Matter. February 16, Science 10/20 Chemistry Review Mixtures. Element. Unit B - Chemistry. Compound. Pure Substances

Transcription

1 Unit B - Chemistry Science 10/20 Chemistry Review Mixtures Matter Pure Substances Homogeneous Heterogeneous Compound Element What are the vertical columns on the periodic table called? Groups or Families What are the horizontal rows on the periodic table called? Periods Terms to know: Metals Non-Metals Metalloids

2 malleable Shiny Dull Mostly Solid elements Ductile Mostly Gases Poor Conductor Looking closer at matter... Atoms are the smallest unit of an element. Atoms can be broken down into: 1. Electron 2. Proton 3. Neutron e - p + nº Good conductor METALS NON METALS Compound - union of two or more elements. Bonds between atoms in a compound can be: 1. Ionic - transfer of electrons; electrostatic force. Ex. 2. Covalent - sharing of electrons Bond Song Ex. Common Types of Bonds Video Clip Who remembers how to name? 1. Identify substance class you are working with. (Ionic, Molecular, Acid, Element, Atom..) 2. If Ionic - recall binary, multivalent, polyatomics - Criss/Cross Rule 3. If Molecular - did you have to memorize it? If now - prefix system 4. Acids - use naming rules in databook 5. Element/Atom - is it polyatomic? Use databook!

3 Naming Review: Ionics (binary, multivalent, polyatomic & hydrates) Molecular (memorized, prefix system) Acids (Rule I, II, III) Molar mass - Use your databook. Ex. Water Ex. Ammonium sulfate Moles Moles Mass Mass Moles N A Ex. representative unit Ex. What is the mass of 4.65 X 10 2 mol of glucose? Ex. What is the chemical amount of 6.7 g of cobalt (II) chloride? Formula

4 Types of Reactions Video Clip Review of Chemical Reactions and Balancing Equations: There are 6 types of chemical reactions: Simple composition or formation: Simple decomposition: (this is when a compounds breaks into smaller parts) compound element + element element + element compound Combustion: (the burning of a substance in O2) Single replacement: (1 element replaces the element in a compound) element + compound new element + new compound substance + O2 oxides note: if the substance has C, CO2 is produced if the substance has H, H2O is produced if the substance has S, SO2 is produced, if the substance has N, NOx is produced

5 Double replacement: (all the ions switch partners) compound + compound new compound + new compound Other Balancing equations: Rules: 1. Law of Conservation of Mass 2. Write the correct chemical formulas for the reactants and products. Balancing Practice: 1. Combustion of Methane 2. Zinc metal placed in hydrochloric acid. 3. Identify all the atoms on the reactant side and identify all the similar atoms on the product side. 4. Compare the numbers of atoms on each side and try to balance them by adding coefficients on each side. 3. lead (II) iodide solution reacts with potassium chloride solution. ** Combustion -- Use the CHO rule!

6 February 16, 2015 Section 1.1 Products of Combustion Reactions Combustion Reactions A combustion reaction is a chemical reaction that occurs in the presence of oxygen and results in the production of an oxide and water with the emission of energy An important example of a combustion reaction is the combustion of a hydrocarbon, like a fuel or cellular respiration. IMP: Product = Emission! Examples of Combustion! Demo - Burning a candle/food coloring/water/pie plate - cellular respiration - pg. 155 part 1 - burning a metal (Mg) Page 156 Balancing Combustion Reactions Page 156 -The combustion of carbon compounds, like wood or other forms of biomass (plant matter) or hydrocarbons, like methane or natural gas, results in the production of carbon dioxide and water. Carbon dioxide, CO2, is an important gas with respect to life on Earth and is involved in the carbon cycle as follows: Cellular respiration - product Photosynthesis - reactant Carbon dioxide is also a greenhouse gas, which is a gas in the atmosphere that has the ability to absorb heat or thermal energy, preventing the loss of Earth s thermal energy into space. This is believed to be the major cause of global warming. Greenhouse Effect Video Clip Global Warming & C Cartoon Carbon Dioxide Oxides of Carbon

7 Oxides of Carbon monoxide, CO: - Result of the incomplete combustion of a carbon compound due to the limited supply of oxygen. - Formed during the incomplete combustion in automobiles and is very dangerous to your health. - CO is very similar to the oxygen molecule and competes with oxygen for binding sites on the hemoglobin molecule. Thus, in the presence of carbon monoxide, your body will not receive a sufficient supply of oxygen, resulting in cell death. Video Clip 1:31min Oxides of Sulfur - Many fuels contain sulphur, like coal crude oil and tar sands, and also natural gas, which contains sulphur, in the form of hydrogen sulphide, H 2S gas, or sour gas. This gas is toxic to humans and also forms an acidic solution if combined with water. Removing sour gas from natural gas is called sweetening - Sometimes gas wells, release a small quantity of natural gas that is ignited during a flaring process. This process releases sulphur dioxide and sulphur trioxide into the atmosphere. Flaring Video 2:30 min Oxides of Sulphur Oxides of Nitrogen - Nitrogen, N 2(g), comprises about 78% of our atmosphere. - If a combustion reaction temperature is high enough, C, (in automobiles and furnaces then the nitrogen gas present in air, will react with the oxygen to produce oxides of nitrogen; NO (g) - nitrogen monoxide NO 2(g) - nitrogen dioxide These are commonly called NO x compounds. Page 161

8 Oxides of Metals - Metals, like mercury and lead, are also emissions of combustion reactions and can combine with oxygen to produce metal oxides. Monitoring Emissions in Alberta e30/unitab_cd/source/unitb/unitbmm.html - Video Clip from Textbook CD Particulates - Other emissions of a combustion reaction may include small particles of matter, like soot, ash, and even organic compounds, like benzene (a carcinogen). Section 1.2: Chemistry of Acids and Bases Empirical Properties of Acids, Bases and Neutral Solutions Acid Base Neutral Cl H Empirical definitions = descriptions of the responses of substances to tests performed during an experiment. eg: Why is H 2S (g) sour? (When H 2S (g) is dissolved in water it forms an aqueous solution, H 2S (aq) which is acidic. This gives it a sour property.

9 Properties of Acids: 1. taste sour ( ie: or acetic acid acid or vinegar, and lemon juice or citric acid) 2. acids in solution will conduct electricity and are electrolytes 3. turn blue litmus red 4. acids will react with many metals to form hydrogen gas 5. acids can be neutralized with bases or basic solutions acids will react with bases to form water and a salt. Properties of Bases: 1. bases taste bitter 2. feel slippery 3. bases in solution will conduct electricity and are electrolytes, 4. bases turn red litmus paper blue 5. bases can be neutralized by acids or acidic solutions, bases will react with acids to form water and a salt. Acid/Base Theory: Acids are a special group of chemical compounds. All acids dissolve in water to form an electrolytic solution. An electrolytic solution is able to conduct an electric current because of the presence of positive and negative ions that are able to move freely in a solution. Page 170 Properties of Neutral Substances: neutral substances can be electrolytic (if solute is an ionic compound), neutral substances do not change red or blue litmus. Arrhenius' First Theory: The 1 st definition of an acid focussed on the ability of acids to form ions by identifying that all acids contain the hydrogen ion, H +. Thus the Arrhenius definition of an acid is a compound, like HCl, that contains a hydrogen ion, H + and a negative ion, Cl -. A base is a compound, like NaOH, that forms a hydroxide ion, OH -, and a positively charged ion, Na +. If you were Arrhenius and used his first theory, what would predict these substances to be classified as? Justify with a reaction. Ca(OH) 2(s) KNO 3(s) Let's Look at these reactions: HF (g)

10 The Arrhenius first theory/definition of acids and bases had 2 limitations: 1. Substances like Na 2CO 3(aq) do not have a OH - ion, yet they have all the properties of a base and substances like AlCl 3(aq) do not have a H +, yet they have all the properties of an acid. 2. Scientists doubted the possibility of the existence of a free H + ion in water. They reasoned that the H + ion would immediately attach to a water molecule to form a hydronium ion, H 3O + (aq). The 2 nd definition/modified theory of an acid utilized the existence of H 3 O + (hydronium ion) and the evidence that chemical reactions really involve the collisions between the molecules of substances. First Theory Modified Theory HCl (g) Page 172 The Bronsted-Lowry Theory: PROTON MOVEMENT - During a acid-base chemical reaction, a hydrogen ion, H +, is transferred from an acid (donor) to a base (acceptor) to produce a conjugate acid and a conjugate base. - an acid is a substance that donates or loses a hydrogen ion, H +, to another substance during a chemical reaction. - a base is a substance that accepts or gains a hydrogen ion, H +, from another substance during a chemical reaction. -a conjugate acid is an acid formed when a base accepts a hydrogen ion, H +. -a conjugate base is a base formed when an acid donates a hydrogen ion, H +. Proton Hopping Here is the mechanism!! Experiments proved that in an acid-base reaction, a collision between a water molecule and the acid resulted in a transfer of a H + ion to the water molecule to produce the hydronium ion, H 3O +, followed by a collision of the hydronium ion with the base, resulting in the transfer of the H + to the base. This is described as proton hopping from the acid to the base. ns/nh3eqtg.html

11 USE YOUR DATABOOK!! Page 173 in Textbook as well! Follow these 5 steps to write a reaction: 1.Find the 2 solutions that are reacting. 2. Identify the acid and base. Stronger acid is higher on the table- always choose the highest one if both are listed! The base is the non-acid (or weak acid). 3. Write the reactants side of the equation. 4. Find conjugate form of acid and base. 5. Write conjugate forms on products side of the equation. Follow along on page 174 in your textbook! Follow along on page 175 in your textbook!

12 The concentration of acids can be represented using a ph scale A ph of 7 is considered to be a neutral solution A ph less than 7 is acidic A ph more than 7 is basic Measuring Acids with ph ph = -log[h 3O + (aq)] Lower the ph = Higher the [H 3O + (aq)] ph will tell us: 1. How quickly the solution will react. 2. How much change the acid may cause. 3. The amount of base required to neutralize the acid. 4. The amount of base or metal it will react with. - Since the ph is a number that represents the hydronium ion concentration, then: -a solution with a ph of 7.00 has a concentration of 1.00 x 10-7 mol/l of hydronium ions or mol/L. -a solution with a ph of 6.00 has a hydronium ion concentration of 1.00 x 10-6 mol/l or mol/l or 10 times as much. Each whole number division on the ph scale represents a 10-fold difference in the concentration. Page 182 Lower ph values represent higher concentrations of the hydronium ion. The scale represents dilute acids. For very concentrated acids, the ph values can be lower than 0 or negative values. Page 181

13 Page 182 Example 1.7 Using Indicators to estimate ph: An indicator is a substance that changes color in response to the change in ph of a system. Page 184 & Databook Section 1.3: Impact of Acid Deposition on Ecosystems Scientists continually conduct investigations to determine whether there is a change in the environment due to its ability to cope with stress from pollution, such as acid deposition. - the process by which acids are chemically formed in the atmosphere and then deposited to the Earth as: Page 185 Ex wet deposition - [acid precipitation (rain, snow, hail) and condensation from acid fog.] 2. dry deposition - [acid dust from dry air]

14 What are the causes of acidic deposition? Recall Sources of CO 2(g) From the production & emission of gases into the atmosphere. Carbon dioxide Nitrogen dioxide Sulfur dioxide What could make these emissions? Think back! If these emissions are manmade = anthropogenic Equation: Equation: Cellular respiration Hydrocarbon Combustion Recall Sources of SO 2(g) emission are: Sour gas processing at gas plants and oil sands plants natural gas contains large amounts of H 2 S (g) Electrical industry The burning of coal releases SO 2(g) Pulp and Paper industry Chemical industry Recall Sources of NO 2(g) emission are: N 2(g) and O 2(g) are present in the air, but do not react with each other under normal conditions, however, whenever these gases are present near intense heat, they react to form N 2O (g), NO 2(g), and N 2O 4(g). The intense heat required for the reaction between N 2(g) and O 2(g) occurs at sources where fuel is burned at high temp. (650 0 C) - main source of this is vehicle emissions. Ore producing or smelting plants To recover metals from the metal sulphides in ores, the ores are roasted or combined with O 2(g). During this process large amounts of SO 2(g) are released.

15 What happens when these oxides of carbon, sulphur and nitrogen enter the air? They can react with water to make ACID DEPOSITION! Page 178 What is the effect of wind and the jetstream on acid deposition? Wind patterns in Alberta (prevailing westerlies) and the jetstream carry acid deposition far distances. What are the effects of acidic deposition: 1. Acid deposition may increase the hydronium ion, H 3O +, concentration of water and thus decrease the ph of the water, thus increasing the acidity of lakes and streams. This can be devastating to aquatic life. A certain ph is required by aquatic life and a change in the ph can destroy this life. The jet stream = rapidly moving air due to cold and warm fronts meeting (West to East) Some lakes have granite strata (metal deposits) and when acids react with this strata, they cause metal ions to be released into the water environment. This is called leaching. Some metals released are Cd, Hg, Pb, As, Al, and Cr which are all toxic to living organisms. eg: Al impairs gill function of fish

16 2. Acid deposition may also react chemically with other substances in the water. The ph of most bodies of water in Alberta is above 7.0 and as high as 8.3, making them slightly basic or alkaline due to t he presence of a naturally occurring base, carbonate ions CO 3 2- (aq), in the water. These carbonate ions, CO 3 2- ions, are present in water due to the dissociation of dissolved minerals in the water, such as calcium carbonate, CaCO 3, (from limestone) and magnesium carbonate, MgCO 3. Statues thus soils in Alberta, have a high potential for neutralizing acidic deposition. The neutralization of acids by bases that prevents any change in the ph of a soil or lake is called buffering. The effects of acid deposition on metals and other structures: Metals--- acids are the main cause of corrosion of metals eg. rust on bridges, light poles, vehicles, etc. Marble statues and buildings-----acids react with the main component of marble and limestone, which is CaCO 3(s), so the structures are slowly dissolving. Corrosion The effects of acidic deposition on plant life: Most plants have a limited tolerance to variations in ph and few plants can survive in soils with a low ph. Page 195 A change in the ph of soils can convert these nutrients into an insoluble form that is unattainable by the roots of plants. Page 194

17 Acid deposition may also release harmful metal ions into the soil, like Al 3+, Hg 2+ etc, through a process called leaching, which are destructive to plant growth and toxic to animals through biomagnification. Section 1.4:Quantifying Acid Deposition and Monitoring its Effects Data collected from scientific investigations can be categorized as: 1. Qualitative data: Page Quantitative data: Titration: Titration involves a technique for determining the concentration of a substance by adding a measured quantity that it is known to react with until an endpoint is reached. Here is what the set up looks like: Page 207

18 In a titration, a solution of unknown concentration is titrated with a solution of known concentration, called the standard solution. An indicator such as bromothymol blue or phenolphthalein is added to the solution in the flask so that a visible color change will indicate when the reaction is complete. If 5.75 ml of a mol/l standard solution of HCl is required to neutralize 125 ml of NaOH, find the concentration of the NaOH solution. Equation: Equipment: This is called titrating to an end point. Your purpose is to find the volume of standard solution required to neutralize a certain volume of unknown solution with an unknown concentration. If 4.25 ml of a mol/l standard solution of H 2 SO 4 is required to Ex. neutralize 50 ml of KOH, find the concentration of the unknown KOH solution. Strong and Weak Acids: Demo - Page 213 H 2 SO 4(aq) + 2KOH (aq) K 2 SO 4(aq) + 2H 2 O (l) Strong Acid HCl + H 2 O CH 3 COOH + H 2 O Weak Acid

19 Strong Base Weak Base Buffering NaOH (aq) F - (aq) - Net effect of a buffer is to maintain the ph at a relatively constant level. Section Learning from Acid Deposition 1. Electrostatic Precipitator - uses electric fields to collect fly ash (small particles of sand and other unburned material that remains after coal is combusted). 2. Scrubber - used to remove a gas from a mixture. Ex. SO 2(g) from coal combustion 3. Catalytic Converter - used to remove NO x(g), CO (g) and hydrocarbons from vehicle exhaust. What if we don't remove NO 2(g)? It collects in the troposphere and makes photochemical smog VOCs (volatile organic compounds) can react with this to make PAN (peroxyacetyl nitrate) a respiratory irritant. Beijing, China 4. Liming - neutralize acid in soil or water by adding base.