Assignment 16 A incorrect

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1 Assignment 16 A 1- What is the concentration of hydronium ions in a solution with a hydroxide-ion concentration of M at 25 C? a) M b) M c) M d) M (The [H + ] = K w /[OH ].) 2- Calculate the ph of a solution if its [OH ] = M and indicate whether the solution is acidic, basic, or neutral. a) 11, basic b) 17.2, basic c) 3.15, acidic d) 10.8, acidic e) 10.8, basic (The ph = log[h + ], where [H + ] = K w /[OH ]. Since the ph is greater than 7, the solution is basic.) 3- If the ph of a solution is 6.30, what are the molar concentrations of H + (aq) and OH (aq) at 25 C? a) M and M b) M and M c) M and M d) M and M e) M and M ([H + ] = 10 ph = = [OH ] = K w /[H + ] = [ ]/[ ] = M) 4- Which of the following acids, if in solutions of equal concentration, is the most acidic? Assume all act as monoprotic acids. a) boric acid, K a = b) lactic acid, K a = c) saccharin, K a = d) phenol, K a = e) All of these acids are equally acidic because they are all of equal concentration. (The "acidity" of an acid solution depends on the amount of dissociated H + in solution. The greater the value of K a, the more H + is in solution, and the greater the acidity.) 5- Hydroxylamine, HONH 2, is a weak base. Write the K b expression for hydroxylamine. a) K b = [HONH 2 ]/ [HONH 3 + ][OH ] b) K b = [HONH 3 + ][OH ]/[H 2 O][HONH 2 ] c) K b = [H + ][ONH 2 ]/[HONH 2 ] d) K b = [HONH 3 + ][OH ]/[HONH 2 ] e) K b = [NH 2 + ][OH ]/[HONH 2 ] (A weak base reacts with water to form a hydroxide ion and its conjugate acid.) 6- Predict whether aqueous solutions of the following compounds are acidic, basic, or neutral. Find the incorrect answer. a) KNO 3 ; neutral b) NaC 2 H 3 O 2 ; basic

2 c) Co(NO 3 ) 2 ; acidic d) NaCN; basic e) KClO; acidic (KClO is derived from a weak acid and a strong base; it forms a basic solution.) 7- Which one of the following 0.1 M solutions would have a ph of 7.0? a) Na 2 S b) NH 4 Cl c) KF d) CuSO 4 e) NaNO 3 (This is a salt derived from a strong acid and a strong base.) 8- Which of the following statements is false? a) A Lewis base is an electron pair donor. b) Acid dissociation constants for hydrolysis reactions involving metal ions generally increase with decreasing charge on the metal ion. c) Metal ions show acidic properties. d) A Lewis acid does not have to contain a proton, which is transferable. e) Salts dissolve in water due to the attraction of the positive and negative ions for water molecules. (They generally increase with increasing charge.) 9- Given the following K a values, HC 2 H 3 O 2 K a = HClO 3 K a = HCN K a = HF K a = HOCl K a = which of the following is the weakest base? a) ClO 3 b) C 2 H 3 O 2 c) CN d) OCl e) F (Since HClO 3 is a relatively strong acid, this will be a very weak base.) 10- Which of the following does not represent the conjugate base of the acid listed? a) SO 4 2 for HSO 4 b) NH 3 for NH 4 + c) H 2 SO 4 for HSO 4 d) HS for H 2 S e) ClO for HclO (This is wrong. SO 4 2 is the conjugate base of HSO 4, whereas H 2 SO 4 is the conjugate acid of HSO 4.) 11- Which of the following is/are strong acid(s)? (i) HNO 3 (ii) HF (iii) HCl (iv) H 2 S a) (ii) and (iii) only b) (i) and (iii) only c) (i) only d) (ii) only

3 e) (i) and (iv) only f) (iii) only (Both of these acids are 100 percent ionized in aqueous solution.) 12- Calculate the ph of a solution made by adding 2.00 g of lithium oxide, Li 2 O, to enough water to make L of solution. a) b) c) d) e) (The concentration of the hydroxide ion is M.) 13- The ph of a 0.25 M solution of base, B, is Calculate the K b for base B. a) b) c) d) e) (The concentration of hydroxide ion equals ) 14- A 0.10 M aqueous solution of which of the following salts will have the lowest ph? a) Ni(NO 3 ) 2 b) KNO 3 c) BaBr 2 d) Ca(NO 3 ) 2 e) KCl (This solution will be slightly acidic, having a low ph, since the Ni 2+ is a weak acid.) 15- Which of the following statements is false? a) The larger the number of nonprotonated oxygen atoms in an oxyacid, the stronger the acid. b) The larger the electronegativity of the central atom, the weaker the oxyacid. c) In a series of acids that have the same central atom, acid strength increases with the number of nonprotonated oxygen atoms bonded to the central atom. d) In general, the acidity of hydrides increases from left to right in a given row of the periodic table. e) Hydrotelluric acid, H 2 Te, is a stronger acid than H 2 S because Te has a larger radius than S. (This is false. The trend is in the opposite direction.) 16- Which one of the following cannot act as a Lewis base? a) CN b) NH 3 c) F d) Cl e) Cr 3+ (This does not have an electron pair to donate.) 17- In the following reaction, the BF 3 is serving as a(n) acid. BF 3 + F BF 4 a) Lewis b) Brønsted-Lowry c) Arrhenius d) all of these

4 (This involves sharing a pair of electrons between the acid and the base.) 18- What accounts for the fact that chromium exhibits several oxidation states in its compounds, whereas aluminum exhibits only the +3 oxidation state? a) Al forms a smaller cation. b) Al has partially filled d orbitals. c) Cr has partially filled d orbitals. d) Cr is called a transition metal. (The partially filled orbitals can exist in different electron configurations.) 19- Calculate the ph of a solution made by adding 2.0 g of lithium oxide, Li 2 O, to enough water to make 0.60 L of solution. a) 7.00 b) c) 0.95 d) e) (The concentration of the hydroxide ion is M.) 20- Phenol is a weak acid with one acidic hydrogen. The ph of a M solution of phenol is Calculate K a. a) b) c) d) e) (The [H + ] = M.) 21- A M solution of a weak acid, HX, is 9.4 percent ionized. Using this information, calculate K a for HX. a) b) c) d) e) (The concentrations of both H + and X - are M.) 22- Barbital is a weak monoprotic acid with K a = What is the ph of a M solution of barbital? a) 3.82 b) 5.91 c) d) e) (The hydrogen-ion concentration is M.) 23- Calculate the molar concentration of OH ions in a M solution of ethylamine, C 2 H 5 NH 2, (K b = ). What is [OH ] and the ph of this solution? a) M, 2.60 b) M, c) M, d) M, e) M, 11.40

5 (Enough of the ethylamine is protonated to change its concentration in solution, and this was accounted for in the calculation using the quadratic formula.) 24- The ph of a 0.25 M solution of base, B, is Calculate the K b for base B. a) b) c) d) e) (The concentration of hydroxide ion equals )