Question

Please answer part 1 and 2. On part 2, I keep getting the wrong sig figs please make sure they are correct. Thank you!

Part 1:

A chemist dissolves 669. mg of pure sodium hydroxide in enough water to make up 170. mL of solution. Calculate the pH of the solution. (The temperature of the solution is 25 °C.) Be sure your answer has the correct number of significant digits. x 6 ?

Part 2:

Answer 1

1)

Molar mass of NaOH,

MM = 1*MM(Na) + 1*MM(O) + 1*MM(H)

= 1*22.99 + 1*16.0 + 1*1.008

= 39.998 g/mol

mass(NaOH)= 699 mg

= 0.699 g

use:

number of mol of NaOH,

n = mass of NaOH/molar mass of NaOH

=(0.699 g)/(40 g/mol)

= 1.748*10^-2 mol

volume , V = 1.7*10^2 mL

= 0.17 L

use:

Molarity,

M = number of mol / volume in L

= 1.748*10^-2/0.17

= 0.1028 M

[OH-] = 0.1028 M

use:

pOH = -log [OH-]

= -log (0.1028)

= 0.988

use:

PH = 14 - pOH

= 14 - 0.988

= 13.012

Answer: 13.01

2)

A)

use:

pKa = -log Ka

2.2 = -log Ka

Ka = 6.31*10^-3

Answer: 6*10^-3

B)

use:

pKa = -log Ka

= -log (1.4*10^-10)

= 9.8539

Answer: 9.85

C)

use:

pKa = -log Ka

= -log (1.26*10^-9)

= 8.8996

Answer: 8.900

The one with greater value of Ka is stronger acid.

Strength of acid is:

A > C > B