Reacting Masses - Worked Example

Step by step video showing you how to do the reacting masses calculations. In these questions, you are given the mass of the limiting reactant and asked to calculate the mass of a product, using the balanced chemical equation.

If you are practising, here are some questions for you to try. Show your full working out and see if you arrive at the correct answer:

1. 56 grams of water (H2O) react with sodium (Na) to produce sodium hydroxide (NaOH) and hydrogen gas (H2). Calculate the mass of hydrogen produced. The balanced chemical equation for the reaction is: 2Na + 2H2O  2NaOH + H2

Answer: 3.12 grams

2. Calculate the mass of potassium oxide (K2O) produced from 126 grams of potassium (K) reacting with oxygen (O2) in excess. The balanced chemical equation for the reaction is: 4K + O2  2K2O

Answer: 152 g

3. 34 grams of magnesium (Mg) react with chlorine (Cl2), which is in excess. Calculate the mass of magnesium chloride (MgCl2) produced. The balanced chemical equation for the reaction is:
Mg + Cl2  MgCl2

Answer: 140 grams

4. Excess sulfuric acid (H2SO4) reacts with 23 grams of copper oxide (CuO). Calculate the mass of copper sulfate (CuSO4) that would form. The balanced chemical equation for the reaction is:
CuO (s) + H2SO4 (aq) → CuSO4 (aq) + H2O (l)

Answer: 46.1 grams

[wallacehu]

very clear explanation. Easy to follow and understand

[gregtheegg]

I never comment on videos, but I appreciate you so much, I now feel confident on my end of year test. EVERYONE LIKE

[Uma.uniaaa]

Explained beautifully! Thank you, I was stressing out.

[emilia]

THANK YOUU SOO MUCH - Until now I couldn't fully comprehend the method of working out reacting masses but now thanks to your very concise and clear explanation I DO ! :)

[insync]

Your techniques is very good but instead of using moles we can calculate like this, this is a easy method.
first -
find the relative atomic mass of 4Fe
so, 4 x 56 = 224g
secondly find the atomic mass of iron oxide
iron = (56 x 2)
= 112
112 x 2 (because there are 2 moles in iron)*
=224g
Oxygen = (16 x 3)
=48
48 x 2 ( because there are 2 mole in oxygen)
= 96g
Now we add the masses 224 + 96
= 320g


We know that
4fe 2fe(2)O(3)
224g - 320g
45g - ?

224 g produce 320g grams of iron oxide, how much does 45g produce?
45 x 320
= 64.28g = 64.23g ( 3 sgf)
224
If you guys found this easy try this one or try another one.
your choice.

[zebamaryam]

Thank you for explaining so clearly!!!

[alphaskeli]

i love how simple this man makes it thx

[sujatadasroy]

very nice video, well explained and clear!

[henrycarr]

Just saved me cause I have a chemistry mock tomorrow and fully get this now, thanks.

[TakaiwanaMazarura]

you have made chemistry pretty easy for me

[josephgrant]

such as great explanation thank u, such a different feeling than someone who is terrible at explaining stuff

[jaehyahyuk]

Thank you!!! Nice short video with great explanation.

[Faridbuza]

Thank you so much for this clear explanation. You should do more videos. You're a really great teacher. Thank you ❤

[CrispPlate]

Thank you... You helped me sooo much! 🙏🙏

[emilymonk]

Lol am I the only one who still doesn’t get it

[samanthavirchow]

I'm confused how you found the ratio of 4:2?

[watashiwaaziz]

Since you have the mol ratio, and the no. Of mol for iron, you could just cross multiply, ( quicker method k

[ksumar]

I think the solution can be simplified much easily without the mole concept:
From the equation we know that:
4Fe + 3O2 ---> 2Fe2O3
(56x4=224) of Iron produces 320g of Fe2O3
(twice as much as mole of Fe=160g)
Therefore, if
224g 320g Fe2O3
give would produce:
45 x 320/224 = 64.3g of Iron III Oxide!

[cocopeppi]

why dont we have to worry about the oxygen in 1:54 ?

[servantofgod]

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