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Ks4 quantitative chemistry (boardworks)

This document discusses representing chemicals using symbols and formulae. It explains that each element has a unique chemical symbol, and provides examples of common element symbols. It also discusses how molecular and ionic compounds are represented using chemical formulae, including showing atom ratios and charge. The document provides examples of writing formulae for different types of compounds from their names or component elements and masses. It emphasizes that chemical formulae provide important information about the composition of substances.

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Quantitative Chemistry © Boardworks Ltd 2005
Representing Chemicals Symbols and formulae © Boardworks Ltd 2005
Chemical Symbols of elements • Each element has a symbol. • Many you can predict from the name of the element. • And some you can’t! Name Atom Symbol Name Atom Symbol Hydrogen H H Sodium Na Na Oxygen O O Copper Cu Cu Nitrogen N N Silver Ag Ag P P Lead Pb Pb Phosphorus © Boardworks Ltd 2005
Chemical formula of elements • Each element has a symbol. • Some elements exist as particular numbers of atoms bonded together. Atom Molecule Formula O O O2 N • This fact can be represented in a formula with a number which shows how many atoms. O N N N2 H H H H2 P P P PP P4 © Boardworks Ltd 2005
The formula of molecular compounds • Molecular compounds have formulae that show the type and number of atoms that they are made up from. Name Methane Formula H H C H H Carbon dioxide Water O C O H H O CH4 CO2 H2O © Boardworks Ltd 2005
The formula of ionic compounds • Ionic compounds are giant structures. • There can be any number of ions in an ionic crystal - but always a definite ratio of ions. - + - ++ + - - + -+ - -+ + -- + + -+ +- -+ + Sodium chloride A 1:1 ratio Name Ratio Formula Sodium chloride 1:1 NaCl Magnesium chloride 1:2 MgCl2 Aluminium chloride 1:3 AlCl3 Aluminium Oxide 2:3 Al2O3 © Boardworks Ltd 2005
Ions with groups of atoms • Some ions are single atoms with a charge. Chloride Cl- Cl- nitrate nitride N3- N3- NO3- Sulphide S2- S2- Sulphate SO42- O N O- O O O- S O- O • Other ions consist of groups of atoms that remain intact throughout most chemical reactions. • E.g. Nitrate and sulphate ions commonly occur in many chemical reactions. © Boardworks Ltd 2005
Use of brackets in formulae • Ions like nitrate and sulphate remain unchanged throughout many reactions. • Because of this we tend to think of the sulphate ion as a “group” rather than a “collection of individual” sulphur and oxygen atoms. • This affects how we write formulae containing them. Aluminium sulphate contains two Al ions and three sulphate ions. • We write it as Al2(SO4)3 Not Al2S3O12 • Similar rules apply to ions such as nitrate NO3-, hydroxide OH-, etc. © Boardworks Ltd 2005
Activity Use the information to write out the formula for the compound. 1) Calcium bromide CaBr2 (One calcium ion, two bromide ions) 2) Ethane (Two carbon atoms, six hydrogen atoms) C2H6 3) Sodium oxide (Two sodium ions, one oxygen ion) Na2O 4) Magnesium hydroxide (One magnesium ion, two hydroxide ions) 2 Mg(OH) 5) Calcium nitrate (One calcium ion, two nitrate ions) Ca(NO3)2 © Boardworks Ltd 2005
The Masses of chemicals © Boardworks Ltd 2005
• • • • Atomic Mass of elements The atoms of each element have a different mass. Carbon is given a relative atomic mass (RAM) of 12 . The RAM of other atoms compares them with carbon. Eg. Hydrogen has a mass of only one twelfth that of carbon and so has a RAM of 1. • Below are the RAMs of some other elements. Element Symbol Times as heavy as carbon R.A.M Helium He one third 4 Beryllium Be three quarters 9 Molybdenum Mo Eight 96 Krypton Kr Seven 84 Oxygen O One and one third 16 Silver Ag Nine 108 Calcium Ca Three and one third 40 © Boardworks Ltd 2005
Formula Mass • For a number of reasons it is useful to use something called the formula mass. • To calculate this we simply add together the atomic masses of all the atoms shown in the formula. (N=14; H=1; Na=23; O=16; Mg=24; Ca=40) Substance Formula Ammonia NH3 14 + (3x1)=17 Na2O (2x23) + 16 =62 Magnesium hydroxide Mg(OH)2 24+ 2(16+1)=58 Calcium nitrate Ca(NO3)2 40+ 2(14+(3x16))=164 Sodium oxide Formula Mass © Boardworks Ltd 2005
Percentage Composition • It is sometimes useful to know how much of a compound is made up of some particular element. • This is called the percentage composition by mass. % Z = (Number of atoms of Z) x (atomic Mass of Z) Formula Mass of the compound E.g. % of oxygen in carbon dioxide (Atomic Masses: C=12. O=16) CO2 Formula = Number oxygen atoms = 2 Atomic Mass of O = 16 Formula Mass CO2 = 12 +(2x16)=44 % oxygen = 2 x 16 / 44 = 72.7% Carbon Oxygen 80 60 40 20 0 % © Boardworks Ltd 2005
Activity • Calculate the percentage of oxygen in the compounds shown below % Z = (Number of atoms of Z) x (atomic Mass of Z) Formula Mass of the compound Formula Atoms of O MgO 1 16 24+16=40 K2O 1 16 (2x39)+16 =94 16x100/94=17% NaOH 1 16 23+16+1 =40 16x100/40=40% 32 32+(2x16)= 64 32x100/64=50% SO2 2 Mass of O Formula Mass %age Oxygen 16x100/40=40% © Boardworks Ltd 2005
Activity • Nitrogen is a vital ingredient of fertiliser that is needed for healthy leaf growth. • But which of the two fertilisers ammonium nitrate or urea contains most nitrogen? • To answer this we need to calculate what percentage of nitrogen is in each compound © Boardworks Ltd 2005
Activity • Formulae: Ammonium Nitrate NH4NO3: Urea CON2H4 Formula Atoms of N Mass of N NH4NO3 2 28 CON2H4 2 28 Formula Mass %age Nitrogen 14+(1x4)+14+(3x16)= 80 28x100 /80 = 35% 12+16+(2x14+(4x1)= 28x100 /60 = 46.7% 60 Amm.Nitrate Atomic masses H=1: C=12: N=14: O=16 Urea 50 And so, in terms of % nitrogen urea is a better fertiliser than ammonium nitrate 40 30 20 10 0 1st Qtr © Boardworks Ltd 2005
Formula from Composition by mass. © Boardworks Ltd 2005
Formula Mass • When a new compound is discovered we have to deduce its formula. • This always involves getting data about the masses of elements that are combined together. • What we have to do is work back from this data to calculate the number of atoms of each element and then calculate the ratio. • In order to do this we divide the mass of each atom by its atomic mass. • The calculation is best done in 5 stages: © Boardworks Ltd 2005
• We found 3.2g of copper reacted with 0.8g of oxygen. What is the formula of the oxide of copper that was formed? (At. Mass Cu=64: O=16) Substance Copper oxide 1. Elements Cu 2. Mass of each element (g) 3.2 3. Mass / Atomic Mass 4. Ratio 5. Formula O 0.8 0.8/16 =0.05 3.2/64 =0.05 1:1 CuO © Boardworks Ltd 2005
• We found 5.5g of manganese reacted with 3.2g of oxygen. What is the formula of the oxide of manganese formed? (Atomic. Mass Mn=55: O=16) Substance Manganese oxide 1. Elements Mn 2. Mass of each element (g) 5.5 3. Mass / Atomic Mass 4. Ratio 5. Formula O 3.2 3.2/16 =0.20 5.5/55 =0.10 1:2 MnO2 © Boardworks Ltd 2005
Activity • A chloride of silicon was found to have the following % composition by mass: Silicon 16.5%: Chlorine 83.5% (Atomic. Mass Si=28: Cl=35.5) Substance 1. Elements 2. Mass of each element (g per 100g) 3. Mass / Atomic Mass 4. Ratio Divide biggest by smallest 5. Formula Silicon Chloride Si Cl 83.5 16.5 16.5/28 =0.59 83.5/35.5 =2.35 Cl÷Si = (2.35 ÷ 0.59) = (3.98) Ratio of Cl:Si =4:1 SiCl4 © Boardworks Ltd 2005
Activity • Calculate the formula of the compounds formed when the following masses of elements react completely: (Atomic. Mass Si=28: Cl=35.5) Element 1 Element 2 Atomic Masses Formula FeCl3 Fe = 5.6g Cl=106.5g Fe=56 Cl=35.5 K = 0.78g Br=1.6g K=39: Br=80 KBr P=1.55g Cl=8.8g P=31: Cl=35.5 PCl5 C=0.6g H=0.2g C=12: H=1 CH4 Mg=4.8g O=3.2g Mg=24: O=16 MgO © Boardworks Ltd 2005
Formula from Charges on ions © Boardworks Ltd 2005
Charges on ions. • Many elements form ions with some definite charge (E.g. Na+, Mg2+ and O2-). It is often possible to work out the charge using the Periodic Table. • If we know the charges on the ions that make up the compound then we can work out its formula. • This topic is covered in more detail in the Topic on Bonding but a few slides are included here on how to work out the charges on ions and use these to deduce the formula of simple ionic compounds. © Boardworks Ltd 2005
Charges and Metal ions • Metals usually lose electrons to empty this outer shell. • The number of electrons in the outer shell is usually equal to the group number in the Periodic Table. • Eg. Li =Group 1 Mg=Group2 Al=Group3 Li 2.1 Li+ Mg 2.8.2  Mg2+ Al 2.8.3  Al3+ © Boardworks Ltd 2005
Charges and non-metal ions • Elements in Groups 4 onwards generally gain electrons and the number of electrons they gain is equal to the Group Number. • Oxygen (Group 6) gains (8-6) =2 electrons to form O2• Chlorine (Group 7) gains (8-7)=1 electron to form Cl- O 2.62. 8O O2- Cl 2.8.7 2.8.8 Cl  Cl© Boardworks Ltd 2005
Activity 0 7 6 5 4 3 2 1 • Copy out and fill in the Table below showing what charge ions will be formed from the elements listed. H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Symbol Group No Charge Li N Cl Ca K Al O Br Na 1 5 7 2 1 3 6 7 1 1+ 3- 1- 2+ 1+ 3+ 2- 1- 1+ © Boardworks Ltd 2005
The formulae of ionic compounds This is most quickly done in 5 stages. Remember the total + and – charges must =zero • Eg. The formula of calcium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Br Ca Br Ca Br 2+ 1Br 2 1 CaBr2 BrCa2+ Br- 2 electrons © Boardworks Ltd 2005
The formulae of ionic compounds • Eg. The formula of aluminium bromide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula Al Br 3+ 1Br 3 1 AlBr3 Br- Br Al Br 3 electrons Br Al3+ BrBr© Boardworks Ltd 2005
The formulae of ionic compounds • Eg. The formula of aluminium oxide. 1. 2. 3. 4. 5. Symbols: Charge on ions Need more of Ratio of ions Formula 2e- Al Al 3+ O 2O 3 (to give 6 e-) 2 Al2O3 O2- O Al3+ 2e- Al 2e- O O O2Al3+ O2© Boardworks Ltd 2005
Activity • The formulae of ionic compounds Eg. The formula of magnesium chloride. 1. 2. 3. 4. 5. Symbols: Mg Charge on ions 2+ Need more of Cl Ratio of ions Formula 1e- Mg 1e- Cl Cl Cl 11:2 MgCl2 ClMg2+ Cl- © Boardworks Ltd 2005
Activity • The formulae of ionic compounds Eg. The formula of sodium oxide. 1. 2. 3. 4. 5. Symbols: Na O Charge on ions 1+ 2Need more of Na Ratio of ions 2:1 Formula Na2O Na Na 1e- Na+ O 1e- O2Na+ © Boardworks Ltd 2005
Activity • Using the method shown on the last few slides, work out the formula of all the ionic compounds that you can make from combinations of the metals and non-metals shown below: •Metals: Li Ca Na Mg Al K •Non-Metals: F O N Br S Cl © Boardworks Ltd 2005
Representing Chemical reactions: Equations. © Boardworks Ltd 2005
Word Equations • All equations take the general form: Reactants Products Word equations simply replace “reactants and products” with the names of the actual reactants and products. E.g Reactants Magnesium + oxygen Sodium + water Magnesium + lead nitrate Nitric acid + calcium hydroxide Products Magnesium oxide Sodium hydroxide + hydrogen Magnesium nitrate + lead Water + calcium nitrate © Boardworks Ltd 2005
Activity • Write the word equations for the descriptions below. 1. The copper oxide was added to hot sulphuric acid and it reacted to give a blue solution of copper sulphate and water. Copper oxide + sulphuric acid copper sulphate + water 2. The magnesium was added to hot sulphuric acid and it reacted to give colourless magnesium sulphate solution plus hydrogen Magnesium + sulphuric acid Magnesium sulphate + hydrogen © Boardworks Ltd 2005
Activity • Write the word equations for the descriptions below. 3. The methane burned in oxygen and it reacted to give carbon dioxide and water. methane + oxygen Carbon dioxide + water 4. The copper metal was placed in the silver nitrate solution. The copper slowly disappeared forming blue copper nitrate solution and needles of silver metal seemed to grow from the surface of the copper copper + Silver nitrate Copper nitrate + silver © Boardworks Ltd 2005
Chemical Equations • Step 1: Write down the word equation. • Step 2: Replace words with the chemical formula . • Step 3: Check that there are equal numbers of each type of atom on both sides of the equation. If not, then balance the equation by using more than one. • Step 4: Write in the state symbols (s), (l), (g), (aq). Reactants magnesium + oxygen Mg + O2 Products magnesium oxide MgO Oxygen doesn’t balance.Need 2 MgO and so need 2 Mg 2Mg + O2 2Mg(s) +O2(g) 2MgO 2MgO(s) © Boardworks Ltd 2005
Chemical Equations • • • Step 1: Write down the word equation. Step 2: Replace words with the chemical formula . Step 3: Check that there are equal numbers of each type of atom on both sides of the equation. If not, then balance the equation by using more than one. • Step 4: Write in the state symbols (s), (l), (g), (aq). Reactants sodium + water Na + Products hydrogen + sodium hydroxide H2O Hydrogen doesn’t balance. + 2Na 2Na(s) 2H2O + 2H2O(l) + H2 NaOH Use 2 H2O, NaOH, 2Na + 2NaOH H2 H2(g) + 2NaOH(aq) © Boardworks Ltd 2005
Chemical Equations • • • Step 1: Write down the word equation. Step 2: Replace words with the chemical formula . Step 3: Check that there are equal numbers of each type of atom on both sides of the equation. If not, then balance the equation by using more than one. • Step 4: Write in the state symbols (s), (l), (g), (aq). Reactants magnesium + lead nitrate Mg + Pb(NO3)2 Already balances. Mg(s) + Pb(NO3)2(aq) Products magnesium nitrate + lead Mg(NO3)2 + Pb Just add state symbols Mg(NO3)2(aq) + Pb(s) © Boardworks Ltd 2005
Activity • Below are some chemical equations where the formulae are correct but the balancing step has not been done. Write in appropriate coefficients (numbers) to make them balance. Reactants 2 AgNO3(aq) CH4(g) + Mg(s) 2 NaOH + Products CaCl2(aq) 2 O2(g) + Ca(NO3)2(aq) + 2 AgCl(s) CO2(g) Ag2O(s) + H2SO4(aq) + 2 H2O(g) MgO(s) + 2 Ag(s) Na2SO4(aq) + 2 H2O(l) © Boardworks Ltd 2005
Reacting Masses © Boardworks Ltd 2005
Conservation of Mass • New substances are made during chemical reactions • However, the same atoms are present before and after reaction. They have just joined up in different ways. • Because of this the total mass of reactants is always equal to the total mass of products. • This idea is known as the Law of Conservation of Mass. Reaction but no mass change © Boardworks Ltd 2005
Conservation of Mass • There are examples where the mass may seem to change during a reaction. • Eg. In reactions where a gas is given off the mass of the chemicals in the flask will decrease because gas atoms will leave the flask. If we carry the same reaction in a strong sealed container the mass is unchanged. Gas given off. Mass of chemicals in flask decreases HCl Mg 11.71 Same reaction in sealed container: No change in mass © Boardworks Ltd 2005
Reacting Mass and formula mass • The formula mass in grams of any substance contains the same number of particles. We call particles this amount of substance 1 mole. Atomic Masses: H=1; Mg=24; O=16; C=12; N=14 Symbol Formula Mass H2 1x2 MgO 24 + 16 CH4 12 + (1x4) HNO3 1+14+(3x16) Contains 1 mole of hydrogen molecules 1 mole of magnesium oxide 1 mole of methane molecules 1 mole of nitric acid © Boardworks Ltd 2005
Reacting Mass and Equations • By using the formula masses in grams ( moles) we can deduce what masses of reactants to use and what mass of products will be formed. Atomic masses: C=12; carbon + oxygen C + + 2 x 16 carbon dioxide O2 12 O=16 12g 32g CO2 12+(2x16) 44g So we need 32g of oxygen to react with 12g of carbon and 44g of carbon dioxide is formed in the reaction. © Boardworks Ltd 2005
Activity • What mass of aluminium and chlorine react together? Atomic masses: Cl=35.5; aluminium Al=27 + chlorine 2Al + 3Cl2 2AlCl3 2 x 27 + 3 x (2x35.5) 2x (27+(3x35.5) 213g 267g 54g aluminium chloride So 54g of aluminium react with 213g of chlorine to give 267g of aluminium chloride. © Boardworks Ltd 2005
Activity • What mass of magnesium and oxygen react together? Atomic masses: Mg=24; magnesium + oxygen O=16 Magnesium oxide Mg + O2 2 x 24 + 2x16 2x(24+16) 32g 80g 2 48g 2 MgO So 48g of magnesium react with 32g of oxygen to give 80g of magnesium oxide. © Boardworks Ltd 2005
Activity • What mass of sodium chloride is formed when sodium hydroxide and hydrochloric acid react together? Atomic masses: Na = 23 O = 16 H = 1 Cl = 35.5 Sodium + hydroxide + NaOH + hydrochloric acid HCl Sodium chloride + NaCl + 23+1+16 1+35.5 23+35.5 40g 36.5g water H2O 58.5g (2x1)+16 18g So 40g of sodium hydroxide react with 36.5g of hydrochloric acid to give 58.5g of sodium chloride. © Boardworks Ltd 2005
• It is important to go through the process in the correct order to avoid mistakes. Step 1 Word Equation Step 2 Replace words with correct formula. formula Step 3 Balance the equation. Step 4 Write in formula masses. masses Remember: where the equation shows more than 1 molecule to include this in the calculation. Step 5 Add grams to the numbers. © Boardworks Ltd 2005
Activity Reacting Mass and Scale Factors • We may be able to calculate that 48g of magnesium gives 80g of magnesium oxide – but can we calculate what mass of magnesium oxide we would get from burning 1000g of magnesium? There are 3 extra steps: Step 1 Will 1000g of Mg give more or more less MgO than 48g? Step 2 I need to scale up the 48g ? to 1000g. What scale factor does this give? 1000 = 20.83 48 Step 3 If 48g Mg gives 80g of MgO What mass does 1000g give? 20.83 x 80 Answer 1667g © Boardworks Ltd 2005
Activity • Mg + CuSO4 MgSO4 + Cu • 24 64+32+(4x16) 24+32+(4x16) 64 • 24g 160g 120g 64g What mass of copper will I get when 2 grams of magnesium is added to excess (more than enough) copper sulphate? Step 1 Will 2g of Mg give more or less Cu than 24g? Step 2 I need to scale down the 24g to ? 2g. What scale factor does this give? Step 3 If 24g Mg gives 64g of Cu What mass does 2g give? Answer less 2 = 0.0833 24 0.0833 x 64 5.3 g © Boardworks Ltd 2005
Activity • CaCO3 CaO + CO2 • 40+12+(3x16) 40+16 12+(2x16) • 100g 56g 44g • What mass of calcium oxide will I get when 20 grams of limestone is decomposed? Step 1 Will 20g of CaCO3 give more or less CaO than 100g? Step 2 I need to scale down the 100g to ? 20g. What scale factor does this give? Step 3 If 100g CaCo3 gives 56g of CaO What mass does 20g give? Answer less 20 = 0.20 100 0.20 x 56 11.2g © Boardworks Ltd 2005
Reacting Mass Industrial Processes • Industrial processes use tonnes of reactants not grams. • We can still use equation and formula masses to calculate masses of reactants and products. • We simply swap grams for tonnes. • E.g. What mass of CaO does 200 tonnes of CaCO3 give? CaCO3 100 CaO + CO2 56 So 100 tonnes would give 44 56 ? tonnes And 200 tonnes will give more Scale factor = 200/100 =2 56 So mass of CaO formed = 2 x? tonnes = 112 tonnes © Boardworks Ltd 2005
Activity • Iron is extracted from iron oxide Fe2O3 • E.g. What mass of Fe does 100 tonnes of Fe2O3 give? Fe2O3 + 160 3CO 2Fe 84 112 So 160 tonnes would give And 100 tonnes will give Scale factor = + 3CO2 + 132 112 tonnes ? less 100/160 =0.625 So mass of Fe formed = 0.625 x 112 ? = 70 tonnes © Boardworks Ltd 2005
Activity • Ammonia is made from nitrogen and hydrogen • E.g. What mass of NH3 is formed when 50 tonnes of N2 is completely converted to ammonia? N2 28 + 3H2 2NH3 6 34 So 28 tonnes would give 34 ? tonnes And 50 tonnes will give more than 28 tonnes Scale factor = 50/28 =1.786 So mass of NH3 formed = 1.786 x 34 ? = 60.7 tonnes © Boardworks Ltd 2005
Na is the symbol for? 1. 2. 3. 4. Nitrogen Nickel Neodynium Sodium © Boardworks Ltd 2005
Which of these does NOT exist as a diatomic molecule (2 bonded atoms)? 1. 2. 3. 4. Nitrogen Oxygen Calcium Chlorine © Boardworks Ltd 2005
How many oxygen atoms are represented in the formula Pb(NO3)2? 1. One 2.Two 3.Three 4.Six © Boardworks Ltd 2005
What is the formula mass of MgCl2 ? Mg=24 Cl=35.5 1. 2. 3. 4. 59.5 83.5 95 119 © Boardworks Ltd 2005
What is the formula mass of Mg(OH)2 ? Mg=24 O=16 1. 2. 3. 4. H=1 41 42 57 58 © Boardworks Ltd 2005
What is the percentage nitrogen in ammonium sulphate (NH4)2SO4? 1. 2. 3. 4. 21% 42% 63% 84% © Boardworks Ltd 2005
What is the formula of a compound containing 1.4g nitrogen and 3.2g of oxygen? (N=14 O=16) 1. N2O 2. NO 3. NO2 4. N2O3 © Boardworks Ltd 2005
What is the formula of a compound containing 6.5g zinc and 1.6g oxygen? (Zn=65 O=16) 1. ZnO 2. Zn2O3 3. ZnO2 4. Zn2O © Boardworks Ltd 2005
What is the formula of a compound formed between Cr3+ ions and O2- ions? 1. CrO 2. Cr2O3 3. CrO2 4. Cr3O2 © Boardworks Ltd 2005
What is the formula of a compound formed between Cr3+ ions and OH- ions? 1.CrOH3 2.Cr3OH 3.Cr(OH)3 4.Cr2OH3 © Boardworks Ltd 2005
What is the word equation for the reaction described below? A small piece of strontium metal was added to water. It fizzed giving off hydrogen gas leaving an alkaline solution of strontium hydroxide. 1.Strontium + water 2.Strontium + water 3.Strontium + water 4.Strontium + water hydrogen + strontium hydride oxygen + strontium hydroxide hydrogen + strontium hydrate hydrogen + strontium hydroxide © Boardworks Ltd 2005
What numbers a - d are needed to balance the equation? Strontium + water a Sr + b H2O 1 2 3 4 a=1 a=1 a=1 a=1 b=1 b=2 b=1 b=1 hydrogen + strontium hydroxide c H2 + d Sr(OH)2 c=1 c=1 c=2 c=1 d=1 d=1 d=1 d=2 © Boardworks Ltd 2005
What is the mass of 2 moles of magnesium nitrate Mg(NO3)2? 1. 2. 3. 4. 86g 134g 148g 296g © Boardworks Ltd 2005
How many moles of iron atoms is 280g of iron? (Fe=56) 1. 2. 3. 4. One mole Two moles Four moles Five moles © Boardworks Ltd 2005
When iron rusts it forms the iron oxide Fe2O3. What mass of oxygen reacts with 112g of iron? (Fe=56 O=16) 1. 1g 2. 16g 3. 48g 4. 168g © Boardworks Ltd 2005
Hydrogen reacts with chlorine to form hydrogen chloride HCl. H2 + Cl2 2HCl What mass of hydrogen chloride will be obtained from 4g of hydrogen gas? (H=1 Cl=35.5) 1 2 3 4 36.5g 73g 109.5g 146g © Boardworks Ltd 2005