Sodium oxide, Na2O, is a white solid. (a) Draw a dot and cross diagram to show the ions in sodium oxide. (b) (i) Sodium oxide reacts with water. An aqueous solution of sodium hydroxide is made. Write the balanced symbol equation for this reaction, including state symbols. (ii) Sodium hydroxide neutralises acids. It is an alkali. Which ion do solutions of alkalis contain? (iii) A salt is made when sodium hydroxide neutralises sulfuric acid. Name this salt. (iv) A sample of hydrochloric acid has a pH of 1.04. A student adds water to the hydrochloric acid until the pH is 3.04. The concentration of hydrogen ions decreases. Calculate the factor by which the hydrogen ion concentration has decreased.

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Sodium oxide, Na2O, is a white solid - OCR Gateway - GCSE Chemistry - Question 21 - 2020 - Paper 3

Question 21

Sodium oxide, Na2O, is a white solid. (a) Draw a dot and cross diagram to show the ions in sodium oxide. (b) (i) Sodium oxide reacts with water. An aqueous solutio... show full transcript

Worked Solution & Example Answer:Sodium oxide, Na2O, is a white solid - OCR Gateway - GCSE Chemistry - Question 21 - 2020 - Paper 3

Step 1

Draw a dot and cross diagram to show the ions in sodium oxide.

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Answer

In sodium oxide (Na2O), sodium ions (Na⁺) and oxide ions (O²⁻) are involved. The dot and cross diagram would depict the sodium ions as circles with a cross inside (indicating they lose their outer electron) and the oxide ion as a larger circle filled with dots (indicating it gains two electrons). Thus, there are two sodium ions for each oxide ion.

Step 2

Write the balanced symbol equation for this reaction, including state symbols.

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Answer

The balanced symbol equation for the reaction of sodium oxide with water is:

$\text{Na}_2\text{O}(s) + \text{H}_2\text{O}(l) \rightarrow 2\text{NaOH}(aq)$

Step 3

Which ion do solutions of alkalis contain?

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Answer

Solutions of alkalis contain hydroxide ions, represented as OH⁻.

Step 4

Name this salt.

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Answer

The salt formed when sodium hydroxide neutralises sulfuric acid is sodium sulfate, which can be represented as Na₂SO₄.

Step 5

Calculate the factor by which the hydrogen ion concentration has decreased.

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Answer

The pH scale is logarithmic. The change in pH from 1.04 to 3.04 represents:

$\Delta \text{pH} = 3.04 - 1.04 = 2.00$

The factor decrease in hydrogen ion concentration is given by:

$\text{Factor} = 10^{\Delta \text{pH}} = 10^2 = 100$

Thus, the hydrogen ion concentration has decreased by a factor of 100.

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Sodium oxide, Na2O, is a white solid - OCR Gateway - GCSE Chemistry - Question 21 - 2020 - Paper 3

Worked Solution & Example Answer:Sodium oxide, Na2O, is a white solid - OCR Gateway - GCSE Chemistry - Question 21 - 2020 - Paper 3

Draw a dot and cross diagram to show the ions in sodium oxide.

Write the balanced symbol equation for this reaction, including state symbols.

Which ion do solutions of alkalis contain?

Name this salt.

Calculate the factor by which the hydrogen ion concentration has decreased.

Join the GCSE students using SimpleStudy...

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