data h2o;
input a w;
cards;
2 1.008
1 16
;
run;
proc print data=h2o;
run;

options mprint;
%let chemdata=h2o;
%let molecule=Water(H2O);

%macro molarmass;
  data mmm;
  set &chemdata;
  mm=sum(a*w);
  ;
  proc means data=mmm sum noprint;
  var mm; 
  output out=mmsum sum=;
  run;
  title "Molar mass for &molecule"; 
  proc print data=mmsum;
  var mm;
  run;
  title;
%mend;

%molarmass

data sucrose;
input a w;
cards;
12 12.01
22 1.008
11 16
;
run;
* no need to rerun macro if it worked before and is same SAS session;
* NEED to reset %LET variables;
%let chemdata=sucrose;
%let molecule=Sucrose;
%molarmass