a student decides to find the molar enthalpy for the reaction between phosphoric acid and calcium hydroxide. they have a 0.250 m solution of ca(oh)2, which they will use; they can only find a 2 m stock solution of h3po4. if they want 236 ml of a 0.22 m solution of h3po4, how many ml of the stock solution should they use to prepare their solution by diluting the stock?

The triprotic acid phosphoric acid, also called orthophosphoric acid, is present as a viscous liquid. 74.3 mls H3PO4 needed to prepare their solution by diluting the stock.

What is phosphoric acid and calcium hydroxide?

The triprotic acid phosphoric acid, also called orthophosphoric acid, is present as a viscous liquid. Both humans and laboratory animals' skin, eyes, and other mucous membranes are irritated or damaged by it. The possibility for irritation in its salts, however, is substantially lower.
An inorganic solid with the chemical formula H3PO4, phosphoric acid is an odorless, colorless substance that contains phosphorus. It is frequently found as an 85% aqueous solution, which is a syrupy liquid that is colorless, odorless, and non-volatile.
Slaked lime, often known as calcium hydroxide, is an inorganic substance having the chemical formula Ca(OH)2. When water is combined with quicklime (calcium oxide), a colorless crystal or white powder is created.

First part:

Use V1M1 = V2M2 for such a dilution problem.

V1 = initial volume = ?

M1 = initial molarity = 2.1 M

V2 = final volume = 285 ml

M2 = final molarity = 0.31 M

(V1)(2.1)( = (285)(0.31)

V1 = 40.7 mls of 2.1 M H3PO4 are needed

Second part:

Utilising 0.28 M H3PO4, find mls needed to react with 125 ml of 0.250 M Ca(OH)2.

The balanced equation for this reaction is: 3Ca(OH)2 (aq) + 2H3PO4 (aq) ---> Ca3(PO4)2 (s) + 6H2O (l)

First we'll discover the moles of Ca(OH)2 present:

125 ml x 1 L/1000 ml x 0.250 mol/L = 0.03125 mols Ca(OH)2 present

From the balanced equation, we now find moles of H3PO4 needed:

0.03125 mols Ca(OH)2 x 2 mols H3PO4 / 3 mols Ca(OH)2 = 0.0208 mols H3PO4 needed

Finally, we find volume (mls) of H3PO4 needed:

0.0208 mols H3PO4 x 1 L / 0.28 mols = 0.0743 L x 1000 ml/L = 74.3 mls H3PO4 needed.

To learn more about phosphoric acid refer to:

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