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1. You want to prepare 50cm cube of 0.1m NaOH frrom exactly 50%(wt/wt) NaOH solution....

1. You want to prepare 50cm cube of 0.1m NaOH frrom exactly 50%(wt/wt) NaOH solution. What volume of the 50% solution is required?
2, what is a primary standard? Can KOH be used as a primary standard? Explain.
3. An aqueous sample is analysed and found to contain 4% NaOH.
(i). Calculate the concentration of the molar concentration of the solution assuming the density of water is 1.00g/cm cube.
(ii). If the solution is neutralized with 1.0M H2SO4, what volume of the acid will be needed.?

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Answers (4)

isaaq
2 months ago
1.solution.
First of all what is the Molar conc of 50% wt/wt of NaOH?
50% wt/wt means 50g NaOH/100g water.
If we assume density of water is 1...
then you have 50g NaOH /100mL water.
thus the mass conc = 50g/0.1L (note that 0.1L = 100 mL).
thuse mass conc = 500g/L.
but molar mass of NaOH is ~ 40g/mol
and more so molar conc = mass conc/ molar mass
therefore the molar conc = 500g/L ÷ 40g/L
= 12.5mol/L or 12.5M
now using C1V1 = C2V2 .....(1)
where C1 is the initial molar conc = 12.5M
V1 is the volume of the initial solution you will need to measure out = unknown.
C2 is the Molar conc of the solution you want to prepare = 0.1 M
V2 is the volume of the solution you want to prepare = 50mL.
thus making V1 subject of the formula from equation (1) you will have ;
V1 = (C2V2)/C1
thus V1 = 0.4 mL.
  • isaaq: so just measure out 0.4 ml into a 50mL flask and make up the volume to the mark.
    Like 0    Dislike 0   2 months ago
  • isaaq: question three(3).
    a. 1.0M

    b. 50 mL (assuming the basis of the % is same with the volume of base)
    Like 0    Dislike 0   2 months ago
  • isaaq: number 2.
    A primary standard ideally:
    has a high molecular weight, is available in a pure state, is stable and doesn't readily absorb or lose water.

    KOH can not be used as a primary standard as it has low mole. wt, it readily absorbs CO2 and water from the air and is not available in a pure form.
    Like 0    Dislike 0   2 months ago
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