Your current SOP for making a caustic solution for removing tartrates in your ta

Question

Your current SOP for making a caustic solution for removing tartrates in your tanks calls for using 100 grams of NaOH in 10 Liters of water. You want to try using KOH to reduce the sodium in your wastewater. Part I: How many moles of NaOH are in 100 grams expressed in 1 decimal (use 40 grams for the molecular weight of NaOH)? Part II What is the molar concentration of your NaOH solution according to the SOP expressed in 2 decimals? Part III: How many grams of KOH per 10 liters of water would you need to weigh to get the same molar concentration (use 56 grams for the molecular weight of KOH) expressed with no decimal? Your current SOP for making a caustic solution for removing tartrates in your tanks calls for using 100 grams of NaOH in 10 Liters of water. You want to try using KOH to reduce the sodium in your wastewater. Part I: How many moles of NaOH are in 100 grams expressed in 1 decimal (use 40 grams for the molecular weight of NaOH)? Part II What is the molar concentration of your NaOH solution according to the SOP expressed in 2 decimals? Part III: How many grams of KOH per 10 liters of water would you need to weigh to get the same molar concentration (use 56 grams for the molecular weight of KOH) expressed with no decimal?

Explanation / Answer

I) The number of moles of a substance you have is simply the weight you have in grams, divided by the molecular mass for that compound. So, we simply divide 100 by 40 to give an answer of 2.5 mol.

II) The number of moles of a compound in a solution is found by multiplying its concentration by its volume (in litres).

Working backwards, we divide the number of moles (2.5) by the volume (10) to give the concentration of 0.25 mol/L.

III) We already know that we can make a 0.25 mol/L solution by dissolving 2.5 mol in 10 litres. All that remains is to find the weight of 2.5 mol of KOH, given by multiplying 2.5 by its molecular weight (56), for a final answer of 140 g.

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