CHEM 1A Midterm 2 ALEKS Notes F2019 PDF

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CHEM 1A Midterm 2 Notes  4.6 Describing Reactions in Solution ● molecular equation gives the overall reaction stoichiometry bot not the actual forms of the reactants in solution ● in a complete ionic equation, all substances that’re strong electrolytes are rep’d as ions ● spectator ions: ions that don’t participate directly in a rxn soln (i.e. all the ions that don’t become part of the solid (s) product) ○ the result is the net ionic equation 4.7 Selective Precipitation 4.8 Stoichiometry of Precipitation Reactions ● must find LR first in reactions that take place in solutions ● first step is always to write down the species that’re present in the solution ● to obtain the moles of the reactants, use the volume of a particular solution and its molarity (M)

ans: 8.76 g NaCl

ans: 15.2 g PbSO4 

ans: 18.34% 4.9 Acid-Base Reactions ● ● ●

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OH— ion is such a strong base that for purposes of stoichiometry it is assumed to react completely w/ any weak acid dissolved in water (weak acid = weak electrolyte) see neutralization reaction acid-base titrations are an example of volumetric analysis, a technique in which 1 soln is used to analyze another ○ titrant: the soln to carry out the analysis equivalence point or stoichiometric point: the point in titration at which enough titrant has been added to react exactly w/ substance being determined ○ marked with a change of color in the indicator reqs for successful titrations ○ concentration of titrant must be known, i.e. standard solution ○ reaction btwn titrant and substance being analyzed ○ equivalence point must be known ○ goal is to choose an indicator whose endpoint (when indicator changes color) coincides w/ stoichiometric point — commonly phenolphthalein, colorless in acid and turns pink at endpoint when acid is titrated w/ base ○ volume of titrant req’d to reach stoichiometric point must be known as accurately as possible

-2

ans: 8.75 x 10 L HCl (easy)

ans: 0.007 mol H2O, 0.123 mol OH—  4.10 Oxidation-Reduction Reactions ● redox reactions: rxns in which 1+ e— are transferred ○ e.g. combustion rxns ■ C’s ON in CO2 is +4 ■ O2 is usually the oxidizing agent ? ● nonmetals w/ the highest attraction for shared e— is in upper right hand corner of periodic table ○ F > O > B ≈ Cl ● noninteger oxidation states are a thing (e.g. Fe3 O4) ● balancing redox equations using the oxidation states method — find the coefficients for the reactants that will make the total increase in ox’n state balance the total decrease

coeff ratios: 3:4:3:2 ●

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balancing redox equations using the half-reaction method - ○ half-reactions: a separated reaction involving either an oxidation or reduction

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

  4.12 Simple Oxidation-Reduction Titrations ●

3 of most common oxidizing agents are aqueous solns of — potassium permanganate (KMnO4), potassium dichromate (K2Cr 2O7 ), and cerium hydrogen sulfate [Ce(HSO4) 4]

ans: 53.75%  CH 4 Book Problems Solutions (Link)

   Predicting whether a compound is ionic or molecular

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Predicting the products of a neutralization reaction ● neutralization reaction occurs when strong acids and bases meet in solution ○ acid is neutralized when just enough base is added to react exactly w/ all the acid in the soln ● products of neutralization reaction = water and salt  HNO3 + Ba(OH)2

… ans:

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  3 major microscopic (molecular-level) models of acids: 1) Arrhenius model defines an acid as a substance that releases H+ cations in aqueous solution. 2) Brønsted-Lowry model defines an acid as a substance that can donate protons. 3) Lewis model defines an acid as a substance that can accept donation of a pair of valence electrons from a base. common acids — HCH3CO2 (acetic acid), H3 C6 H 5O3 (citric acid), HC3H 5 O3 (lactic acid), HCl (hydrochloric acid), H2 SO4 (sulfuric acid), H3PO4 (phosphoric acid), HNO3 (nitric acid)  3 major microscopic (molecular-level) models of acids: 1) Arrhenius model defines a base as a substance that releases OH− anions in aqueous solution. 2) Brønsted-Lowry model defines a base as a substance that can accept protons. 3) Lewis model defines a base as a substance that can donate a pair of valence electrons to an acid.  A compound is an Arrhenius acid if it increases the concentration of OH− anions when it dissolves in water. ● e.g. HCl (g) H+ (aq) + Cl−

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

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acidic hydrogens are the atoms of the hydrogen that a molecule can release when the compound behaves as an acid ● many acids have both acidic and non-acidic hydrogens, e.g. acetic acid has 1 acidic H and 2 non-acidic H’s HCH3 CO2(aq) H+(aq) + CH3 CO2 −(aq) polyprotic acid is an acid with more than one acidic hydrogen (e.g. H2SO 4 has 2 acidic H’s) monoprotic acid only has one acidic hydrogen (e.g. HCl, HNO3) ● only 1 acidic hydrogen but may have more than 1 hydrogen  Predicting and naming ionic compounds formed by two elements

 Stoichiometry: Dilution

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 Stoichiometry: Calculating molarity using solute mass

 Simple Reactions: Assigning oxidation numbers oxidation state of an atom when in a compound = how many more valence electrons the atom controls ● positive oxidation states fewer electrons ● negative oxidation states more electrons ● e.g. oxygen atoms in H2O are in oxidation state -2, holds 2 more electrons ● e.g. hydrogen atoms in H2O are in oxidation state +1, holds 1 less electron important to know for oxidation-reduction reactions, or redox reactions steps ● if atomic ion, oxidation state is usually its charge (e.g. NaCl, Na+ = +1 , Cl- = -1) ● diatomic molecules have oxidation state of 0 (e.g. Cl2 , O2)

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

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note: Ag has an ox state of +1 Stoichiometry: Using molarity to find solute moles and solution volume

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 Simple reactions: Identifying oxidized and reduced reactants in a single-displacement reaction oxidized reactant = the one that LOSES electrons reduced reactant = the one that GAINS electrons Loss of Electrons means Oxidation, and Gain of Electrons means Reduction. LEO the lion says "GER!"

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 try to determine just by looking at it  Simple reactions: Identifying precipitation, combustion and acid-base reactions precipitation reactions take place in solution ● all reactants and possibly some products are aqueous (aq) ● at least one product is solid (s) ● most are double replacement reactions ○ e.g. AgNO3 (aq) + NaCl(aq) AgCl(s) + NaNO3 (aq) combustion reactions: molecular compound reacts with O2 to form CO2 and H2O ● usually involves CXH YO Z; other compound may also involve P, N, S, Cl acid-base reactions: H+ is transferred from one compound to another ● acid loses the H+ ● base gains the H+ ● most acid-base reactions are double-replacement reactions ○ e.g. HI(aq) + NaOH(aq) NaI (aq) + H2O(l) 

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

precipitation double replacement acid-base double replacement combustion // decomposition // 

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 Simply reactions: Identifying acids and bases by their chemical formula

 acid base

molecular ionic

 Simple reactions: Identifying oxidized and reduced reactants in a metal-nonmetal reaction

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MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

Simple reactions: Writing net ionic equations break up the aqueous compounds into ions, DON’T break up solid spectator ions: ions that appear on both sides of the equation in equal numbers that don’t participate in reaction net ionic equations = chemical reactions w/ spectator ions dropped ● the result is a precipitation reaction, where 2 aq compounds solid

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 Simple Reactions: Predicting the products of dissolution

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  Simple Reactions: Recognizing reduction and oxidation

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  Simple Reactions: Predicting precipitation (fix the crop to see the answers)

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MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

 Simple Reactions: Identifying oxidizing and reducing agents

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 Advanced material: Writing the half-reactions of a single-displacement reaction

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 Writing and balancing complex half-reactions in acidic solution

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  Writing and balancing complex half-reactions in acidic solution

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 NO2(g)

NO 3- (aq)

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

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 Simple reactions: Determining the volume of base needed to titrate a given mass of acid ● need to know how many mol of OH— needed

 Advanced Material: Balancing a complex redox equation in acidic or basic solution

MIDTERM 1 / HOMEPAGE / GAUCHOSPACE / PERIODIC TABLE / ° CH 5 NOTES /

 Simple reactions: Determining the molar mass of an acid by titration 1. write a balanced equation ○ diprotic acid = H2 A ○ monoprotic acid = HA 2. find mass of base (NaOH) using given its M and mL 3. convert mol NaOH to mol of A— 4. use mol of A— and its given grams to find the molar mass of A—

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  Simple Reactions: Standardizing a base solution by titration...