Design Challenge: An All-Night Toe Warmer for a Snow Campout

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Design Challenge: An All-Night Toe Warmer for a Snow Campout

Use test data on grain size and water to design a warmer that releases thermal energy all night.

Test 1: How fine should the iron be?

Read the passage and study Table 1. Then answer the questions.

Warm Toes in a Snow Shelter

1Every January, Scout Troop 214 spends two nights sleeping in snow shelters that the scouts dig into deep drifts. The air outside often drops to −12 °C at night, and the inside of a shelter usually stays a little below freezing. Last year, several scouts said that cold toes kept them awake. This year, troop leader Ms. Odalys Fuentes gave scouts Thandiwe Mokoena and Ilias Petrakis a design challenge: build a toe warmer that slips into a pocket at the foot of a sleeping bag and stays warm from bedtime until morning.

2Ms. Fuentes explained how many store-bought warmers work. Inside a cloth pouch, iron reacts with oxygen from the air and slowly forms rust, a new substance. Salt and water speed the reaction up, and a light, spongy mineral called vermiculite holds the water. Each pouch is kept in an airtight bag until it is needed. Following the scouts' plan, Ms. Fuentes, wearing gloves and goggles, filled each test pouch with 20 g of iron, 2 g of salt and 5 g of vermiculite and sewed it shut.

3The troop set two criteria for a pouch. First, it must read 35 °C or more at every reading from the 1-hour reading through the 8-hour reading, so it warms up soon after bedtime and lasts the night. Second, it must stay below 50 °C at every reading, because a pouch that is too hot can burn skin even through a sock.

4For Test 1, the scouts changed only the size of the iron grains: fine powder, coarse powder or small filings. Each pouch had 6 mL of water. Ms. Fuentes opened the bags at the same moment, and each pouch went inside a rolled-up fleece blanket in her garage, which stayed at 2 °C. A probe taped to each pouch recorded its temperature. As a control, a fine-powder pouch with 6 mL of water stayed closed in its airtight bag inside a fourth blanket. It read 2 °C for the whole test. After the test, the iron in the three open pouches had turned reddish-brown.

Table 1. Pouch Temperature in Test 1 (°C)
Time (h)	Fine powder	Coarse powder	Filings
0	2	2	2
0.5	52	38	14
1	56	42	20
2	50	44	24
4	30	42	26
6	16	40	26
8	6	38	25
10	2	30	24

1.

In the first half hour, the fine-powder pouch warmed by °C.

2.

Which result is the best evidence that the warmth came from a reaction with the air, not from the garage or the blankets?

A. The filings pouch was still at 24 °C at the 10-hour reading.B. The fine-powder pouch was the hottest pouch at the 1-hour reading.C. The garage stayed at 2 °C for the whole length of the overnight test.D. The closed control pouch stayed at 2 °C while the open pouches warmed.

3.

Use the criteria in paragraph 3. Match each pouch to the description of its results.

4.

Each pouch held the same 20 g of iron. Why did the fine powder get hotter than the coarse powder but cool off much sooner?

A. Fine grains pack tightly together, so the garage's cold could not get into that pouch until 4 hours.B. Fine grains have more surface for oxygen to reach, so the iron reacted faster and was used up sooner.C. Fine grains hold more thermal energy from the factory, so they gave off their stored heat in the first hour.D. Fine grains are a different substance from coarse grains, so they form a different product.

5.

The scouts' bedtime is 9 p.m., and they get up at 5 a.m. Suppose a scout opens a coarse-powder pouch at 4 p.m., while the troop is setting up camp. Based on Table 1, what would most likely happen?

A. It would be too hot to use at 9 p.m., because it would keep warming up for 5 hours.B. It would stay above 35 °C until 5 a.m., because the reaction waits until the bag is zipped.C. It would be warm at bedtime but drop below 35 °C in the middle of the night.D. It would stay near 2 °C until bedtime, because the cold air at camp stops the reaction.

Test 2: How much water?

For Test 2, the scouts used coarse powder in every pouch and changed only the amount of water. Everything else was done as in Test 1. Use Table 2 and the passage.

Table 2. Coarse-Powder Pouches With Different Amounts of Water
Water (mL)	Highest temp. (°C)	Temp. at 8 h (°C)	How the mix felt
0	9	4	Dry and loose
3	33	28	Barely damp
6	44	38	Damp
12	31	30	Soggy

6.

The highest temperature with 6 mL of water was °C higher than the highest temperature with 12 mL of water.

7.

The soggy 12 mL pouch warmed less than the 6 mL pouch. Which explanation fits the passage and Table 2 best?

A. The extra water filled the spaces between grains, so less oxygen could reach the iron.B. The extra water put out the reaction, the same way water puts out a campfire flame.C. The extra water turned the iron into rust before the bag was opened, so it was used up.D. The extra water held more cold from the garage, which it passed on to the iron grains.

8.

Match each result to what it shows about the reaction in the pouch.

Packing for the campout

Use everything on this sheet to answer.

9.

Fourteen scouts are going on the campout. Each scout uses one new pouch on each of the 2 nights, and each pouch holds 20 g of iron.

The troop needs g of coarse iron powder. It is sold in 250 g bags, so the troop must buy at least bags.

10.

Which path best describes the energy that warms a scout's toes during the night?

A. Water in the pouch soaks up warmth in the garage and gives it back slowly during the night.B. Cold from the toes flows into the pouch, where the salt turns it into warmth for the sock.C. The reaction of iron and oxygen releases thermal energy, which flows into the sock and toes.D. Thermal energy from the scout's feet flows into the iron, which starts the reaction and keeps it going.

11.

Ilias's younger brother says, “The pouches don't make heat. The factory heats up the salt and water, and they store it until you open the bag.” Do you agree? Write a claim, use evidence from Tables 1 and 2 and paragraph 4, and explain where the thermal energy that warms the pouch comes from. Then say which design the troop should pack.