Question

How many moles of oxygen gas are needed to react completely with 17.9 mL Mg, with a density of 1.74 g/mL?

unbalanced equation: Mg + O2 “yields”/ MgO

0.212 mol O2

0.641 mol O2

1.28 mol O2

2.56 mol O2

Answer 1

2Mg + O2 -> 2MgO

Answer 2

`\(Mg + O_2 \rightarrow 2MgO\)` = \(Mg + O_2 \rightarrow 2MgO\)

Have you tried anything yet?

Answer 3

Yeah balancing the equation is the first step

Answer 4

I balanced the equation. I'm assuming I find the volume by dividing the mass by the density?

Answer 5

You are given with volume and density

Answer 6

You have to find the mass first.

Answer 7

Well do I have to find the mass?

Answer 8

ok.

Answer 9

\(mass = density ~ * Volume \)

Yes, you do have to find the mass. Let me give the rason for that.

Answer 10

17.9 x 1.74 gram Mg = 31.15 gram Mg

Answer 11

gram Mg what type of unit is that...?

Answer 12

*reason.

You have : \(2Mg + O_2 \rightarrow 2 Mg O\)

Now, 2 moles of Mg react with 1 moles of Oxygen gas ( O_2) to form 2 moles of MgO

So, if you will find the number of moles of Mg required, then you can easily find the required moles of O_2

Answer 13

okay.

Answer 14

gram Mg means gram of magnesium.

Answer 15

Okay.

Answer 16

So, now, what we have is :

Density (unit is gram per mL ) = ?

Volume (unit is mL ) = ?

Answer 17

1.74 g/mL

Answer 18

17.9 mL Mg

Answer 19

right! now, find the mass using mass = volume * desnity

Answer 20

*density (typo)

Answer 21

31.15 g Mg

Answer 22

Right. So, now, we need to find the number of moles of Mg :

Number of moles = Given mass / Molar mass

What is the atomic mass of Magnesium (Mg) ?

Answer 23

24.31

Answer 24

g

Answer 25

Good! So, find the number of moles now.

Answer 26

1.281

Answer 27

mol

Answer 28

so C?

Answer 29

-_-

Answer 30

what's wrong @No.name

Answer 31

Correct, now, see :

2 moles of Mg react with 1 moles of Oxygen gas to yield 1 mole of MgO

i.e. 2 * moles of Mg should be equal to 1 mole of oxygen

Answer 32

Let @mathslover explain

Answer 33

That correct was for "no. of moles =1.281 "

Answer 34

So it's D? 1.28 * 2 =2.56

Answer 35

Oops wait..

2 moles of Mg react with 1 moles of Oxygen gas to yield 1 mole of MgO

i.e. 2 * moles of Mg should be equal to 1 mole of oxygen


This was wrongly phrased. Wait please.

Answer 36

Nah, I'm just dumb IG...

Answer 37

@No.name seems to think so too

Answer 38

no u r smart

Answer 39

hmm

Answer 40

what we found is 1.28 moles of Mg which is actuall equal to 2 *moles of Mg

Answer 41

well, thanks

Answer 42

so divide by 2 and get 0.64

Answer 43

Right!

Answer 44

yay

Answer 45

Thanks @mathslover

Answer 46

and @No.name

Answer 47

You're welcome @Lena772 ! Good Luck.