Calculate the amount of acid and base needed for a specific pH or the pH when gi

Question

Calculate the amount of acid and base needed for a specific pH or the pH when given a specific amount of acid and base 34)To make a buffer with a pH of 7 using hypochlorous acid (K 3.5 x 103) a student adds ?kat 0.250 moles of HCIO to a beaker with 200.0 mL of water. How many moles of NacIo should she add to the beaker? aIf: oka a) 0.088 mol b) 0.25 mol c) 0.58 mol d) 0.71 mol e) 1.4 mol log L ?? shouldshe add to the beaker? 09 ? 35) To prepare a strychnine (Kb18x106 solution with a pH-9 what ratio (in decimal form of strychnine to its chloride salt will be required? a) 0.745 b) 1.32 c) 2.67 d) 3.21 e) 5.56 36) A buffer is formed from the combination of 0.50 moles of nitrous acid (Ka 4.5 x 10-4) and 0.50 moles of sodium nitrite in 1.00 liters of water. a) What is the pH of the buffer solution? (4 points b) If 10.0 mL of 1.00MI HCl solution is added to 100.0 mL of the buffer solution the pH be? (4 points) Answer: 3,17 37) How many moles of HOI should be added to 0.80 moles of NaOl in 500.0 mL of solution to create a buffer with a pH 10.50? Ka HOl - 2.3 x 1011 a) 0.80 mol b) 0.91 mol c) 1.0 mol d) 1.1 mol e) 1.2 mol te Volume IL Actount for dinor do it in males hen or do it in males

Explanation / Answer

Answer:

34) Given pH=7 and Ka=3.5x10^-8 for hypochlorous acid.

pKa=-logKa=-log(3.5x10^-8)=7.456

Given moles of HClO=0.250 mol and volume=200 mL=0.2 L,

Therefore [HClO]=0.250mol/0.2 L=1.25M, [NaClO]=? salt

From Henderson-Hasselbalch equation

pH=pKa+log[salt]/[acid]

7=7.456+log[NaClO]/(1.25)

log[NaClO]/(1.25)=-0.456

[NaClO]=(1.25) X 10^-0.456=0.4375M.

Moles of NaClO=molarity xVolume=0.4375 mol/L X 0.2 L=0.0874 mol.

Moles of NaClO~0.088 mol.

Option (a) correct.

35) Given pH=9, Ka=1.8x10^-6 then pKa=-logka=-lgo(1.8x10^-6)

pKa=5.745

Here acid is Strychnine and salt is strychnine chloride

From Henderson-Hasselbalch equation

pH=pKa+log[salt]/[acid]

log[salt]/[acid]=9-5.745=3.255

[salt]/[acid]=10^3.255=1800.

We have to find [acid]/[salt]=1/1800=5.56x10^-4

The ratio [strychnine]/[strychnine-Cl]=5.56 (in decimal form).

Option (d) is correct.

As per guidelines I have to answer first question. But I answered two for you.

Thanks and I hope you like it.

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