Astudent cleaned a crucible with hcl. after pouring the hcl into the waste container, the crucible was neither rinsed with water nor dried before the student added the nahco3-nacl mixture. the crucible contained some residual hcl. how would this affect the calculated percentage of nahco3 in the mixture

The calculated percentage of NaHCO3 will be lower than it should be. The HCl left in the crucible will react with the NaHCO3. The formula is HCl + NaHCO3 = NaCl + H2O + CO2 The key thing to note is that some of the NaHCO3 will be converted to NaCl so it will look like the original concentration of NaHCO3 is lower than it should be.