Answer:
Step-by-step explanation:
Molecular weight is the mass of substance containing 1 Avogadro's Number of particles which is 6.023 x 10²³ particles. Such is calculated by adding the formula weights of all elements in the compound of interest. For Pb(NO₃)₂ the molecular weight is 1Pb + 2N + 6O = 1(207g/mol) + 2(14g/mol) + 6(16g/mol) = 331g/mol.
For the problem, it is asking for the number of moles Pb(NO₃)₂ in the given mass of 170g of the substance. Such is calculated by dividing the given mass (170g) by molecular weight (331g/mol).
moles of Pb(NO₃)₂ in 170g = given mass (170g)/molecular weight (331g/mol) = 0.51 mole of Pb(NO₃)₂.