Question

維生素A₁中含C的質(zhì)量分?jǐn)?shù)為83.9%，H為10.5%，O為5.6%，其相對(duì)分子質(zhì)量是286，則維生素A₁化學(xué)式為（ ）
A．C₁₉H₂₈O₂
B．C₂₀H₁₄O₂
C．C₂₀H₃₀O
D．C₁₉H₄₂O

Answer 1

【答案】分析：可通過選項(xiàng)中化學(xué)式的計(jì)算，與題中數(shù)據(jù)進(jìn)行對(duì)比，相符者即為維生素A₁的化學(xué)式．
解答：解：A、C₁₉H₂₈O₂相對(duì)分子質(zhì)量=12×19+1×28+16×2=288；
B、C₂₀H₁₄O₂相對(duì)分子質(zhì)量=12×20+1×14+16×2=286；H元素質(zhì)量分?jǐn)?shù)=≈5%
C、C₂₀H₃₀O相對(duì)分子質(zhì)量=12×20+1×30+16=286；H元素質(zhì)量分?jǐn)?shù)=≈10.5%
D、C₁₉H₄₂O相對(duì)分子質(zhì)量=12×19+1×42+16×1=286；C元素質(zhì)量分?jǐn)?shù)=≈79.7%
故選C
點(diǎn)評(píng)：由相對(duì)分子質(zhì)量排除A項(xiàng)，由C元素質(zhì)量分?jǐn)?shù)排除D項(xiàng)，B、C中C元素質(zhì)量分?jǐn)?shù)相等但由H元素質(zhì)量分?jǐn)?shù)排除B項(xiàng)．