Concentration. Mass of solution (kg)

Transcription

1 Chem 2A/2B Term 2 Notes A 1 Coghlan Chemistry 2A/2B Term 2 Notes A Concentration The of dissolved in a particular of solvent or solution is called the. There are four main ways of expressing concentration; 1. grams per litre, g L percentage composition by mass. 3. parts per million, ppm. 4. moles per litre, mol L -1. Grams per litre This is the number of of dissolved per litre of. Percentage composition by mass Concentration(% by mass)= Mass of solute (g) x 100 Mass of solution (g) Wine, 12% alcohol, has g of ethanol, C 2 H 5 OH per g of wine. 3% Hydrogen peroxide solution has Vinegar contains 4.0% CH 3 COOH so there are of CH 3 COOH dissolved per of solution Parts per million ppm = Mass of solute (mg) Mass of solution (kg) For vinegar ppm = 4.0 x = ppm CH 3 COOH > 750 ppm NaCl in water is unfit for human consumption.

2 Chem 2A/2B Term 2 Notes A 2 Coghlan Moles per litre (the usual unit of concentration in Chemistry) The concentration or of a solution is the number of of dissolved per of. A 1.00 mol L -1 solution of NaCl contains ( )= g of NaCl in 1 litre of solution. 1.0 mol L -1 = 1.0 M Usual unit Laboratory use only A 2.00 mol L -1 H 2 SO 4 solution contains ( 2.00 x [{2 x 1.008} {4 x 16.00}] = 196 g L -1 H 2 SO 4 c = n V Where c concentration, mol L -1 n number of moles V volume, L Ex/ What mass of solid NaOH must be dissolved to make ml of a mol L -1 NaOH solution? Dilution This formula can only be used when you are required to dilute a solution. Where c 1 initial concentration, mol L -1 c 1 V 1 = c 2 V 2 V 1 initial volume, L c 2 final concentration, mol L -1 V 2 final volume, L Ex/ 185 ml of a 2.50 mol L -1 solution of nitric acid is to be diluted to 1.76 mol L -1. How much distilled water must be added to the original solution?

3 Chem 2A/2B Term 2 Notes A 3 Coghlan Physical and Chemical Changes A physical change occurs without the composition of the original substance i.e. the and of atoms/molecules/formula units remain the. A chemical change occurs when a substance with molecules/formula units with different is formed. A chemical change is characterised by one or more of the following; change Precipitate Smell change production - effervescence Physical Properties of Matter Determing these properties does not change the compostion of the substance. Chemical Properties of Matter Determing these properties does the chemical of the substance. AA Set Check this

4 Chem 2A/2B Term 2 Notes A 4 Coghlan Chemical Equations Reactant A(x) + Reactant B(y) Product C(z) + Product D(p) (s) solid (aq) aqueous product is in product is (g) gas (l) - liquid States are expected in tests, exams and assignments. Balancing Rules 1. The number of atoms of each element on both sides of the equation must be equal. 2. The total charge on both sides of the equation must be equal. 3. Equations are balanced by adding numbers at the front of formulae nowhere else. EC Set 6 Solubility Rules OK!!!! This is a list that tells you what ionic substances are when mixed together. These rules are always given to you in test or exam situations in both Yr 11 & 12. The list also gives you colours of ions and hence colours of precipitates. Precipitation reactions The solubility rules tell you which and will come together and form a solid ( ) when mixed in solution. Write the equation for any reaction that occurs when solutions of barium chloride and sodium sulfate are mixed.

5 Chem 2A/2B Term 2 Notes A 5 Coghlan Steps 1. Write down a list showing all species present. 2. Using solubility rules, determine reacting species (if any) and spectator ions (colours of spectator ions). 3. Overall ionic equation showing reacting species only show states (aq) or (s) and colour of precipitate. Exercise Write balanced ionic equations showing what happens when solutions of each of the following are mixed. Give the colours of any precipitates and write an observation for the reaction that does not involve observation of the precipitate. If there is no reaction, write N.R. 1. copper(ii) sulfate and sodium carbonate. 2. lead nitrate and barium chloride. 3. sulfuric acid and barium nitrate. 4. sodium phosphate and calcium chloride. 5. mercury(ii) nitrate and potassium iodide. 6. nickel sulfate and potassium hydroxide. 7. silver nitrate and rubidium phosphate. 8. sodium chloride and potassium sulfate. 9. mercury(i) nitrate and sodium chloride. 10. caesium chloride and silver nitrate. AA , Set 11 EC Set 20

6 Chem 2A/2B Term 2 Notes A 6 Coghlan Reaction Stoichiometry Stoicheion (Greek) - element Metron (Greek) - measure The calculation of quantitative relationships among elements and compounds as they undergo chemical reactions. Ex/ Zinc react with phosphoric acid to produce hydrogen according the to the reaction Zn(s) + H 3 PO 4 (aq) Zn 3 (PO 4 ) 2 (aq) + H 2 (g) If 7.50 moles of H 3 PO 4 fully react calculate the number of moles of a. Zn b. Zn 3 (PO 4 ) 2 c. H 2 that take part in the reaction. Step 1. Always write a balanced equation first. 3Zn(s) + 2H 3 PO 4 (aq) Zn 3 (PO 4 ) 2 (aq) + 3H 2 (g) 3 moles + 2 moles 1 mole + 3 moles Step 2. Start with what you know. n(h 3 PO 4 ) = 7.50 mol Step 3. Work out what you want to know. n(zn) = 3/2 n(h 3 PO 4 ) = 3/2 x 7.50 = 11.2 mol n(zn 3 (PO 4 ) 2 ) = 1/2 n(h 3 PO 4 ) = 1/2 x 7.50 = 3.75 mol n(h 2 ) = 3/2 n(h 3 PO 4 ) = 3/2 x 7.50 = 11.2 mol Always work in moles

7 Chem 2A/2B Term 2 Notes A 7 Coghlan Mass Mass Calculations Ex/ What mass of mercury can be produced by heating g of mercury(ii) oxide? Ex/ Zinc oxide (the white stuff on surfers faces) is neutralised by sulfuric acid. If 2.00 g of water are produced, find the mass of the zinc sulfate produced. Technique Balanced equation Mass of known Moles of known Moles of unknown Mass of unknown Mass Volume Calculations By experiment it has been found that the volume occupied by one of any gas at (standard temperature and pressure; 273 K and kpa) is 22.4 L. Molar volume of any gas = 22.4 L The equal volumes can be understood because in the phase the of gas are so apart they have no on one another. Ex/ Find the volume occupied at STP of 3.40 g of ammonia.

8 Chem 2A/2B Term 2 Notes A 8 Coghlan Ex/ 2.06 g of methane, CH 4, are completely burnt in air to form only water and carbon dioxide. Calculate the volume of carbon dioxide produced at STP. AA , Set Volume Mass Calculations Ex/ 12.7 L of oxygen measured at STP are required to totally burn some magnesium ribbon. Calculate the mass of a. magnesium burned and b. magnesium oxide formed. Volume volume Calculations Ex/ What volume of hydrogen and what volume of nitrogen is required to produce 20.0 L of ammonia, NH 3, at STP? EC Set 17, 18, 22 Semester 1 Examination will cover all the work we have covered up to this point.

9 Chem 2A/2B Term 2 Notes A 9 Coghlan Kinetic Theory of Gases 1. All gases consist of /molecules. 2. These particles are in constant. All motion at 273 o C. 3. is caused by collisions between the and the container. These collisions are (no energy loss). 4. is related to the E K of the particles (E K = ½ m v 2 ) 5. is related to the E K of the. Note: Gas particles show four types of energy energy kinetic energy kinetic energy energy (attraction and/or repulsion between particles). When a substance is, energy in the form of either E K and/or E P is to the making up the substance. is the energy that changes the energy of a substance. The energy is the total energy ( + E P ) of the substance. Temperature is a of the E K of the of the substance.

10 Chem 2A/2B Term 2 Notes A 10 Coghlan At the temperature, the velocity of a gas is than the velocity of a heavy gas. Consider H 2 and Cl 2 at the same temperature. EC Set 1 Gas Pressure - Boyle s Law As the on a gas, its volume decreases. Pressure is proportional to volume. Where P 1 initial pressure, kpa, mm Hg, atmospheres P 1 V 1 = P 2 V 2 P 2 final pressure, kpa, mm Hg, atmospheres V 1 initial volume, L, ml V 2 final volume, L, ml Only works if there is no change.

11 Chem 2A/2B Term 2 Notes A 11 Coghlan les_law_graph.html Ex/ A certain mass of gas has a volume of 7.40 L at mm Hg pressure. If it is compressed to 967 ml, find the compressing pressure. Ex/ By how much does the volume of a gas change if its pressure decreases by a factor of 0.68 with no change in temperature? Charles Law Volume and temperature As the temperature of a gas, its increases. Volume is directly to temperature.

12 Chem 2A/2B Term 2 Notes A 12 Coghlan Where V 1 = V 2 T 1 T 2 V 1 initial volume, L, ml V 2 final volume, L, ml T 1 initial absolute temperature, K T 2 final absolute temperature, K works if there is no change. Ex/ To what temperature must 72.3 L of O 2 at 13.0 o C be heated to treble its volume provided pressure remains constant? Constant Volume Law As the temperature of a gas, its increases. Pressure is to temperature. P 1 = P 2 T 1 T 2 Where P 1 initial pressure, kpa etc.

13 Chem 2A/2B Term 2 Notes A 13 Coghlan P 2 final pressure, kpa etc. T 1 initial absolute temperature, K T 2 final absolute temperature, K Only works if there is no change. Combined Gas Law As the temperature of a gas increases, its pressure and its volume. Pressure is proportional to temperature and proportional to. P 1 V 1 = P 2 V 2 T 1 T 2 Where V 1 initial volume, L, ml V 2 final volume, L, ml P 1 initial pressure, kpa etc. P 2 final pressure, kpa etc. T 1 initial absolute temperature, K T 2 final absolute temperature, K Ex/ A He weather balloon has a volume of 38.6 L at 20.0 o C and mm Hg pressure. It is released and bursts when the temperature was 40.0 o C and pressure 80.0 mm Hg. What was its volume just prior to bursting?

14 Chem 2A/2B Term 2 Notes A 14 Coghlan Ex/ 20.0 ml of ethene (C 2 H 4 ) is burnt in 80.0 ml of oxygen gas both at o C and kpa. Calculate a. the volume composition of the final mixture when the original conditions of temperature and pressure are restored b. the total volume occupied by the mixture at STP. Real Gases A gas behaves and obeys the laws (and molar volume) if there is force acting. Gases do not behave ideally if T >>> 100 o C (T >> BP) T <<< 100 o C P >>> kpa Avogadro s Hypothesis Equal volumes of gases under the same of and contain the same of molecules. Molar volume of any gas = 22.4 L n = V_ 22.4

15 Chem 2A/2B Term 2 Notes A 15 Coghlan States of Matter Matter exists in four states, solid,, gas and. The last state only occurs at very temperatures and is not in the scope of our study. Property Solid Liquid Gas Shape Volume Compressibility Diffusion Diagram Solids and Liquids Liquids The which make up the liquid may be o liquid. o, paraffin. o molten. Because of the intermolecular, there are intermolecular. If a L changes to a G, these forces must be overcome so when a L G (, ) is required to overcome the intermolecular forces. This energy actually the intermolecular distance. If this distance is enough, a is formed.

16 Chem 2A/2B Term 2 Notes A 16 Coghlan L Potential Energy No temperature change G Temperature ( o C) (101.3 kpa) Time The required to change a liquid to a gas with no change in is called the heat of. H 2 O(l) kj H 2 O(g) (101.3 kpa) H 2 O(g) H 2 O(l) kj (101.3 kpa) Solid + E P Liquid Latent heat of fusion H 2 O(s) kj H 2 O(l) (At the same temperature) (101.3 kpa) Evaporation Occurs at temperature In a system pressure In an open system, the equilibrium will be disturbed and particles will. The high E K particles will evaporate and therefore the E K of the remaining particles and the of the liquid decreases.i.e. Evaporation causes cooling. Note: Addition of in a liquid raises its and decreases its. salty water boils above 100 o C; salt on snowy roads decreases the MP so the ice melts.

17 Chem 2A/2B Term 2 Notes A 17 Coghlan Changes of Phase Heating Curve for Increasing E P * Increasing E K # water Temperature Time Vaporisation Freezing Melting Summary A B C D A constant, E P B E K, E P (essentially) C E K constant, D E K, E P

18 Chem 2A/2B Term 2 Notes A 18 Coghlan Vapour Pressure When P is constant P total = P atmos + P H2O(g) This P H2O(g) is the pressure at a temperature. At constant presssure, a physical exists. Number of molecules = Number of molecules. Vapour pressure depends on of liquid some liquids have higher intermolecular forces than other liquids and hence vapour pressure. Vapour pressure does not depend on the because each gas behaves independently. Boiling Boiling occurs when vapour pressure equals external pressure. At the surface of the boiling water, P bubble = P atmos boiling For H 2 O at 200 kpa BP = 120 o C kpa BP = 100 o C 78 kpa BP = 93 o C (Top of Mt. Kosciusko). Boiling is helped by sites on the surface of the boiling vessel these can be, scratches or otherwise spots on the surface. The presence of salts or undissolved solids the vapour pressure and hence BP.

19 Chem 2A/2B Term 2 Notes A 19 Coghlan Solutions A solution is a mixture usually in phase. Note 1. All gaseous are homogeneous i.e. solutions. 2. solutions do exist opal,, obsidian. Liquid solutions Liquid in Liquid Solid in Liquid Solutions. Gas in Liquid is the liquid. is that which in the liquid. amounts of dissolved causes differing physical of the solution. conductivity,,, BP. A solution is one which contains as much dissolved as at that. At saturation; Number of potassium permanganate units dissolving = Number of potassium permanganate units crysallising. A physical is reached. An solution is not in equilibrium.

20 Chem 2A/2B Term 2 Notes A 20 Coghlan Factors affecting solubility 1. Temperature generally for solutes, as T while for solutes, solubility as T. 2. of solute and solvent. This includes such things as size and polarity of. 3. over the liquid this only applies if the solute is a. Units of solubility g of solute per 100 g of solution. At 20 o C, the solubility of NaCl in H 2 O is 35 g per 100 g of solution. Molar heat of solution The in water process always has an energy associated with it. The lattice needs to and the between the and water molecules tends to energy. The energy involved or molar heat of solution is the energy either or when one of the dissolves in water. Electrolytes When is the solvent for a solute, an solution is formed. NaCl(s) Na + (aq) + Cl - (aq)

21 Chem 2A/2B Term 2 Notes A 21 Coghlan The that already existed in the ionic lattice have not the solution has only up the lattice and allowed the to move from their lattice. The process is called. Such a solution will now conduct because it has charge (ions). Solutions that conduct electricity are called. Strong electrolytes are substances that exist essentially as in solution. All soluble compounds are electrolytes. Ionic substances like AgCl and Mg(OH) 2 that are basically insoluble are still considered strong electrolytes because the small amount that does dissolve completely. like HCl, H 2 SO 4, HNO 3, HBr, HI, HClO 4 are because they fully in solution. HCl(l) H + (aq) + Cl - (aq) The ions did already exist in the liquid. The process has the bond and produced the that are now free to move in solution. The process is called. Weak electrolytes are substances which only produce a small of their total as ions in solution and so are conductors.

22 Chem 2A/2B Term 2 Notes A 22 Coghlan < 1% CH 3 COOH (l) H + (aq) + CH 3 COO - (aq) NH 3 (g) CO 2 (g) Non-electrolytes do not produce charge and do not conduct in any form. Most substances fall into this category. is classified as a non-electrolyte. Concentration The of dissolved in a particular of solvent or solution is called the. There are four main ways of expressing concentration; 5. grams per litre, g L percentage composition by mass. 7. parts per million, ppm. 8. moles per litre, mol L -1. Grams per litre This is the number of of dissolved per litre of. Percentage composition by mass Concentration(% by mass)= Mass of solute (g) x 100 Mass of solution (g) Wine, 12% alcohol, has 12 g of ethanol, C 2 H 5 OH per 100 g of wine.

23 Chem 2A/2B Term 2 Notes A 23 Coghlan 3% Hydrogen peroxide solution Vinegar contains 4.0% CH 3 COOH Parts per million ppm = Mass of solute (mg) Mass of solution (kg) For vinegar ppm = 4.0 x = CH 3 COOH > 750 ppm NaCl in water is unfit for human consumption. Moles per litre The concentration or of a solution is the number of of dissolved per of. A 1.00 mol L -1 solution of NaCl contains ( )= 58.4 g of NaCl in 1 litre of solution. 1.0 mol L -1 = 1.0 M Usual unit Laboratory use only A 2.00 mol L -1 H 2 SO 4 solution contains ( 2.00 x [{2 x 1.008} {4 x 16.00}] = 196 g L -1 H 2 SO 4 c = n V Where c concentration, mol L -1

24 Chem 2A/2B Term 2 Notes A 24 Coghlan n number of moles V volume, L Ex/ What mass of solid NaOH must be dissolved to make ml of a mol L -1 NaOH solution? Exercise 1. What mass of solute is required to prepare (a) ml of 0.10 mol L -1 NaOH solution? (b) cm 3 of 1.00 M H 2 SO 4 solution? (c) 25 ml of mol L -1 Ba(OH) 2 solution? (d) 15 ml of 1.0 x 10-4 mol L -1 C 12 H 22 O 11 solution? 2. Calculate the concentrations of the following solutions; (a) 10.0 moles of HCl in 2.00 L of solution. (b) 1.7 g KI in ml of solution. (c) 50.0 g NaOH in L of solution. (d) 17.0 g NH 3 in ml of solution. 3. How many moles in (a) 2.0 L of 3.0 mol L -1 HCl? (b) 250 ml of 1.50 mol L -1 K 2 CO 3? (c) 40 ml of mol L -1 KMnO 4? (d) 25 ml of 0.40 mol L -1 NaOH? (e) 625 ml of 0.20 mol L -1 HNO 3? 4. Calculate the concentrations in (i) mol L -1 (ii) g L -1

25 Chem 2A/2B Term 2 Notes A 25 Coghlan (iii) % by mass (iv) ppm of (a) 0.50 moles of KCl dissolved in 620 ml of solution. Density of KCl = 1.40 g ml -1 (b) 1.37 moles of NaOH dissolved in 1.23 L of solution. Density of NaOH = 1.32 g ml -1 Dilutions When a solution is diluted by adding water, the number of moles of solute remains. So, you can find n = cv for the original solution, and then c new = n V new OR c 1 V 1 = c 2 V 2 Where c 1, V 1 initial concentration and volume c 2, V 2 final concentration and volume Ex/ What volume of distilled water must be added to 15.0 ml of a mol L -1 KOH solution to reduce its concentration to mol L -1? EC Set 21