2.

Given the following reaction2Na2S2O3 + AgBr

NaBr + Naz[Ag (S203) 2]

a. How many moles of Na2S2O3 are needed to react completely with 42.7 g of AgBr?

0.454moles

Explanation:

Calculate the molar mass of AgBr

Ag=108

Br=80

Molar mass = 108+80

Molar mass=188g/mol

It's mole to gram question

2moles of Na2S2O3 = 188g of AgBr

X moles of Na2S2O3=42.7g of AgBr

Cross multiply

188x=2*42.7

X = 85.4/188

X=0.454moles