CHEM 217 Lecture Notes - Lecture 4: Sodium Bicarbonate, Electronegativity, Solubility

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Unit 4

4.1 (N O T I MPO R TAN T)

4.2 WR I TI N G/ B A LA N C IN G C H E MI C AL EQUA T IO NS

oCombustion reaction: substance combines with oxygen to form one or more oxygen containing

compounds.

oAlso emit heat

oProcedure guidelines for balancing

o1. Write skeletal equation by writing chemical formulas for reactants and products

o2. Balance atoms that occur in more complex substances first. Always balance atoms in

compounds before atoms in pure elements

o3. Balance free elements

o4. Check

4.3 SO L UT I ONS AN D SO LUB I L IT Y

oReactions involving reactants dissolved in water are among the most common and important

oA homogeneous mixture of two substances, such as salt and water, is a solution

Majority is solvent and minority is solute

Consider salt water and sugar water – can no longer see them but taste is present

oAn aqueous solution is one in which water is the solvent

oWhen a solid is put into a liquid solvent, the attractive forces that hold the solid together (solute-solute

interactions) compete with the attractive forces between solvent molecules and the solid (solvent-solute

interactions)

EL E CTR O LY T E A ND N ONE L EC T RO L YTE SO L UTI O NS

oA salt solution will conduct electricity while a sugar solution does not

oDifference between the way ionic compounds and molecular compounds dissolve in water illustrates a

fundamental difference between types of solutions

oIonic compounds:

Dissociate into their component ions when dissolved in water

Dissolved NaCl doesn’t contain any NaCl units but rather dissolved Na+ Cl- ions that act

as charge carriers, allowing solution to conduct electricity

Subtances that dissolve in water to form solutions that conduct electricity are

electrolytes

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Substances like NaCl that completely dissociate into ions in water are strong electrolytes

and resulting solutions are electrolyte solutions

oMolecular compounds:

most dissolve as molecules which remain intact once dissolved.

Sugar dissolves because the attraction between sugar molecules and H2O overcomes

sugar’s attraction to its own molecules

Intact sugar molecule homogeneously mixed with water molecules

Compound that don’t dissociate into ions are called nonelectrolytes – nonelectrolyte

solutions don’t conduct electricity

oUnlike soluble ionic compounds that contain ions and dissociate in water, acids are molecular

compounds that ionize in water

Acids:

Molecular compounds but they do ionize (form ions) in water when dissolved

Strong acids (like HCl) completely ionize in solution

oSince strong acids completely ionize they’re also strong electrolytes

oWe represent the complete ionization of a strong acid with a single

reaction arrow between the acid and its ionized form

HCl (aq) -> H+ (aq) + Cl- (aq)

oBut, many acids are weak acids that don’t completely ionize

oFor example, CH3OOH is acetic acid and is weak

oA solution of a weak acid is composed mostly of the nonionized form of the acid molecules – only a

small percentage of acid molecules ionize.

oWe represent the partial ionization of a weak acid with

opposing half affows between the reactants and products

CH3COOH (aq) -> <- H+ (aq) + CH3COO- (aq)

oWeak acids classified as weak electrolytes and they conduct electricity only

weakly

SOLUBILITY OF IONIC COMPOUNDS

Not all ionic compounds dissolve completely in water AgCl remains solid and appears as white powder at the

bottom of water

oGenerally, compound termed soluble if it dissolves in water and insoluble if not

oBut oversimplification: solubility is a continuum and even insoluble compounds dissolve to some

extent

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oNo easy way to tell if a compound’s soluble but can follow set of empirical rules chemists have

inferred

Rules to be followed in orger, e.g. the rules with smaller number take precedence

*Notice that when compounds with polyatomic ions like NO3- dissolve, the polyatomic

ions dissolve as intact units

1. All salts containing cations of group 1 metals and ammonium ions (NH4+) are soluble

2. All nitrates (NO3-) ethanoates (acetates, CH3COO-), chlorates (ClO3-) and perchlorates

(ClO4-) are soluble

3. Salts containing Ag+, Pb2+ and Hg2+ are insoluble

4. Most chlorides (Cl-) bromides (Br-) and Iodides (I-) are soluble

5. Sulfates (SO42-) are soluble, except for those containing Ca2+, Sr2+, Ba2+

6. Carbonates (CO32-) Hydroxides (OH-) oxides (O2-) Phosphates (PO43-) and sulfides (S2-)

are generally insoluble.

4.4 P R ECIP ITA T ION R E A CT I O NS

oin which a solid or precipitate forms when we mix two solutions. Common in chemistry

oKey to predicting precipitation is to understand that only insoluble compounds form precipitates

oIn precipitation reaction, two soluble compounds combine and an insoluble compound precipitates

oEx. both KI & Pb(NO3)2 are soluble and exist in their respective solutions as K+, I-, Pb2+ and NO3- -

once they mix, two new compounds – one or both of which might be insoluble – are possible

In this case, KNO3 is soluble but PbI2 is not and precipitates

oA molecular equation shows complete neutral formulas for each compound in reaction as if they exist as

molecules but because of their solubility in (aq) they exist as ions

oWe can better represent the dissociated nature of dissolved ionic compounds

oCould be written as a complete ionic equation that lists all of the ions present as either reactants

of products in a chemical reaction

In complete ionic equation, some ions appear on both sides: spectator ions and do not

take part in reactions. To simplify: can omit them: Pb2+ + 2I- -> PbI2 (s)

This net ionic equation is most useful because it shows only the species that

take part in the reaction

oWriting equations for precipitation reaction

o1. Write the formula of the 2 compounds being mixed as reactants

o2. Write ions that are present when the two ionic compounds dissolve in water and determine

the possible products that are formed

o3. use solubility rules to determine whether any of the possible products are insoluble

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Document Summary

1 ( n o t i m p o r t a n t ) 2 w r i t i n g / b a l a n c i n g c h e m i c a l e q u a t i o n s o. Combustion reaction: substance combines with oxygen to form one or more oxygen containing compounds. o. Procedure guidelines for balancing o o o o: write skeletal equation by writing chemical formulas for reactants and products, balance atoms that occur in more complex substances first. Always balance atoms in compounds before atoms in pure elements: balance free elements, check. 3 s o l u t i o n s a n d s o l u b i l i t y o. Reactions involving reactants dissolved in water are among the most common and important o. A homogeneous mixture of two substances, such as salt and water, is a solution.

Related Questions

Science Tutor: Chemistry Name: Mixtures, Solutions, &Compounds: Chemical Equations Date Chemical Equations If a chemical symbol can be thought of as a letter and a chemical formula as a word in the language of chemistry, then a chemical equation is a statement or sentence. A chemical equation is a shorthand way of describing a chemical reaction between two or more substances. A "+ sign means "combines with." An arrow points away from the reactants and toward the products (See page 10), and an arrow means "yields." 2Na + Cl2 â 2NaCl means sodium combines with chlorine to yield sodiumn chloride (salt) Look closely at the equation above. Notice the "2" in front of NaCI on the right and Na on the left. That 2, called a coefficient, is necessary to make this equation balance. Remember Antoine Lavoisier? (Page 15) Matter is neither created nor destroyed in a chemical reaction. The same number of each kind of atom must be on both sides of a chemical equation. Because chlorine only exists as a molecule consisting of two chlorine atoms, it requires two atoms of sodium to yield two molecules of salt (NaCI). This illustrates another important law stated clearly by the French chemist Joseph-Louis Proust in 1799. Chemical compounds always combine in certain specific fixed proportions. Wherever sodium and chlorine combine, two atoms of sodium will be necessary to react with one molecule of gaseous chlorine. 1 . For the equation 2Mg + O2â 2MgO + energy: A. List the reactant or reactants 2Hato B. List the product or products C. How many atoms of magnesium does it take to combine with one molecule of oxygen? D. How many molecules of magnesium oxide are produced in this reaction? 2. Hydrogen can combine with oxygen to produce water. We could write the equation like this: H2 + O2 â H2O. But this equation is unbalanced! Rewrite this equation with the correct coefficients so that an atom of oxygen doesn't disappear! (Be careful. If you add a coefficient to one side you may have to adjust the other. Count all the atoms.) 3. Now that you have the idea, balance the following equations: A, Pho, â PbO + 02 C. Ca + H2O â Ca(OH)2 + H2 How is following a recipe to mix up a batch of biscuits (or any other food item) similar to Proust's law for chemical reactions? 4. OMark Twain Media, Inc., Publishers 17

1. Consider the unbalanced equation for the reaction of solid lead with a silver nitrate solution.

_____Pb (s) + ______AgNO3 (ac) â ______Pb(NO3)2 (ac) + _______Ag (s)

a. Balance the equation.

b. How many moles of silver nitrate are required to react completely with 9.3 mol of lead?

c. How many moles of silver, Ag, are formed by the complete reaction of 28.4 mol of Pb?

2. For the following reaction: _____CaO (s) + _____CO2 (g) â _____CaCO3 (s), Calculate how many grams of CaCO3, are formed when 2.4 g of CaO Do they react completely with CO2?

3. For the following reaction: 2 Li (s) + F2 (g) â 2 LiF (s), find the reagent limiting with the amounts of 1.0 mol of Li and 1.0 mol of F2.

4. For the next reaction, determine the limiting reagent, calculate the yield Theoretical product in grams with 5.5 g of Al and 19.8 g of Cl2.

2 Al (s) + 3 Cl2 (g) â 2 AlCl3 (s)

5. Consider the reaction between NiS2 and O2:

2 NiS2 (s) + 5 O2 (g) â 2 NiO (s) + 4 SO2 (g)

When 11.2 g of NiS2 react with 5.43 g of O2, 4.86 g of NiO are obtained. Determine the limiting reagent, the theoretical yield of NiO and the% yield for the reaction.

6. How many atoms of mercury are in 5.8 mol of mercury?

7. Complete the following table:

Element Moles Mass Number of molecules

8. How many grams of sodium are there in 1.00 g of each of the following compounds?

a. Na3PO4

b. NaC7H5O2

c. Na2C6H6O7

9. A sample of 4.78 g of aluminum reacts completely with oxygen to form 6.67 g of aluminum oxide. Use the data to calculate the percent of composition by mass.

10. Citric acid, the compound responsible for the bitter taste in lemons, has the following composition: C - 37.51%

H - 4.40%

O - 58.29%

Calculate the empirical formula.

11. A compound containing phosphorus and oxygen has a molar mass of 219.9 g / mol and an empirical formula of P2O3. Find the molecular formula of compound.

12. It is a term used in chemistry, to describe a system in which a

or more substances, are mixed or dissolved homogeneously in another

substance.

a. Mixture

b. Solution

c. Compound

d. None of the above

13. It is the component that is in a solution, in smaller quantity.

a. Solution

b. Solvent

c. Solvent

d. Soluto

14. It is the component that is in a solution in greater quantity.

a. Solution

b. Solvent

c. Solvent

d. The answers b and c are correct.

15. The quantitative expression of the dissolved amount of solute in a quantity determined solvent is known as:

a. Solution

b. Volume

c. Concentration

d. Stoichiometry

16.Express the moles of solute among the liters of solution

a. Molality

b. Molarity

c. % weight by volume

d. % weight by weight

17.Express the moles of solute between kg of solvent

a. Molarity

b. ppm

c. ppt

d. Molality

18. What is the molarity of a solution prepared by dissolving 7.50 g of nitrate of magnesium, Mg (NO3) 2 in enough water to prepare 25.0 mL of solution?

a. 10.3 M

b. 5.6 M

c. 6.5 M

d. 2.03 M

19. How many grams of sodium chloride, NaCl are needed to prepare 125 mL of 0.037 M NaCl solution

a. 1.021 M

b. 0.268 M

c. 0.201 M

d. 0.500 M

20. Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.

21. A solution of ethylene glycol contains 21.2 g of ethylene glycol (C2H6O2) in 85.4 mL of water. Calculate the freezing point and the boiling point of the solution. (Assume the water density is 1.00 g / mL)

22. At what volume should you dilute 75 mL of a 10.0 M solution of H2SO4 to obtain a 1.75 M solution of H2SO4.

HERE IS HOW THIS IS GOING TO WORK! IF YOU ANSWER THE QUESTIONS IWILL GIVE YOU THE 3K POINTS + MORE AFTER I REPOST IT.

2. The amount of heat involved in the synthesis of 1 mole of acompound from its elements, with all substances in their standardstates at 25*C, is called _________.

3. What is a valid unit for specific heat?

4. Use Hess's Law to find the heat of reaction in the examplebelow.

N2O4 (g) ----> 2NO2 (g)

Given that:

N2O4 (g) ----> N2 (g) + 2O2 (g) (Delta H =-9.7kJ)

2NO2 (g) ----> 2O2(g) + N2(g) ( Delta H= -67.7kJ)

5. Use Hess's Law to find the heat of reaction in the examplebelow. (Example doesn't exist btw.)

6. (Delta H) for the formation of rust (Fe2O3) is -826 kJ/mol. Howmuch energy is involved in the formation of 5 grams ofrust?

7. How many kilocalories of heat are required to raise thetemperature of 50g of aluminum from -5*C to 35*C? (Specific heat ofAluminum = 0.21 cal/g*C)

8.Calculate the (Delta H) for this reaction:

Zn(s) + Cu (2+ ion)(aq) ---> Zn(2+) + Cu(s)

(Delta H) for Cu(2+) = +64.4 kJ/Mol; (Delta H) for Zn(2+) = -152.4kJ/mol

9. The following equation shows the reaction that occurs whennitroglycerine explodes.

4C3H5O9N3 ----> 12CO2 + 6N2 + O2 +10H2O + 1725 Kcal

Is this reaction exothermic , endothermic, a combustion reaction ,or a combination reaction?

10. What does it mean for ammonia, (NH3) to have a (Delta H f) =-46 kJ/mol?

(for example: Define heat of formation. What does a negative heatof formation mean? what do the units of kJ/mol mean?)

11. What is the maximum amount of KCl that can dissolve in 500g ofwater?

(solubility of KCl is 34 g/ 100g of water at 20*C)

12.List the ways(operations) that can help make a substancedissolve faster in a solvent?

13. If a crystal added to an aqueous solution causes many particlesto come out of solution, the original solution was (saturate,unsaturated, supersaturated).

14. What is the number of moles of solute in 165 mL of a 0.82 Msolution?

15. What mass of NaCl is needed to make 350 mL of a 1.00 Msolution?

16. Colligative properties depend upon...

17. If one mole of each of these solutes in added to the sameamount of water, which solution has the highest boiling point?(glucose, aluminum sulfate, magnesium acetate, copper (I)chloride)

18. When an acid reacts with a base, what compounds areformed?

19. If the [H+] in a solution is 1x10^(-13) mol/L, what is the[OH-]?

20. If the [OH-] = 1x10^-6 mol/L, what is the pH of thesolution?

21. For a solution to be considered acidic what must be thehydrogen-ion concentration?

22. Which of the following represents a Bronsted-Lowry conjugateacid-base pair?

a) SO3(2-) and SO2 b) CO3(2-) and CO c) H3O and H2 d) NH4(+) and NH3

23. With solutions of "strong" acids and "strong" bases, the word"strong" refers to ...

24. What are the products of Al(OH)3 + H2CO3?

25.What is the concentration of hydrochloric acid if 5.0 mL of acidis neutralized by 30.0 mL of 2.00M sodium hydroxide.

26. At equilibrium, what is the rate of production of reactantscompared with the rate of production of products?

27. What is the equilibrium constant for the following reaction2SO3 ---> 2SO2 + O2

28. How does an increase in pressure affect the following reaction?2SO3 (g) --> 2SO2(g) +O2(g)

29.What stresses would shift the reaction to the right?

2SO3(g) ==> 2SO2(g) + O2(g)

30. The Keq of a reaction 4.9 x 10^(-7). Are products or reactantsfavored at equilibrium?

31. In which of these systems is the entropy decreasing?

a) air escaping from a tire b) snow melting c) a gas condensing d) salt dissolving inwater

32. If an atom is reduced in a redox reaction, what must occur toanother atom in the system?

33. Identify the oxidizing agent in the following reaction: 2Na + S---> Na2S

34. What are transferred in an oxidation -reductionreaction?

35. Give the oxidation number for each atom in KMnO4.

36. Which atom has a change in oxidation number of +4 in thefollowing reaction?

K2Cr2O7 + H2O + S ----> KOH + Cr2O3 +SO2

37. What is the oxidation number of sulfur in each of the following:

a. SO3 c.SO2(2-)

b. Na2SO4 d. S2O4 (2-)

38.Fe(3+) ----> Fe represents oxidation, reduction, orhydrolysis?

39. When the half reactions Br2+ 2e- -----> 2Br- and Na---->e- + Na(+) are combined the balanced redox equation is_____________________ ( WRITE the BALANCED REDOX eq)

40. To balance the oxygen and hydrogen for a redox reaction thattakes place in basic solution, it is necessary to use whichsubstance?

41. What particle completes this nuclear equation? 55/25 Mn + 2/1 H====> _____ +2 1/0 n

42. The half-life of tungsten-182 (182/74 W) is 1.1x10^(17) years.How long would it take for a 376.2 kg sample to decay until only123.0 grams remain?

43. After 3 days, the quantity of certain radioisotope is reducedfrom 13.6 grams to 1.9 grams. Calculate the half-life of theisotope.

44. What is the name of the compound having the formulaC8H18.

45. What is the name of the following compound:

CH3---CH2----CH---CH2--C

I \

CH3 OH

46. What is an isomer? Give an isomer of hexane (C6H14) and drawit's structure.

47. What is the name of the hydrocarbons with double covalentbonds?

48. Draw the stucture for 3-methylbutanoic acid.

49. Draw the structure for methylbenzene?

50. What is the name of the following compound:

CH3----C-----CH3

CH3

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CHEM 217 Lecture Notes - Lecture 4: Sodium Bicarbonate, Electronegativity, Solubility

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