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QUESTION

# How many NaOH is required to neutralize 1500cm^3 of 0.1N HCl? a. 60g b. 6g c. 4g d. 40g

The answer is b) 6 g

Start by writing the balanced chemical equation for this

NaOH_((aq)) + HCl_((aq)) -> NaCl_((aq)) + H_2O_((l))

Notice that you have a 1:1 between sodium hydroxide and hydrochloic acid; this means that a complete would require equal numbers of moles of sodium hydroxide and hydrochloric acid.

Now, you know that the hydrochloric acid solution has a normality of 0.1 N. Normality is simply a measure of reactivity, meaning that it is calculated by taking into account how a substance behaves in a particular reaction.

Hydrochloric acid dissociates in aqueous solution to rpoduce

HCl_((aq)) -> H_((aq))^(+) + Cl_((aq))^(-)

The net ionic equation for your reaction will be

OH_((aq))^(-) + H_((aq))^(+) -> H_2O_((l))

In your case, a 0.1 N solution means that the hydrochloric acid solution provides 0.1 moles of protons, H^(+), per liter to the reaction.

Since 1 mole of "HCl" produces 1 mole of H^(+), the of the solution will be equal to "0.1 mol/L".

The volume of the solution will be

1500color(red)(cancel(color(black)("cm"^3))) * ("1 dm"""^3)/(1000color(red)(cancel(color(black)("cm"^3)))) = "1.5 dm"""^3

This means that you can now calculate how many moles of hydrochloric acid took part in the reaction (remember that "1 dm"^3 = "1 L")

C = n/V implies n = C * V

n_"HCl" = 0.1 "moles"/color(red)(cancel(color(black)("L"))) * 1.5color(red)(cancel(color(black)("L"))) = "0.15 moles HCl"

The aforementioned mole ratio tells you that the number of moles of sodium hydroxide needed to neutralize this many moles of hydrochloric acid is

n_(NaOH) = n_(HCl) = "0.15 moles"

To get the mass of sodium hydroxide needed, use its molar mass

0.15color(red)(cancel(color(black)("moles"))) * "40.0 g"/(1color(red)(cancel(color(black)("mole")))) = color(green)("6 g")