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Grade 5 · Science

Track mass in a closed system

Account for all matter, including gas, when interpreting a stated closed-system mass measurement.

6 authored questions + worked example

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Worked example

A sealed bag contains 100 g of water and 10 g of sugar. The sugar dissolves, and nothing enters or leaves. What is the total mass of these contents?

Answer & why

Answer: 110 g

100 + 10 = 110 g; dissolving does not remove the sugar's matter.

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All questions

All 6 authored questions for this skill.

Question 1

In a sealed bottle, a reaction forms gas. The bottle, lid and contents were weighed together. Which material belongs in the final system mass?

  1. The gas as well as the other contents.
  2. Only the solid residue.
  3. Only the visible liquid.
  4. Everything except the gas.
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: The gas as well as the other contents.

Gas is matter and remains inside the measured sealed boundary.

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Question 2

An open cup and contents lose 4 g while water vapor escapes. Which observation explains why this is not a closed-system test?

  1. The cup was visible.
  2. The initial mass was recorded.
  3. The balance displayed grams.
  4. Matter crossed the cup's boundary.
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: Matter crossed the cup's boundary.

Escaping vapor carries matter out of the measured system.

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Question 3

A sealed bag and contents measure 175 g before ice melts. No leaks occur. Which final reading is consistent with mass conservation?

  1. 350 g
  2. 0 g
  3. 175 g
  4. 150 g
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: 175 g

Melting changes state but does not change the mass of the closed system.

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Question 4

A covered container measures 300 g. Afterward it measures 295 g and a leak is found. What should be checked before claiming mass disappeared?

  1. Whether grams stopped being a mass unit.
  2. Whether 5 g of material escaped.
  3. Whether all matter became weightless.
  4. Whether the container's color changed.
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: Whether 5 g of material escaped.

A boundary leak can account for missing measured material without matter being destroyed.

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Question 5

A sealed bag contains 100 g of water and 10 g of sugar. The sugar dissolves, and nothing enters or leaves. What is the total mass of these contents?

  1. 90 g
  2. 10 g
  3. 100 g
  4. 110 g
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: 110 g

100 + 10 = 110 g; dissolving does not remove the sugar's matter.

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Question 6

A sealed container and everything inside it measure 240 g before a reaction. No matter crosses the boundary. What mass should the same complete system have afterward?

  1. 480 g
  2. 240 g
  3. 0 g
  4. 120 g
A hint

Check the system boundary and include every material inside it before comparing masses.

Answer & why

Answer: 240 g

The closed system retains its matter even when substances change.

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