a couple of pennies have a mas of 5.2 grams. Asuming that the pennies are 100% percent copper, how many moles of copper are the pennies

5.2g copper (Cu) => 0.082 moles copper (2 sig.figs.)

Explanation:

mole conversions:

grams to moles => divide by formula wt.

moles to grams => multiply by formula wt.

gas volumes to moles => divide volume by 22.4Liters/mole (STP conditions only)

This problem:

mass to moles => divide by formula wt.

mass = 5.2g = 5.2g/63.5g/mole = 0.082 moles copper (2 sig.figs.)

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

the density of gold = 19.3 g/cm3

the relation between density and mass and volume is

density = mass / volume

given :

mass of gold = 13 g

density = 13g / volume = 19.3

volume = 13 /19.3 = 0.67 cm^3

thus volume of gold nugget = 0.67 cm^3