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What mass of water is produced when 8.0g of hydrogen reacts with…

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What mass of water is produced when 8.0g of hydrogen reacts with excess oxygen?

A. 8.0g

B. 16.0g

C. 36.0g

D. 72.0g

QUICK ANSWER…

D

DETAILS…

To resolve this, we must write out the balanced equation thus: 2H₂ + O₂→ 2H₂O

From this balanced equation we can infer that:

2 moles of hydrogen is required to form 2 moles of water

Now, we have to determine how many moles of hydrogen is equivalent to a mass of 8g

2g of H = 1 mole, therefore,

8g of H = x mole.

Cross multiplying to solve for x, we have:

2x = 8

x = 8/2 = 4moles

this implies that 4 moles of hydrogen is present.

Now, if from the balanced equation,

2 moles of H₂ forms 2 moles of H₂O, then

4 moles of H will form Y moles of H₂O

Cross multiplying to find Y, we have:

2Y = 4(2) = 8

Y = 8/2 = 4

This implies that the number of moles of water formed = 4 moles.

Now converting these 4 moles of water to grams, we have:

Molar mass of HO = 2 + 16 = 18g

This implies that 1 mole of HO = 18g, therefore,

4 moles will be = 4 × 18 = 72g

SHORT-CUT

There’s a short cut solution,

using the balanced equation,

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2H₂ + O₂→ 2H₂O

mass of 2H₂ = 2(2) = 4g

mass of 2H₂O = 2(2+16) = 2(18) = 36g

this implies that:

4g of hydrogen gas produces 36g of water, therefore,

8g of hydrogen gas will produce X

cross multiplying to solve for X, we have:

X(4) = 8(36)

X = (8 × 36)/4 = 72g

Now for the right answer to the above question:

  1. Option A is incorrect.
  2. Option B is incorrect.
  3. C is incorrect.
  4. D is the correct answer.

KEY-POINTS…

You may please note these/this:

  • For accuracy and clarity purposes, you must write out the balanced chemical equation of questions like this.
  • The importance of writing out the balanced equation is to properly understand the mole ratios involved, and to make your assumptions properly.
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/ culled from 2020 JAMB-UTME chemistry past question 32 /

What mass of water is produced when 8.0g of hydrogen reacts with... » QuizTablet
What mass of water is produced when 8.0g of hydrogen reacts with... » QuizTablet

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