Question

If 143 grams of chromium react with an excess of oxygen, as shown in the balanced chemical equation below, how many grams of chromium oxide can be formed?
4Cr + 3O2 -> 2Cr2O3

Answer 1

@phi

Answer 2

@shamil98

Answer 3

@ParthKohli

Answer 4

@Preetha

Answer 5

@petiteme

Answer 6

(a) Find the number of moles of chromium.
(b) Find the number of moles of chromium oxide.
(c) Find the number of grams of chromium oxide.

Answer 7

ok thanks

Answer 8

no problem

Answer 9

but how do i find the gram of CrO?

Answer 10

No you don't, it's asking for the gram of Cr2O3

Answer 11

ok

Answer 12

i got the 2 numbers, what do i do next?
103.992
47.997

Answer 13

What numbers are these?

Answer 14

the numbers after i multiplied them. So 103.992 is Cr's mole number x 2
And 47.997 is 15.999 x 3

Answer 15

Multiplying Cr's mole number x 2 doesn't get you anything -_-

Answer 16

;(

Answer 17

then what should i do afterwards?

Answer 18

convert 143 grams of chromium to moles

Answer 19

oh!!

Answer 20

yep :)

Answer 21

143 x 1/255.981= 0.559?

Answer 22

i dont know

Answer 23

@JFraser

Answer 24

what is that 0.559 that you have? what UNIT should it have?

Answer 25

so is it correct, other than the units missing?

Answer 26

hello?

Answer 27

....

Answer 28

0.559g/Cr?

Answer 29

phi could you help?

Answer 30

when you divide mass by molar mass, you get units of moles. you've just found the moles of chromium.

now use the balanced reaction to find the moles of chromium (II) oxide that get formed

Answer 31

thanks!!

Answer 32

you start with 143 grams of chromium
a mole of chromium weighs 52 grams

\[ \frac{ 143 \text{ g}}{52 \text{ g/mole}} = 2.75 \text{ moles} \]

Answer 33

ok

Answer 34

if you are kind enough sir, could you also help (later) with another question?

Answer 35

your equation says
4Cr + 3O2 -> 2Cr2O3

the 4 Cr must be the 2.75 moles
on the other side we have 2 Cr2 O3
which is ½ the # of molecules (i.e. moles) of Cr
in other words, for every 4 molecules of Cr we get 2 molecules of Cr2 O3
that means 2.75/2 moles = 1.375 moles of Cr2 O3

Answer 36

ok?

Answer 37

4 molecules of Cr combine with 3 molecules of oxygen to give 2 molecules of chromium oxide.

That means you have ½ as many molecules of chromium oxide as molecules of chromium.
(4 mol of Cr become 2 mol of chromium oxide)

If you started with 2.75 moles * 6.0221415 10^23 molecules / mole of chromium
you will end up with half that many or
1.375 moles * 6.0221415 10^23 molecules / mole

if you want that in grams, you add up how much each molecule weighs.

1 mole (that is , 6.0221415 10^23 molecules ) of \( Cr_2O_3\) weighs 52*2+16*3= 152 grams

Answer 38

THANKS DOOD