ammonia molecules (NH3) do. Mark the following sentences as true (T) or false (
F). -Intermolecular forces are formed among the atoms of water molecules.
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Practice I: Chemistry IGCSE 1) Explain the following processes related to changes of states of matter. -Melting: .................................................................................................................................. -Vaporization: ........................................................................................................................... -Freezing: .................................................................................................................................. -Condensation: .......................................................................................................................... -Sublimation: ............................................................................................................................. 2) Complete the following sentences with proper arrows. Atoms in a solid Atoms in a liquid Atoms in a gas
...move very fast. ....can only vibrate but not move. ....move fast.
3) Describe what is meant by diffusion of a liquid or a gas. .................................................................................................................................................... .................................................................................................................................................... .................................................................................................................................................... 4) The atom is composed by three types of particles: protons, neutrons and electrons. Mark the following sentences as true (T) or false (F). -Electrons are particles with positive charge. -Protons are particles with positive charge. -Neutrons are neutral particles. -The mass of an electron is similar to the mass of a proton. -The mass of a neutron is similar to the mass of a proton. -Electrons are light particles. -Neutrons and protons are heavy particles. 5) The symbol of the carbon atom is What is the atomic number of carbon? .............. What is the mass number of carbon? ................. How many protons does the carbon atom have? ......... How many neutrons does the carbon atom have? ....... 6) Remind that the first electronic shell can contain up to 2 electrons and that the second and third electronic shells can contain up to 8 electrons each. Draw the electrons in the following representation of the oxygen atom, which has atomic number of 8.
7) Complete the following sentences with proper arrows. In the covalent bond In the ionic bond In the metallic bond
...some electrons are free to move forming a “sea of electrons”. ...some electrons are shared between two atoms. ...one atom gives an electron and another one takes it.
8) A representation of the methane molecule (CH4) is as follows. Which type of bond does methane have? ....................... How many of these bonds are present in the methane molecule? ........
9) Classify these ions into cations or anions, then try to write the formula and the name of the ionic compound that can be formed. Na+ Cl-
Type of ion .................. ..................
Ca2+ F-
.................. ..................
Formula of the ionic compound
Name of the ionic compound
.............................
...................................
..............................
....................................
10) Molecules of liquid water interact each other by means of intermolecular forces. Also liquid ammonia molecules (NH3) do. Mark the following sentences as true (T) or false (F). -Intermolecular forces are formed among the atoms of water molecules. -Intermolecular forces are formed among the molecules of water. -Intermolecular forces are weak forces. -When heating liquid water to form gas we break the covalent bonds. -Intermolecular forces form between electron rich parts of the molecules and electron deficient ones. -Ammonia molecules have a boiling point of -33ºC while water molecules have a boiling point of 100ºC. Intermolecular forces in ammonia are weaker as compared to the ones in water.
Practice II: Chemistry IGCSE 1) The figure below represents a type of solid we have studied.
Fill these sentences with appropriate words: -This solid is an ............. compound. -This solid is made up with ............ that have positive charge and ............ that have negative charge. -The melting and boiling points of this solid are ............. -This solid .............. conduct electricity and heat in solid state. 2) The figure below represents a type of solid we have studied.
Fill these sentences with appropriate words: -This solid is a ............. compound. -This solid is made up with ............ that have positive charge and ............ that have negative charge and are free to move. -The melting and boiling points of this solid are ............. -This solid ......... conduct electricity and heat in solid state. 3) Complete the following table: Type of solid Ionic Metallic Covalent Molecular
State at room temperature
Melting and boiling points
Examples
4) The figure below represents a molecular solid, in this case it is water in form of ice H2O(s). Fill the gaps naming the type of bond (or force) that is present inside the molecules of water and also among the molecules of water: Which type of bond is the strongest one? Why the hydrogen atoms of a molecule of water are close to the oxygen atoms of other molecules of water?
5) Write names and formulas for these ionic compounds: Name
Formula
NaCl
Calcium chloride
MgCl2
Sodium sulfate
BeCl2
Sodium nitrate
CaSO4
Iron (III) chloride
Fe(NO3)3
Copper (II) fluoride
CuSO4
Tin (IV) oxide
NaF
Lead (II) chloride
MgF2
Aluminum phosphate
6) Mark the following sentences as true (T) or false (F). -Diamond is made of carbon atoms and represents a covalent solid. -Carbon atoms in diamond are joined together by using ionic interactions. -Diamond has a low melting point. -Diamond does not conduct electricity. 7) Symbol Si(s) represents silicon in its solid state. Write down what is meant by the following symbols of elements or molecules: H2O(l) represents water in ..................
H2(g) represents hydrogen in ........................
Au(s) represents gold in .....................
NaCl(aq) represents sodium chloride in .....................
Practice III: Chemistry IGCSE 1) We want to study the reaction rate of the process: CaCO3(s) + HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l) For doing that we measure the concentration of carbon dioxide over time, obtaining the following curve:
a) Draw in the same figure a similar curve representing the concentration of hydrochloric acid over time. b) How these factors will affect the reaction rate? -Increase of temperature: ........................................ -Increase of hydrochloric acid concentration: ................................... -Addition of a catalyst: .......................................... 2) Explain what is meant by theory of collisions and by activation energy. ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 3) Mark as true or false the following sentences concerning the speed of reactions: The rate of a reaction is the same along all time. The rate of reaction is higher in the first steps of the reaction. At the end of the reaction, the reaction rate is null. A catalyst does react with the reactants. Catalysis is an important industrial process. An explosion is a very slow chemical reaction. The oxidation of iron is a very fast chemical reaction. The catalysts finds an alternative route of the reaction with higher activation energy. 4) Name these oxides, left for metallic oxides, right for non-metallic ones: Na2O ...................................
CO2 ................................
CaO .....................................
SO3 ................................
SnO ......................................
NO ..................................
5) What is acid rain, and what is the chemical agent most involved in that effect? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................
6) Write down two example reactions in which a metal oxidizes: ................................................................................................................................................................ 7) Concerning the reactivity series, order the following metals from most to least reactive: Li, Cu, Ca, Au : ................................................... 8) The reaction Mg(s) + CuSO4(aq) → MgSO4(aq) + Cu(s) is a redox reaction. a) What is the expectator ion? ........................................ b) What is the reaction of oxidation in its ionic form? .......................................................... c) What is the reaction of reduction in its ionic form? .......................................................... d) How many electrons are involved in this reaction? ........................................................... 9) Balance and put generic names to the following chemical reactions: CH4 + O2 → CO2 + H2O SO2 + H2O → H2SO3
..........................................................
CaO + H2O → Ca(OH)2 N2 + O2 → NO3
.....................................................
......................................................
...................................................................
H2O2 → H2O + O2
...............................................................
Na + H2O → NaOH + H2
.................................................
Mg + H2O → Mg(OH)2 + H2
...............................................
Practice IV: Chemistry IGCSE 1) Follow the example and put the names of these acids: Element F fluorine Cl .......... Br .......... I .............
Anion F- fluoride .................. .................. ..................
Acid HF hydrofluoric acid ................................. ................................. ..................................
2) Classify these substances into acid, neutral or basic according to the pH: Lemon juice Pure water Orange juice Bleach Blood
pH=2.3 pH= 7.0 pH=3.0 pH=10.7 pH=7.35
............. ............. ............. ............. ..............
3) Describe what is an acid and a base using the Brönsted-Lowry theory, and put some examples. ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 4) Acids can be used to react with metals to form a salt and hydrogen gas. See the example and write the rest of reactions, also balance them if needed. Ca + HCl → CaCl2 + H2 Na + HCl → Mg + HCl → Na + H2SO4 → K + H2SO4 → Mg + H2SO4 → 5) The following reaction represents a neutralization reaction. Explain what is happening in terms of proton transfer: NH3 + HCl → NH4Cl ................................................................................................................................................................ ................................................................................................................................................................ ............................................................................................................................................................... 6) Neutralization reactions are used to form salts, balance the following reactions: NaOH + HCl → NaCl + H2O Ca(OH)2 + HCl → CaCl2 + H2O KOH + HF → KF + H2O Ba(OH)2 + H2SO4 → BaSO4 + H2O LiOH + H2SO4 → Li2SO4 + H2O
7) Write down, in the form of a chemical reaction, this sentence: “We can obtain sodium nitrate salt by making the reaction of sodium hydroxide with nitric acid”. ................................................................................................................................................................ 8) Using the table of your book regarding the solubility of salts, classify into soluble and insoluble: NaCl : CaCl2 : AgCl : BaSO4 : CaCO3 :
PbCl2 : Pb(OH)2 : ZnCO3 : NH4Cl : KNO3 :
9) Write the names of the salts shown in exercise 8. ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 10) What is a titration? Write down an example reaction in which we can use this process to form an insoluble salt (a precipitate). Also complete the picture indicating the reactants and the product.
................................................................................................. ................................................................................................. ................................................................................................. ................................................................................................. ................................................................................................. ................................................................................................. ................................................................................................. .................................................................................................
Starting point
Ending point
Practice V: Chemistry IGCSE 1) How can we obtain pure water from sea water? And alcohol from a mixture of alcohol and water? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 2) Wines of bad quality contain colorants which are additives. We want to test for the quality of three wines (W1, W2, W3) and we have in the lab some pure colorants (C1, C2, C3). For doing that we use a chromatography obtaining the following result: Which colorants contain wine 1 and wine 3? .................................................................................................... What is the wine of best quality? Why? ....................................................................................................
3) Propose a simple experiment or process to identify the following substances: Sodium cation in NaCl(s) ........................................................................................................................ Carbonate in a solution .......................................................................................................................... Chloride in a solution of NaCl(aq) ........................................................................................................... 4) Complete the sentences with proper arrows: Neon is a Palladium is a Sodium is an
.....transition metal. .....noble gas. .....alkaline metal.
5) Mark the sentences as true (T) or false (F): Potassiums reacts very strongly with water. Silver reacts very strongly with water. Cesium is more reactive than sodium. Fluorine at room temperature is a gas. Chlorine at room temperature is a liquid. Bromine at room temperature is a liquid. 6) Write down the names of three metals which are liquid at room temperature. ................................................................................................................................................................
7) Metals of group 1 react with water forming hydroxides and hydrogen gas. See the example and complete the next reactions: Na + H2O → NaOH + H2 Li + H2O → K + H2O → 8) Halogen elements tend to form anions gaining one electron X + 1e- → XWe know that fluorine is more reactive than chlorine and that the atomic size of fluorine is smaller compared to the atomic size of chlorine. Explain why fluorine is more reactive than chlorine in terms of electron attraction. ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 9) Write a definition of the process named electrolysis. ................................................................................................................................................................ ................................................................................................................................................................ 10) In the electrolysis of NaCl(aq) we obtain chlorine (Cl2) and hydrogen (H2), complete and balance the following reactions and indicate which one is a reduction and which one is an oxidation. Also indicate the states of each substance. Cl- (aq) → ............... H+(aq) + ........ → ................... Complete these sentences with proper arrows: Chloride is going to react in the Hydrogen cation is going to react in the Cation hydrogen Anion chloride
....cathode. .....anode.
....gives electrons to the ....takes electrons from the
......anode . .....cathode.
Practice VI: Chemistry IGCSE 1) What is an exothermic reaction? And and endothermic reaction? What is the sign of the enthalpy of an exothermic reaction? And of an endothermic reaction? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 2) Draw four energy diagrams for the following reactions. A: Exothermic reaction with high activation energy. B: Exothermic reaction with low activation energy. C: Endothermic reaction with high activation energy. D: Endothermic reaction with low activation energy.
3) What does the Le Chatelier principle state concerning reversible reactions? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 4) The following general reaction is reversible A(g) + 2B(g) ↔ C(g) ∆H= -300 KJ/mol. Explain how the percentage of C(g) in the equilibrium mixture will change by modifying these conditions: a) Increase of temperature: ................................................ b) Increase of pressure: ...................................................... c) Addition of a catalyst: .................................................... 5) The following general reaction is reversible A(g) + B(g) ↔ 3C(g) ∆H= 400 KJ/mol. Explain how the percentage of C(g) in the equilibrium mixture will change by modifying these conditions: a) Increase of temperature: ................................................ b) Increase of pressure: ...................................................... c) Addition of a catalyst: .................................................... 6) What is the name of the chemical process used to form ammonia? Write down the reaction of ammonia formation indicating the states of each substance. ................................................................................................................................................................ ................................................................................................................................................................
7) What is the use of sulfuric acid? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 8) In the electrolysis of sodium chloride in solution NaCl(aq) three important substances are formed. Identify the three substances according to this information: Substance A is a colorless gas → Substance B is a base formed with the cation → Substance C is a green toxic gas used to form bleach→ 9) What is the natural source (mineral) of aluminum? Write also the chemical name and the chemical formula of this material. What we have to do to obtain aluminum in its metallic state Al(s), a reduction or an oxidation of the mineral? ................................................................................................................................................................ ................................................................................................................................................................ ................................................................................................................................................................ 10) What is steel and what are the advantages of steel in front of iron? ................................................................................................................................................................ ................................................................................................................................................................
Practice VII: Chemistry IGCSE 1) Write down structural formulas for the following organic compounds: Methane Butane 2-Butene 2,2-Dimethylpentane 2) Write the names of the following organic compounds: CH3-CH2-CH2-CH2-CH2-CH3
CH2=CH2
CH3-CH2-CH-CH2-CH3 | CH3
CH3-CH2-CH=CH2
CH3-CH=CH-CH2-CH2-CH3
CH3-CH2OH
3) What is the molecular formula of the alkane formed with 20 carbon atoms? And with 10 atoms? ................................................................................................................................................................ 4) Alkanes react with oxygen in a very exothermic reaction called combustion, products are carbon dioxide and water. Write the reactions of combustion of the following compounds (balance them when needed): Combustion of butane: ........................................................................... Combustion of propane: .......................................................................... 5) Complete the following reactions of petroleum cracking: C15H32 → 2C2H4 + ........
C12H26 → 2C2H4 + ........
6) What type of molecule is nylon? What are the uses of nylon? Say another example of the same type of molecule. ................................................................................................................................................................ ................................................................................................................................................................
Practice VIII: Chemistry IGCSE 1) Methane (CH4) reacts with oxygen in an exothermic reaction called combustion. Products are carbon dioxide and water. The balanced reaction is shown: CH4(g) + 2O2(l) → CO2(g) + 2H2O(l) Relative atomic masses of the elements are: MC=12 g/mol, MH=1 g/mol, MO=16 g/mol. a) Calculate the molecular weight of methane, water, carbon dioxide and oxygen gas. b) Calculate the percentage of carbon which is in methane and in carbon dioxide. c) We obtain 1000 g of methane from a chemical provider, and we use enough oxygen to make the reaction possible. How many grams of carbon dioxide are we going to obtain? d) If we measure the carbon dioxide at normal conditions, how much volume of carbon dioxide in gas phase are we going to obtain? Consider than, in this case, 1 mol of gas has a volume of 22.4 dm3. e) At the end of the experiment we measure the mass of carbon dioxide, and we get 2500 g. What is the yield of this reaction?
Practice IX: Chemistry IGCSE 1) The electrolysis of magnesium chloride consists in these reactions: Mg2+(aq) + 2e- → Mg(s) 2Cl-(aq) → Cl2(g) + 2ea) What is the reaction of oxidation? And the reaction of reduction? b) If we use an electric current of 10 A during 100 s, how many grams of solid magnesium are we going to obtain in the cathode? c) Using the same conditions, how many grams of chlorine gas are we going to obtain in the anode? MMg=24.30 g/mol. MCl=35.5 g/mol. 2) Calculate an approximate value of the enthalpy of the reaction of ammonia formation: N2(g) + 3H2(g) → 2NH3(g) Use the information below: Bond
∆H (kJ/mol)
N≡N
945
H-H
436
N-H
388
Is the reaction exothermic or endothermic? 3) Calculate the amount of energy necessary for heating up 2 kg of liquid water from 20ºC to 60ºC. Consider that the specific heat of water is C=4180 J / kg ºC. 4) We use an acid-base titration to calculate the concentration of NaOH. For that we get HCl in a concentration of 0.5 mol/dm3 and we waste at the end of the experiment 0.2 dm3 of the acid. a) Write the reaction of neutralization between NaOH and HCl. b) Draw the apparatus we need for doing the titration, indicate where is the HCl and the NaOH. c) Calculate the concentration of the NaOH if the experiment was made using 0.1 dm3 of NaOH.
