Answer
Approximately 6.86g.
Work Step by Step
1. Convert the mass of $O_2$ to nº of moles:
$mm(O_2) = 2*16 = 32g/mol$
$n(moles) = \frac{mass(g)}{mm}$
$n(moles) = \frac{7.5}{32}$
$n(moles) = 0.234$
2. Using the proportion gave in the balanced equation:
$\frac{2}{3} = \frac{x}{0.234}$
$3x = 0.234 * 2$
$x = \frac{0.468}{3}$
$x = 0.156 moles (CO_2)$
3. Convert that number to grams:
$mm(CO_2) = 12*1 + 16*2 = 44g/mol$
$mass(g) = n(moles) * mm$
$mass(g) = 0.156 * 44$
$mass (g) = 6.864$
