a) K2O
\(\%mK=\dfrac{2.39}{2.39+16}.100\approx82,979\%\\ \rightarrow\%mO\approx17,021\%\)
b) Mg(OH)2
\(\%mMg=\dfrac{24}{24+2.\left(16+1\right)}.100\approx41,38\%\\ \%mO=\dfrac{16.2}{24+2.\left(16+1\right)}.100\approx55,17\%\\ \rightarrow\%mH=\dfrac{2.1}{24+2.\left(16+1\right)}.100\approx3,45\%\)
c) Al2(SO4)3
\(\%mAl=\dfrac{27.2}{27.2+3.\left(32+4.16\right)}.100\approx15,79\%\\\%mS=\dfrac{3.32}{27.2+3.\left(32+4.16\right)}.100\approx28,07\%\\ \rightarrow\%mO\approx56,14\% \)
d) Na2CO3
\(\%mNa=\dfrac{2.23}{2.23+12+3.16}.100\approx43,40\%\\ \%mC=\dfrac{12}{2.23+12+3.16}.100\approx11,32\%\\ \rightarrow\%mO=\dfrac{3.16}{2.23+12+3.16}.100\approx45,28\%\)
