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Calcium hydroxide, Ca(OH)2, is neutralized by hydrochloric acid, HCl, and the products are calcium chloride and water. You have a sample of calcium hydroxide that you know contains 2.6x1024 hydroxide ions, based on an analysis of the sample. How many grams of HCl are required to react with the available calcium hydroxide?



Answer :

n = m/Mr   (n= number of moles of a compound; m= mass of a compound; Mr = formula mass of a compound)

Rearranged: m = nxMr

Using the balanced equation for the reaction; Ca(OH)2 + 2HCl ---> CaCl2 + 2H2O   we can see that there are 2 moles of OH- ions for every 2 moles of HCl and therefore we need to react the same number of moles of HCl as moles of OH- ions:

n, OH- ions = 2.6x10^24 mol

therefore:

n, HCl = 2.6x10^24 mol

Mr, HCl = 36.5 (use periodic table and the molecular masses of each element in the compound to find)

To calculate the mass of HCl needed, we multiply the number of moles of HCl and the Mr of HCl:

(2.6x10^24) x 36.5 = 9.49x10^25 g of HCl is required


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