2. Platinum metal has a density of 21.4 g/mL. If the block measures 3 cm, by 0.03 m, by 40 mm how much does it weigh in milligrams?

80mg

Explanation:

Given parameters:

Density of Platinum metal = 21.4g/mL

Dimension of the metal  = 3cm by 0.03m by 40mm

Unknown:

Weight of the metal in milligrams?

Solution:

Density is the mass per unit volume of a substance.

Mathematically;

          Density  =

Volume of the platinum metal  = l x w x h

 Let us convert the dimension of the metal to the same unit;

            3cm x 0.03m x 40mm

    convert to cm;

           100m = 1cm

           0.03m  =   = 0.0003cm

     -- 40mm;

            1mm = 0.1cm

           40mm  = 40 x 0.1  = 4cm

Volume of the metal  = 3 x 0.0003 x 4  = 0.0036cm³

1mL = 1cm³; so volume  = 0.0036mL

     Mass of the metal  = 21.4 x 0.0036  = 0.08g

       1g  = 1000mg

     0.08g  = 0.08 x 1000 = 80mg

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g