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AP Chemistry Ch 4: Stoichiometry

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If 200 mL of 0.60 M of aqueous magnesium chloride is added to 400 mL of distilled water, what is the concentration of the magnesium ion and chloride ion in the resulting solution? Mg (2+)...............Cl (-) a) 0.2 M 0.2 M b) 0.2 M 0.4 M c) 0.4 M 0.4 M d) 2.0 M 2.5 M

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Cards (36)

Section 1

(36 cards)

If 200 mL of 0.60 M of aqueous magnesium chloride is added to 400 mL of distilled water, what is the concentration of the magnesium ion and chloride ion in the resulting solution? Mg (2+)...............Cl (-) a) 0.2 M 0.2 M b) 0.2 M 0.4 M c) 0.4 M 0.4 M d) 2.0 M 2.5 M

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magnesium chloride = MgCl2 1:2 ratio 0.6 M / 3 atoms = 0.2 use ration to find concentrations for each atom answer: B

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A 1 M solution of table salt (NaCl) is considered to be 1 M Na (+) and 1 M Cl (-). This means that table salt is a... a) strong electrolyte b) weak electrolyte c) nonelectrolyte d) strong acid

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strong electrolytes are easily broken (ionic) and conduct electricity when dissolved in water answer: A

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When NH3 is added to Cu (2+) (aq), a precipitate initially forms. Its formula is... a) Cu(NH)3 b) Cu(NO3)2 c) Cu(OH)2 d) Cu(NH3)2 (2+)

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solubility rules say OH (-) bonded with a metal is insoluble answer: C

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why are salts not able to conduct electricity while solid, but conduct electricity when liquid?

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When they are solid, salts consist of separate ions held in a fixed lattice, but when they are liquid, the ions are free to move and conduct electricity

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reduction

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gain of electrons

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A student is given a sample of pure, white, crystalline substance. Which of the following would be the most useful in providing data to determine if the substance is an ionic compound? a) examining the crystals of the substance under a microscope b) determining the density of the substance c) testing the electrical conductivity of the crystals d) testing the electrical conductivity of an aqueous solution of the substance

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answer: D

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the interaction between solute particles and water molecules, which tends to cause a salt to fall apart in water is called... a) hydration b) polarization c) dispersion d) coagulation

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this is just vocab answer: A

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example of a precipitation reaction: Pb (2+) +2I (-) -->

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PbI2 (SOLID)

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When solutions of acetic acid and sodium hydroxide react, which of the following are not present in the net ionic equation? I. hydrogen ion a) I and II II. acetate ion b) II and III III. sodium ion c) I and III IV. hydroxide ion d) I and IV

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reaction: CH3COOH + NaOH --> NaCH3COO + OH H net ionic equation (because its an acid base reaction, only look at transferring H+) H (+) +OH (-) --> H2O answer: D

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acid base reaction

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reaction involving the transfer of a hydrogen ion between reactant species

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On the basis of electronegativity, which of the following arranges the binary compounds in order of increasing bond polarity? a) CH4 < SiCl4 < SF4 b) CH4 < SF4 , SiCl4 c) SF4 < CH4 < Si Cl4 d) SiCl4 < SF4 < CH4

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electronegativity increases from bottom to top and from left to right on the periodic table answer: A

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Which of the following elements are oxidized and reduced in the reaction? 2 H2O2 --> 2 H2O + O2

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oxygen is both oxidized and reduced oxygen in 2 H2O2 loses one O oxygen in O2 got one O

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Atoms of which element are reduced in the following reaction? 2Na2O2 (s) + S (s) + 2H20 (l) --> 4 NaOH (aq) + SO2 (aq) a) S, each atom loses 4e- b) Na, in Na2O2, each atom loses 1 e- c) O, in Na2O2, each atom gains 1 e- d) O, in H2O, each atom gains 1 e-

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reduction involves gain answer: D

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example of a redox reaction: 2Ce (4+) + 2I(-) -->

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I2 + 2Ce (3+) Ce gave one e- to I

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All of the following reactions: 2Al (s)+ 3Br2 (l) --> 2AlBr3 (s) 2Ag2O (s) --> 4Ag (s) + O2 (g) CH4 (l) + 2O2 (g) --> CO2 (g) + 2H2O (g) can be classified as.... a) oxidation reduction reactions b) combustion reactions c) precipitation reaction d) A and B

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answer: A

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which of the following aqueous solutions contains the greatest number of ions? a) 400 mL of 0.1 M NaCl b) 300 mL of 0.1 M CaCl2 c) 200 mL of 0.1 M FeCl3 d) 200 mL of 0.1 M KBr

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use mol/L= M a) NaCl = 2 ions (0.1 M)(0.4 L) = 0.04(2 ions) = 0.08 mol b) CaCl = 3 ions (0.1 M)(0.3 L) = 0.03(3 ions) = 0.09 mol c) FeCl3 = 4 ions (0.1 M)(0.2 L) = 0.02(4 ions) = 0.08 mol d) KBr = 2 ions (0.1 M)(0.2 L) = 0.02(2 ions) = 0.04 mol answer: B

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To gravimetrically analyze the silver content of a piece of jewelry made from an alloy of Ag and Cu a student dissolves a small preweighed sample in hno3, ag+ (aq) and cu2+(aq) ions form in the solution. Which of the following should be the next step in the analytical process? a) centrifuging solution to isolate the heavier ions b) evaporating the solution to recover the dissolved nitrates c) adding enough base solution to bring the pH up to 7.0 d) adding a solution containing an anion that forms an insoluble salt with only one of the metal ions

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now that the ions are in the water, we need to get then out- make them a solid with a solution that binds with only one metal ion to make an insoluble salt answer: D

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In writing the complete ionic equation for the reaction (if any) that occurs when aqueous solutions of KOH and Mg(NO3)2 are mixed, which of the following would not be written as ionic species a) KOH b) Mg(NO3)2 c) Mg(OH)2 d) KNO3

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ionic species= aqueous, so the answer is the only one that is solid reaction: KOH + Mg(NO3)2 --> KNO3 + Mg(OH)2 (aq) (aq) (aq) (s) find those from solubility rules answer: B

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The net ionic equation of calcium bromide and sodium phosphate contains which of the following species? a) 2Br (-) (aq) b) PO4 (3-) (aq) c) 2Ca3(PO4)2 (s) d) 3Ca (2+) (aq)

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reaction: 3CaBr2 + 2Na3PO4 --> Ca3(PO4)2 + 6NaBr (aq) net ionic equation: 3Ca (+) + 2PO4 (2-) --> Ca3(PO4)2 answer: D

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consider the following unbalanced oxidation reduction reaction: Fe (2+) + Br2 --> Fe (3+) + Br (-) In the balanced equation, the net number of e- transferred is... a) 1 b) 2 c) 3 d) 4

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balanced equation: 2Fe (2+) + Br2 --> 2Fe (3+) + 2Br (-) Fe loses 2 e- and Br gains 2 e- answer: B

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what bonds to hydrogens and negative atoms make?

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hydrogen bonds

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In which of the following species is the oxidation state for nitrogen the greatest? a) NO b) NO2 c) N2O d) N2O5

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a) N + (-2) = 0 N= +2 b) N + 2(-2) = 0 N= +4 c) 2N + (-2) = 0 N= +1 d) 2N + 5(-2) = 0 N= +5 answer: D

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net ionic equation

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Includes only those compounds and ions that undergo a chemical change in a reaction in an aqueous solution

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redox reaction

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A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.

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example of a net ionic equation: 2Li + 2H2O-->

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2Li (+) + 2OH (-) + H2

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oxidation

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loss of electrons

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consider 100 mL of a 1 M solution of NaCl in a beaker. After several days, you test the solution and find that is has a concentration of 1.33 M. How much water must have evaporated? a) 20 mL b) 25 mL c) 75 mL d) 80 mL

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find mol of NaCl with M= mol/L and set equal to new concentration 10 mol/ x = 1.33 M subtract this from 100 because you found what is left and the question asked how much evaporated answer: B

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When solutions of strontium chloride and sodium sulfate react, which of the following is a spectator ion? a) strontium ion b) chloride ion c) sodium ion d)sulfate ion e) two of these

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reaction: SrCl2 + 2NaNO3 --> Sr(NO3)2 + 2NaCl2 net ionic equation: Sr (2-) + 2NO3 (-) --> Sr(NO3)2 spectators: Cl and Na answer: E

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When dissolved in water, strong acids...

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do not ionize completely

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A 23 g sample of a compound contains 12 g of C, 3 g of H, and 8 g of O. What is the empirical formula of the compound? a) CH3O b) C2H6O c) C3H9O2 d) C4H12O2

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this one you can do by looking at the charges of the atoms because the final molecule has to be non polar a) (-4) + 3(+1) + (-2) = -3 b) 2(-4) + 6(+1) + (-2) = 0 c) 3(-4) + 9(+1) + 2(-2) = -7 d) 4(-4) + 12(+1) + 2(-2) = 0, can be simplified to B answer: B

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when dissolved in water, weak strong acids...

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break apart into ions

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when is a molecule insoluble in water?

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a molecule is insoluble in water when the molecule is non polar ex: CCl4

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example of an acid base reaction: HOAc + NH3-->

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NH4 (+) + OAc (-) HOAc gave its H to ammonia

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precipitation reaction

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a reaction in which an insoluble substance forms and separates from the solution

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in which of the following does nitrogen have an oxidation state of +4? a) HNO3 b) NO2 c) N2O d) Nh4Cl

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a) HNO3= (+1) + N + 3(-2)= 0 N=+5 b) NO2= N + 2(-2)= 0 N=+4 c) N2O= 2N + (-2)= 0 N=+1 d) NH4Cl= N + 4(+1) + (-1)= 0 N= -3 answer: B

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Diabetics often need injections of insulin to help maintain proper blood glucose levels in their bodies, How many moles of insulin are needed to make up 45 mL of 0.0062 M insulin solution? a) 0.00028 mol b) 0.00056 mol c) 0.14 mol d) 0.28 mol

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45 mL = 0.045 L M = mol/L mol = M x L (0.00062 M)(0.045 L) = 0.00028 mol answer: A

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