Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

chemistry > key concepts in chemistry > Flashcards

key concepts in chemistry Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Chemistry flashcards Periodic Table flashcards Chemistry 101 flashcards Organic Chemistry 101 flashcards
1
Q

What are atoms?

A

Tiny particles of matter that make up everything in the universe

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Who was the first to discover an atom?

A

John Dalton

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What did John Dalton say about the atom?

A

Described atoms as solid spheres and that different spheres made different elements

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What did JJ Thomson say about the atom?

A

1987 - plum pudding model
(Ball with positive charged and negative electrons inside it)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What did Ernest Rutherford say about the atom?

A

There’s a tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What was Ernest’s Rutherford’s gold foil experiment about?

A
  • fired positively charged alpha particles at thin sheet of gold foil
  • most particles went through but some deflected more than expected
  • small amount bounced straight back
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What did Neils Bohr say about the atom?

A
  • Electrons can only exist in fixed shells (each shell has a fixed energy)
  • Bohr’s theory was accepted by many scientists
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the relative mass and charge of a proton?

A

Mass - 1
Charge - +1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is the mass and relative charge of a neutron?

A

Mass - 1
Charge - 0

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the relative mass and charge of a electron?

A

Mass - 0.0005
Charge - -1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Why do atoms equal the same amount of protons and electrons?

A

It cancels out the charge (atoms and nucleus are neutral)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why is the nucleus of an atom very small compared to the overall size of an atom?

A

Protons and neutrons take up a tiny amount of space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Where is most of the mass concentrated in an atom?

A

The nucleus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Where is the mass and atomic number on an element?

A

Mass - top
Atomic - bottom

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The mass number tells you what?

A

Total number of protons and electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is an isotope?

A

Different forms of the same element that have the same number of protons but different amount of neutrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

How do you calculate the number of neutrons from an element?

A

Mass number - atomic number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Isotopes have what same number?

A

Atomic number but different mass numbers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How to work out relative atomic mass?

A

(sum of isotope abundance x isotope mass number) + (sum of isotope abundance x isotope mass number) divided by abundance of all isotopes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

How did Mendeleev sort the periodic table?

A

Sort the elements based on atomic mass

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Why did Mendeleev leave gaps in the periodic table?

A

For new undiscovered elements, like germanium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

When Mendeleev put the elements in relative atomic mass, why was this not always true?

A

Because of the presence of isotopes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Based on protons, what could be found

A

The atomic number

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

The rows in period tables are called what?

A

Periods

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What do the periods show in the periodic table?

A

How many shells are present

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What do the groups show from the periodic table?

A

How much electrons are left on the last shell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

The left side of the periodic table is what?

A

Metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

The right side of the periodic table is what?

A

Non metals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the electron shell rule in terms of numbers

A

2,8,8

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Give the electronic configuration of aluminium (atomic number = 13)

A

2,8,3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

In what group and period would you expect to find the element with the electronic configuration 2,8,8,2?

A

Group 2 period 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What are ions?

A

Charged particles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

When atoms gain or lose electrons, what do they form?

A

Ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

When atoms form ions, what are they trying to do?

A

Get a full outer shell

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What are anions? (Negative ions)

A

Form when atoms gain electrons - more electrons than protons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

What are cations? (Positive ions)

A

Form when atoms lose electrons - more protons than electrons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

If two electrons are lost what is the charge?

A

+2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

If 3 electrons are gained, what is the charge?

A

-3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Fe(2+) has a 2+ charge and an atomic number of 26, how much electrons does it have?

A

24 (26-2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

What ions do group 1 form?

A

1+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

What ions do group 2 form?

A

2+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What ions do group 6 make?

A

2-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What ions does group 7 make?

A

1-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

What are ionic compounds made of?

A

Positive charge and negative charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

The suffix ‘ide’ is used when?

A

Compounds containing two different elements (NaCl)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

The suffix ‘ate’ is used when?

A

Where oxygen is present (NO) - nitrate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

When a metal and non metal, react what is this called?

A

Ionic bonding

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

In terms of electron transfer, how does sodium and chlorine react to form sodium chloride?

A

Sodium has one electron on its outer shell so, it will lose the electron leaving sodium with a 1+ charge. Since chlorine has 7 electrons on its outer shell and having gained the electron from sodium, it will have a 1- charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

What is the chemical formula of water?

A

H20

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

What is the chemical formula of ammonia?

A

NH3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

What is the chemical formula of carbon dioxide?

A

CO2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What is the chemical formula of hydrogen?

A

H2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

What is the chemical formula of chlorine?

A

Cl2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

What is the chemical formula of oxygen?

A

O2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

What is ion chemical formula of ammonium?

A

NH4+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

What is ion chemical formula of hydroxide?

A

OH(-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

What is ion chemical formula of nitrate?

A

NO3(-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

What is ion chemical formula of carbonate?

A

CO3(2-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

What is ion chemical formula of sulfate?

A

SO4(2-)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

How do you work out ionic equations?

A
  • balance the equation
  • write out all the aqueous ions separately
  • cross out the same on the both sides
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

Write the ionic equation for HNO3(aq) + NaOH(aq) - NaNO3 (aq) + H2O(l)

A

H+(aq) + OH-(aq) - H2O(l)

62
Q

What symbol is for oxidising?

A

Ball with fire

63
Q

What is the oxidising harzard?

A

Provides oxygen which allows other materials to burn more easily (liquid oxygen)

64
Q

What is the hazard symbol for harmful?

A

Exclamation mark

65
Q

What is the harmful hazard?

A

Can cause reddening, irritation or blistering of the skin (bleach)

66
Q

What is the hazard symbol for environmental hazard?

A

Dead tree and fish

67
Q

What is the evironmental hazard?

A

Harmful to organisms and to the environment (mercury)

68
Q

What is the hazard symbol for highly flammable?

A

Fire

69
Q

What is highly flammable hazard?

A

Catches fire easily (petrol)

70
Q

What is the hazard symbol for toxic?

A

Skull

71
Q

What is the toxic hazard?

A

Can cause death by swallowing, breathing in or absorption through skin (hydrogen cyanide)

72
Q

What is the hazard symbol for corrosive?

A

Hand and test tubes

73
Q

What is the corrosive hazard?

A

Destroys materials including living tissues like eyes and skin (concentrated sulfuric acid)

74
Q

How do you work out the chemical formula of an ionic compound?

A
  • write out the formulas of the ions
  • the overall charge must be zero (balance it)
75
Q

What is the chemical formula of calcium nitrate?

A
  • Ca(2+), NO3(-)
  • To balance the 2+ charge, you need two NO3(-) ions:
    • (+2) + (2 x -1) = 0
  • the formula is Ca(NO3)2
76
Q

How big are ionic compounds in ionic lattices

A

Giant

77
Q

Do ionic lattices have strong or weak electrostatic forces of attraction?

A

Strong

78
Q

Regular lattices have _______ charged ions in all directions

A

Oppositely

79
Q

A single crystal of sodium chloride is one of the giant ionic lattice, explain this?

A

The Na+ and Cl- ions are held together in a regular lattice, throughout the lattice, the Na+ and Cl- ions alternate

80
Q

What are properties of ionic compounds

A
  • high melting and boiling points due to strong attraction (large amounts of t of energy to overcome this attraction)
  • don’t conduct electricity due to ions being in fixed positions (but when ionic compounds melt, ions are free to move and carry electric charge)
  • dissolve easily in water due to ions separate and free to move in the solution so they’ll carry an electric charge
81
Q

What are models that represent ionic lattices?

A

Ball and stick - help to visualise structures (3D), more realistic, don’t correct show correct scales of atoms or ions
3D models - show the arrangement of ions but only the outer layer
2D representations - good for showing how the atoms are connected, bad for showing the shape of the substance and size of the atom
Dot and cross diagrams - good for showing how compounds or molecules are formed and where electrons in the bonds or ions came from

82
Q

Explain why calcium chloride, an ionic compound, has a high melting point?

A

Strong attraction between the ions

83
Q

What is a covalent bond?

A

Strong bond that forms when a pair of electrons is shared between two atoms

84
Q

Simple molecular substances are made up of molecules containing a few atoms joined by what?

A

Covalent bonds

85
Q

Hydrogen (H2) in terms of covalent bonding?

A

Hydrogen atoms have one more electron so they need one more to complete the first shell, they can form a single covalent bond with another hydrogen atom to achieve this.

86
Q

Hydrogen chloride (HCl) in terms of covalent bonding?

A

Both atoms only need one more electron to complete their outer shells

87
Q

Water (H2O) in terms of covalent bonding?

A

In water molecules, an oxygen atom shares a pair of electrons with two H atoms to form two single covalent bonds

88
Q

Oxygen (O2) in terms of covalent bonding?

A

An oxygen atom needs two more electrons to complete its outer shell, in oxygen gas each oxygen atom forms a double covalent bond with another oxygen atom

89
Q

Methane (CH4) in terms of covalent bonding?

A

Carbon has four outer electrons which is half a full shell, it can form four covalent bonds with hydrogen atoms to fill up its outer shell

90
Q

Carbon dioxide (CO2) in terms of covalent bonding?

A

In carbon dioxide molecules, a carbon atom shares two pairs of electrons with two oxygen atoms to form two double covalent bonds

91
Q

What is the size of simple molecules?

A

(10)-10m

92
Q

What are properties of simple molecular substances?

A
  • the atoms within the molecule are held together by very strong covalent bonds but the forces of attraction are very weak
  • melting and boiling points are very low as very easy to break the forces of attraction, not the covalent bond
  • most are gases or liquids at room temperature
  • as molecules get bigger, strength of intermolecular forces increases and increases melting and boiling points
  • don’t conduct electricity as no free ions or electrons
  • some are soluble and some aren’t
93
Q

What are polymers made of?

A

Covalently bonded carbon chains

94
Q

When are polymers made?

A

Lots of small molecules called monomers join together

95
Q

Why is oxygen a gas at room temperature?

A

The intermolecular forces between molecules of oxygen are weak and don’t need much energy to break. This gives oxygen a low boiling point so it’s a gas at room temperature

96
Q

Why doesn’t nitrogen conduct electricity?

A

Nitrogen molecules aren’t charged and don’t contain any free electrons or ions

97
Q

What are properties of giant covalent structures?

A
  • bonded to eachother by strong covalent bonds
  • high melting and boiling points (lots of energy needed to break the bonds)
  • aren’t soluable in water
  • usually don’t contain charged particles, so don’t conduct electricity
98
Q

What are the main giant covalent structures and fullerenes?

A

Diamond
Graphite
Graphene

99
Q

Describe diamond as a covalent structure

A
  • made up of a network of carbon atoms that each form four covalent bonds
  • high melting point (lots if energy to break)
  • hold the atoms in a rigid lattice structure makes diamond really hard (used to strengthen cutting tools)
  • doesn’t conduct electricity as no free ions or electrons
100
Q

Describe graphite as a giant covalent structure

A
  • each carbon atom only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons
  • no covalent bonds between the layers/held together weakly (soft and slippery, used as a lubricating material)
  • high melting point (covalent bonds in the layers need loads of energy to break)
  • conducts electricity as one of the electrons on the outer shell is free to move
101
Q

Describe graphene as a fullerene

A
  • one layer of graphite
  • sheet of carbon atoms joined together in hexagons
  • sheet is just one atom thick, making it a two dimensional substance
102
Q

The molecular formula c60 (buckminsterfullerene) forms what?

A

A hollow sphere made up of 20 hexagons and 12 pentagons - stable molecule that forms soft brownish-black crystals

103
Q

What do the fullerenes form?

A

Spheres and tubes

104
Q

What are fullerenes shaped like

A

Closed tubes or hollow balls

105
Q

What are fullerenes made up of?

A

Carbon atoms arranged in hexagons, pentagons or heptagons

106
Q

What can fullerenes be used for?

A

Used to cage other molecules (forms around another molecule and gets trapped inside) - used to deliver a drug to cells in the body

107
Q

Fullerenes have a _____ surface area, it helps them to make what?

A

Large surface area
Helps to make industrial catalysts

108
Q

Nanotubes are what?

A

Fullerenes

109
Q

What are nanotubes like and what are they used for?

A

Tiny cylinders of graphene as they conduct electricity
Can be used for strengthening materials without adding the weight (sports equipment)

110
Q

In chemical reactions, what is always conserved?

A

Mass

111
Q

During a chemical reaction, no atoms are destroyed or made, what does this mean?

A

There are the same number and types of atoms on each side of a reaction equation. The total mass before and after doesn’t change (precipitation reaction)

112
Q

If the mass changes, what is involved?

A

A gas

113
Q

If mass increases in a reaction, it’s because at least one of the reactants is a gas that’s found in the air, why does this happen?

A
  • before the reaction, gas floats in the air
  • when gas reacts to form part of the product, it becomes contained inside the reaction vessel
  • so the total mass of the stuff inside the reaction vessel increases
114
Q

If mass decreases in a reaction, it’s because some or all reactants are either solid,liquid or aqueous and one product is a gas ,why does this happen?

A
  • before the reaction, any solid, liquid or aqueous reactants are contained in the reaction vessel
  • if the vessel isn’t enclosed, the gas can escape as its formed
  • total mass of the stuff inside the reaction vessel increases
115
Q

What does metallic bonding involve?

A

Delocalised electrons

116
Q

How does delocalised electrons link to metallic bonding?

A

Electrons in the outer shell of the metal atoms are delocalised. There are strong forces of electrostatic attraction between the positive metal ions and the shed negative electrons. These forces of attraction atoms together in a regular structure (very strong)

117
Q

What are substances held together by metallic bonding?

A

metallic elements and alloys

118
Q

Physical properties of metals

A

Electrostatic forces are strong
High melting and boing point
Shiny solids at room temperature
Aren’t soluble in water
More dense than nonmetals as the ions in the metallic structure are packed close together
Layers of atoms in a pure metal can slide over each other malleable
Good conductors of electricity heat as delocalised electrons carry electrical charge and heat energy

119
Q

Physical properties of non metals

A

Dull looking, more brittle, have lower boiling point, don’t generally conduct electricity and often have low density

120
Q

What’s the difference between nonmetals and metals in terms of electrons?

A

Nonmetals tend to gain electrons to form full outer shells
Metals lose electrons to gain full outer shells

121
Q

Copper is a metallic element. State what property of copper makes it suitable for using an electrical circuit and explain why it has this property.

A

Is a good electrical conductor as it contains delocalised electrons which are able to carry an electric charge

122
Q

How to find the relative formula mass?

A

Add the relative atomic mass together

123
Q

Find the relative formula mass of magnesium chloride (MgCl2)

A

RAM = mg - 24
= cl - 35.5 x 2
24+71=95
Relative formula mass = 95

124
Q

Find the empirical formula of glucose, C6 H12 O6

A
  • divide them by largest number that goes in 6,12,6 - 6
    6/6 = 1 12/6 = 2
    Empirical formula of glucose = CH2O
125
Q

Compound X has the empirical formula C2H6N. The relative formula mass of compound X is 88. Find the molecular formula of compound X.

A
  • find the relative formula mass of the empirical formula
    C = 2 x 12, H = 6 x 1, N = 14
    = 44
  • divide the relative formula mass of the compound by the empirical formula
    = 88/44 = 2
  • times them by the compound
    C = 2 x 2 = 4, H = 6 x 2 = 12, N = 1 x 2 = 2
    Molecular formula of compound X = C4H12N2
126
Q

How to calculate the percentage mass of an element in a compound?

A

Atomic mass x number of atoms in the element divided by relative formula mass of the compound
X100

127
Q

Find the percentage mass of sodium in sodium carbonate, Na2CO3

A

Na = 23, C = 12, O = 16
Relative formula mass of compound = (2x23) + 12 + (3x16) = 106
(23x2)/106
Ans x 100 = 43%

128
Q

Calculate the relative formula mass of ethanol, C2H5OH

A

46

129
Q

What is the empirical formula of a compound with the molecular formula C4H8Cl2

A

C2H4Cl

130
Q

What is Avogadro’s constant and what is used for?

A

6.02 x10)23
Moles

131
Q

How many atoms are there in 5 moles of oxygen gas?

A

6.02 x 10)23 x 5 =3.01 x 10)24
3.01 x 10)24 x 2 = 6.02 x 10)24 ( x2 as there is 2 atoms in each molecule of oxygen gas

132
Q

How to work out the number of moles?

A

Mass in g (of element or compound) divided by relative formulae mass of compound or RAM of element

133
Q

How many magnesium atoms are in 60g of magnesium? (RAM (Mg) = 24)

A
  • convert mass into moles
    60/24 = 2.5 moles
  • multiply number of moles by avogardo’s constant
    6.02 x10)23 x 2.5
    = 1.505 x 10)24
134
Q

How many molecules of ammonia are present in 3.5 moles of ammonia gas?

A

3.5 x 6.02 x 10)23
= 2.107 x 10)24

135
Q

How many atoms are present in 81.4g of calcium hydroxide, Ca(OH)2? RFM = 74

A

81.4/74 = 1.1
1.1 x 6.02 x 10)23
= 6.622 x 10)23 x 5
= 3.311 x 10)24

136
Q

How to work out mass from moles and RFM?

A

moles x RFM

137
Q

How can concentration be calculated ? g dm)-3

A

mass of solute/volume of solution

138
Q

how to calculate volume in terms of concentration?

A

mass/concentration

139
Q

How to calculate mass in terms of concentration

A

Concentration x volume

140
Q

What is 1000cm3 in dm3

A

1dm3

141
Q

What is 1000cm3 in dm3

A

1dm3

142
Q

Calculate the concentration in g dm-3 of a solution that contains 0.60g of salt in 15cm3 of solvent

A

15/1000 = 0.015
0.60/0.015
=40 g dm-3

143
Q

How would you calculate the empirical formula of a metal oxide through an experiment?

A
  1. Get a crucible and heat it until it’s red hot (this will make sure it’s clean and has no trace of oil or water from previous experiments)
  2. Leave the crucible to cool, then weigh it, along with its lid
  3. Add some clean magnesium ribbon to the crucible. Reweigh the crucible, lid and magnesium ribbon. The mass of the magnesium you’re using is this reading minus the initial reading for the mass of the crucible and lid.
  4. Heat the crucible containing the magnesium. Put the lid on the crucible so as to stop any bits of solid from escaping, but leave a small gap to allow oxygen to enter the crucible.
  5. The crucible strongly for about 10 minutes, or until the magnesium ribbon has turned white.
  6. Allow the crucible to cool and the crucible with the lid and its contents. The mass of the magnesium oxide you have is this reading minus the initial reading for the mass of the crucible and lid.
144
Q

Student heats 1.08 g of magnesium ribbon in a crucible so it completely reacts to form magnesium oxide. The total mass of magnesium oxide formed was 1.80 g. Calculate the empirical formula of magnesium oxide.

A

Mass of O = 1.80 - 1.08 = 0.72g
Moles (Mg) 1.08/24 = 0.045 moles Moles (O) 0.72/16 = 0.045 moles
Lowest number ratio
1:1
Empirical formula = MgO

145
Q

A 45.6 g sample of an oxide of nitrogen contains 13.9g of nitrogen. What is the empirical formula of the nitrogen oxide?

A

45.6 - 13.9 = 31.7
Moles (O) = 31.7/16 =1.98125 Moles (N) 13.9/14 = 0.99…
1.98125/0.99.. = 2
0.99/0.99 = 1
Empirical formula = NO2

146
Q

What is a limiting reactant ?

A

Reactant that’s used up in the reaction

147
Q

How to work out the amount of product from the limiting reactant?

A
  1. Write our balanced equation
  2. Work out the RFM of the reactant and product
  3. Find out how many moles there are of the substance you know the mass of
  4. Used the balanced equation to work out how many moles there’ll be of the other substance
  5. Use the number of moles to calculate the mass
148
Q

Limiting reactants - calculate the mass of aluminium oxide, Al2O3, formed when 135g of aluminium is burned in air.

A

4Al + 3O2 - 2Al2O3
Al = 27 Al2O3 (2x27) + (3x16) = 102
135/27 = 5
2.5 x 102 = 255g

149
Q

How to balance equations using reaction masses?

A
  1. Divide the mass of each substance by its RFM to find number of moles
  2. Divide number of moles of each substance by smallest number of moles in the reaction
  3. If needed, multiply all the numbers by the same amount to make them all whole numbers
  4. Write the balanced symbol equation for the reaction by putting the numbers infront of the formulas
150
Q

Paula burns a metal in oxygen. There is a single product, an oxide of the metal. Given that 25.4 g of X burns in 3.2g of oxygen, write a balanced equation for this reaction. RAM (X) = 63.5, RFM (X oxide) = 143.0

A

Work out the mass of the metal oxide produced because it’s the only product the mass of the metal oxide produced must equal to the total mass of reactants
25.4+3.2=28.6 of X oxide
Divide the mass of each substance by its relative formula mass or relative atomic mass to calculate how many moles of each substance reacted or were produced
X = 25.4/63.5 = 0.40 mol. O2 = 3.2/32.0 = 0.10 mol. X oxide = 28.6/143.0 = 0.20 mol.
Divide by the smallest number of moles which is 0.10
0.40/0.10=4.0. 0.10/0.10 = 1.0. 0.20/0.10=2.0.
The numbers are all whole numbers so you can write out the balance symbol equation right away
4X + O2 - 2(X oxide)
The oxide of the must have a chemical formula containing X and O atoms

chemistry (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions