Question

10. 17.5 g of NaOH were dissolved in 350 mL of water. The solution was titrated with HNO3 to a methyl orange endpoint (methyl orange is a pH indicating dye that is yellow in base but turns red when the solution turns acidic). What volume of 0.250 M HNO3 will be required to reach a methyl orange endpoint?

Answer 1

Answer:

1750mL

Explanation:

First let us calculate the number of mole of NaOH. This is illustrated below:

Molar Mass of NaOH = 23 + 16 + 1 = 40g/mol

Mass of NaOH = 17.5g

Number of mole = Mass /Molar Mass

Number of mole of NaOH = 17.5/40 = 0.4375mol

Next, let us calculate the molarity of NaOH. This is illustrated below:

Mole = 0.4375mol

Volume = 350mL = 350/1000 = 0.35L

Molarity = mole /Volume

Molarity of NaOH = 0.4375/0.35 = 1.25M

Now, let us write a balanced equation for the reaction.

NaOH + HNO3 —> NaNO3 + H2O

From the equation,

nA = 1

nB = 1

Now we can calculate the volume of the acid by doing the following:

Ma = 0.250 M

Va =?

Mb = 1.25M

Vb = 350mL

MaVa / MbVb = nA/nB

0.250 x Va / 1.25 x 350 = 1

Cross multiply to express in linear form

0.250 x Va = 1.25 x 350

Divide both side by the 0.250

Va = (1.25 x 350) / 0.250

Va = 1750mL

Therefore, the volume of HNO3 required is 1750mL