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This question is about gases - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1

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This question is about gases. (a) When sodium is added to water, hydrogen gas is produced. Which observation shows that a gas has been produced? (b) Some damp lit... show full transcript

Worked Solution & Example Answer:This question is about gases - Edexcel - GCSE Chemistry Combined Science - Question 6 - 2022 - Paper 1

Step 1

Which observation shows that a gas has been produced?

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Answer

When sodium is added to water, the observation that indicates a gas has been produced is (B) effervescence is seen. Effervescence signifies that gas bubbles are forming, indicating a reaction is taking place.

Step 2

Which gas bleaches damp litmus paper?

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Answer

The gas that bleaches damp litmus paper is (A) carbon dioxide. This gas reacts with water to form carbonic acid, which is capable of changing the color of the litmus paper.

Step 3

Calculate the mass of carbon dioxide that has been released.

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Answer

To find the mass of carbon dioxide released during the heating of calcium carbonate, we can use the following calculation:

  1. Start with the initial mass of calcium carbonate: 5.000g.

  2. Subtract the mass of the solid remaining (2.800g) from the initial mass:

    extMassofCO2=5.000g−2.800g=2.200g ext{Mass of } CO_2 = 5.000g - 2.800g = 2.200g

Thus, the mass of carbon dioxide released is 2.20g (to three significant figures).

Step 4

Explain, using Figure 9, why helium is inert.

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Answer

Helium is inert because it has two electrons in its outer shell, which is full. This stability means that helium does not readily gain, lose, or share electrons during chemical reactions. Being in group 18 of the periodic table, helium is classified as a noble gas, which are known for their lack of reactivity.

Step 5

State one property of helium, apart from it being inert, that makes it suitable for filling balloons.

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Answer

One property of helium that makes it suitable for filling balloons is that it is less dense than air. This property allows balloons filled with helium to rise in the atmosphere.

Step 6

Explain how the relative amount of each of the gases in Figure 10 has increased or decreased over time.

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Answer

Over time, the composition of Earth's atmosphere has changed due to various natural processes and human activities.

  1. Carbon Dioxide: Initially present in large amounts, carbon dioxide levels have decreased due to the formation of oceans and the absorption of CO<sub>2</sub> by water. Human activities, particularly burning fossil fuels, are now increasing CO<sub>2</sub> levels due to emissions.

  2. Water Vapour: This gas was prevalent in the early atmosphere but has decreased as the planet cooled, allowing water to condense into liquid form. The water vapour levels have fluctuated but overall remain low in the current atmosphere.

  3. Oxygen: Originally in very low concentrations, oxygen levels have increased significantly due to photosynthesis. Plants and cyanobacteria produce oxygen as a by-product of photosynthesis, significantly enhancing its concentration in the atmosphere.

These changes reflect both natural evolution of the atmosphere and human contributions.

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