You are given a sample containing 0.90 moles of a . a) how many atoms are in the sample if the substance is copper? . b) how many atoms are in the sample if the substance is silver? . c) how many molecules are present in the sample if the substance is benzene, c6h6? .

For every mole of any substance or element, the total number of atoms is 6.022 x 10^23. This is called the avogadro's number. Hence, for a) for a 0.90 mole copper, the number of atoms is 5.42 x10^23. This also applies for B) which gives silver as given. For c), the number of molecules present in a compound is also the same. Thus, for a,b,and c, the answer is 5.42 x10^23.

1) according to the law of conservation of mass ,in all chemical reactions total mass is unchanged

Answerthis solution will not form a precipitateexplanationsolubility equilbrium:         pbf₂(s)  ⇄ pb²⁺(aq) + 2 f⁻(aq)the solubility product expression is    (we exclude solids from the equilibrium expression).now suppose we have the trial ion product q, which we can define as    then, we can interpret  q as the product of the concentration of the ions that we have and ksp as the product of the ion concentrations that are needed to form a saturated solution.if q > ksp, then that implies that there will be a surplus of ions that exceed the amount that is required to form a saturated solution. a precipitate will then form (the precipitate continually  forms until the surplus ions are removed and q is decreased to ksp's value).if q = ksp, the saturated solution that forms is barely saturated and the precipitate will be minimal.if q < ksp, then the ion concentration will not be enough to form a saturated solution (so no precipitate).using our information, we calculate the trial ion product:     since q = 2.7  × 10⁻⁸ < ksp =  4  ×  10⁻⁸, a precipitate will not form.