Substances, Mixtures, and Solubilitychapter 21

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Transcript Substances, Mixtures, and Solubilitychapter 21

 Substances are composed of atoms and elements  Substance is matter that has the same fixed composition, can’t be broken down by physical processes  Physical processes: boiling, changing pressure, cooling, or sorting  Chemical process: change the original substance into new substance(burning, chemical reactions, reaction to light)  REVIEW :Atom have specific protons for each element

 Two or more elements chemically combined in specific combinations and composition   H 2 O, NaCl, H 2 SO 4 , Water, salt, sulfuric acid

Mixtures

are combinations of substances that are not bonded together and can be separated by physical processes (salt water, granite, salt and pepper) 

Heterogeneous Mixtures

: mixture where substances are not mixed evenly ◦ ◦ Areas have different compositions Seeds in watermelon, minerals in granite, cereal in milk

Homogeneous mixtures

: contains 2 or more substances that are

evenly mixed

but are not chemically bonded together Shampoo, sugar water, Kool-Aid are examples 

Solutions

is another name for

homogeneous mixtures

 Solutions form when a

solute

(salt) dissolves in a

solvent

(water)  Forming solids from a solution ◦

Crystallization

occurs when cooling or evaporation takes place and leaves a solid ◦

Precipitates

forms from a chemical reaction that produces a substance that isn’t soluable in solution and drops out

 Liquid solid solutions: solid (solute) dissolves in liquid(solvent) salt in water  Liquid gas solutions: gas is dissolved in a liquid (gas dissolved in water: carbonated water)  Liquid-liquid solutions: both solute and solvent are liquids ( vinegar and water)

 Smaller amount of one gas (solute) is dissolved in a larger amount of gas (solvent)  ◦ Both solvent and solute are gases Example: Our atmosphere contains 78% Nitrogen and would be the solvent and other gases in atmosphere would be the solute

 In solid solutions, the solvent is a solid  Solute can be a gas, liquid, or solid  Solid-solid solution: alloys are mixture of 2 or more metals melted together and mixed (brass, steel)

Water the Universal Solvent

◦ Aqueous refers to a solution of where water is the solvent ◦ Water can dissolve may different solutes

 Molecular Compounds: ◦ Water is formed by

sharing

electrons between 2 atoms of H and 1 atom of Hydrogen ◦ Water molecules when combined have areas of electrical charges that attract opposite charges, thus are polar charged

 When compounds are formed by gaining or losing electrons to bond elements together  When atoms gain and lose electrons the number of electrons change and give an overall charge on the atoms  Opposite charge atoms attract and hold each other together

 Because of the polar charge of water areas of water molecules attract the charged particles of ionic compounds and break them up  ( Page 627 figure 8 )

 Water molecules moves in between sugar molecules and separate them (thus dissolving)  What will dissolve?

 ◦ ◦ Like dissolves like Polar solvents dissolve polar solutes (salt and water) Nonpolar solvents dissolves non polar solutes

 If you have a polar molecule and nonpolar molecule (unlike polar molecules) they will not dissolve and will not form a solution  Oil is a nonpolar molecule that will not mix with polar water, therefore these two substances will no form a solution

 Solubility is a measurement of how much a solute will dissolve in a given amount of solvent  It is described as how much solvent can be dissolved in 100 ml of solvent at a certain temperature Potassium chromate Barium sulfide At [email protected] C grams dissolved in 100 ml wataer 63 g .00025 g

 Liquid solid solutions: temperature affects how much solutes can be dissolved  Usually an increase in temperature allows ◦ more solute to be dissolved Notice on chart that NaCl and CaCO 3 become less soluble in higher temperatures

 Liquid-gas solutions: increase in temperature decrease the solubility of a gas dissolved in it  Carbon dioxide is dissolved under pressure in water in pop cans ◦ Opening a warm can of pop vrs a cold can, the gas is released much faster and leaves the solution under warmer conditions faster

 A

saturated solutions

can hold no more solute in solution at a given temperature or pressure  It will fall to bottom of solvent  A hot solution can hold more solute than at lower temperatures and when cooling the hot saturated solution a

supersaturated

solution may form

 Rate of dissolving is sped up by: ◦ Increasing temperature ◦ Crushing the solute ◦ Stirring the solution

Concentration

of a solution tells you how much solute is present compared to ◦ the amount of solvent It is recorded by using percent of solute is compared to solvent ◦ Juices concentration are written by 15%, 20% etc

  When a solute is added to water (salt water) and you want to freeze it , a lower temperature is needed (to freeze salt water could be 31℃) If you want to boil salt water a greater temperature is needed to boil it

Acids

: are substances that release positive H+ ions in water called a hydronium ion  When an acid mixes with water, acid dissolves and releases H+ ion

 Sour taste  Conduct electricity  Corrosive (break down substances)  React strongly with metals releasing H gas

 Vinegar (acetic acid), citric acid, ascorbic acid we are familiar with 

H 2 SO 4

◦ (sulfuric acid) Production of fertilizers, batteries, paint 

HCl

(hydrochloric acid) ◦ Muratic acid used in pickling that removes impurities from the surfaces of metals, cleans motar, bricks 

HNO 3

(nitric acid) use in fertilizer, dyes, and plastic

Bases

are substances that accept H+ ions and give off to a solution of water with OH- ions

 Feels soapy, slippery  Taste bitter  Corrosives  Conduct electricity

 Cleaning products  Your blood is basic in solution  NaOH (sodium Hydroxide) is known as lye and is used to make soap, clean ovens, unclog drains  CaOH (calcium hydroxide) often called lime is put on athletic fields to mark lines

pH

is the measure of how acidic or basic a solution is  Ranges from 0-14 where neutral pH is at 7  Below 7 covers the range of acid solutions (closer to 0 is more acidic0  Above 7 covers range of basic solutions (closer to 14 is more basic)

      Some acids are helpful (HCl in stomach to digest food however too concentrated HCl will eat away on tissue If more H+ (hydronium ions) are present the higher the acidic content (lower pH) Bases with large amounts of OH- ions (hydroxide) have greater concentrations and are more basic (higher pH) Each number on pH is 10 fold greater or smaller than the number before it: Comparing ph3 to ph1 is a difference of 2 2 10 2 means that there is a difference of 100 times more acidic

Indicators

are compounds that react with acidic and basic solutions and produce certain colors to indicate their acidity or basicity tendencies

  Neutralization is the reaction of an acid with a base When an acid and a base are combined, they will neutralization each other and the resulting pH will be 7   NaOH + HCl NaCl + H 2 O Base acid salt water