Why is it important to measure the mass of an atom?

What substance has a mass of 9.5g and volume of 2.1cm^3

Which liquid (h2o, h2o + soap, or h2o + salt) has the strongest cohesion and adhesion? (need now plz)

Insoluble sulfide compounds are generally black in color. which of the following combinations could yield a black precipitate? check all that apply. na2s(aq)+kcl(aq) li2s(aq)+pb(no3)2(aq) pb(clo3)2(aq)+nano3(aq) agno3(aq)+kcl(aq) k2s(aq)+sn(no3)4(aq)