How many moles of sodium cyanide (NaCN) would be needed to produce 2.1 moles of sodium sulfate (Na2SO4)?
H2SO4 + 2NaCN → 2HCN + Na2SO4

4.2 moles of sodium cyanide (NaCN) would be needed to produce  2.1 moles of sodium sulfate (Na₂SO₄).

Explanation:

The balanced reaction is:

H₂SO₄ + 2 NaCN → 2 HCN + Na₂SO₄

By reaction stoichiometry (that is, the relationship between the amount of reagents and products in a chemical reaction), the following amounts of moles of each compound are necessary:

Then you can apply the following rule of three: if by stoichiometry to produce 1 mole of sodium sulfate 2 moles of sodium cyanide are necessary, then to produce 2.1 moles of sodium sulfate how many moles of sodium cyanide are necessary?

amount of moles of sodium cyanide= 4.2 moles

4.2 moles of sodium cyanide (NaCN) would be needed to produce  2.1 moles of sodium sulfate (Na₂SO₄).