Question

Using dimensional analysis:

1) Prepare 1 L of 0.05 M NaOH using a 1 L volumetric flask and 6 M NaOH as the NaOH source. Calculate the amount of 6 M NaOH needed.

2) Calculate the mass of KHP needed to completely react with approximately 35.00 mL of 0.05 M NaOH

I got the correct answers to be 1) 8.33 ml NaOH and 2) 0.357 g KHP, but I didn't use dimensional analysis. I just need to know how to use dimensional analysis to get those answers.

Answer 1

1) to calculate volume of NaOH required

Use the formula C₁V₁ =C₂V₂

Where, C₁ = initial concentration = 6 M

V₁ = initial volume = ?

C₂ = final concentration = 0.05M

V₂ = final volume = 1 L = 1000 ml

C₁V₁ =C₂V₂ Thus

V₁ = C₂V₂ /C₁

Substitute the value in above equation

V₁ = 0.05 X 1000/ 6 = 8.33 ml

to prepre 1 L 0.05 M NaOH from 6 M NaOH required volume = 8.33 ml

2) Balanced chemical reaction is

KHC₈H₄O₄ + NaOH   $\rightarrow$ NaKC₈H₄O₄ + H₂O

no. of mole = molarity X volume of soltion in liter

35 ml = 0.035 liter

no.of mole of NaOH = 0.05 X 0.035 = 0.00175 mole

According to reaction KHP and NaOH react with each other in equimolar proportion (1:1 retio) therefore to react with 0.00175 mole of NaOH required KHP = 0.00175 mole

KHP = 0.00175 mole

molar mass of KHP = 204.22 g/mole

gm of substance = no. of mole X molar mass

gm of KHP needed = 0.00175 X 204.22 = 0.357 gm

0.357 gm KHP required