-just for the two bits you want.
  3. Apply the rule: divide to get one, then multiply to get all)
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5
Q

What is a mole?

A

One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass(Ar or Mr) for that substance.

E.g iron has an Ar of 56 so one mole of irons weighs exactly 56g
E.g nitrogen gas N2 has an Mr of 28 (2x14) so one mole of N2 weighs exactly 28g

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6
Q

How do you find the number of moles in a given mass?

A

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

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7
Q

How many moles are there in 42g of carbon?

A

No. of moles= mass g divided by Mr= 42 divided by 12=3.5 moles

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8
Q

What happens in ionic bonding?

A

Atoms gain or lose electrons to form charged particles called ions which are strongly attracted to one another (because of the attraction of opposite charges).

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9
Q

Giant ionic structures are in what arrangement?

A

A closely packed regular lattice arrangement.

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10
Q

Why do giant ionic structures have high melting points and boiling points.

A

Because there are very strong chemical bonds between all the ions in the structure.

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11
Q

Why do when giant ionic structures dissolve, they form solutions that conduct electricity?

A

Because when dissolved, the ions separate and are all free to move in the solution. These free moving charged particles allow the solution to carry electric current.

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12
Q

Why do giant ionic structures conduct electricity when molten?

A

When the substance melts, the ions are free to move and so they will carry an electric current.

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13
Q

What groups are most likely to form ions?

A

Groups 1,2,6 and 7.

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14
Q

What happens during covalent bonding?

A

The atoms share electrons with other atoms so that they both feel that they have a full outer shell.

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15
Q

What’s the main difference between giant covalent structures and giant ionic structures?

A

Giant covalent structures have no charged ions.

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16
Q

What are the main characteristics of giant covalent structures?

A

All atoms are bonded to each other by strong covalent bonds, they have very high melting and boiling points, they don’t conduct electricity-not even when molten (except for graphite), they are usually insoluble in water.

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17
Q

What are two important examples of giant covalent structures?

A

Diamond and graphite (which are both only made from carbon atoms).

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18
Q

Why does Diamond not conduct electricity?

A

Because it has no free atoms.

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19
Q

Why are diamonds ideal cutting tools?

A

Because each carbon atom forms four covalent bonds in a very rigid covalent structure, which makes diamond the hardest natural substance.

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20
Q

Why has diamond got a very high melting point?

A

Because it has very strong covalent bonds.

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21
Q

Why is graphite slippery?

A

Because each carbon atom only forms three covalent bonds, creating sheets of carbon atoms which are free to slide over each other.

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22
Q

How do graphite pencils work?

A

The layers of carbon atom sheets are held together so loosely that they can be rubbed off onto paper.

23
Q

Why does Graphite have a high melting point?

A

Because the covalent bonds need a lot of energy before they can break.

24
Q

Why is graphite used for electrodes?

A

Because only three out of carbons four outer electrons are used in bonds, so there are lots of spare electrons. This means graphite conducts electricity.

25
Q

What is the mass number of an atom?

A

The total number of protons and neutrons.

26
Q

What is the atomic number of an atom?

A

The number of protons.

27
Q

How do you find the number of neutrons in an atom?

A

Subtract the atomic number from the mass number.

28
Q

Explain what is meant by the term isotope.

A

Isotopes are: different atomic forms of the same element, which have the SAME number of PROTONS but DIFFERENT numbers of NEUTRONS.

29
Q

What decides the chemistry of an element?

A

The number of electrons.

30
Q

Why are the melting and boiling points very low for simple covalent structures?

A

Due to the weak intermolecular forces.

31
Q

Metal properties are all due to…..

A

The sea of free electrons.

32
Q

Where do the free electrons in metallic structures come from?

A

The outer shell of every metal atom in the structure.

33
Q

Why are metals good conductors of heat and electricity?

A

Because the free electrons are free to move.

34
Q

What holds the atoms together in a regular metallic structure?

A

The free electrons.

35
Q

What allows the atoms to slide over each other, causing metals to be malleable?

A

The free electrons.

36
Q

Four substances were tested for various properties with the results below. Identify the bonding in each substance.

Substance. Melting point. Boiling point. Good electrical conductor?
A. -218.4 -182.96 No
B. 1535 2750 Yes
C. 1410 2355 No
D. 801 1413 When molten

A

A. Simple Molecular
B. Metallic
C. Giant Covalent
D. Ionic

37
Q

How large are nanoparticles?

A

1-100 nanometers across.

38
Q

Nanoparticles contain fullerenes, but what is it?

A

Molecules of carbon, shaped like hollow balls or closed tubes. Each carbon atom forms 3 covalent bonds with its neighbours, leaving free electrons that can conduct electricity.

39
Q

Fullerenes can be joined together to form….

A

Nanotubes.

40
Q

Why are nanotubes strong?

A

Due to all the covalent bonds.

41
Q

What are nanotubes used for?

A

To reinforce graphite in tennis rackets and to make stronger, lighter building materials.

42
Q

Why are nanotubes used in tiny electric circuits for computer chips?

A

Because they conduct electricity.

43
Q

Why would nanoparticles help make great industrial catalysts?

A

Because they have a huge surface area.

44
Q

Smart materials behave differently depending on the….

A

Conditions, e.g temperature.

45
Q

Give an example of a smart material.

A

Nitinol - a shape memory alloy.

46
Q

What is atom economy?

A

The percentage of reactants changed to useful products.

47
Q

What is the equation for atom economy?

A

Total Mr of useful products

Divided by X 100

Total Mr of reactants

48
Q

Hydrogen gas is made on a large scale by reacting natural gas (methane) with steam.
Ch4(g) + H2O = CO(g) + 3H2(g)

Calculate the atom economy of this reaction.

A

1.) identify the useful product - hydrogen gas

2.) work out Mr of the reactants and of the useful product:
Ch4: 12+(4x1) = 16
H2O: (2x1)+16 = 18
3H2: 3x(2x1) = 6
So Mr of useful products = 6
Mr of reactants = 16+18=34

3.) Use the formula to calculate the atom economy:
6 divided by 34 x100 = 17.6%

49
Q

What is high atom economy better for?

A

Profits and the environment.

50
Q

Why is a high atom economy better for profits and the environment?

A
  1. ) pretty obviously, lots of waste is a major problem.
  2. ) reactions with a low atom economy use up resources very quickly.
  3. ) at the same time they produce loads of waste materials that have to be disposed of safely.
  4. ) that tends to make those reactions unsustainable.
  5. ) for the same reasons low atom economy isn’t profitable.
  6. ) raw materials are expensive to buy, and waste products can be expensive to remove and dispose of responsibly.
  7. ) the best way around this problem is to find a use for the waste products.
  8. ) use a reaction that has lots of useful by-products.
  9. ) the reactions with the highest atom economy have only one product.
  10. ) those reactions have an economy of 100%.
51
Q

What does percentage yield tell you about an experiment?

A

It’s overall success. It compares what you think you should have got with what you get in practice (actual yield).

52
Q

The lower the percentage yield, the better the reaction.

higher worse

A

The higher the percentage yield the better the reaction.

53
Q

What is the formula for percentage yield?

A 
Percentage yield = actual yield (grams)
                                divided by                           X100
                                predicted yield (grams)
54
Q

Name four reasons why yields can’t be 100%:

A
  1. ) the reaction is reversible: not all reactants change into product.
  2. ) filtration
  3. ) transferring liquids
  4. ) unexpected reactions
55
Q

How do you find out how many moles are in a given volume?

A

Number of moles=volume in litres x moles per litre of solution.

Chemistry (4 decks)

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