Subtract 2.5×10^-5 from 8.0×10^-3 with regards to significant numbers.

8.0 x 10⁻³

Explanation:

(8.0×10⁻³)  - (2.5×10⁻⁵)

= (8.0×10⁻³)  - (2.5 × 10⁻² x 10⁻³)   (factor out 10⁻³)

= 10⁻³  [ 8 - (2.5 x 10⁻²) ]

= 10⁻³  [ 8 - 0.025 ]

= 10⁻³  [ 7.975 ]

= 7.975 x 10⁻³

however we can observe that both original numbers are expressed to 2 significant figures, hence we must express our answer also in 2 significant figures by rounding 7.975 to 8.0, thereby giving us:

8.0 x 10⁻³

  the grams     of oxygen gas   that can be produced     is 20.6   grams of o₂

calculation

2liclo₃ →   2 licl + 3 o₂

step 1:   find the moles of liclo₃

moles = mass÷ molar mass

from periodic table the molar mass of liclo₃ =6.9 +35.5   +(16 x3) =90.4 g/mol

moles=38.7 g÷90.4 g/mol=0.4281   moles

step 2:   use the   mole ratio   to calculate the moles of o2

from equation above, liclo₃: o₂   is 2: 3  

therefore the moles of   o₂=0.4281 moles x3/2 =0.6422   moles

step 3: find mass   of o₂

mass= moles x molar mass

from periodic table the   molar mass of   o₂ = 16 x2= 32 g/mol

mass=0.6422   moles   x   32 g/mol = 20.6 grams of o₂

well clustered together.

points close on a scatter diagram