The diagram shows a model of a water molecule. hydrogen atom. oxygen atom covalent bond (a) Explain, in terms of electrons, how a covalent bond is formed between an oxygen atom and a hydrogen atom. (b) Calculate the relative formula mass of water, H₂O. (Relative atomic masses: H = 1.0, O = 16) (c) Hydrogen burns in oxygen to form water. (i) Write the balanced equation for this reaction. (ii) In an experiment the mass of water obtained was 2.0 g. The theoretical yield for this experiment was calculated to be 4.0 g. Calculate the percentage yield. (iii) Suggest one reason why less than 4.0 g of water was obtained in this experiment.

GCSE Edexcel Chemistry Percentage yield: The diagram shows a model of a w

The diagram shows a model of a water molecule - Edexcel - GCSE Chemistry - Question 4 - 2012 - Paper 1

Question 4

The diagram shows a model of a water molecule. hydrogen atom. oxygen atom covalent bond (a) Explain, in terms of electrons, how a covalent bond is formed between... show full transcript

Worked Solution & Example Answer:The diagram shows a model of a water molecule - Edexcel - GCSE Chemistry - Question 4 - 2012 - Paper 1

Step 1

Explain, in terms of electrons, how a covalent bond is formed between an oxygen atom and a hydrogen atom.

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Answer

A covalent bond is formed when an oxygen atom shares electrons with hydrogen atoms. Oxygen has six electrons in its outer shell and needs two more to achieve a full octet. Each hydrogen atom has one electron and can share that with the oxygen atom. Thus, one hydrogen atom shares its electron with the oxygen, and the other hydrogen atom shares its electron, resulting in a stable molecule of water (H₂O) with two covalent bonds.

Step 2

Calculate the relative formula mass of water, H₂O.

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Answer

To calculate the relative formula mass of water, H₂O, we sum the relative atomic masses of its constituent elements:

Each hydrogen (H) has a mass of 1.0. Since there are two hydrogen atoms:

$2 imes 1.0 = 2.0$
The oxygen (O) has a mass of 16.0.

Thus, the total relative formula mass of water is:

$2.0 + 16.0 = 18.0$

Step 3

Write the balanced equation for this reaction.

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Answer

The balanced equation for the combustion of hydrogen in oxygen to form water is:

ightarrow 2H_2O$$

Step 4

Calculate the percentage yield.

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Answer

Percentage yield is calculated using the formula:

$ext{Percentage Yield} = rac{ ext{Actual Yield}}{ ext{Theoretical Yield}} imes 100$

For this experiment:

Actual Yield = 2.0 g
Theoretical Yield = 4.0 g

Plugging in the values:

$ext{Percentage Yield} = rac{2.0}{4.0} imes 100 = 50 ext{%}$

Step 5

Suggest one reason why less than 4.0 g of water was obtained in this experiment.

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Answer

One reason why less than 4.0 g of water was obtained could be due to experimental losses, such as water evaporation or measurement inaccuracies during the process.

The diagram shows a model of a water molecule - Edexcel - GCSE Chemistry - Question 4 - 2012 - Paper 1

Worked Solution & Example Answer:The diagram shows a model of a water molecule - Edexcel - GCSE Chemistry - Question 4 - 2012 - Paper 1

Explain, in terms of electrons, how a covalent bond is formed between an oxygen atom and a hydrogen atom.

Calculate the relative formula mass of water, H₂O.

Write the balanced equation for this reaction.

Calculate the percentage yield.

Suggest one reason why less than 4.0 g of water was obtained in this experiment.

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