# Chemical Calculations

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#1

In a reaction sodium hydroxide and hydrochloric acid are reacted together. if 40 g of sodium hydroxide are used how much Hydrochloric acid is use start with a balanced symbol equation
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2 years ago
#2
NaOH + HCl = H2O + NaCl

What you're given in the question is the mass of sodium hydroxide (NaOH), so you can work out the number of moles of sodium hydroxide.
Moles = mass/relative formula mass
The relative forumula mass of NaOH is the total relative atomic masses of sodium, oxygen and hydrogen which is 23 + 16 + 1 = 40
Now find the moles of NaOH, which is 40g/40 = 1 mol

You can use the mole ratios in the balanced equation to find out how many moles of HCl are needed to react with 1 mole of NaOH. The ratio is 1 : 1, so if the moles of NaOH are 1, the moles of HCl are also 1.

Now you need to find the mass of HCl. You know the number of moles and can work out the relative formula mass (1 + 35.5 = 36.5)
Moles = mass/relative formula mass, so mass = moles x relative formula mass
Mass of HCl = 1 mole x 36.5 = 36.5g
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