chem 2 final

Arrange the following amines in order of decreasing base strength. Rank from strongest to weakest base.

(CH3)2NH, CH3NH2, NH3, NH2Br -Changing the base strength of an amine by the addition of different groups to the amine N atom is used in the synthesis of organic compounds. Often a group such as an electronegative −C=O is added to keep the amine from reacting. This procedure is referred to as adding a "protecting group."

Since soap and detergent action is hindered by hard water, laundry formulations usually include water softeners—called builders—designed to remove hard water ions (especially Ca2+ and Mg2+) from the water. A common builder used in North America is sodium carbonate. Suppose that the hard water used to do laundry contains 75 ppm Ca2+ (reported as CaCO3). What mass of Na2CO3 is required to remove 90.0% of these ions from 15.5 L of laundry water? (Ksp(CaCO3)=4.96×10−9). Express your answer to two significant figures and include the appropriate units.

1 ppm = 1 mg/1 Kg 75 ppm = 75 mg / 1Kg moles CaCO3 = 0.075 g/100 g/mol= 0.00075 moles in 15.5 L = 0.0075 of CaCO3 90 x 0.675/100=0.00675 0.00675 x 106 (na= 22.99x2, c= 12.01, o=16x3) =0.7155=0.72

What will the concentration of Cd2+ at the moment before Fe2+ begins to precipitate?

1.8 x 10^-14 / 1.86 x 10^-9 9.6 x 10^-6

You wish to prepare an HC2H3O2 buffer with a pH of 4.14. If the pKa of is 4.74, what ratio of C2H3O2-/HC2H3O2 must you use?

4.14-4.74= -0.6 10^-0.6 = 0.2511 =0.25

At what pH will precipitation of Al(OH)3 begin if 5.60 lb of aluminum sulfate, Al2(SO4)3, is added to 1750 gallons of water (with a negligible change in volume)? Express your

7.20 lb = 3265.9 g moles Al2(SO4)3 = 3265.9 g/ 342.13 g/mol = 9.52moles Al3+ = 2 x 9.52 =19.0 2150 gallons = 8138.6 L [Al3]= 19.0 / 8138.6 =0.00233 M 1.3 x 10^-33 = 0.00233 [OH-]^3 [OH-]= 8.22 x10^-11 M pOH = 10.1 pH = 3.9

Which of the following solutions is a good buffer system?

A solution that is 0.10 MHCN and 0.10 MLiCN

If you wanted to clean out your coffee cup, would it be better to use an acidic or basic cleaning solution? Why?

Acidic. Calcium carbonate is more soluble in acidic solution because the carbonate ion is a weak base and will react with the acid in the cleaning solution.

Identify the Brønsted-Lowry acid, the Brønsted-Lowry base, the conjugate acid, and the conjugate base in each reaction: (a) C5H5N(aq)+H2O(l)⇌C5H5NH+(aq)+OH−(aq) (b) HNO3(aq)+H2O(l)⇌H3O+(aq)+NO3−(aq)

Brønsted−Lowry acid: HNO3, H2) (a) Brønsted−Lowry base: C5H5N, H2O (b) Conjugate acid: C5H5NH+, H3O+ Conjugate base: OH-, HNO3- - In reaction (a), H2O is the acid because it donates a proton to C5H5N and forms the conjugate base, OH−. Since C5H5N accepts the proton, it is the base, and it forms the conjugate acid, C5H5NH+. - In reaction (b), HNO3 is the acid because it donates a proton to H2O and forms the conjugate base, NO3−. Since H2O is the proton acceptor, it is the base, and it forms the conjugate acid, H3O+

A solution of Na2CO3 is added dropwise to a solution that contains 1.13×10−2 M Fe2+ and 1.53×10−2 M Cd2+. What concentration of CO32− is need to initiate precipitation? Neglect any volume changes during the addition.

CdCO3(s) <=> Cd2+(aq) + CO32-(aq) Ksp = [Cd2+][CO32-] = 1.80 x 10-14 [Cd2+] = 1.53×10−2 M 1.53×10−2 M x [CO32-] = 1.80 x 10-14 1.80 x 10^-14/ 1.53×10^−2 M [CO32-] = 1.18 x 10-12 M FeCO3(s) <=> Fe2+(aq) + CO32-(aq) Ksp = [Fe2+][CO32-] = 2.10 x 10-11 [Fe2+] = 1.13×10−2 M 1.13×10−2 M x [CO32-] = 2.10 x 10-11 2.10 x 10^-11 / 1.13 x 10^-2 [CO32-] = 1.86 x 10-9 M [CO32-] = 1.18 x 10-12 M CO32− be at the moment before Fe2+ begins = 1.86 x 10-9 M

The stomach excretes ________ to kill microorganisms and to activate enzymes that break down food.

HCl

Arrange the following oxoacids in order of decreasing acid strength. Rank from strongest to weakest acid.

HClO3, HClO2, HClO, HBrO

Consider these two acids and their Ka values: HF: 6.8×10−4 HClO: 2.9×10−8 Which acid is stronger? HF or HClO

HF The larger Ka, the stronger the acid. The larger Ka indicates that HF is stronger.

What is the symbol for the equilibrium constant that describes calcium carbonate dissolving in water?

Ksp

A 0.175 M weak acid solution has a pH of 3.25. Find Ka for the acid. Express your answer to two significant figures.

The Ka for a weak acid, HA, is given by Ka=[H3O+][A−]/[HA] By using the fact that [H3O+]=[A−] and given the initial concentration of the weak acid, HA, the Ka of the weak acid can be calculated from the equation: Ka=(10^−3.25)(10^−3.25)/ 0.175−10^−3.25= 1.8×10^−6

Determine the molar solubility for Zn(OH)2 in pure water. Ksp for Zn(OH)2 is 3.00 x 10-17.

Zn(OH)2 <----------> Zn+2 + 2OH- Ksp = [Zn+2] [OH-]2 [Zn+2] = S moles / L [OH-] = 2S moles / L 3.00 x 10-17 = [S] [2S]2 3.00 x1 0-17 = 4S3 S3 = 7.5 x 10-18 (click math then cube root) S = 1.96 x 10-6 moles / L S = molar solubility = 1.96 x 10-6 moles /L

Calculate the ratio of CH3NH2 to CH3NH3Cl required to create a buffer with pH = 10.22.

[CH3NH2]/[CH3NH3Cl] =10^(pH−pKa) =10^(10.22−10.64) =0.38

What is the pH of a solution made by mixing 50.00 mL of 0.100 M HCl with 15.00 mL of 0.100 M KOH? Assume that the volumes of the solutions are additive.

[H+] = 15x0.1 = 1.5 millimoles [OH-]= 50 x0.1= 5 millimole resultant= [OH-] = 5 - 1.5/65= 0.0538 pOH = 1.27 pH = 14-pOH = 12.73= 1.273

Calculate the pH of a solution that contains 7.8 x 10-6 M OH- at 25°C.

[H+]=10^-14/[OH-] at 25 celsius so [H+]=10^-14/(7.8*10^-6)=1.282*10^-9 so pH=-log[H+]=-log (1.282*10^-9) =8.892

A strong electrolyte ______ in solution.

completely ionizes

Identify the food that does NOT irritate the wall of the stomach.

egg white

A 50.0 mL sample of 0.200 M sodium hydroxide is titrated with 0.200 M nitric acid. Calculate the pH in the titration after the addition of 60.0 mL of 0.200 MHNO3.

pH=−log[H3O+] =−log0.0120 mol H3O+−0.0100 mol H3O+ / 0.050 L+0.060 =−log0.0020 mol H3O+ / 0.110 L = 1.74

What is the [H3O+] of a 0.100 M solution of HClO? HClO has a Ka = 2.9 × 10−8?

sqr root ka +c sqr root 2.9 × 10^−8 + 0.100 sqr root 29 x 10^−10 5.4 x 10^-5

Does ΔG become more negative or more positive as the temperature increases?

ΔG becomes more positive as the temperature increases. Since the value of ΔS is negative, increasing the temperature of the reaction results in a more positive value of ΔG.