Convert 7.2 x 10^-5 from scientific notation into standard notation

720 000

Explanation:

7.2

×

10

5

is already expressed in

standard form

I believe you mean express as

original number

To do this consider

10

5

or more generally

10

n

where n is an integer.

• If n > 0

move decimal point n places to the right

• If n < 0

move decimal point n places to the left

here n = 5 > 0, hence move decimal point 5 places to the right.

⇒

7

∙

2

→

720000

∙

⇒

7.2

×

10

5

=

720

000

Explanation:

first, consult an activity series chart to determine if al is more reactive than fe. it is, so it will replace the fe. now, one can continue with the problem.

next, make sure you have a correctly balanced equation.

3feo + 2al ==> 3fe + al2o3

now, determine which reactant (feo or al) is in limiting supply.

moles feo present = 125 g x 1 mole/71.8 g = 1.74 moles

moles al present = 25.0 g x 1 mole/26.98 g = 0.927 moles

since from the balanced equation, it take 3 mol feo for every 2 mol al, al will be limiting.

you can determine this simply by dividing moles of each by their coefficient in the balanced equation. for example: 1.74/3 = 0.58 and 0.927/2 = 0.464. al is less, so it is limiting.

finally, using the stoichiometry in the balanced eq. determine mass of fe that can be produced from 0.927 moles of al.

0.927 moles al x 3 moles fe/2 moles al x 55.8 g/mole = 77.6 g

the correct option is c.

isotopes refers to different forms of the same element with the same atomic number but different mass number as a result of difference in their neutron numbers. isotopes have different relative atomic mass but share the same chemical properties.