Demonstrate an understanding of chemical ideas relating to acids and bases A.S.1.5 2014
States of Matter Fixed Shape
Particle theory • Matter is made up of tiny particles (Atoms & Molecules) • Particles are in constant motion. • Particles of Matter are held together by strong forces • Heat (energy) affects the movement of the particles. The higher the temperature, the faster the speed of the particles.
Structure of the atom • Nobel prize Chemistry 1908 • Atomic model 1911 • First person to transmute Nitrogen to oxygen 1919 • $100 note
ATOMS Atoms are the building blocks of all matter. An atom is made up of smaller bits called… Protons +ve Nucleus 1 Electrons -ve Outside 0 Neutrons neutral 1 Nucleus All atoms have a defined number of protons.
ELEMENTS An elementis a substance made up of only 1 type of atom. There are about 112 different atom types therefore there are 112 elements. These are shown on the periodic tableof the elements. On the periodic table each atom type has its information. For example… Atomic no. Symbol Name Mass no.
11 B 5 PERIODIC TABLE Atomic no. Any atom can be identified by the atomic no., the symbol or by the name. For instance... Symbol Name H 1 Iron 26 Magnesium Mg The information from the table can also be shown as:
11 B 5 WHAT IT MEANS The Atomic Number: = number of protons = number of electrons (as an atom has the same of each) The Mass Number: = number of protons + neutrons - why are electrons not included in the mass no? They have no mass! So for Boron… Protons = Electrons = Neutrons = What about Phosphorus? Protons = Electrons = Neutrons = 15 5 15 5 5.811 16
Learning Check Select the correct symbol for each: A. Calcium 1) C 2) Ca 3) CA B. Sulfur 1) S 2) Sl 3) Su C. Iron 1) Ir 2) FE 3) Fe
Learning Check Select the correct name for each: A. N 1)neon 2)nitrogen 3)nickel B. P 1)potassium 2)phlogiston 3)phosphorus C. Ag 1) silver 2)agean 3)gold
Isotopes Elements can occur with different from expected mass numbers. E.g. Carbon • The extra 2 neutrons increase the mass number but don’t alter its charge
Test Yourself • Explain why 12C and 13C are neutral and consider the atomic structure to discuss how the mass of each atom differs.
ELECTRON ARRANGEMENT Electrons are very fast moving. They are arranged in shells around the nucleus. The first shell fits… The second fits… The third fits… So the electron shell configuration for 12Mg would be… 2 e 8 e 8 e 2, 8, 2 What is the electron configuration of Li (2,1) Ca (2,8,8,2) P (2,8,5) What element is represented by 2,8,7 (Cl) 2,6 (O) 2,8,1 (Na)
GROUPS The columns in the periodic table are called groups. Groups of elements share similar reactivity. This is because they have the same number of valence electrons. As you go down a group the reactivity increases. Group 1 are the alkali metals properties: good conductors solid at room temperatures can be cut with a knife low densities and melting points Group 17 are the Halogens
Periods • The rows in the periodic table are called periods. • Atom’s size decreases from left to right in a given period
Learning Check A. Element in Group XVII, Period 4 1) Br 2) Cl 3) Mn B. Element in Group II, Period 3 1) beryllium 2) magnesium 3) boron
IONS An ion is an atom that has gained or lost electrons meaning it is negatively or positively charged. Atoms do this to get a full outer (valence) electron shell and so becomes more stable (less reactive). The atom will get a full outer shell the simplest way it can, e.g. for 12Mg: - Electron arrangement of 2, 8, 2 - it will LOSE 2 electrons (become 2, 8) - Now it has 10 electrons, but still has 12 protons. It has a 2+ charge. The ion is called Mg2+. Superscript is used for ion charges
IONIC COMPOUNDS The ions that have been formed are now attracted to oppositely charged ions. So Mg2+ will be attracted to Cl-. This forms an ionic compound. Naming rules: - The positive ion is first, and the negative second. - The negative ion ends in –ide, e.g. The sulfur atom becomes the sulfide ion. Exceptions: NO3- (nitrate) SO42- (sulfate) CO32- (carbonate) HCO3- (hydrogen carbonate)
Ionic Bonding • Na + Cl 2,8,1 2,8,7
IONIC FORMULAE So Mg2+ will be attracted to Cl-. Because Mg is 2+ and Cl is only 1-, Mg will attract 2 Cl’s. The compound formed will be MgCl2. The subscript shows that the are 2 Cl’s for each Mg. If the starting ions were Cu2+ and S2-, the 2 ions have the same charge. So each Cu will only attract 1 S. The compound formed will be CuS. There is never any charges on the final product - they balance out
Bases that dissolve in water are called alkalis. It is difficult to test the pH of bases that do not dissolve in water.
DIFFICULT ONES NO3 Mg NO3 What is the formula for Magnesium Nitrate? Find the 2 ions on your table of ions… Mg2+ and NO3- This means that there are 3 oxygens attached to the Nitrogen – don’t let them get lost! So for each Mg we will need 2 NO3’s: The shorthand way of writing this is: Mg(NO3)2 The brackets are needed to show that we want 2 of the whole thing – you always need them if you have 2 of an ion with more than 1 bit. (polyatomic ions) NH4+ and S2- Fe3+ and OH- Al3+ and SO42- = (NH4)2S = Fe(OH)3 = Al2(SO4)3
Brønsted – Lowry definedAcid/Base reactions • Involve the transfer of Hydrogen ions (H+) • H+ is a proton • Acids – donate H+ in solution • Water dissociates to form hydronium and hydroxide ions H3O+ and OH- • Bases – accept H+ in solution HCl(g) + H2O(l) H3O+ (aq) +Cl-(aq) NH3(g) + H2O(l) NH4+ (aq) +OH-(aq) Acid or Base?
Acid/Base reactions • Involve the transfer of Hydrogen ions (H+) • H+ is a proton • Acids – donate H+ in solution • Water dissociates to form hydronium and hydroxide ions H3O+ and OH- • Bases – accept H+ in solution HCl(g) + H2O(l) H3O+ (aq) +Cl-(aq) NH3(g) + H2O(l) NH4+ (aq) +OH-(aq) Water can act as both it is amphiprotic Acid or Base?
ACIDS AND BASES H2SO4 NaOH Sulphuric Acid Sodium Hydroxide HCl NH4OH Hydrochloric acid Ammonium Hydroxide Can be identified using INDICATORS. Universal indicator Litmus (paper or solution)
Acids • A dilute acid has lots of water and a small amount of acid • A concentrated acid has lots of acid and not much water so must be handled carefully • A strong acid (HCl) releases lots of H+ • A weak acid (ethanoic) releases fewer H+
INDICATORS Using small samples of the 2 types of indicator find out if the following are acidic, basic, or neutral. Red Red ACID Red Green NEUTRAL Blue Red Red ACID Red Red ACID BASE Blue Blue BASE Blue Blue
Acid Reactions • Acid + Base Salt + Water • Acid + Metal Salt + Hydrogen • Acid + Carbonate Salt + Water + Carbon Dioxide • Hydrochloric acids form CHLORIDE salts • Nitric acid forms NITRATE salts • Sulfuric acid forms SULFATE salts
METAL OXIDES & HYDROXIDES Metals form basic oxides and hydroxides. If bases dissolve in water they are called alkalis. When bases react with acids it is called a neutralisation reaction. General equation: Acid + Base Metal Salt + Water Word equation: Sulfuric acid + Copper Oxide Copper Sulfate + Water Symbol equation: CuSO4 + H2O H2SO4 + CuO
METAL CARBONATES AND HYDROGEN CARBONATES Carbonates have CO32- e.g. MgCO3 is Magnesium Carbonate. Hydrogen Carbonates (or Bicarbonates) have HCO3- e.g. Zinc Bicarbonate would be… Zn(HCO3)2 The reactions with acids have neutral products, but we also get… CO2 General equation: Metal Carbonate Salt + Water + CO2 Acid + Word equation: Hydrochloric acid + Magnesium Carbonate Magnesium Chloride + Water + Carbon Dioxide Symbol equation: 2 HCl + MgCO3 MgCl2 + H2O + CO2
Metal reactions General Equation Word Equation • Metal + Oxygen → Metal oxide • Aluminium + Oxygen → Aluminium oxide • 4Al + 3O2 → 2Al2O3 • Metal + Water → Metal hydroxide + Hydrogen • Aluminium + Water → Aluminium Hydroxide + Hydrogen • 2Al + 6H2O → 2Al(OH)3 + 3H2 • Metal + Acid → Metal salt + Hydrogen • Magnesium + Hydrochloric acid → Magnesium Chloride + Hydrogen • Mg + 2HCl → MgCl2 + H2 Formula Equation
METAL REACTIONS Metal + Oxygen Metal Oxide 1. METAL + OXYGEN Metals react in air to give metal oxides. Heating increases the rate of this reaction. Metal oxides are Basic, but only the first 2 groups of the periodic table are alkalis (bases that dissolve in water). An example: Magnesium is reacted in the air (with O2) to produce a white powder, which turns litmus paper blue. Write the word and balanced symbol equation for the reaction. Magnesium + Oxygen Magnesium oxide 2 Mg + O2 2 MgO General eqn: Ionic bond
Metal + Water H2 + a Hydroxide 2. METAL + WATER Metals react in water to give Hydrogen gas (H2) and a Metal Hydroxide. Reaction speed depends on the reactivity of the metal, but only the more reactive metals react with water. An example: Sodium reacts violently when placed in water. The gas produced sometimes explodes. As this occurs universal indicator changes from green to purple. Group 1 metal reactions Sodium + Water H2 + Sodium Hydroxide 2 2 Na + H2O H2 + NaOH 2 General eqn:
Metal + Acid H2 + a Salt 3. METAL + ACID Metals react in acid to give Hydrogen gas (H2) and a metal salt. Reaction speed depends on the reactivity of the metal. These ones react with acids. An example: Magnesium fizzes when placed in a test tube with Hydrochloric acid. The gas produced explodes with a squeaky pop. Magnesium + Hydrochloric acid H2 + Magnesium Chloride 2 Mg + HCl H2 + MgCl2 General eqn:
ALUMINIUM Aluminium is high on the reactivity series, but never seems to do anything. Why? Aluminium forms an oxide coating very quickly. Aluminum oxide is shiny and silver so it looks like the metal but it doesn’t react. That is why aluminium is used for many things even though it is reactive. This is worth remembering. Examiners love to ask about it.
THE GAS TESTS Hydrogen gas (H2) is colourless, odourless, less dense than air and neutral. How do we test for it? It burns with a distinctive “squeaky pop”. Try it. In a test tube add 2 mL (about 2cm) of HCl, and 1cm of Mg ribbon. Collect under thumb and explode! What type of reaction is this? Write the equation
Oxygen gas (O2) is colourless, odourless, the same density as air and neutral. How do we test for it? It relights a glowing splint. Try it. In a test tube add 2 mL (about 2cm) of Hydrogen peroxide (H2O2), and add a tiny pinch of Manganese dioxide. Collect under thumb and see how many times you can relight your splint.
Carbon Dioxide gas (CO2) is colourless, odourless, more dense than air and basic. How do we test for it? It turns limewater milky Try it. In a test tube add 2 mL (about 2cm) of HCl, and add a limestone chip (CaCO3). Bubble into limewater using a collection tube and observe over a couple of minutes. What type of reaction is this? Write the equation
Rates of Reaction • Factors increasing the rate of reaction • Surface area • Concentration • Temperature • Catalyst/Enzyme • Pressure
CORROSION Corrosion, or tarnishing, or oxidation is the name given to the (usually) slow reaction of metals to give a metal oxide. Rusting is the special name for the corrosion of iron into iron oxide (Fe2O3), or rust. For corrosion to occur there must be 2 other things present… Water (H2O) and Oxygen (O2)
cars and aeroplanes needed for spare parts are often stored in the desert because there is less moisture in the atmosphere slower rusting.
Anchor from the Empress of Asia Deep water has little dissolved oxygen and is very cold. Rust happens very slowly. Once iron is brought to the surface, however, it rusts very fast.
The nucleus ATOMIC STRUCTURE REVISION Recap: Atoms made of: Protons Neutrons Electrons Atoms become ions by gaining or losing electrons to get a full outer shell. As they are charged particles, ions are attracted to oppositely charged ions so that the charges are balanced. Cu2+ + O2- CuO Mg2+ + OH- Mg(OH)2