Chemistry: Key Concepts Flashcards
1
Q
Magnesium + oxygen > ?
A
Magnesium oxide
2
Q
2Mg + O(little2) > ?
A
2MgO
3
Q
Balance: Fe + Cl(little2) > FeCl(little3)
A
2Fe + 3Cl(little2) > 2FeCl(little3)
4
Q
Hydrogen and Oxygen molecules are formed in a reaction where water splits apart. State the word and symbol equation.
A
Water > hydrogen + oxygen
2H(little2)O > 2H(little2)+O(little2)
5
Q
What’s the state symbol for solid?
A
s
6
Q
What’s the state symbol for liquid?
A
l
7
Q
What’s the state symbol for gas?
A
g
8
Q
What’s the state symbol for aqueous?
A
aq
9
Q
What does aqueous mean?
A
Dissolved in water
10
Q
What is the chemical formula of water?
A
H(little2)O
11
Q
What is the chemical formula of ammonia?
A
NH(little3)
12
Q
What is the chemical formula of hydrogen?
A
H(little2)
13
Q
What is the chemical formula of carbon dioxide?
A
CO(little2)
14
Q
What is the chemical formula of chlorine?
A
Cl(little2)
15
Q
What is the chemical formula of oxygen?
A
O(little2)
16
Q
What is the formula of Ammonium?
A
NH(little4)^+
17
Q
What is the formula of hydroxide?
A
OH^-
18
Q
What is the formula of nitrate?
A
NO(little3)^-
19
Q
What is the formula of carbonate?
A
CO(little3)^2-
20
Q
What is the formula of Sulfate?
A
SO(little4)^2-
21
Q
When do ions form?
A
When atoms or groups of atoms gain or lose electrons to form charged particles
22
Q
What is in an ionic equation?
A
Reacting particles and the products they form
23
Q
How do you write an ionic equation?
A
Balance the symbol equation, then take out any aqueous ions present on both sides of the equation
24
Q
Write the ionic equation for the following reaction: CaCl(little2)(aq) + 2NaOH(aq) > Ca(OH)(little2)(S) + 2NaCl(aq)
A
1: write out equation showing all aqueous ions separately
Ca^2+ (aq) + 2Cl^-(aq) + 2Na^+(aq)+2OH^-(aq)>Ca(OH)(little2)(S)+2Na^+(aq)+2Cl^-(aq)
2: To get to ionic equation, cross out anything that’s the same on both sides of the equation
Ca^2+(aq)+2OH^-(aq)>Ca(OH)(little2)(S)
(Overall charge should be the same on both sides)
25
Ca^2+(aq)+2OH^-(aq)>Ca(OH)(little2)(S)
Work out charge on left hand side
(2+)+(2x1-)=0
26
Write the ionic equation for the following reaction: HNO(little3)+NaOH(aq)>NaNO(little3)(aq)+H(little2)O(l)
H^+(aq)+OH^-(aq)>H(little2)O(l)
27
What does the hazard symbol showing an O with a flame on mean?
Oxidising: provides oxygen which allows other materials to burn more fiercely
28
What does the hazard symbol showing a fish and tree mean?
Environmental hazard: harmful to organisms and to the environment
29
What does the hazard symbol showing skull and crossbones mean?
Toxic: can cause death
30
What does the hazard symbol showing an exclamation point mean?
Harmful: can cause irritation, reddening or blistering of the skin
31
What does the hazard symbol showing a fire mean?
Highly flammable: catches fire easily
32
What does the hazard symbol showing test tubes a bench and a hand mean?
Corrosive:destroys materials including living tissue
33
What three things do you need to consider in a risk assessment?
Work out how likely it is that something would go wrong, how serious it would be if it did go wrong, then how to reduce this risk
34
A student is carrying out an experiment using two chemicals. Chemical A is corrosive and chemical B is highly flammable. Suggest appropriate safety precautions the student could take to minimise the risks associated with these chemicals.
The student should wear goggles, gloves and a lab coat while handling chemical A, and should also use low concentrations of chemical A. When handling chemical B, student should take care to keep it away from naked flames.
35
Who described the atom structure as a solid sphere? When?
John Dalton, 19th century
36
Describe the solid sphere model
Different solid spheres made up different elements. An atom was completely solid.
37
Who and when came up with the 'plum pudding' atom model? How did he prove previous model wrong?
1897, J J Thomson concluded atoms weren't solid spheres because his measurements or charge and mass showed atom must contain smaller, negatively charged particles (electrons)
38
Describe a plum pudding model
A positively charged sphere with small negatively charged electrons inside
39
Who and when came up with the nuclear atom model? How did he prove previous model wrong?
1909, Ernest Rutherford. Famous gold foil experiment: positively charged alpha particles fired at thin sheet of gold.
40
During the famous gold foil experiment, what did they expect to see happen?
Expecting particles to pass straight through sheet or be slightly deflected, because positive charge of each atom was very spread out through solid 'pudding' of atom
41
During the famous gold foil experiment, what actually happened?
Most particles went straight through, some were deflected more than expected, small number were deflected backward
42
Describe the theory of the nuclear atom
Tiny tiny positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons. Most of the atoms is empty space.
43
Who came up with the Bohr model? How did he prove previous model wrong?
Niels Bohr. Electrons in a cloud around nucleus would be attracted to nucleus, causing atom to collapse.
44
Describe the Refined Bohr Model
Electrons were contained in shells, exist in fixed orbits, shells have a fixed energy.
45
How do scientists validate/propose a theory?
Back it up by evidence. Fit them to evidence and put research up for peer review.
46
Describe the gold foil experiment and how it disproves the plum pudding model of the atom.
During gold foil experiment, alpha particles were fired at a thin sheet of gold. Plum pudding model predicted alpha particles would pass through sheet/be slightly deflected. Most particles DID pass through, but a few were deflected more than expected, some bounced right back. This suggested atom was Mostly empty space, with positive nucleus in the centre.
47
Draw and label a diagram to show the Bohr model of an atom
Nucleus in the middle, shells with electrons on them
48
What do atoms make up?
All subtances
49
What are the three things an atom contains?
Protons neutrons and electrons
50
What is relative mass?
Measured mass on a scale where the mass of a proton or neutron is 1
51
What is relative mass measured in?
Atomic mass units
52
Relative mass of a proton?
1
53
Relative mass of a neutron?
0.0005
54
Relative charge of a proton?
+1
55
Relative charge of a neutron?
0
56
Relative charge of a electron?
-1
57
What are protons neutrons and electrons classified as?
Subatomic particles
58
Describe a proton
Heavy and positively charged
59
Describe a neutron
Heavy and neutral
60
Describe an electron
Has hardly any mass and is negatively charged
61
Where in the atom is the nucleus?
Middle of atom
62
What does nucleus of atom contain?
Protons and neutrons
63
What charge does a nucleus have? Why?
Positive due to the protons
64
Where is the mass of the atom?
Concentrated in the nucleus
65
How big is nucleus compared to whole atom?
Tiny
66
How do electrons move in the atom?
Around the nucleus In electron shells
67
How are electrons charged?
Negatively charged
68
What are the size of electrons in an atom?
Tiny, but shells cover lots of space
69
What determines the size of the atom?
The size of electron shells
70
What is the atomic radius of a atom?
About 10^-10m
71
What can we say about the number of protons and electrons in an atom?
They are the same
72
What is the overall charge of an atom? Why?
Neutral, because it has the same number of protons and electrons
73
What is an ion?
An atom or group of atoms that has gained or lost electrons
74
Why do electrons and protons cancel each other out in an atom?
Charge of electrons is same size as charge of protons, so they cancel each other out
75
If an ion has a 2- charge, what can we say about number of electrons in relation to number of protons?
Two more electrons than protons
76
What does the atomic number tell us?
How many protons an atom has
77
Can the proton number of an element change?
Nope
78
What does the mass number tell us?
Total number of protons + neutrons
79
Where in the nuclear symbol for an atom is the mass number?
On top
80
Where in the nuclear symbol for an atom is the atomic number?
Bottom
81
How do you work out the number of neutrons in an atom?
Subtract atomic number from mass number
82
A certain neutral atom of potassium has an atomic number of 19 ad a mass number of 39 give the number of electrons, protons and neutrons in the atom
```
Electrons = 19
Protons = 19
Neutrons = 39-19=20
```
83
Why is an isotope
A different form of an element, with the same number of protons as original, but different number of neutrons (same atomic number, different mass number)
84
In a nucleus symbol on the periodic table, which number is the relative atomic mass number?
The larger number
85
What is relative atomic mass of an element?
The average mass of one atom of an element (compared to 1/12 of the mass of one atom of carbon-12)
86
If an element only has 1 isotope, it's relative atomic mass will be the same as what?
It's mass number
87
What letters are relative atomic mass represented by?
Ar
88
If an element only has more than one isotope, it's relative atomic mass is what?
The average of the mass numbers of all the different isotopes, taking into account how much there is of each one
89
What does isotopic abundances mean?
Different isotopes of an element occurring in different quantities
90
How do you work out the relative atomic mass of an element?
Find the average mass of all its atoms
91
How do you find the average mass of all the atoms of an element?
Multiply each relative isotopic mass by its relative abundance, and add up the results. Divide by the sum of the isotopic abundances (if abundances are given as percentages, this will be 100)
92
Boron has two isotopes, boron-10 and boron-11. Given that the relative abundances of boron-10 and boron-11 are 4 and 16 respectively, work out the relative atomic mass of boron
1)Multiply each relative isotopic mass by its relative abundance, and add up the results.
(10x4)+(11x16)=216
2) Divide by the sum of the isotopic abundances
216 divided by (16+4)=10.8
93
The isotope boron-11.. what is the relative isotopic mass?
11
94
Bromine has an atomic number of 35 and has two stable isotopes: bromine-79 and bromine-81. Given that 51% of bromine atoms are bromine-79, and 49% are bromine-81, work out the relative atomic mass of bromine. Give your answer to the nearest whole number.
(79x51)+(81x49)=7998
| 7998/100=79.98=80
95
How did early chemists try to find out more about elements?
By looking at patterns in the elements properties
96
Who made the first proper periodic table? When?
Dmitri Mendeleev, 1869
97
How did Dmitri Mendeleev order his table?
Elements with similar chemical properties in columns, in order of atomic mass, with gaps left where an element was missing
98
What helped confirm the idea of Dmitri Mendeleev's table?
The fact he could correctly predict the properties of undiscovered elements using the other elements in that column
99
What are the first two left columns (from left) of the periodic table called?
Reactive metals
100
What is the third (from left) to ninth (from left) row of the periodic table called?
Transition metals
101
On the periodic table, what are the elements on the right of the transition metals under the 'staircase line' called?
Transition metals
102
On the periodic table, what does the 'staircase line' do?
Separates metals from non metals
103
Why is the far right column of the periodic table called?
Noble gases
104
What is the section of elements above the staircase line on the right side of the periodic table (excluding last column) called?
Non metals
105
What can you say about elements in the same column?
They have similar chemical properties
106
What can we say the group number which the element belongs to corresponds to?
To the number of electrons it has in it's outer shell
107
How many electrons in its outer shell will a group 1 element have?
1
108
How many electrons in its outer shell will a group 7 element have?
7
109
How many electrons in its outer shell will a group 0 element have?
8
110
What are the rows (horizontal) in periodic tables called?
Periods
111
What can we say the period number which the element belongs to corresponds to?
The number of shells of electrons it has
112
What are electron shells sometimes known as?
Energy levels
113
How many electrons can go in the first shell of a atom? Second shell?
First=2
| Second + = 8
114
Give the electronic configuration of aluminium. Draw a diagram.
Diagram= nucleus, 3 shells, 3 electrons on outer shell
2.8.3
Atomic no.=13
115
When do simple ions form?
When atoms gain or lose electrons
116
What are ions?
A single atom or group of atoms that are Charged particles
117
Why do atoms become ions?
Because they're trying to get a full outer shell
118
If an atom has a full outer shell, what is this called?
A stable electronic structure
119
What is the name for negative ions?
Anions
120
What is the name for positive ions?
Actions
121
What is an anion?
Negative ion
122
What is a cation?
Positive ion
123
When do anions form?
When atoms gain electrons - they have more electrons than protons
124
When do cations form?
When atoms lose electrons -they above more protons than electrons
125
How can we say the charge of an ion relates to how many electrons it loses or gains?
They are the same
126
If an atom loses 2 electrons, what is the charge of the ion?
2+
127
If an atom gains 3 electrons, what is the charge of the ion?
3-
128
How many electrons does the ion F^- have?
F- has a single negative charge, so it must have one more electrons than protons. F has an atomic number of 9, so has 9 protons. So F- must have 9+1=10 electrons
129
How many electrons does the ion Fe^2+have?
Has a 2+ charge, so it must have two more protons than electrons. Fe has an atomic number of 26, so has 26 protons, so Fe^2+ must have 26-2=24 electrons
130
Which groups in the periodic table are most likely to form ions?
1 and 2 and 6 and 7
131
What charge of ions will group 1 elements form?
1+
132
What charge of ions will group 2 elements form?
2+
133
What charge of ions will group 6 elements form?
2-
134
What charge of ions will group 7 elements form?
1-
135
What are ionic compounds made of?
A positively charged part and a negatively charged part
136
What is the overall charge of any ionic compound? What does this mean?
Zero. All negative charges in the compound must balance all the positive charges
137
What can we say about ions ending in -ate (e.g. Nitrate)
They're negative ions containing oxygen and at least one other element
138
What can we say about ions ending in -ide (e.g. Chloride), and what is the one exception to this rule
They're negative ions containing only one element (apart from hydroxide ions which are OH-)
139
Work out the chemical formula of calcium nitrate
1) write out the formulas of the calcium nitrate ions
Ca^2+, NO(little3)^-
2) the overall charge must be zero, so work out ratio of Ca:NO(little3) that gives an overall neutral charge
To balance 2+ charge on Ca^2+, you need two NO(little3)^- ions: (+2)+(2x-1)=0
The formula is Ca(NO(little3))(little2)
140
Ca(NO(little3))(little2)
| What do the brackets show you?
You need two of the whole nitrate ion
141
In chemistry, what are the three types of bonding?
Ionic, covenant and metallic
142
What is ionic bonding?
When a metal an non metal react together, the metal atom loses electrons to form a cation, and non metal gains these electrons to form an anion. These oppositely charged ions are strongly attracted to each other by electrostatic forces, this attraction is called an ionic bond
143
What is the phrase that describes ionic bonding
Transfer of electrons
144
What are dot and cross diagrams used for?
To show how ionic compounds are formed
145
What is a dot and cross diagram? What does it do?
They show the arrangement of electrons in an atom or ion. Each electron is represented by a dot or cross, so they can show which atom the electrons in an ion originally came from
146
Draw a dot and cross diagram for sodium chloride (NaCl)
(Check page 84 for answer)
The sodium atom gives up its outer electron, becoming an Na^+ ion. The chlorine atom picks up the electron, becoming a Cl^- (chloride) ion
147
Draw a dot and cross diagram for Magnesium Oxide (MgO)
(Check page 84 for answer)
The magnesium atom gives up its two outer electrons, becoming an Mg^2+ ion. The oxygen atom picks up the electrons, becoming an O^2- (Oxide) ion
148
Draw a dot and cross diagram for magnesium chloride (MgCl(little2))
The magnesium atom gives up its two outer electrons, becoming an Mg^2+ ion. The two chlorine atoms pick up one electron each, becoming two Cl^- (chloride) ions
149
Draw a dot and cross diagram for sodium oxide (Na(little2)O)
Two sodium atoms each give up there single outer electron, becoming two Na^+ ions. The oxygen atom picks up the two electrons, becoming an O^2- ion
150
Describe, in terms of electronic transfer, how sodium (Na) and chlorine (Cl) react to form sodium chlorine (NaCl)
Each sodium atom loses an electron to form an Na^+ ion. Each chlorine atom gains an electron to form a Cl^- ion. The oppositely charged ions are attracted to each other by electrostatic attraction.
151
How can we describe the structure of an ionic compound?
They have a regular lattice structure
152
Describe the structure of ionic compounds, in detail
Ionic compounds have giant ionic lattice structures. Ions form closely packed regular lattice. There are strong electrostatic forces of attraction between oppositely charged ions in all directions
153
What can we say about the properties of ionic compounds?
They all have similar properties
154
What is the melting/boiling point of ionic compounds?
High
155
Why do ionic compounds have a high melting and boiling point?
Due to strong attractions between ions. It takes a large amount of energy to overcome this attraction.
156
Can solid ionic compounds conduct electricity? Why?
No, ions are fixed in place and can't move
157
Can melted ionic compounds conduct electricity? Why?
Yes, ions are free to move so can carry an electric current
158
Can or can't most ionic compounds dissolve easily in water?
Can
159
If an ionic compound is dissolved in water, can or can't it conduct electricity? Why?
The ions have separated and are free to move in the solution, so they'll carry an electric current
160
What are the three types of models that show ionic structure?
2D representations, Dot and Cross diagrams, 3D models
161
How does 2D representation model show ionic structure? Give two drawbacks of this model.
Displayed formulas of molecules show what atoms something contains, and how atoms are connected.
1: don't show shape of substance
2: don't give any idea about sizes of the atoms
162
How does dot and cross diagrams model show ionic structure? Give two drawbacks of this model.
Show how compounds or molecules are formed and where electrons in the bonds or ions came from.
1: don't usually show anything about size of the atom or ions
2: don't show how atoms or ions are arranged
163
How does 3D models show ionic structure? Give a drawbacks of this model.
Models of ionic sold is show arrangement of ions
| 1: they can only show the outer layer of a substance
164
What are the three ways of creating a ball and stick model to show ionic compounds?
Draw them, make with plastic molecular model kits, or as computer models
165
What is 2 positive and 2 negatives of ball and stick models to show ionic compounds structure?
Help visualise structures
More realistic than 2D drawings
Misleading- make it look like there are large gaps between atoms
Don't show correct scales of atoms or ions
166
What is a covelant bond?
A strong bond that forms when a pair of electrons is shared between two atoms
167
What structure do substances containing covalent bonds usually have?
Simple molecular substances
168
Draw a dot and cross diagram showing covalent bonding in hydrogen
Check page 86
169
Draw a dot and cross diagram showing covalent bonding in hydrogen chloride
Page 86
170
Draw a dot and cross diagram showing covalent bonding in water
Page 86
171
Draw a dot and cross diagram showing covalent bonding in oxygen
Page 86
172
Draw a dot and cross diagram showing covalent bonding in methane
Page 86
173
Draw a dot and cross diagram showing covalent bonding in carbon dioxide
Page 86
174
What is the chemical formula for hydrogen?
H(little2)
175
What is the chemical formula for hydrogen chloride?
HCl
176
What is the chemical formula for water?
H(little2)O
177
What is the chemical formula for oxygen?
O(little2)
178
What is the chemical formula for carbon dioxide?
CO(little2)
179
What is the chemical formula for methane?
CH(little4)
180
In a stick and ball model (to show ionic compound structure)there is a space left between atoms/ions, what does this space represent?
The space where electron clouds interact
181
What is the general size of simple molecules? What is the general size of bonds between these molecules
10^-10m (Small af)and 10^-10m
182
What can we say about strength of covelant bonds and forces of attraction between molecules?
Covalent bond = strong
| Forces of attraction between molecules = very weak
183
What can we say about the melting/boiling point of simple molecular compounds? (High or low) Why?
Low boiling point, because only need to break feeble intermolecular forces, not covalent bonds. Molecules easily parted
184
What can we say about most molecular substances at room temperature ?
They're gases or liquids
185
What can we say about molecule size, strength of intermolecular forces and melting and boiling points, in relation to each other?
Bigger molecules > increased strength of molecular forces > melting and boiling point Increase
186
Do molecular compounds conduct electricity? Why?
No, they don't contain any free electrons or ions
187
What can we say about simple molecular solubility in water?
Some are soluble and some aren't
188
What are polymers?
Polymere are molecules made up of long chains of covalently bonded carbon atoms
189
When are polymere formed?
When lots of small molecules called monomers join together
190
What are the four properties most giant covalant structures have?
All atoms are bonded to each other by strong covalent bonds
Very high melting and boiling points as lots of energy is needed to break covalent bonds
Don't contain charged particles, don't conduct electricity (except graphite + graphene)
Aren't soluble in water
191
What are the three main examples of carbon based giant covalent structures?
Diamond, graphite and graphene
192
Explain the structure of diamond
Diamond is mad up of a network of carbon atoms that each form four covenant bonds
193
Why is diamond so hard?
Because the strong covalent bonds hold the atoms in a rigid lattice structure
194
Does diamond conduct electricity? Why?
No, it has no free electrons or ions
195
Describe the structure of graphite, and how this effects the material.
Each carbon atom only forms three covalent bonds, creating sheets of carbon atoms arranged in hexagons. No covalent bonds between layers, so they're free to move over each other, making graphite soft and slippery
196
Due to graphites nature, what is it ideal to be used as?
A lubricating material
197
Is the melting point of graphite high or low? Why?
High, covalent bonds in the layers need lots of energy to break
198
Can graphite conduct electricity? Why?
Yes, because only one out of each carbons four outer electrons are used in bonds, so each carbon atom has one electron that's delocalised (free) and can move
199
Describe the structure of Graphen es
Graphen is a type of fullerene, and is one layer of graphite. It's a sheet of carbon atoms joined together hexagons. The sheet is just on atom thick, making it a 2D compound.
200
What are fullerenes?
Fullerenes are are molecules of carbon, shaped like closed tubes or hollow balls
201
Describe the general structure of fullerenes
Mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons (rings of five carbons) or heptagons (rings of seven carbons)
202
What can fullerenes be used for? How? How could this be practically applied in the world?
To 'cage' other molecules, fullerenes structure forms around another atom in a molecule, which is trapped inside, could be used to deliver a drug directly to cells in body
203
What could fullerenes be used to make and why?
They have a huge surface area so can be used to make industrial catalysts, as individual catalyst molecules could be attached to the fullerenes
204
Give three examples of fullerenes
Graphene, nanotubes, buckminsterfullerene
205
Describe what buckminsterfullerene is? (Molecular formula, structure, type of molecule/what it forms)
Fullerenes that Has the molecular formula C(little60) and forms a hollow sphere made of 20 hexagons and 12 pentagons. It's a stable molecule that forms soft brownish-black crystals
206
Describe what nanotubes are? (Structure, electricity conduct?, what can be used for and why, practical application)
Fullerenes that are like tiny cylinders of graphene. They conduct electricity. High tensile strength (don't break when stretched) so can strengthen materials without adding weight. Could strengthen sports equipment that needs to be strong while being lightweight.
207
What does metallic bonding involve?
Delocalised electrons
208
What structure do metals consist of?
Giant structure
209
Describe the structure of a metal atom
Giant structure, electrons in outer shell are delocalised
210
What is metallic bonding?
strong forces of electrostatic attraction between the positive metal ions and shared (between ions) negative electrons. These forces of attraction hold atoms together in a regular structure.
211
How strong is metallic bonding?
Very strong
212
What compounds are held together by metallic bonding?
Metallic elements and alloys
213
What in a metallic bond produces all the properties of metals?
The delocalised electrons
214
What is the melting boiling point of metals? Why? What does this mean for the properties of the compound in room temperature?
High melting boiling point, because electrostatic forces between the metal ions and the delocalised sea of electrons are very strong so need lots of energy to be broken . They're generally shiny solids at room temperature
215
Are metals soluble in water?
Nope
216
What can we say about the general density of metals compared to non metals, and why is this?
Metals are denser than non metals as the ions in metallic structure are packed close together
217
Why are pure metals malleable? What does malleable mean?
The layers of atoms in a pure metal can slide over each other, making metals malleable - this means they can be hammered or rolled into flat sheets
218
Can metals conduct electricity /heat? Why?
Yes'm be shed delocalised electrons carry electrical current and thermal energy through the material
219
Do all metals have metallic bonding?
Yep
220
Why do metals and non metals have different properties?
Metals = metallic bonding
| non metals = no metallic no metallic bonding
221
What can we say about metals and non metals in terms of gaining and loosing electrons
Non metals = gain electrons
| Metals = loose electrons
222
Where do metals and non metals tend to be on the periodic table?
Non Metals = top (H) and right hand side
| Metals = bottom (transition metals) and left hand side
223
What can we say about conservation of mass in a chemical reaction?
Mass is always conserved
224
What is conservation of mass? What does this mean?
When no atoms are destroyed and no atoms are created, meaning there are same number and types of atoms on both sides of reaction equation
225
Give an example and explain an experiment used to show conservation of mass in a closed system
Precipitation reaction: two solutions react and an insoluble solid, called a precipitate, forms in the solution
226
A mass appears to increase in a chemical reaction, in an unsealed reaction vessel. Why?
At least one reactant is a gas found in air, and products are solids, liquids or aqueous. Gas becomes part of product, total mass of stuff inside the reaction vessel increases.
227
Give an example of mass seeming to increase in a chemical reaction, in an unsealed reaction vessel
Metal in an unsealed container reacts with oxygen from air, so mass inside container increases. Mass of metal oxide produced equals total mass of the metal and the oxygen that reacted from air,
Metal (S) + oxygen (g) > metal oxide (s)
228
A mass appears to decrease in a chemical reaction, in an unsealed reaction vessel. Why?
Some or all of reactants are solids, liquids or aqueous and at least one product is gas. Before reaction, solid liquid or aqueous are in vessel. As it turns to gas, gas escapes.
229
Give an example of mass seeming to decrease in a chemical reaction, in an unsealed reaction vessel
Metal carbonate thermally decomposes in an unsealed container to form a metal oxide and carbon dioxide ga, the mass of the container will appear to decrease as carbon dioxide escapes. In reality, mass of the metal oxide and carbon dioxide produced will equal mass of metal carbonate that reacted
Metal carbonate (S) > metal oxide (s) + carbon dioxide (g)
230
What is relative formula mass represented by?
Mr
231
What is relative formula mass?
The relative atomic masses of all the atoms in its formula added together
232
Find relative formula mass of magnesium chloride MgCl(little 2)
Use periodic table to find relative atomic masses of magnesium and chlorine. Add up relative atomic masses of all atoms in the formula to beg the relative formula mass
```
Ar(Mg) = 24
Ar(Cl) = 35.5
Mr(MgCl(little2)) = 24+(2x35.5)
= 24+71=95
Mr of MgCl(little2) = 95
```
233
Find the relative formula mass of calcium hydroxide. Ca(OH)(little2)
```
Ar(Ca)=40
Ar(O)=16
Ar(H)=1
Mr(Ca(OH)(little2)) = 40 + [(16+1)x2]
=40+34=74
Mr of Ca(OH(little2)) = 74
```
234
What can we say the Mr of a compound is equal to?
To the mass in grams of 1 mole of the compound
235
Wat does the empirical formula of a compound tell you?
The smallest whole number ratio of atoms in the compound
236
Find the empirical formula of glucose, C(little6) H(little12) O(little6)
Numbers in the molecular formula of glucose are 6,12 and 6
To simplify ratio, divide them by the largest number that goes into 6,12 and 6: 6
C: 6/6=1
H:12/6=2
O:6/6=1
Empirical formula of glucose is CH(little2)O
237
What can you use empirical formula of a compound with Relative formula mass to find?
It's molecular formula
238
Compound X has the empirical formula C(little2)H(little6)N. the Mr of compound X is 88. Find the molecular formula of compound X
Start by finding the Mr of the empirical formula. The Ar of carbon is 12, the Ar of Hydrogen is 1 and the Ar of nitrogen is 14.
Divide the Mr of the compound by the Mr of the empirical formula.
To get molecular formula, multiply everything in the empirical formula by the result (here, 2)
Mr(C(little2)H(little6)N) = (2xAr(C))+(6xAr(H))+Ar(N)
=(2x12)+(6x1)+14
=24+6+14=44
88/44=2
C: 2x2=4
H:6x2=12
N:1x2=2
Molecular formula of impound X is C(little4)H(little12)N(little2)
239
What is the Mole? What is it equal to?
An amount of particles, equal to a number called Avogadro's constant. It's 6.02x10^23
240
What can we say about Avogadro's constant in predation to weight?
When you get that number (6.02x10^23) of atoms or molecules, of any element or compound, they weigh exactly the same number of grams as re relative atomic mass Ar (or relative formula mass Mr) of the element or compound
241
One mole of atoms or molecules of any substance will have a mass in grams equal to what?
the relative particle mass (Ar or Mr) for that substance
242
How much will one mole of carbon weigh?
Carbon has Ar of 12 so one mole weighs exactly 12g
243
How much will one mole of nitrogen gas weigh?
```
Nitrogen gas (N(little2)) has an Mr of 28 (2x14)
One mole of nitrogen gas weighs exactly 28g
```
244
How much will one mole of hexane (C(little6)H(little14)) weigh?
Mr of 86 ((6x12)+(14x1))
| So one mole of hexane weighs exactly 86g
245
One mole of carbon weighs 12g
One mole of nitrogen gas weighs 28g
One mole of hexane weighs 86g
What can you say about how many particles they contain?
All contain the same number of particles, one mole, 6.02x10^23 particles
246
How many atoms are there in five moles of oxygen gas?
Multiply Avogadro's constant by the number of moles you have to find the number of particles
There a few two atoms in the ach molecule of oxygen gas, so Multilpy your answer by 2
6. 02x10^23 z5=3.01x10^24
3. 01x10^24x2=6.02x10^24
247
What is the equation for number of moles?
Number of moles = mass in g (of element or compound) / Mr (of compound) or Ar (of Element)
248
How many Magnesium atoms are there in 60g of magnesium? Ar of Mg= 24
Convert mass into moles using the equation
Moles = mass / Ar
= 60/24=2.5 moles
Multiply the number of moles by Avogadro's constant to find the number of atoms
6.02x10^23x2.5
=1.505 x 10^24
249
You need to get from a number of particles to a number of moles. What do you do to do this?
Divide by 6.02x10^23
250
How many moles are th re in 66g of carbon dioxide?
Mr of carbon dioxide is (CO(little2)) = 12 + (16x2) = 44
| Moles = mass / Mr = 66/44 = 1.5 moles
251
What mass of carbon is there in 4 moles of carbon dioxide?
Mass = moles x Ar(C)
| = 4 x 12 = 48g
252
What is concentration?
A measure of how crowded things are
253
What can we say about how he amount of solute dissolved into a given volume in relation to concentration of the solution
More solute = more concentrated
254
What is concentration measured in?
g dm ^-3
| Grams per dm^3
255
1 gram of stuff dissolved into 1 dm^3 of solution has a concentration of ?
1 g dm^-3
256
1 dm^3 = ? Litre/s = ? Cm^3
1 litre, 1000cm ^3
257
What's the equation for finding concentration from the mass of a solute?
Concentration = mass of solute / volume of solution
258
What is volume of a solution measured in?
dm^3
259
What is mason solute measured in?
Grams
260
25g of copper sulphate is dissolved in 500cm^3 of water. What's the concentration in g dm^-3?
Make sure values are right units. Volume needs to be converted to dm^3"
1000cm^3 = 1dm^3, 500cm^3 = (500/1000)dm^3=0.5dm^3
Now substitute values into the formula
Concentration = 25/0.5=50g dm^-3
261
What mass of sodium chloride is in 300cm^3 of solution with a concentration of 12g dm^-3
```
Rearrange formula so mass is by itself
Mass = concentration x volume
Put the volume into the right units
300cm^3 = (300 / 1000) dm^3 = 0.30 dm^3
Substitute the values into the rearranged formula
Mass = 12 x 0.30 = 3.6g
```
262
What can we use to work out empirical formulas of a compound?
The masses of the element it contains
263
A sample of hydrocarbon contains 36g of carbon and 6g of hydrogen . Work out the empirical formula of the hydrocarbon.
Remember: moles = mass/Mr
Work out how many moles of each element you have
Work out the smallest whole number ratio between the moles of C ajd H atoms to get the empirical formula
```
Ar(C)= 12
Moles of C = 36/12=3moles
Ar(H)=1
Moles of H = 6/1 = 6 moles
Ratio C:H = 3:6
Divide both by /smallest/ 3
Ratio C:H = 1:2
Empirical formula is CH(little 2)
```
264
6 steps of an experiment that can be used to calculate empirical formula of a metal oxide
1) heat crucible until red hot. (Cleans it)
2) leave crucible to cool. Then weigh (along with lid)
3) add clean magnesium ribbon to crucible. Reweigh, with lid + ribbon
New reading - initial reading = mass of magnesium
4) heat crucible with magnesium. Put on lid, leave small gap so oxygen can enter.
5) heat strongly for around 10 mins, or until magnesium ribbon turns white
6) allow to cool. Reweigh crucible with lid + contents.
Mass of magnesium oxide = new reading - initial reading
265
A student heats 1.08g of magnesium ribbon in a crucible so it completely reacts to form magnesium oxide. The total mass of magnesium oxide formed was 1.80g. Calculate empirical formula of magnesium oxide.
1) extra mass in magnesium oxide came from oxygen, work out mass of oxygen
Mass of O= 1.80-1.08=0.72g
2) work out the number of moles of magnesium and oxygen atoms involved in the reaction
Moles of Mg = 1.08 / 24 = 0.045 moles
Moles of O = 0.72 / 16 = 0.045moles
3) work out lowest whole number ratio between Mg and O by dividing moles of both by the smallest number
Mg = 0.045 / 0.045 = 1
O = 0.045 / 0.045 = 1
Ratio = 1:1
Empirical formula of magnesium oxide is MgO
266
When do reactions stop? What do we call the other reactants?
When one reactant is used up. The others are 'in excess'
267
What's the reactant that's used up in a reaction called?
A limiting reactant
268
What can we say about the limiting reactant in terms of the amount of product formed? What does this mean for the reaction?
They're directly proportional. More limiting reactant means more reactant particles to take part in reaction, meaning more product particles are made (as long as other reactants are in excess)
269
What can we use the limiting reactant to calculate?
The amount of product
270
Give the 5 steps of the calculation used to calculate the mass of a product formed from a liming reactant, using a balanced chemical equation. What else can this method be used to calculate?
1) write out the balanced equation
2) work out relative formula mass (Mr) of reactant and product you're interested in
3) find out how many moles there are of the substance you know the mass of
4) use balanced equation to work out how many moles there'll be of the other substance (how many moles of product will be made by this many moles of reactant)
5) use number of moles to calculate mass
Can also be used to find out mass of a reactant needed to produce a known mass of a product
271
What can be used to calculate the mass of a product formed from a liming reactant?
A balanced chemical equation
272
Calculate the mass of aluminium oxide, Al(little2)O(little3) formed when 135g of aluminium is burned in air
1) write out the balanced equation
4Al + 3O(little 2) > 2Al(little2)O(little3)
2) calculate relative formula masses of the reactants and products you're interested in
Al:27
Al(little2)O(little3): (2x27)+(3x16)=102
3) calculate the number of moles of aluminium in 135g
Moles = mass / Mr = 135/27= 5
4)look at the ratio of moles in the equation
4 moles of Al react to produce 2 moles of Al(little2)O(little3) - half the number of moles are produced. So 5 moles of Al will react to produce 2.5moles of Al(little2)O(little3)
5) calculate mass of 2.5 moles of aluminium oxide
Mass = moles x Mr = 2.5 x 102 = 255g
273
Magnesium oxide, MgO, can be made by burning magnesium in air. What mass of magnesium is needed to make 100g of magnesium oxide?
1) Write our the balanced equation
2Mg + O(little2) > 2MgO
2) Work out the relative formula masses of the reactants and products you're interested in
Mg: 24
MgO: 24 + 16 = 40
3) calculate the number of moles of magnesium oxide in 100g
Moles = mass / Mr = 100/40 = 2.5
4) Look at the ratio of moles in the equation
2 moles of MgO are made from 2 moles of Mg. So 2.5 moles of MgO will be formed from 2.5 moles of Mg
5) Calculate the mass of 2.5 moles of Mg
Mass = moles x Mr = 2.5 x 24 = 60g
274
What can we use to work out a balanced symbol equation?
The masses of the reactants and products that took part in the reaction
275
Give the four steps working out a balanced symbol equation using given masses and reactants of products that took part in the reaction
1) divide the mass of each substance by its relative formula mass to find the number of moles
2) divide the number of moles of each substance by the 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 these numbers in front of the formulas
276
Paula burns a metal, X, in oxygen. There is a single product, an oxide of the metal. Given that 25.4g of X burns in 3.2g of oxygen, write a balanced equation for this reaction. Ar of X = 63.5 and Mr of X Oxide = 143.0
1) Work out the mass of metal oxide produced. Because it's the only product the mass of metal oxide produced must equal the total mass of its reactants.
25.4+3.2=28.6g of X oxide
2) Divide the mass of each substance by its Mr or Ar to calculate how many moles of each substance reacted or were produced
X: 25.4/63.5=0.40 mol
O(little2): 3.2/32.0 = 0.10mol
X oxide: 28.6/143.0 = 0.20mol
3) divide by the smallest number of moles, which is 0.10:
X: 0.40/0.10=4.0
O(little2): 0.10/0.10=1.0
X oxide: 0.20/0.10=2.0
4) the numbers are all whole numbers, so you can write out the balanced symbol equation straight away.
4X + O(little2) > 2(X oxide)
5) the oxide of X must have a chemical formula containing X and O atoms. In order for the equation to balance, each molecule of X oxide must contain one O atom and two X atoms. 4X + O(little2) > 2X(little2)O
277
8.1g of zinc oxide (ZnO) were put in a crucible with 0.30g of carbon and heated until they reacted. Given that the balanced chemical equation for this reaction is: 2ZnO + C > CO(little2) + 2Zn, work out the limiting reactant in this reaction
1) Divide the mass of each substance by its Mr or Ar to find how many moles of earful substance were reacted
ZnO: 8.1/81 = 0.10 mol
C: 0.30/12 = 0.025 mol
2) divide by the smallest number of moles, which is 0.025
ZnO: 0.10/0.025=4.0
C: 0.025/0.025=1.0
3) compare the ratios between the moles of products with the balanced chemical equation
In the balanced equation, ZnO and C react in a ratio of 2:1. Using the masses, there is a 4:1 ratio of ZnO to C. So, ZnO is in excess, and C must be the limiting reaction.
