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					    Preparation for A-level Chemistry                 - The Language of Chemistry




        In Chemistry we use chemical formulae and equations to describe what substances
        are made from and what happens during chemical reactions. Practicing using these
        can make the subject much easier to understand. For anyone who is unfamiliar with
        them, Chemistry might seem like a foreign language.

        This assignment lets you practice the skills that you have from GCSE and helps you
        to become more fluent in the language of Chemistry.

        Sections 1, 2 and 3 contain information, examples and some practice questions.
        Read the introduction to each section and then try to answer the questions. Do your
        best, some of them are harder than others. Answers are provided at the end so you
        can see how you have done. Make sure that you understand where you have made
        mistakes if you get any questions wrong. You will be able to ask your teacher for
        help if needed at the start of term.

        Section 4 contains a set of questions for you to answer and give to your teacher at the
        start of the AS Chemistry course.




Hmck 2012 language of chemistry
Section 1       Chemical Formulae

Chemists use chemical formulae and equations to describe in
detail, what substances are made from and what happens in
chemical reactions.

There are different types of chemical formula.

Molecular Formulae
A hydrogen molecule has the formula H2      H–H           (2 H atoms joined by a single bond)

An oxygen molecule has the formula O2       O=O           (2 O atoms joined by a double bond)

A water molecule has the formula H2O             O        (2 H atoms bonded to 1 O atom)

                                           H         H

The equation for hydrogen reacting with oxygen is:
                      2H2 + O2  2H2O
This means that 2 molecules of hydrogen react with 1 molecule of oxygen to form 2 molecules of
water.


Questions on molecular formulae

   1.   a) How many H atoms are there in 100 H2 molecules?
        b) How many H atoms are there in 100 H2O molecules?
        c) How many O atoms are there in 100 H2O molecules?
        d) How many H2O molecules would contain a total of 50 H atoms?
        e) How many H2O molecules could you make from 50 O2 molecules?


   2. Vitamin C (ascorbic acid) has the formula C6H8O6
      a) How many H atoms are there in 1000 vitamin C molecules?
      b) How many C atoms are there in 1000 vitamin C molecules?
      c) How many O atoms are there in 500 vitamin C molecules?
      d) How many O2 molecules could be formed by breaking down 1 vitamin C molecule?
      e) How many O2 molecules could be formed by breaking down 500 vitamin C molecules?


   3. Muscles use glucose as an energy source. When it is oxidised it forms carbon dioxide and
      water.
             Glucose = C6H12O6 Carbon dioxide = CO2               Water = H2O
        a) How many C atoms are there in 1 glucose molecule?
        b) How many H atoms are there in 1 glucose molecule?
        c) How many C atoms are there in 1 carbon dioxide molecule?
        d) How many H atoms are there in 1 water molecule?
        e) How many CO2 molecules would be formed by oxidising a glucose molecule?
        f) How many H2O molecules would be formed by oxidising a glucose molecule?



Hmck 2012 language of chemistry
Empirical formula
This shows the simplest whole number ratio of numbers of atoms (or ions) of different elements in a
compound.

Examples.         The compound butene has the molecular formula C4H8.
                  Get the simplest ratio by dividing both of the numbers in the formula by 4.
                  So butene has the empirical formula CH2

                  The compound propene has the molecular formula C3H6.
                  Get the simplest ratio by dividing both of the numbers in the formula by 3.
                  So propene also has the empirical formula CH2

Questions on empirical formula

      4.   Work out the empirical formula of each of the compounds below.
           a) Ethene (molecular formula C2H4)
           b) Hydrogen peroxide (molecular formula H2O2)
           c) Phosphoric(V) oxide (molecular formula P4O10)
           d) Glucose (molecular formula C6H12O6)



Ionic compounds These are generally metal / non-metal compounds
Metallic elements form positive ions. Non-metallic elements form negative ions.

In solid ionic compounds the ions form lattices held together
by strong electrostatic attraction between the opposite charges.

The number of positive and negative charges must be equal
to give an electrically neutral compound.
The formula of an ionic compound shows the ratio of postive to
negative ions. (ie. the empirical formula)


Here is a reminder of some common ions (shown by Periodic Table group)
              Positive ions                      Negative ions
group 1        group 2      group3              group 6      group 7
Li+                                             O2-          F-
Na+             Mg  2+
                             Al   3+
                                                S2-          Cl-
K+              Ca2+                                         Br-
Rb+             Sr2+                                          I-
Cs+             Ba2+
                                                others
others
  +                2+             3+            CO32- (carbonate)    OH- (hydroxide)
H               Fe          Fe                  SO42- (sulfate)     NO3- (nitrate)
NH4+            Cu2+        Cr3+
(ammonium)
                Zn2+




Hmck 2012 language of chemistry
Example: potassium carbonate K+2CO32- contains two K+ ions and one CO32- ion. The charges
cancel out. More examples are below (note how brackets can be used to avoid confusion when larger
ions such as OH- and NO3- are involved).

lithium chloride  = Li+ Cl-           magnesium bromide = Mg2+Br-2
aluminium oxide = Al2O3               magnesium nitrate = Mg2+(NO3-)2
calcium hydroxide = Ca2+(OH-)2        ammonium sulfate = (NH4+)2SO42-


Questions on formulae of ionic compounds

5. Write the correct formulae for:

a) potassium fluoride _________            b) sodium carbonate _________

c) lithium sulfate       _________         d) sodium nitrate      _________

e) lithium hydroxide _________             f) calcium nitrate     _________

g) barium sulfate        _________         h) aluminium nitrate   _________

i) sodium oxide          _________         j) aluminium sulfate   _________




Answers are at the end of section 3               Score for section 1 =   __________
                                                                              30




Hmck 2012 language of chemistry
Section 2                Chemical Equations
A chemical equation shows what happens during a chemical reaction

When you write a chemical equation you need to make sure that there is the
same number of each type of atom on both sides.

Example:

                                 magnesium      + oxygen             magnesium oxide

unbalanced:                            Mg(s)        +    O2 (g)        MgO(s)     x    incorrect

balanced:                              2Mg(s)       +     O2 (g)        2MgO(s)    correct

This equation shows that 2 moles of magnesium atoms react with 1 mole of oxygen molecules to
make 2 moles of magnesium oxide.
(The mole is the unit used by chemists to count numbers of atoms and molecules)

Note    The equation is balanced by putting numbers in front of the formulae
        The chemical formulae of the substances in the equation do not change.

To check if an equation balances or not, count the numbers of atoms of each type on each side.
Remember - there must be an equal number of each type of atom on each side.

Here is another example:

unbalanced:                     H2SO4 (aq) + NaOH (aq)           Na2SO4 (aq) + H2O (l)             x   incorrect

balanced:                       H2SO4 (aq) + 2 NaOH (aq)            Na2SO4 (aq) + 2 H2O (l)     correct

Questions on balancing equations
1. Balance the following equations
a)     Na    +           S      Na2S
b)     Ca    +           O2      CaO
c)     Na    +           Cl2      NaCl
d)     Al    +           Cl2  AlCl3
e)     Al    +       O2          Al2O3
f)   HCl     +            Mg  MgCl2          +       H2
g)     H2O + Na                   NaOH + H2
h)     H2O + Ca                   Ca(OH)2 + H2
i)     CH4           +     O2        CO2     +       H2O
j)     HCl       +       CaCO3     CaCl2         +     CO2 +     H2O
k)     CuO       +        CH4          Cu    +       H2O + CO2


Hmck 2012 language of chemistry
More equations

The mole is the unit of measurement used by chemists to count numbers of atoms and molecules

2. Here is the equation for methane gas burning in oxygen
         CH4    +    2 O2     CO2     + 2 H2O
    This equation shows that 1 mole of methane reacts with 2 moles of oxygen to make 1 mole of
    carbon dioxide plus 2 moles of water.

    a)   How many moles of CO2 would be formed by burning 5 moles of methane?
    b)   How many moles of H2O would be formed by burning 5 moles of methane?
    c)   How many moles of CH4 would have to be burned to make 10 moles of CO2?
    d)   How many moles of CH4 would have to be burned to make 10 moles of H2O?


3. Here is a slightly more complicated one, the equation for glucose reacting with oxygen.
         C6H12O6    +    6O2       6CO2   + 6H2O
    a)   How many moles of CO2 would be formed by burning 2 moles of glucose?
    b)   How many moles of H2O would be formed by burning 2 moles of glucose?
    c)   How many moles of glucose would have to be burned to make 60 moles of CO2?
    d)   How many moles of oxygen would be needed to burn 6 moles of glucose?


4. Here is an even more complicated one. Nitroglycerine C3H5N3O9, is a liquid high explosive.
   On detonation, it decomposes rapidly to form a large number of gas molecules. The equation
   for this decomposition is given below. (Note: all of the products are gases)

                        4C3H5N3O9(l)  12CO2(g) + 10H2O(g) + 6N2(g) + O2(g)

    a)   How many moles of C3H5N3O9(l) are shown reacting in this equation?
    b)   How many moles of CO2 would be formed by exploding 1 mole of nitroglycerine?
    c)   How many moles of H2O would be formed by exploding 1 mole of nitroglycerine?
    d)   How many moles of N2 would be formed by exploding 1 mole of nitroglycerine?
    e)   How many moles of O2 would be formed by exploding 1 mole of nitroglycerine?
    f)   How many moles of gas in total would be produced by exploding 1 mole of nitroglycerine?



Answers are at the end of section 3                 Score for section 2 =    __________
                                                                                 25




Hmck 2012 language of chemistry
    Section 3           Some more calculations
    Chemists often have to do calculations involving amounts of substances. Follow the same
    methods as in the examples below to answer questions 1 to 5

    Example 1
     5 moles of methane gas produce 220g of carbon dioxide when burned in oxygen. What mass of
    carbon dioxide would be produced by burning 1 mole of methane?
                                                               Answer: 220 ÷ 5 = 54g

    Example 2
     0.25 moles of propane gas produce 33g of carbon dioxide when burned in oxygen. What mass of
    carbon dioxide would be produced by burning 1 mole of propane?
                                                                Answer: 33 ÷ 0.25 = 132g

    Example 3
    1 mole of butane gas produces 176g of carbon dioxide when burned in oxygen. What mass of
    carbon dioxide would be produced by burning 0.5 mole of butane?
                                                                Answer: 132 x 0.5 = 66g

    Questions
    1. 10 moles of methane gas produce 440g of carbon dioxide when burned in oxygen. What mass
       of carbon dioxide would burning 1 mole of methane produce?

    2. 2.5 moles of propane gas produce 330g of carbon dioxide when burned in oxygen. What mass
       of carbon dioxide would burning 1 mole of propane produce?

    3. 1 mole of propane gas produces 132g of carbon dioxide when burned in oxygen. What mass of
       carbon dioxide would burning 0.2 mole of propane produce?

    4. 3 moles of sulfur produces 294g of sulfuric acid. What mass of sulfuric acid would 1 mole of
       sulfur produce?

    5. 1 mole of glucose produces 264g of carbon dioxide gas when oxidised. What mass of carbon
       dioxide would the oxidation of 0.25 moles of glucose produce?



        Answers are on the next page                      Score for section 3 =     _________
                                                                                        5



        Total score = _______
                        60




Hmck 2012 language of chemistry
                                                         Answers

Answers to questions in Section 1

Question 1         a) 200 b) 200 c) 100 d) 25 e) 100

Question 2         a) 8000 b) 6000 c) 3000 d) 3 e) 1500

Question 3         a) 6 b) 12 c) 1     d) 2 e) 6 f) 6

Question 4         a) CH2    b) HO    c) P2O5 d) CH2O

Question 5         a) KF b) Na2CO3 c) Li2SO4 d) NaNO3 e) LiOH f) Ca(NO3)2 g) BaSO4 h) Al(NO3)3
                   i) Na2O j) Al2(SO4)3


Answers to questions in Section 2

Question 1
a)   2Na     +      S  Na2S
b)   2Ca     +      O2  2CaO
c)   2Na     +      Cl2  2NaCl
d)   2Al     +      3Cl2  2AlCl3
e)   4Al     +     3O2  2Al2O3
f)   2HCl      +     Mg  MgCl2 +  H2
g)   2H2O     +    2Na  2NaOH + H2
h)   2H2O     +    Ca  Ca(OH)2 + H2
i)   CH4       +     2O2  CO2 + 2H2O
j)  2HCl     +     CaCO3  CaCl2 + CO2 + H2O
k) 4CuO        +   CH4  4Cu + 2H2O + CO2

Question 2         a) 5 b) 10 c) 10 d) 5

Question 3         a) 12 b) 12 c) 10 d) 36

Question 4         a) 4 b) 3 c) 2.5    d) 1.5 e) 0.25 f) 7.25


Answers to questions in Section 3

1. 44.0g           2. 132g            3. 26.4g          4. 98.0g   5. 66.0g




Hmck 2012 language of chemistry
Hmck 2012 language of chemistry
Section 4                   Problem Sheet                   Name ____________________

1. When propane gas burns in air it forms carbon dioxide and water vapour.
     Propane = C3H8        Carbon dioxide = CO2           Water = H2O
       a) How many C atoms are there in 1 propane molecule?                         _______
       b) How many H atoms are there in 1 propane molecule?                         _______
       c) How many C atoms are there in 1 carbon dioxide molecule?                  _______
       d) How many H atoms are there in 1 water molecule?                           _______
       e) How many CO2 molecules would be formed by burning one propane molecule?   _______
       f) How many H2O molecules would be formed by oxidising a propane molecule?   _______



2. Work out the empirical formula of each of the compounds below.
       a) Benzene (molecular formula C6H6)                                          _______
       b) Pentene (molecular formula C5H10)                                         _______
       c) Cyclohexane (molecular formula C6H12)                                     _______
       d) Fructose (molecular formula C6H12O6)                                      _______



3. Write the correct chemical formula for each of the ionic compounds below
a) potassium chloride _________                b) sodium sulfate        _________
c) lithium carbonate _________                 d) potassium oxide       _________
e) calcium oxide         _________             f) magnesium nitrate     _________
g) barium bromide        _________             h) aluminium hydroxide   _________




4. The following equations are not balanced. Add numbers to balance them.
   a)     K + S           K2S
   b)     Ba    + O2           BaO
   c)     Cu    + O2           CuO
  d)      P     + Cl2  PCl3
  e)       P    + O2           P4O10
  f)      HCl     + Fe  FeCl2           +   H2
  g)      H2O + K              KOH + H2
  h)      Fe2O3 + 3CO  Fe + CO2
   i)     Al2O3     Al         +   O2


Hmck 2012 language of chemistry
5. The equation for propane gas burning in oxygen is
        C3H8     +    5O2     3CO2         + 4H2O
This equation shows that 1 mole of propane reacts with 5 moles of oxygen to make 3 moles of carbon
dioxide plus 4 moles of water.

 a) How many moles of CO2 would be formed by burning 3 moles of propane?                        _______
 b) How many moles of H2O would be formed by burning 3 moles of propane?                        _______
 e) How many moles of propane would have to be burned to make 12 moles of CO2?                   _______
 f) How many moles of propane would have to be burned to make 12 moles of H2O?                   _______




6.   a) 5 moles of propane gas produce 660g of carbon dioxide when burned in oxygen. What mass of
        carbon dioxide would burning 1 mole of propane produce?
                                                                                      ________

     b) How many moles of propane gas would need to be burned to produce 330g of carbon dioxide?
                                                                                              ________


7.   Use any information sources that you like to look up a chemical equation for a chemical reaction
     that you think is interesting. Write it out and try to explain what it shows as in the introduction to
     question 5 above.

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Here is a useful website that you could use to do some further reading about the chemical elements.
An interactive Periodic Table          http://www.webelements.com/




Hmck 2012 language of chemistry

				
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