Question

An analysis of sodium dichromate gives the following mass percentages: 17.5% Na, 39.7% Cr, and 42.8% O. What is the empirical formula of the compound?

Answer 1

An analysis of sodium dichromate gives the following mass percentages: 17.5% Na, 39.7% Cr, and 42.8% O. What is the empirical formula of the compound?

**Solution:**

For 100g of sodium dichromate:

m(Na)=17.5g

m(Cr)=39.7g

m(O)=42.8g

n(Na)=m(Na)/M(Na)=17.5/23=0.76mol

n(Cr)=m(Cr)/M(Cr)=39.7/52=0.76 mol

n(O)=m(O)/M(O)=42.8/16=2.67mol

n(Na):n(Cr):n(O)=0.76:0.76:2.67

n(Na):n(Cr):n(O)=1:1:3.5

n(Na):n(Cr):n(O)=2:2:7

empirical formula of sodium dichromate Na₂Cr₂O₇

**Answer:** Na₂Cr₂O₇