UNIT 4 Solutions and Solubility Chapter 8 - Solutions and Concentration

Transcription

1 UNIT 4 Solutions and Solubility Chapter 8 - Solutions and Concentration Types of Solutions The simplest solutions contain 2 substances: 1. SOLVENT o o 2. SOLUTE o When solute dissolves in a solvent, and the substances can be. Solutions are mixtures and can be. Steel Kool-aid Air Most common solutions are The most common of these are where is the Many substances dissolve easily. These substances are said to be with each other. Ex.

2 Some substances dissolve in each other. These are said to be. Ex. SOLUBILITY is a measurement of. Ex. The solubility of NaCl in H 2 O at. A SOLUTION is a solution that. If we try to add of NaCl to 100mL of H 2 O, it will An SOLUTION is a solution. Solutes described as have a solubility of Solutes described as have a solubility of Solutes described as have a solubility of Factors Affecting Rate of Dissolving and Solubility The measures how fast a. This rate is dependent on many factors. 1. a. b. 2. a.

3 3. a. b. The reason that one substance dissolves in another is because of The forces include the attraction between: When the force of attraction between particles is the attraction between particles a is formed. The between particles determines solubility Recall the Thought Lab on pg. 288: Iodine was insoluble in water. This means that the. Also the force of attraction between (intermolecular forces) are strong. Iodine was soluble in kerosene. The force of attraction between than the attraction between as well as between.

4 INTERMOLECULAR FORCES In Unit 1 you learned the difference between polar and non-polar molecules. Recall water: Water is polar because it appears to other molecules to have. Molecules like this are said to have a. A DIPOLE consists of. Remember how water sticks to water? This is a result of the. These are called.

5 This is a type of. They act between molecules. These forces are about as an ionic or covalent bond ( ) A special type of dipole-dipole attraction happens when. Because these atoms are so, H gets a positive charge that is. This leads to. When substance are dissolved in a the the of the ionic compound are attracted to different. This is known as. In an each cation and anion will be surrounded by. Each ion is said to be and can move freely in the solution making it an (sol n with the ability to conduct electricity). ionic compounds are soluble but. To predict solubility : Large difference Small difference

6 When are mixed with water, most are. This is because many are. Exceptions are and. Both of these form with water. However, covalent compounds are soluble in solvents. In general. - solutes dissolve in solvents. - solutes dissolve in solvents. Some substances behave as both polar and non-polar substances. is an example

7 Factors Affecting Solubility Don t get confused with. 1. Molecule Size Temperature - - When a solid dissolves to break bonds between particles. - - This is true for. - For energy is not required so temp has on solubility - When dissolve in liquids they actually lose energy, so 3. Pressure - Changes in pressure have on solid and liquid solubility - The solubility of a gas is - For example in a 2L pop bottle the pressure of CO 2 is. Solubility of CO 2 in the. When you open the bottle, the pressure of CO 2, solubility!

8 Concentration of Solutions Mass/Volume Percent Chemists often express the concentration of an as the MASS. It is usually expressed as a It can also be referred to as This is different from solubility. (mass per unit volume) Ex 1. A pharmacist adds 4.0 ml of H2O to 8.00g of powdered drug. The final volume of the solution is 6.00mL. What is the percent (m/v) of the solution? What is the concentration in g/100ml? Ex 2. Trisodium phosphate (TSP) is used as a cleaner to prep surfaces before painting. The recommended concentration of TSP is 1.7% (m/v). What mass of TSP is required to make 4.0L of solution?

9 Mass / Mass Percent The of a solution containing a solid solute dissolved in a liquid solvent can be expressed as the and is called (you might also see it as w/w percent) Many metal alloys have their concentration expressed as percent (m/m) Ex1. Dental amalgam used as dental fillings is made by mixing mercury, silver and tin. If a sample of a dental filling has a mass of 1.35g and after heating the solution you obtain g of silver, what is the mass/mass percent of silver in dental amalgam and how much would you need to make 100g of dental amalgam?

10 Volume / Volume Percent When mixing 2 liquids it is common to express. This may also be referred to as Ex 1. Rubbing alcohol is an antiseptic. It is sold as 70% (v/v). What volume of isopropyl alcohol is used to make a 500ml bottle? Parts per million and Parts per billion are usually used to express in the ). Both are usually mass/mass relationships. For (ppb) substitute 10 6 with 10 9

11 Ex1. A toxic fungus that grows on peanuts can cause liver damage in humans. The maximum amount of toxin allowed is 25ppb. If 20t of peanuts are to be made into peanut butter, what is the maximum mass of toxin permitted? Ex 2. Mercury is toxic in humans if more than 20mg has accumulated. i.express this in ppm for a 75kg person ii.express this in ppb iii.express this in (m/m) percent

12 Molar Concentration This is the concentration used in chemistry is the Molar [ ] can be referred to as This formula can be shortened to: Units are The advantage of using molar concentrations is that it is related to the # of particles in the solution. None of the other concentrations are. Ex1. A saline solution contains 0.90g of solute dissolved in 100mL of solution. What is the molar concentration? Ex 2. Formalin is a solution containing formaldehyde, CH 2 O, used to preserve biological specimens. What mass of CH 2 O is required to prepare 2.25L of 10.5M solution?

13 Preparing Solutions A soln of known concentration is referred to as a. There are 2 ways to make a standard solution: To prepare a standard solution you use a. These flasks are able to measure to Diluting a Solution You can also make a less concentrated standard solution by adding a measured amount of extra solvent to a solution with a known concentration. Ex. 1 You must make 2.0L of 0.10M sulfuric acid. This acid is sold as 18M. How much of the standard solution do you need to make the new solution? There is an easier way. This formula can be used to solve basic dilution questions. Try the above question again.

14 Chapter 9 Aqueous Solutions Making Predictions about solubility Recall: Soluble Partly or Slightly Soluble Insoluble Factors that affect the solubility of Ionic Substances 1. Ions with small. Ions with large. Increasing the charge. For example: tend to be insoluble, salts soluble. 2. Compounds with than compounds with. ions more closely than. The above can allow you to make some predictions about solubility. What do think about sulfides (compounds with S 2- )?

15 There are many interrelated factors affecting solubility, and must be for solubility. Chemists rely on published data to determine a substance is soluble, soluble it is, and it s to other similar compounds. Stoichiometry in Solution Chemistry These problems are solved the same way as the previous stoichiometry problems you did with the addition of a couple of items: Ex. 1 Calculate the [chloride ions] in mol/l the following solutions: a g of potassium chloride dissolved in 100 ml of solution. b g of calcium chloride in 150 ml of solution c. a mixture of the two solutions in a. and b. assuming the volumes are additive.

16 Ex 2. Rhubarb leaves are poisonous because of the oxalate C 2 O 2-4 ions present in them. If you tested g of leaves by adding calcium chloride to precipitate calcium oxalate and extracted 0.556g of calcium oxalate, what was the mass percent of oxalate ions in the leaves?

17 Ex. 3 Solutions containing silver ions are often mixed with chloride ions to precipitate silver chloride. What is the minimum volume of 0.25mol/L magnesium chloride needed to precipitate all the silver ions in 60mL of 0.30 mol/l silver nitrate?

18 Ex 4. When Hg is used in industry it must be removed from all waste water, because it is toxic. Suppose 50.00mL of 0.045mol/L sodium sulphide is added to 101.4mL of 0.05M mercury (II) nitrate. What mass of mercury (II) sulphide precipitates?

19 Ex 5. Silver chromate Ag2CrO4 is insoluble. Calculate the mass of silver chromate that forms when 50.0mL of 0.25M silver nitrate reacts with 25.0mL of 0.30M sodium chromate.

20 Acids and Bases Chapter 10 Acids and bases are common products. Citrus Fruits Dairy products Soft drinks Underarm odour Oven cleaner Baking Soda Glass Cleaner Acids and bases are groups of chemicals that share similar physical and or chemical properties Properties Acid Bases Taste Indicators Feel Form ions in solution Conduct electricity React with metal React with carbonates

21 Theories of Acids and Bases Since their discovery, people have tried to describe what makes an acid an acid and a base a base. Arrhenius Theory of Acids and Bases In the late 19 th century the Swedish chemist named Svanté Arrhenius discovered that Arrhenius published his theory: - - According to Arrhenius theory, acids (which always contain an H + ion) and bases (which always contain an OH - ion). Arrhenius theory is useful if you are interested in

22 However there are some problems: 1. The ion responsible for making an acid is H +. This happens when acids are added to water. But what happens between? In the 20 th century, chemists discovered that H + ions but are always. A hydrated H + ion is called a 2. Consider the base NH It is limited to acid-base reactions. Brønsted-Lowry Theory of Acids and Bases In 1923 two chemists (independently) came up with a new theory, which helped explain the limitations of the Arrhenius theory. There theory stated: - - Brønsted-Lowry acids also contain an. This means all But,.

23 According to Brønsted-Lowry theory there is only one requirement for an acid-base reaction: This means that any substance can be an acid as long as. The reverse is true as well. Consider HCl added to water Two molecules or ions that are related by the transfer of a proton (H + ) are called a The of an acid is the particle that remains when a proton from the acid. The of a base is the particle that results when the base the proton from the acid. Ex1. Hydrogen bromide is a gas that is soluble in water. The resulting solution is called hydrobromic acid. Identify the conjugate acid-base pairs.

24 Ex.2 Ammonia is soluble in water. It forms a basic solution commonly used in window cleaners. Identify the conjugate acid-base pairs in the reaction between ammonia and water. Ex 3. Identify the conjugate acid-base pairs as well as the acid, base and conjugate acid and base. HCOOH + CN - HCOO - + HCN Strong and Weak Acids and Bases ACIDS In a STRONG ACID the acid. HCl is a strong acid. All the HCl molecules

25 Strong acids include: In a WEAK ACID the acid. On average about 1% Most acids are weak. Acetic Acid is an example of a weak acid The arrows mean this reaction is. Molecules of acetic acid dissociate just as to produce acetic acid molecules.

26 Mono, Di, Tri Protic Acids Some acids contain only a that can dissociate. These are called. Many acids contain. These are referred to as. Sulphuric acid is an example The first dissociation is complete. The remaining hydrogen sulphate ion is a Some acids are. The more dissociations that take place.

27 Bases Strong and weak bases follow the same rules as the acids above. Strong Bases Naming Acids and Their Anions There are 2 kinds of acids: Binary Acids and Oxoacids (oxyacids). Binary Acids are composed of 2 elements:. They have the general formula HX To name: Oxoacids are formed from a that contains To name: 1. 2.

28 3. ph ph stands for the power of hydrogen. Think about water. All aqueous solutions contain ions, even pure water. On average at 25 o C on 2 water molecules in a billion are dissociated at any time. Since ions in solution are required to conduct electricity, pure water is not a conductor. In neutral water the [H 3 O + ] at 25 o C is 1.0x10-7 mol/l Therefore the [OH - ] is also 1.0x10-7 mol/l Compared with neutral water acidic solutions contain [ ] of hydronium ions. Basic solutions contain [ ] of hydronium.

29 The ph scale Powers of 10 Concentrations of hydronium ions ranges from about. The big range and negative powers of 10 are not convenient to work with. The Danish biochemist Søren Sørensen came up with a method to measure [ ] using a logarithmic scale. The logarithm of a number is the power to which you must raise Sørensen defined ph as So water has a ph of Ex 1. Orange Juice has a [hydronium ions] of 2.5x10-4. What is the ph of orange juice? Ex 2. Household ammonia has a ph of What is the concentration of [H 3 O + ]?

30 Neutralization Reactions There are many types of acids and bases and being able to predict the results of reactions between them is important. The reaction between. SALT is an For example sodium nitrate is used to slow the rate of bacterial growth in foods. It can be made by mixing nitric acid with sodium hydroxide. The balanced chemical equations shows: - - For most neutralization reactions there is that a reaction is occurring. To see this we use. Most indicators are, where the the is one colour and its a different colour. Phenolphthalein is an example

31 Calculations involving Neutralization Reactions Ex 1. You have 25.00mL of NaOH left over from your experiment and you want to neutralize it before dumping it in the sink. You find that it takes 19.75mL of HCl to neutralize it. What was the [ HCl ]? Ex. 2 What volume of 0.50M sulfuric acid is needed to react completely with 45mL of 0.85M calcium hydroxide?

32 In a titration experiment, 25.00mL of an aqueous solution of NaOH was required to neutralize 55.00mL of 0.010M HCl. What was the molar concentration of NaOH? Read pg. 399 to 401 and make your own note on ACID-BASE TITRATION.