Question

 What is the radius (in cm) of a cylindrical silicon block (density = 2.03 g/cm³) with the height of 3.20 cm to react with 76.0 g of sodium hydroxide by the reaction below? 

Si_(s) + NaOH_(aq) + H2O_(l) → Na2SiO3_(aq) + H2_(g)

Answer 1

$Si +4NaOH+2H_2O\to 2NaSiO_3+4H_2$

moles of NaOH=$\frac{76}{23+16+1}=1.9$

mole ratio Si : NaOH=2:4=1:2

moles of $Si=1.9/2=0.95$

mass of Si $=0.95\times 28=26.6g$

volume of silicon $=mass/density=26.6/2.03=13.1cm^3$

volume of cylindrical silicon $=\pi \times r^2 \times h=13.1$

$r^2=\frac{13.1}{\pi \times 3.2}=1.303$

$r=\sqrt{1.303} =1.14cm$