McAuley Catholic College
ANSWERS Name: ______________________
McAuley Catholic College JUNIOR SCIENCE
Worksheet 1
Chemical Reactions
Unit 1 Semester 1
Instructions: Work though the exercise over the page.
Marks achieved
Marks possible
25
© R.N.Waters (Xavier Catholic College)
Page 1 of 6
Name: ______________________
WRITING CHEMICAL FORMULAE 1 Chemical formulae are very useful to chemists as they show the numbers and types of atoms that make up chemical compounds. Many people know that the chemical formula for water is H2O, but how many know that this tells us that a water particle is made up of two hydrogen atoms and one oxygen atom, which are chemically combined. Some compounds are very simple and are made up of just two atoms. Others, like the proteins that are found in all living organisms can be made up of tens of thousands of atoms. By following some simple rules we can write the formulae of most of the chemical compounds that we are likely to encounter in this course of study. Chemical names. A chemical compound will always have two, or more, parts to its name. The name of a chemical compound tells us about the numbers and types of atoms that have combined to form it. The name can also be used to help us write the chemical formula of the compound. Sometimes one of the parts of the compound’s name will have a prefix, which indicates how many atoms of that element are present in the formula. The following prefixes are often encountered. Prefix. Mon(o)DiTriTetr(a)Pent(a)Hex(a)Hept(a)Oct(a)Non(a)Dec(a)-
Number of atoms. One Two Three Four Five Six Seven Eight Nine Ten
Example. Carbon monoxide Carbon dioxide Sulphur trioxide Carbon tetrachloride Di-phosphorus pentoxide Uranium hexafluoride Iodine heptafluoride Octane Nonane Decane
Formula CO CO2 SO3 CCl4 P 2O 5 UF6 IF7 C8H18 C9H20 C10H22
I. In the first example, carbon monoxide is made up of one atom of carbon and one atom of oxygen, chemically combined. (When writing chemical formulae we do not write the number 1. This is because the presence of a chemical symbol in the formula tells us that there is at least one atom of that element present in the compound.) In the final example, decane is composed of ten carbon atoms and twenty- two hydrogen atoms chemically combined; a total of thirty-two atoms. Name endings also tell us about the chemical make-up of a compound. Compounds whose name ends in IDE are composed of two elements only. Compounds whose name ends in ATE contain the element oxygen. Compounds whose name contains the prefix PER contain extra atoms of one of the elements. eg Hydrogen oxide H2O, hydrogen peroxide H2O2.
© R.N.Waters (Xavier Catholic College)
Page 2 of 6
Name: ______________________ Valency Number. Each element is assigned a valency number. A valency number is assigned to each group in the periodic table. All the elements in a particular group have that assigned number. An element’s valency number is used to calculate the ratios in which it combines with other elements. Group 1 2 3 4 5 6 7 8
Valency number 1 2 3 4 3 2 1 0
(The noble, or inert, gases are assigned a valency number of zero because they do not react with any other elements.) You will see valency number being used to write chemical formulae in the following sections. Writing formulae for simple, two element, compounds Chemical compounds that are composed of two elements only, can be recognised by their IDE name ending. eg Magnesium oxide is composed of the elements magnesium and oxygen, chemically combined. The chemical formulae of two element compounds can be determined by using the “Valency number” method. The Valency numbers of the elements in a compound can be used to determine the numbers of atoms of each element in the compound. The chemical formula of carbon dioxide will be determined to illustrate the method used to write chemical formulae. Method 1. Write the symbols of the elements that make up the compound. CO 2. Write the valency number of each element at the bottom, right hand side of each symbol. C 4O 2 3. Swap the valency numbers of the elements. C 2O 4 4. Divide the valency numbers by any common denominator that will give whole number answers. (In this case divide by 2.) C 1O 2 5. Re-write the formula omitting the number 1. Formula = CO2 © R.N.Waters (Xavier Catholic College)
Page 3 of 6
Name: ______________________ Use the valency swapping method to determine the formulae of the following two - element compounds.
1. Magnesium oxide
MgO 2. Lithium fluoride
LiF 3. Phosphorus hydride
PH3 4. Calcium chloride
CaCl2 5. Aluminium iodide
AlI3 6. Magnesium nitride
Mg3 N2 7. Sodium oxide
Na2 O 8. Silicon chloride
SiCl4 9. Potassium sulphide
K2 S 10. Hydrogen chloride
HCl
© R.N.Waters (Xavier Catholic College)
Page 4 of 6
Name: ______________________ Writing formulae for two element compounds which contain a variable valency element. If an element can have more than one valency number, then the number is written after the name of the element in the compound. The valency number is written in Roman numerals and is in brackets. eg Iron (II) oxide
FeO
Iron (III) oxide
Fe2O3
The method of writing the formulae for these compounds is exactly the same as shown in the previous section. eg Write the formula of lead (IV) oxide. Write the symbols. PbO Write in the valency numbers. Pb4O2 Swap the valency numbers. Pb2O4 Cancel down. In this case using a common denominator of 2. Pb1O2 Formula = PbO2 Use the valency swapping method to determine the formulae of the following two - element compounds.
1. Copper (II) oxide
CuO 2. Iron (III) chloride
FeCl3 3. Tin (IV) iodide
SnI4 4. Chromium (III) oxide
Cr2 O3 5. Cobalt (II) chloride
CoCl2
© R.N.Waters (Xavier Catholic College)
Page 5 of 6
Name: ______________________ What are the names of the following compounds? 1. MnO2
Manganese Oxide
Name = ……………………………………………………
2. PbO
Lead Oxide
Name = ……………………………………………………
3. CrCl3
Chromium Chloride
Name = ……………………………………………………
4. SnO2
Tin Oxide
Name = ……………………………………………………
5. FeS
Iron Sulfide
Name = ……………………………………………………
6. NaCl
Sodium Chloride
Name = ……………………………………………………
7. CuF
Copper Fluoride Name = …………………………………………………… 8. CaI2
Calcium Iodide Name = …………………………………………………… 9. AlBr3
Aluminium Bromide
Name = ……………………………………………………
10. Li2O
Lithium Oxide Name = …………………………………………………… © R.N.Waters (Xavier Catholic College)
Page 6 of 6
McAuley Catholic College JUNIOR SCIENCE
Worksheet 1
Chemical Reactions
Unit 1 Semester 1
Instructions: Work though the exercise over the page.
Marks achieved
Marks possible
25
© R.N.Waters (Xavier Catholic College)
Page 1 of 6
Name: ______________________
WRITING CHEMICAL FORMULAE 1 Chemical formulae are very useful to chemists as they show the numbers and types of atoms that make up chemical compounds. Many people know that the chemical formula for water is H2O, but how many know that this tells us that a water particle is made up of two hydrogen atoms and one oxygen atom, which are chemically combined. Some compounds are very simple and are made up of just two atoms. Others, like the proteins that are found in all living organisms can be made up of tens of thousands of atoms. By following some simple rules we can write the formulae of most of the chemical compounds that we are likely to encounter in this course of study. Chemical names. A chemical compound will always have two, or more, parts to its name. The name of a chemical compound tells us about the numbers and types of atoms that have combined to form it. The name can also be used to help us write the chemical formula of the compound. Sometimes one of the parts of the compound’s name will have a prefix, which indicates how many atoms of that element are present in the formula. The following prefixes are often encountered. Prefix. Mon(o)DiTriTetr(a)Pent(a)Hex(a)Hept(a)Oct(a)Non(a)Dec(a)-
Number of atoms. One Two Three Four Five Six Seven Eight Nine Ten
Example. Carbon monoxide Carbon dioxide Sulphur trioxide Carbon tetrachloride Di-phosphorus pentoxide Uranium hexafluoride Iodine heptafluoride Octane Nonane Decane
Formula CO CO2 SO3 CCl4 P 2O 5 UF6 IF7 C8H18 C9H20 C10H22
I. In the first example, carbon monoxide is made up of one atom of carbon and one atom of oxygen, chemically combined. (When writing chemical formulae we do not write the number 1. This is because the presence of a chemical symbol in the formula tells us that there is at least one atom of that element present in the compound.) In the final example, decane is composed of ten carbon atoms and twenty- two hydrogen atoms chemically combined; a total of thirty-two atoms. Name endings also tell us about the chemical make-up of a compound. Compounds whose name ends in IDE are composed of two elements only. Compounds whose name ends in ATE contain the element oxygen. Compounds whose name contains the prefix PER contain extra atoms of one of the elements. eg Hydrogen oxide H2O, hydrogen peroxide H2O2.
© R.N.Waters (Xavier Catholic College)
Page 2 of 6
Name: ______________________ Valency Number. Each element is assigned a valency number. A valency number is assigned to each group in the periodic table. All the elements in a particular group have that assigned number. An element’s valency number is used to calculate the ratios in which it combines with other elements. Group 1 2 3 4 5 6 7 8
Valency number 1 2 3 4 3 2 1 0
(The noble, or inert, gases are assigned a valency number of zero because they do not react with any other elements.) You will see valency number being used to write chemical formulae in the following sections. Writing formulae for simple, two element, compounds Chemical compounds that are composed of two elements only, can be recognised by their IDE name ending. eg Magnesium oxide is composed of the elements magnesium and oxygen, chemically combined. The chemical formulae of two element compounds can be determined by using the “Valency number” method. The Valency numbers of the elements in a compound can be used to determine the numbers of atoms of each element in the compound. The chemical formula of carbon dioxide will be determined to illustrate the method used to write chemical formulae. Method 1. Write the symbols of the elements that make up the compound. CO 2. Write the valency number of each element at the bottom, right hand side of each symbol. C 4O 2 3. Swap the valency numbers of the elements. C 2O 4 4. Divide the valency numbers by any common denominator that will give whole number answers. (In this case divide by 2.) C 1O 2 5. Re-write the formula omitting the number 1. Formula = CO2 © R.N.Waters (Xavier Catholic College)
Page 3 of 6
Name: ______________________ Use the valency swapping method to determine the formulae of the following two - element compounds.
1. Magnesium oxide
MgO 2. Lithium fluoride
LiF 3. Phosphorus hydride
PH3 4. Calcium chloride
CaCl2 5. Aluminium iodide
AlI3 6. Magnesium nitride
Mg3 N2 7. Sodium oxide
Na2 O 8. Silicon chloride
SiCl4 9. Potassium sulphide
K2 S 10. Hydrogen chloride
HCl
© R.N.Waters (Xavier Catholic College)
Page 4 of 6
Name: ______________________ Writing formulae for two element compounds which contain a variable valency element. If an element can have more than one valency number, then the number is written after the name of the element in the compound. The valency number is written in Roman numerals and is in brackets. eg Iron (II) oxide
FeO
Iron (III) oxide
Fe2O3
The method of writing the formulae for these compounds is exactly the same as shown in the previous section. eg Write the formula of lead (IV) oxide. Write the symbols. PbO Write in the valency numbers. Pb4O2 Swap the valency numbers. Pb2O4 Cancel down. In this case using a common denominator of 2. Pb1O2 Formula = PbO2 Use the valency swapping method to determine the formulae of the following two - element compounds.
1. Copper (II) oxide
CuO 2. Iron (III) chloride
FeCl3 3. Tin (IV) iodide
SnI4 4. Chromium (III) oxide
Cr2 O3 5. Cobalt (II) chloride
CoCl2
© R.N.Waters (Xavier Catholic College)
Page 5 of 6
Name: ______________________ What are the names of the following compounds? 1. MnO2
Manganese Oxide
Name = ……………………………………………………
2. PbO
Lead Oxide
Name = ……………………………………………………
3. CrCl3
Chromium Chloride
Name = ……………………………………………………
4. SnO2
Tin Oxide
Name = ……………………………………………………
5. FeS
Iron Sulfide
Name = ……………………………………………………
6. NaCl
Sodium Chloride
Name = ……………………………………………………
7. CuF
Copper Fluoride Name = …………………………………………………… 8. CaI2
Calcium Iodide Name = …………………………………………………… 9. AlBr3
Aluminium Bromide
Name = ……………………………………………………
10. Li2O
Lithium Oxide Name = …………………………………………………… © R.N.Waters (Xavier Catholic College)
Page 6 of 6
