Answer in General Chemistry for Bhavya #152342

Q152342

10g of Sodium hydroxide reacts with 6g of Hydrochloric acid to form 12g of Sodium Chloride along with some water. Calculate the mass of water formed in the reaction according to the given information. State the law used by you in calculating this mass.

Solution:

Convert 10g of NaOH and 6 g of HCl to moles by using their molar mass.

molar mass of NaOH = 1 * atomic mass of Na + 1 * atomic mass of O + 1 * atomic mass of H

= 1 * 22.99 g/mol + 1 * 15.999 g/mol + 1 * 1.0079 g/mol

= 39.9969g/mol

moles of NaOH = “=10g NaOH * frac{1mol NOH}{39.9969g NaOH} = 0.2500 mol NaOH” ;

molar mass of HCl = 1 * atomic mass of H + 1 * atomic mass of Cl

= 1 * 1.0079g/mol + 1 * 35.453g/mol

= 36.4609 g/mol

moles of HCl = “=6g HCl * frac{1molHCl}{36.4609g HCl} = 0.1646 mol NaOH ;”

The reaction of NaOH(aq) and HCl (aq) is given as

NaOH (aq) + HCl (aq) —–> NaCl (aq) + H₂O(l) ;

We can see that the mol to mol ratio of NaOH and HCl in the given reaction is 1 :1.

So same moles of NaOH and HCl combine to give NaCl and H₂O_.

0.1646 mol HCl will react with 0.1646 mol of NaOH. The remaining NaOH will remain unreacted

in the solution.

1) To find moles of H₂O formed

The moles of product formed depends on the moles of Limiting reactant present. We now that

HCl is a limiting reactant here and NaOH is present is in excess.

So moles of H₂O depend on moles of HCl present.

The mol to mol ratio of HCl and H₂O is 1: 1.

so moles of H₂O formed = “= 0.1646 mol HCl *” “frac{1mol H_2O}{1mol HClg } = 0.1646 mol H_2O;”

2) To find grams of H₂O formed

Convert 0.1646 mol H₂O to grams using the molar mass of H₂O.

molar mass of H₂O = 2 * atomic mass of H + 1 * atomic mass of O

= 2 * 1.0079 g/mol + 1 * 15.999g/mol

= 2.0159g/mol + 15.999 g/mol

= 18.0148 g/mol

grams of H₂O = 0.1646 mol H₂O * “frac{18.0148g H_2O}{1mol H_2O} = 2.965 g H_2O ;”

In the given question, the quantity with the least number of the significant figure is 6 g HCl. It is in 1 significant figure, so we round up our answer to 1 significant figure.

Hence the mass of H₂O formed is 3 grams.

We have used the Law of Conservation of mass in calculating the mass.

Law of Conservation of mass: For a chemical process in a closed system, the mass of reactants must equal the mass of products formed.

We used the mole ratio of limiting reactant HCl and H₂O for finding the moles of H₂O formed

and then used the molar mass of H₂O for converting ‘moles of H₂O’ to ‘ grams of H₂O’.